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RICHTER'S ORGANIC CHEMISTRY

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ORGANIC CHEMISTRY

OR

CHEMISTRY OF THE CARBON COMPOUNDS

BY

VICTOR VON RICHTER

Edited by Prof. R. Anschutz and Dr H. MSerwein

VOLUME II

CHEMISTRY OF THE CARBOCYCLIC COMPOUNDS

TRANSLATED FROM THE IlTH GERMAN EDITION

BY

E. E. FOURNIER D'ALBE, D.Sc, A.R.C.Sc

AUTHOR or " CONTSMKORARY CHEMISTRY," "tHB ELKCTRON THEORY," ETC.

PHILADELPHIA

P. BLAKISTON'S SON & CO.

I0I2 WALNUT STREET 1922

L-

^v^

■^

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r

PREFACE TO THE ELEVENTH GERMAN EDITION

The second volume of the present work was published in its last edition in 1905 by me in collaboration with ProllKsor Georg Schroeter. Dr Schroeter, who had also rendered extremely able a%stance in the production of the seventh and succeeding editions, was appointed a year ago to the distinguished position of Professor of Chemistry at the Veterinary College in Berhn. Collaboration in the preparation of the present second volume of the treatise was then undertaken by his successor at the Chemical Institute, Dr Hans Meerwein, Assistant Instructor in Organic Chemistry. .

RICHARD ANSCHUTZ. "^

-#M-

•? *--

Since the pubUcation of the second volume seven years have' ^

elapsed, during the last few of which the book was out of print. In the course of these latter years the amount of new subject-matter has undergone a remarkable increase. Consequently, the present volume, in comparison with the last edition, has had to be enlarged by more than nine sheets, in spite of the adoption of a larger size of page, as otherwise the whole character of the edition would have been altered. ^ As in previous editions, a list of the most important interpolations

and additions is given below.

^ Trir, tetra-, penta-, hepta-, octo-, and nonocyclic compounds. — ^Spedal

^ attention is caUed to the ring expansion by the action of nitric acid

^ on cyclo-alkyl methylamine as a new general reaction. The tetra-

methylene group has been supplemented principally by the inclusion

of the simplest examples : cyclobutane, cydobutene, and cydo-

butanone. The simplest saturated, and imsaturated, carbohydrates,

with eight-membered carbon rings, are obtained by the transformation

of pseudo-pelletierin, and have been very dosdy examined. By the

recognition of the constitution of india-rubber as a polymeric dimethyl,

cydo-octadiene, the group of octocarbocydic compounds has gained

considerably in interest.

The class of nonocarbocyclic compounds has had to be added.

Single-nucleus aromatic substances. — ^The historical account of the theory of the aromatic compounds has been supplemented at essential points (p. 28).

Spedal attention is directed to the extremdy consistent sphtting up of benzene and its homologues by the oxidising action of ozone.

Halogen derivatives of benzene carbohydrates. — Recognition of the fact that the capacity for reaction of aromaticaUy combined halogens

40S510

vi PREFACE

can be very considerably increased by the addition of finely divided copper or copper salts, has proved of great practical importance.

Nitrogenous derivatives of benzene carbohydrates. — ^The preparation of opticsdly active dialkyl anilin oxides is worthy of attention.

The behaviour of nitro-diphenylamines in the formation of salts has been more closely examined, and more satisfactory reasons have been given for regarding them as pseudo-acids. As regards new investiga- tions on the diazo-amido-compwunds, the preparation of diazo-benzene amide is particularly important. New methods of obtaining diazo- amido-compounds have been discovered. The discovery of two isomeric, differently coloured, series of salts is important, as regards the constitution of amido-azo-compounds, and their salts. Attention is directed to the production of tetraphenyl-hydrazin and its interesting resolving reacjfions ; see also diphenyl-dihydro-phenazin. The process of reaction in the formation of phenyl-hydrazones, by the action of diazo-benzene salts on aliphatic compounds with easily replaceable hydrogen atoms, has been experimentally elucidated in its individual phases.

The group of aromatic compounds of arsenic has attained greater importance, through the discovery of pharmaceutically valuable substances, such as salvarsan.

Phenols. — ^The consideration of the nitro-phenols as pseudo-acids has gained in interest by the discovery of a red ester of picric acid. The question of the constitution of tiie oxy-azo-benzenes has been finally decided in favour of the azo-formula. Reference may also be made to the discovery of cycHc double esters of the phenol-sulpho- acids : sulphonylides.

Quinones. — ^The discovery of the long -sought o-benzo-quinone should be mentioned in the first place. The nitrogenous derivatives of the quinones have been thoroughly discussed. The investigation of the reactions and constitution of anilin-black by the oxidation of anilin is of the highest importance. Attention may also be called to the remarkable researches regarding the so-caUed two-nucleus quinones of the diphenyl, naphthalin, and anthracene series.

The nitrogenous derivatives of the oxy-phenyUparaffi/n alcohols have been thoroughly discussed, owing to their marked physiological action. Special attention is directed to tibie analysis and synthesis of adrenalin

(P- 370)-

Aromatic aldehydes and ketones, — In this group a series of new

and, in some cases, easily effected sjmtheses should be noted. Special attention should be given to the atom displacements in the trans- formation of the aromatic ethylene glycols, the halogen hydrines, and the ethylene oxides.

Aromatic carbo-acids. — Benzoyl nitrate, benzo-nitrosol acid, benzo- nitrol add, and benzo-nitrile oxide figure as new carboxyl derivatives of benzoic acid. With reference to the constitution of anthranile, the so-caUed dianthranUides must be mentioned, as the true bimolecular anhydrides of the anthranile acids. ThiosalicyHc acid and its progeny have been much used as the basic products for x)Feparing thio- indigo red.

The discovery of di-iodo-tyrosin in certain species of coral is of physiological importance.

PREFACE vii

Single^nucleus aromatic substances with unsaturated side chains, — The discovery of the tri-morphism of allo-cinnamic acid, whereby the previously vague isometry of the cinnamic acids may be regarded as explained, is of x»incipal interest in this field.

Hydro-aronuUic substances. — Inasmuch as by the smooth method of reduction of aromatic compounds, by means of hydrogen and finely divided nickel, the hydro-aromatic substances have become an easily accessible primary material, this field of research has made remarkable progress, mainly by the use of Grignard's reaction. For determina- tions of constitution, especially as regards terpenes, the elegant method of oxidation by means of ozone has proved of great service. For terpene chemistry the synthesis of unsaturated hydrocarbons, with semi-cyclic double linking, is of importance. The tetra- and dihydro- benzenes were subjected to a fresh critical study. Extended synthetic investigations with regard to the cyclo-nitrales have finally led to a synthesis of irone, which, however, is not technically valuable. A curious method for the synthesis of cUif erent hydro-aromatic substances was discovered in the action of chloroform and alkali on o- and p-alkaline phenols. The production of the optically active forms of 4-methyl-cyclo-hexilidene-acetic acid, in which the asymmetry of the molecule is not caused by the presence of an asjrmmetric carbon atom, is of technical interest.

Attention might also be directed to the splitting of cyclic ketones by means of sunlight.

Terpenes. — ^The exceedingly numerous researches made in the entire field of terpene chemistry have necessitated an almost complete re- working, and a partial re-division, in particular of the di-cyclic terpenes. The olefinic terpene group has been enriched by the discovery of odmene and nerol. TTie constitutional determinations of the mono- cyclic terpenes, which may now be regarded as concluded, have been confirmed by numerous syntheses. Thus, dipentene, terpinene, a-phellandrene, sylvestrene, and carvestrene have been obtained in a synthetic manner. A number of analogously composed combinations derived from the terpenes, such as terpinene, terpene, terpinene-cineol, and terpinenol, have ranged themselves alongside of terpin, cineol, and the terpineols. Sabinene and thuyene were associated, by numerous transformations, with terpinene and the terpinenoles. Eucarvone has been examined again, and has been recognised as a heptacarbocycUc combination. The pinene separated from the turpentine oils, has been recognised as a mixture of two linkage-isomeric terpenes, and from these a number of new derived and transformation products are obtained. The transformation of pinene into bomeol and isobomeol, or their esters, has been converted into a technically realisable method for the artificial production of camphor from turpentine oil. A fresh and very thorough treatment of camphene has confirmed the Wagner camphene formula ; nevertheless, this has raised doubts as to the unity of this terpene. Bomylene, camphane, isocamphane, and santene were the subjects of new and fruitful researches. A series of articles on the behaviour of bomeol and isobomeol towards each other, and towards pinene or camphene - chlorohydrate, appear to prove the stereo- isomerism of these combinations. The constitution of fenchone could be accurately ascertained by a series of splitting reactions.

viii PREFACE

Phenylrhenzenes and phenyl fat carbohydrates, — ^A series of naturally occurring substances have been recognised as oxybenzo-phenones, and oxybenzylidene-acetophenones, whi<£i have hitherto been regarded as phenol esters of protocatechu acid and oxy-cinnamic acid.

Important new observations have been made in favour of regarding the coloured salts of triphenyl-carbinole as quinoid combinations ; see also dibenzylidene-acetone.

The benzein, rosamin, and phthalein classes have been increased by further research.

Prominence should be given to diphenylketene, the most easily accessible, and consequently the most thoroughly examined, factor in this class, rich in reactions.

Amongst the most theoretically important researches which have been made in various directions with excellent results, we may mention those relating to hexaphenyl-ethane, and similar combinations, and their dissociation into the corresponding triaryl-methyls.

The diphenyl-butane group has been enriched by notable papers relating to diphenyl-butadiene and diphenyl-butenin.

Condensed nuclei, — Notice should be taken of the virtual tautomery of anthranol and anthrones, as well as of anthra-hydrokinone and oxanthrone. The amido-anthrakinones have repeatedly shown them- selves to be excellent intermediaries for the production of new vat dyes, and so have the dianthrakinonyls and the benzo-anthrones.

Glucosides, — ^There have been new investigations on certain gluco- sides related to amygdalin (p. 719).

Natural dye-stuffs, — Much Ught has been thrown on the complex constitution of cochineal dye.

The above brief review, in the course of which we have only been able to refer to some of the most important recent developments, shows that, in the time which has elapsed, notable progress has been made in nearly all classes of carbocycHc compounds.

RICHARD ANSCHUTZ. HANS MEERWEIN.

Bonn, October 191 2.

CONTENTS

CARBOCYCLIC COMPOUNDS

PAOS

Ring Formation in Cyclo-paraffin Bodies . . . . .3

I.— TRI-. TETRA-, PENTA-, HEPTA-, OCTO-, AND NONOCARBOCYCLIC COMPOUNDS 6

A. TrimethyUne Group, — Trimethylene, Trimethylene-carboxylic Acid 7

B. Tetramethyiene Group. — Tetramethylene, Cycfobutene, Cyclobutanine . 10

C. PetUacarbocyclic Compounds.— Caxaphor, Pentamethylene, Cydopentene,

Cyclopentadiene, Alcohols, Ring Ketones, Adipin Ketones, Diketo- pentametiiylene. Aldehydes and Extra-cyclic Ketones, Carboxylic Acids, Alcohol-carboxylic Acids, Keto-carboxylic Acids, Bicyclo- pentane 13

D. Heptacarbocyclic Compounds, — Suberane, Suberene, Cycloheptadiene,

Tropilidene, Oxy-suberane-carboxylic Acid ..... 22

E. Octocarhocyclic Compounds, — Cyclo^ctane, Azelane .... 25

F. Nonocarbocyclic Compounds ........ 26

II.— HEXACARBOCYCLIC COMPOUNDS . 27

A. MONONUCLEAR AROMATIC SUBSTANCES OR

BENZENE DERIVATIVES

History. General Survey. Isomerism of Benzene Derivatives. Principles of Location for Benzene Substitution Products. Location of the Di- derivatives. Isomerism of the Poly-substitution Products. Constitu- tion of the Benzene Nucleus. Benzene Ring Formations. Benzene Ring Splittings. Splitting by Feeble Oxidation. Splitting by simultaneous i;hlorination and Oxidation. Splitting by Reduction in Alkaline Solutions ......... 27

I. SiNGLS-NUCLEUS BeNZENB DERIVATIVES :

Benzol. Coal-tar. Working of Coal-tar for Aromatic Hydrocarbons. Alkyl-benzols. Allylene. Isomerism and Constitution of

Alkyl-benzols. Xylol. Ethyl-benzol, Mesitylene, Cymol, i

Toluol 49 ^ ^

2. Halogen Derivatives of the Benzene Hydrocarbons :

A. Halogen Substitution Products of Benzene, — Fluoro-benzols,

Bromo-, Chloro-, and lodo-benzols ..... 60

B. Halogen Derivatives of the Alhyl-bensols. — Benzyl and Benzal Com-

pounds. Chloro-, Bromo-, lodo-, and Fluoro-toluol 64

3. Nitrogen Derivatives of Benzene Hydrocarbons ... 67

(i) Nitro-derivatives ofBenxene and the Alkyl-benzols. — ^Nitro-benzols, Nitro-toluols. Nitro-products of the Alkyl-benzols. Nitro- halogen Derivatives of the Alkyl-benzols .... 68

(2) Nitroso-derivatives of Benzene and the Alkyl-benzols. — ^Nitroso-

benzols, Nitroso-toluols ....... 75

(3) P'Alpkyl- or Aryl'hydroxylamines. — Formyl- and Phenyl-hydro-

xylamines. Chloro- and Nitro-compounds. Nitroso-diphenyl- hvdroxylamines ........ 77

^4) fi-Atphyl-nitroso-hydrox^lamines ...... 79

(5) A mido-derivaiives or A nilines, — (a) Primary Phenyl-amines. Their Reduction and Exchange Reactions. Their Properties and Transformations. (6) Secondary and Tertiary Phenyl-amines and Phenyl-ammomum Bases. Phenyl-alkylamine. Separa- tion of Primary, Secx>ndary, and Tertiary Bases. Di-sdkyl- aniline Oxides. Methyl-anilines, (c) Poly-phenyl-amines. (d) Aniline Derivatives of Inorganic Acids, (e) Carboxylic

ix

CONTENTS

PAOX

Derivatives of the Aromatic Primary and Secondary Bases. if) Phenylated Amidins of Formic Acid and Acetic Acid. Carbylamines, Ureas, and Phenyl-ureas, Tliio-ureas, and Hydrazin Derivatives. (#) Phenylated Nitriles and Imides of Carbonic Acid. Phenyl Jbocyanate. Phenyl Sulpho-cyanide. Cyanamide Derivatives. Phenyl-amine Derivatives of Oxalic Acid. Anilides of Dicarboxyuc Acid. AniUdo-carboxylic Acids. Aniline Substitution Products. Aniline Haloids. Nitranilines. Nitro-diphenyl-amines. (A) Nitroso-derivatives of the Primary, Secondary, and Tertiary Amines. . . 79

(5a) Diamines. — Phenylene-diamines. Toluene- and Xylene-di- amines. Condensation of o-Diamines. Differences between 0-, m-, and p-Diamines. Triamines and Tetramines . • 113 Phenyl-niirosaminss. — Nitrosanilides. Nitroso-formanilides 119

;i

Phenyl-nitr amines, — Diazo-benzoic Acids . . .120

r

(8) Diago-compounds. — Aromatic Diazo-derivatives. Diazonium Salts. Diazo-perhalides. Iso-diazo-hydrate. Diazo-benzol- sulphonic Acids. Diazo-benzol Cyanide. Chief Decomposi- tions of Diazo-benzol Salts ...... 121

(9^ Diaxo-amidO'Compounds . . . .132

(10) Dis-diago-amido-compounds. — Reactions and Formations. Diazo- amido-compounds from Primary Aromatic Bases. Mixed Fatty-aromatic Compounds. Phenyl-triazones. Re-arrange- ments of Diazo-amido-compounds . . .132 fii| DiagO'Oxy-amido-compounds. — Diazo-oxy-amido-benzol • ^37 X12) Diago-amido-compounds, — Diazo-benzol-imides. Their trans- formations. Tetrazones . . . • I37

(13) Azoxy-compounds. — ^Their Formation and Behaviour. Azoxy-

benzol .......... 139

(14) AxO'Compounds. — ^Their Classification, Nomenclature, Formation,

and Properties. Indifferent Symmetrical Azo-compounds. Azo-benzols and Azo-toluols. Amido-azo-compounds . .140

(15) Hydrazin Compounds. — Hydrazo-compounds. Hydrazo-benzols

and -toluols. The Benzidin and Semidin Transformations of the Hydrazo-compounds. The Phenyl-hydrazin Group. Phenyl-alkyl-hydrazins. Hetero-ring Formations of Sub- stituted Phenyl-hydrazins. Phenyl-faydrazone and Osazone. Phenyl-hydrazone Transformations. Phenyl-hydrazin Deri- vatives of the Inorganic Acids. CarboxyUc Derivatives of Phenyl-hydrazin. Fatty Acid Derivatives. Alcoholic Acid Derivatives. Phenyl-hydrazin Derivatives of Mono-ketonic Carbonic Acid. Dicarboxylic Acids. Olefin- and Oxy- dicarboxylic Acids. Hetero-ring Formation of Phenyl- hydrazin Derivatives of Dicarboxylic Acids. . . • I45 {16) Hydraxins or Amidrazones. — ^Nitrazones. Phenyl-hydrazo- and Phenyl - azo - aldoximes. Formazyl Compounds. Phenyl- nitroso-hydrazin. Tetrazones. Hydro-tetrazones . .163

4. Aromatic Compounds of Phosphorus, Arsenic, Antimony, Bismuth,

Boron, Silicon, and Tin : Phenyl-phosphene. Phenyl-arsenic Compounds. Phenyl-boron and

-silicon Compounds . . . . . .168

5. Phsnyi. Mbtal Derivatives :

Magnesium - diphenyl. Aryl - magnesium Haloids. Mercury-

diphenyjs ......... 171

6. SuLPHONic Acids :

Formation. Properties and Transformations. Monosulphonic Adds. Benzo-sulphonic Acids. Benzo-sulpho-compounds. Xylol-sulphonic Acids. Poly-sulphonic Acids. Chloro-, Bromo-, lodo-, lodoso-, Nitro-, Niti^so-, and Amido-benzol- sulphonic Acids. Sulphanilic Add. Amido-azo-benzol Acids. Sulphinic Adds. Sulphones and Sulphoxides . . .172

7. Phenols :

Monohydric Phenols. Their Formation and Behaviour. Their Colour Reactions, and Nudear Syntheses. Phenolates. Cresols. Ethyl- and Propyl-phenols. Thym<^. Carvacrol.

CONTENTS xi

PAGE

Derivatives of Monohydric Phenols. Phenol-alcohol Ethers. Phenoxalkylamines. Phenol Ethers. Acid Esters of Phenol. Phenyl Esters of the Phosphoric Acids. Phenyl Carbonates. Phenol Substitution Products. Phenol Haloids. Mono- and Poly-haloid Phenols. Nitro-phenols. Mono-, Di-, Tri-, and Tetra-nitro-phenols. Picric Acid. Haloid Nitro-phenols. Nitroso - compounds. Nitroso - phenol. Nitroso - cresol. Amido-phenols. Their Condensations. Diamido-phenols. Diazo-phenols. Azoxy-phenols. Azo-phenols. Hydrazo- phenols. Thio-derivatives. Mercaptans. Condensation of o-Amido-thio-phenoIs. Phenyl Sulphides. Amido-phenyl- Sulphides. Dihydric Phenc^s. Pyro-catechin. Hetero-ring Formations from Pyro-cate(±Lol. Homolctfrous Pyro-catechols. The Hesorcin Group. Resorcin. Its Ethers and Esters. Nitro- and Thio-resordn. Homologous Kesorcins. Orcin. Hydroquinone Group. Hydroquinone. Homologous Hydro- quinones. Substituted. Hydroquinones. Trihydnc Phenols. Pyrogallol. Phloro-glucin. Tetrahydric Phenols. Penta- and Hexahydro-phenols . . . .183

8. QuiKONES :

Ortho-quinones. Para-quinones. Phenol Addition Products of Quinones. Homologous p-Quinones. Quinone Haloids. Oxy- quinones and Polyquinoyls. Croconic and Leuconic Acid. Nitrogen Derivatives of Quinone. Quinone Dioximes, Imines, and Azines. Indo-^enols. Indo-anilines. Quinone • Phenyl-di-imines. Aniline ^lack. Indamines . . 224

9. Phsmyl-paraffin Alcohols and thsir Oxidation Products . 239

(a) Monohydric Phbnyl-paraffin Alcohols and their Oxida- tion Products: 240

(i) Monohydric Phenyl-paraffin Alcohols. — ^Benzyl Alcohol. Homologous Phenyl-paraffin Alcohols. Derivatives of the Phenyl-paraffin Alcohols. Homologous Phenyl- alkyl Chlorides. Esters of Carboxylic Acid. Nitrogen Derivatives of the Phenyl-paraffin Alcohols. Benzyl- amines. Benzyl-anilines. Benzyl-diazo-compounds, Triazenes, and Azides. Benzyl-hydroxylamines. Sub- stituted Benzyl Alcohols. Formation of Hetero-rings from Derivatives of o-Amido-benzyl Alcohol . . 240

(2) Aromatic Monaldehydes. — Benzaldoximes. Pyrones.

Benzaldehyde. Homologous Benzaldehydes. Deri- vatives of Benzaldehyde. Benzaldehyde Haloids. Nitro-, Nitroso-, Hydroxylamino-, Azoxy-, Azo-, and Amido-benzaldehydes. Hetero-ring Formations of Benzaldehyde ....... 252

(3) AronuUic Monoketones. — Aceto - phenone. Its Homo-

logues. Homo-benzolated Paraffins. Nitro-aceto- phenones. Amido-aceto-phenones. Hetero-ring For- mation of the Aromatic o-Amido-ketones . . 264

(4) AronuUic Monocarboxylic Acids. — Their Formation. Oxi-

dation with Chromic and Nitric Adds. Nuclear Syntheses and Reactions. Benzoic Acid. Its Homo- logues. Alkyl-benzoic Adds. Ethyl-benzoic Adds. Propyl-benzoic Adds. Phenyl-fatty Adds. Hydra- tropic Add ........ 269

(b) Derivatives of the Aromatic Monocarboxylic Acids:

ii) Est&rs of the Monobasic Aromatic Acids . -277

2) Aromatic Acid Haloids. — Benzoyl Chloride, Bromide, and

Nitrate .278

Acid Anhydrides. — Benzoic and Aceto-benzoic Anhydrides 279 Acid Peroxides ........ 280

(5) Thio^acids and Bi-thio-acids . .280 Add Amides. — Benzamide. Benzanilide. HippuricAdd.

Its Salts, Esters, and Nitriles ..... 280 Acid Hydroxides. — Benzoyl-hydrazin •283

Acidyl'Osides. — ^Benzoyl-azide. Hippurazide . 284

1:

II! ill

Xll

CONTENTS

t9)

lO] 12

[14)

U

17

[20) [2i;

Nitriles of the Aromatic Monoccarboxylic Acids, — Benzo-

nitrile. Alphyl Cyanides. Nitriles of the Phenyl-fatty

Acids. Benzyl Cyanide . AmidO'haloids .... Imtdo-chlorides .... PhenyUhydragide Imido-chlorides . Imido-ethers of the Aromatic Acids Thiamides of the Aromatic Acids. — Thio-benzamide

Selenium-benzamide .... Imido-thio-ethers of the Aromatic Carhoxylic Acids Amidines of the Aromatic Carhoxylic Acids. — Benzamidine

Phenyl-benzamidine .....

Dioxy-tetraxoHc Acids ......

Hydraxidins or Amidrazones. — Benzenyl-hydrazidin . Nitraxones, Nitrosaxones, and Phenyl-axoximes Formasyl Derivatives. — Formazyl- and Guanazyl-benzol Hydroxamic Acids, their Ethers and Esters. — Benzo-hydro

xamic Acid. Tribenzoyl-hydroxylamine Haloids of Benxo-hydroxamic Acid Benxo-nitrolic Acid Benxo-nitrosolic Acid . Nitrile Oxides .... A midoximes. — Benzenyl-amidoxime Hydrasidoximes .... Hydroxamoximes Ethyl-orthobenxoic Esters Benzo-trichlorides and -trifluorides . Orthobenxoic Acid Piperidide,

PACB

285 287 287 287 288

288 289

289 290 291 291 292

293 294

294

295

295

295 296

297

297 297 297

(6)

298 300 300

{c) Substituted Aromatic Monocarboxyuc Acids :

(i) Halogen Benzoic Acids ...... 297

(2) lodoso' and lodo-henxoic Adds . . .298

(3) Nitro-monocarboxylic Acids. — Nitro-benzoic Acids. Nitro- haloid and Nitro-phenyl-benzoic Acids

(4^ Nitroso-monocarboxylic Acids. — Nitroso-benzoic Acid >) Hydroxjflamino-carhoxylic Acids .....

Aromatic Amido-monocarboxylic Acids. — ^Anthranilic Acid. Anthranile. Acetyl-antkranile. Dimolecular Anhy- drides of Anthranilic Acid. Kynuric Acid. Di- cyanamino - benzoyl. Methyl - anthranilic Acid. Hetero-rin^ Formations of Anthranilic Acid. Amido- benzoic Acids. Amido-phenyl-fatty Acids. Atroxindol 301 (7) DiaxO'benxoic Acids . . . . . . • 3zz

(S\ Dituo-amido-benxoic Acids (9) Diaxo-imido-benxoic Acids ;ioi Axoxy-benxoic Acids

11) AxO'benzoic Acids

12) Hydraxin-benxoic Acids [13) Phosphine-benxoic Acids 14) StUpho-benxoic Acids. — Saccharin

(d) monohydric oxy-phbnyl-paraffin alcohols and their Oxidation Products :

3" 3" 3" 311 312 312 312

(i) Monohydric Oxy-phenyl-paraffin Alcohols, or Phenyl Alcohols. — Saligenin. Anisyl Alcohol. Pseudo-phenol Haloids. Methylene-quinones. Quinols .

(2) Aromatic Oxy-mono-dldehydes, Phenol-aldehydes. — Salicylic Aldehyde. Anisaldoxime. Homologous Monoxy- benzaldehydes. Proto-catechuic Aldehyde. Vanillin. Piperonal. Tri- and Tetra-oxy-benzaldehydes .

^3) Phenol Ketones . . . . . . .325

(4) Phenol-monocarboxylic Acids. — Salicylic Acid. Sali-

cylates. Anisic Acid. Oxy-toluic and Cresotinic Acids. bxy-mesitylenic Acids. Phloretic Add. Phloretin. Vanillic Acid. Luteolin. Catechin. Gentisinic, Orsellinic, and Gallic Acids. Tannin and Tannic Acids ........ 327

314

321

l\

CONTENTS xiii

(e) POLYHYDRIC AROMATIC ALCOHOLS IN WHICH ONLY ONE HYDROXYL IS PRBSBNT IN EACH SiDB ChAIN, AND THEIR OxiDATION

Products : p^ok

(i) Di' and Trihydric Aromatic Alcohols. — Phthalyl and

Xylylene Alcohols ....... 344

[2) Aldehyde Alcohols ....... 345

[31 Aromatic Dialdehydes ....... 346

[4) Di' and Triketones ....... 347

[5) Alcohol-carhoxylic Acids. — Phthalide. Meconin . -347

[6) Aldehyde Acids, — Phthai-aldehyde Adds. Opianic Acid. 350 Ketone-carboxylic Acids -353 Dicarhoxylic Acids. — Fhthalic Acids and Chlorides.

Phthal^lene tetrachlorides. Phthalimide. Iso- phthalic Acid. Uvitinic Acid. Terephthalic Acid. Aromatic Dicarboxylic Adds with one molecule of Carboxyl in the Nudeus and in the Side Chain. Homo- phthalimide. Aromatic Dicarboxylic Adds having both Carboxyls in different Side Groups . 354

(9) AldehydO'dicarboxylic Acids ..... 364

(10) Tricarboxylic Acids. — Trimellitic and Hemi-mellitic Acids.

Trimesic Add ....... 364

(11) Aromatic Tetracarboxylic Adds. — Pyro-mellitic Add.

Prehnitic and Mellophanic Adds .... 365

ii2^ Aromatic Pentacarboxylic Acid ..... 365 13) Aromatic Hexacarboxylic Acid. — Mellitic and Euchronic

Acids ......... 366

(/) Aromatic Poly alcohols containing more than one Hydroxyl Group in the same Side Chain, and their Oxidation Products :

(i) Phenyl-glycols and Phenyl-glycerin. — Stycerine. Haloid Esters of the Phenyl-glycols. Dihaloids. Ephedrin. Adrenalin ........ 367

Phenyl-alcohol Aldehydes. — Phenyl-tetrose -370

Phenyl Ketols. — Aceto-phenone Alcohol. Amido-aceto- phenone ........ 371

(4) Phenyl-aldehyde Ketones. Phenyl-glyoxal . . -373

Phenyl-parajjin Diketones. — Benzoyl-acetone. Tri- and Tetraketones ........ 374

(6) Phenyl-paraffin Alcohol Acids. — Monoxy-alcohol Adds. Mandelic Adds. Dioxindol. Atro-lactonic Acid. Tropic Add. Phenyl-alanin. Tyrosin. Dioxy- alcohol Adds. StycericAdd. Trioxy-alcohol Acids . 376

!7) Phenyl-paraffin-aldehyde-carboxylic Acids . 386

8) Phenyl - paraffin - ketone - carboxylic A cids. — Ketone - car- boxylic Acids. Phenyl - glyoxylic Add. Isatin. ^ Anthroxanic Add. Cumaranmone. Thio-isatin. Homologous Phenyl-glycol Acids. Phenyl-paraffin ^-ketone-carboxylic Acids. Benzoyl-acetic Add . 387

(9) Phenyl-alcohol-ketone-carboxylic Acids .... 394

(10) Dihetone-carboxylic ^cu{5.---Quinisatin. Benzoyl-pyro- racemic Add ........ 393

(11) Phenyl-paraffin-dicarboxylic Acids. — Phenyl-malonic Add. Phenyl- and Benzyl-succinic Acids .... 396

(12) Phenyl-alcohol'dicarboxylic Acids. — Phenyl- and Benzyl- malic Adds ........ 397

Phenyl-hetone-dicarboxylic Acids, — Benzoyl-malonic Ester 399 Phenyl-oxy-ketone-dicarboxylic Acids .... 400 Phenyl-paraffin-tricarboxylic Acids .... 400

Phenyl'ketO'tricarboxylic Acids ..... 400 (ly) PolyketO'polycarboxylic Acids ..... 400 (18) Phenylene-oxy-dicarboxylic Acids. — Carbo-mandelic Acid.

Acetonyl-phthalide . .. . . . .401

ii9) Phenylene-ketone-dicarboxylic Acids .... 402 201 Tri' and Tetracarboxylic Acids ..... 402 21) Oxy-tri-, -tetra-, and -penta-carboxylic Acids 403

22) Ketane'tricarboxylic Acids ...... 403

it

xiv CONTENTS

{g) Mononuclear Aromatic Substances with Unsatxtratbd

Side Chains : p^c,

la. Olefin-befuenes. — Styrol . 403

16. Acetylene Bensenes. — Phenyl-acetylene . . . '. 407 Ic. Dioiefin-betuols ........ 400

Id. Olefin-acetylene-bensols ...... 408

Ila. Ole fin-phenols. — (A) Olefin-monoxy-benaols, Vinyl-phenol, Chavicol, Anetiiol. (B) Olefin-dioxy-benzols, Eugenol, Safrol. (C) Olefin-trioxy-benzols, Asarone, Elemicin, Myristicin. (D) Olefin-tetraoxy-benzols, Apiol . . 408 lib. Acetyl-anisol and Phenetol . . 413

Ilia. Phenyl-olefin Alcohols and their Oxidation Prodticts. — (la) Phenyl -olefin Alcohols, Styrone. (ib) Oxy- phenyl- olefin Alcohols, Coniferyl Alcohol, (ic) Phenyl-acety- lene Alcohols. (2a) Phenyl-olefin Alcohols, Cinnamic Aldehyde. (2b) Oxy - phenyl - olefin Aldehydes. (3) Phenyl-diolenn Aldehydes. (4a) Phenyl-olefin Ketones. {5) Phenyl-acetylene Aldehydes. (6) Phenyl-acetylene Ketones. (7) Phenyl-diold&n Ketones. (8) Phenyl - olefin - carboxylic Acids, Cinnamic Acid and its Deri- vatives, Haloid Cinnamic Acids, Nitro-cinnamic Acids, Amido - cinnamic Acids, Hydrazin - cinnamic Acids, Sulpho-cinnamic Acids, Homologous Cinnamic Acids, Atropic Acid ........ 413

Illb. Oxy-phenyl-olefin-carboxylic Acids. — (A) Monoxy-phenyl- olefin-carboxylic Acids, Cumarin, Cumaroxime. (B) Dioxy-phenyl-olefin-carboxyUc Acids, Caff^c Acid, Umbelliferone. (C) Trioxy-cinnamic Acids. (D) Tetra- oxy-cinnamic Acids, Fraxetin. (E) Phenyl-acetylene- carboxylic Acids. (F) Phenyl-diolefin-carboxylic Acids, Piperic Acid ........ 426

IV. Compounds which may be considered as Oxidation Pro- ducts of Mononuclear Aromatic Polyalcohols with Un- saturated Side Chains. — (i) Phenylene - oxy - olefin - carboxylic Adds, Iso-cumarin, Iso-carbo-styril, Ber- gaptene. (2) Phenylene - aldehyde - carboxylic Acids. (3) Phenylene-dicarboxylic Acids. (4) Phenyl-olefin- ketols. (5)Phenyl-oxy-olefin-carboxyUc Acids. (6) Phenyl-oxy-dioldBin-carboxylic Acids. (7) Phenyl- dioxy-olefin-carboxylic Aads. (8) Phenyl-olefin-a- keto-carboxylic Acids. (9) Phenyl-diolefin-a-keto-car- boxylic Acids. (10) Phenyl-olefin-j?-ketone-carboxylic Acids. (11) Phenyl-olefin- and -diolefin-y-ketone-car* boxylic Acids. (12) Phenyl-olefin-dicarboxylic Acids. (13^ Phenyl-diolefin-dicarboxylic Acids, Benzal-malonic Acid, Cyano-cinnamic Acid, CinnaiAylidene - malonic Acid, Phenyl-maleic Acid, Cinnamenyl-glutaric Acid. (14) Phenyl-olefin-tricarboxylic Adds. (15) Phenyl- oxy-olefin-dicarboxylic Adds. (16) Phenylene-oxy- olefin-dicarboxylic Adds. (17) Phenylene-oxy-olefin- tricarboxylic Adds ....... 434

B. HYDRO-AROMATIC SUBSTANCES WITH SINGLE

NUCLEUS, HYDRO-BENZOL DERIVATIVES

I. Hydro-aromatic Hydrocarbons ........ 443

I a. Cyclo-hexanes, Hexahydro-bensols, Naphthenes. — Halogen Substitution

Products of the Hexahydro-benzols ...... 444

16. Cyclo-hexenes, Tetrdhydro-benxols, Naphthylenes. — ^Methyl- and Dimethyl-

cydo-hexene .......... 447

IC. Dihydro-benzolSt Cyclo-hexadienes ....... 449

2a. Ring Alcohols cfthe Hydro-aromatic Carbons. — Cyclo-hexanol. Quinite.

Querdte. Iriosite. Phenose . . . . . . '451

2b. Ring Alcohols of Tetrahydro-benjtol •454

2c. Extra-cyclic Hydro-aromatic Alcohols . . . .454

2d. Sulphur Derivatives of Hydro-aromatic Alcohols . . 455

^a. Ring Amines of Hydro-aromaiic Hydrocarbons. — ^Amido-cyclo-hexane . 455

CONTENTS XV

PAGE

36. EMtra-cyclic Hydro-a/ronuUic Amines 436

4. Ring'heiones of the Hydto-aromaHc Hydrocarbons. — Ring-ketones of

Hexahydro-benzol. Ring-ketols. Dihydro-resordn. Tetrahydro- qninone. Rmg-ketones. Tetrahydro-benzol. Ring-ketones of the Dihydro-benzols . -456

5. Hydro-aromatic Aldehydes. — Cyclo-citral ...... 466

6. Extra-cyclic Hydro-aromatic Ketones. — Irone. lonone . 467

7. Hydro-aromattc Carboxylic Acids. — (i) Hydro-aromatic monocarboxylic

Acids, Hexahydro-benzoic Acids, Tetrahydro-benzoic Acids, Di- hydro-benzoic Adds, Aliphatic Adds, Phenyl-fatty Adds, Hexa- hydro-oxy-benzoic Adds, Qninic Add, Shikimic Add, Keto-hydro- monocarboxylic Acid. {2) Hydro-aromatic Dicarboxylic Adds. Hexahydro-dicarboxyHc Adds, Hexahydro-terephthalic Acids. Tetra- hydro-dicarboxyUc Acids, Dihydro-dicarboxylic Adds, Oxy- and Keto-hydro-benzol-dicarboxylic Adds, Succmo-succibic Acid. (3) Hydro-benzol-tricarboxylic Adds. (4) Hydro-benzol-tetracarboxyHc Add 469

TSRPBKBS 484

A. Olefinic Terpene Group, — (i) Olefinic Terpenes, Myrcene, Ocimene,

Isoprene. (2) Olefinic Terpene Alcohols, Geraniol, Nerol, Linalool. (3) Olefinic Terpene Aldehydes, Citronellai, Citral. (4) Olefinic Terpene Adds, Geranic Add .... 487

B. Monocyclic Terpene or Menthane Group. — (i) Limonene and

Dipentene Group, Terpinolene, Terpinene, JRiellandrene. (2) Alcohols of the Monocyclic Terpene or Menthane Group, Mon- add Menthane Alcohols, Secondary Menthols, Tertiary Menthols, Diadd Alcohols, Terpin, Cineol, Tetra-acid Methane Alcohols, Terpineol-menthadiene Alcohols. (3) Bases of the Monocyclic Terpene or Menthane Group. (4) Ring-ketones of the Monocyclic Terpene or Menthane Group, Menthone, Carvenone, Pulegon, Cairvone ...... 491

C. Dicyclic Terpene Group :

I. Sabinane or Tanacetane Group. — ^Thujene. Sabinane . 510

II. Carane Group. — Carone. Eucarvone . . -514

III. Pinane Group. — Pinene. Turpentine Oil. Terebinic Acid.

Mvrtenol. Pinol ....... 515

IV. Camfhane Group, — Camphene. Bomylene. Fenchene.

Monacid Alcohols, santene. Bomeol. Iso-bomeol. Amines. Ketones. Camphor. Campholic Add. Azo-camphor. Camphenone. Campnanic Add. Lauronibc Acid. Apo-caimphoric Add. Fenchone . 522

D. Ses^ui-terpene and Poly-terpene Group, — Cadinene. Santalol . 546 Restns, — Caoutchouc . . •548

C. AROMATIC HYDROCARBONS CONTAINING

SEVERAL NUCLEI

A. Phsmyl-bbnzols and Polyphbnyl-fatty Hydrocarbons -549

I. PhenyUbenzol Grouf. — Diphenyl Group. Benzidin. Benzidin Dyes. Oxy-, Monoxy-, and Dioxy-biphenyls. Quinones of the Diphenyl Series. Coerulignone. Diphenic Acid. Diphenyl- benzol. Tri- and Tetra-phenyl-benzol .... 550

II. Benjtyl-benxol Group. — (i) Hydrocarbons, Diphenyl-methanes. (2) Alcohols, Benzo-hydrols. (3) Ketones^ Benzo-phenones, Halogen Derivatives, Phenyl-anthranile, Diamido-benzo- phenones, Oxy-benzo-phenones, Cotoin. (4) Carboxylic Add 3 of the Diphenyl-methane Group, Diphenyl-methane-carboxylic Adds, Benzo-hydrol-carboxylic Adds, Benzo-phenone-car- boxylic Adds ......... 562

III. Triphenyl-methane Group. — (i) Hydrocarbons, Triphenyl-methane, Nitro-substitution Products. (2) Carbinols, Fuchsine, RosaniHn, Methyl-violet, Phenylated Rosanilins. (3) Phenol Derivatives, Monoxy-triphenyl-methanes . . . .576

IIIa. Phenyl Derivatives of Triphenyl-carbinol, — Triphenyl-carbinols, hydroxylated in a Benzene JNudeus. Benzeins. Rosamines. Aurins and Rosolic Adds. Eupittonic Acid. Triphenyl-

xvi CONTENTS

PAGE

methane-carboxylic Acid. Carboxyl Derivatives of Triphenyl- carbinol Phthalides. Carboxyl Derivatives of the Oxy- triphenyl-carbinols. Phthaleins. Fluorane. Phloxin.

Rhodamins ......... 590

IIIb. Phenyl-biS'diphenyl-methane ....... 602

IIIc. Tetrapkenyl-methane ........ 602

IV. Homoheous Di- and Poty-fhenyl-paraffins. — (a) Gem-diphenyl- paramns and their Derivatives, Diphenyl-ethane, Diphenyl* ketene, Benzilic Acid, Triphenyl-acetic Add. (6) Sym. Diphenyl-ethane Group, Dibenzyl, Stilbene, Tolane, Alcohol and Ketone Derivatives of Dibenzyl, Benzoin, Benzile, Alcohol Derivatives of Stilbene, Carboxylic Acids of the Dibenzyl Group, Dibenzyl-carboxylic Acid, (c) Tri-, Tetra-, Penta-, and Hexaphenyl Group, Benzo-pinacone, Hexaphenyl-ethane. (^ Diphenyl-propane Group, Dibenzyl>ketone, Dypnone. Dibenzol-methane-carboxylic Acids. (e) Diphenyl-outane Group, Diphenacyl, Bidesyl, Dmhenyl-tetra-ketone, Carboxylic Acids, Vulpic Acid. (/) Diphenyl-pentane Group, Di- benzylidene-acetone, Benzamarone-carboxyl Derivatives, {g) Diphenyl-hexene Group, and Higher Homologues. . 603

B. CONDBNSBD NUCLEI ......... 64O

1. Ind^ne and Hydrindene Group. — Indene and its derivatives.

Hydrindene. Diketo-hydnndene. Indacene . 643

2. Naphthalene Group. — Constitution. Isomerisms. Ring Forma-

tions. Decompositions. Homologues .... 650

(i) Halogen Naphthalenes. (2) Nitro-naphthalenes. (3) Nitroso-naphthalenes. (4) Amido-naphthalenes, J^aphthalamines, Naphthylene - diamines. (5) Diazo- and Azo-compounds. (6) Hydrazin Com- * pounds. (7) Sulphonic Acids. (8) Naphthalene- sulphonic Acids. (9) Naphthols, Nitro-, Amido-, and Azo-naphthols, Naphthol-sulphonic Acids, Naphtho-sultone, Thio-naphthols. (lo) Naphtho-

Suinones, Juglone, Nitrogen Derivatives of the faphtho-quinones . . . . .658

(11) Alcohols of the Naphthalene Series and their Oxidation

Products. — (A) Alcohols. (B) Aldehydes and Ketones. (C) Naphthalene-monocarboxylic Acids. (D) Naphthalene Di- and Poly-carboxylic Acids . 676

(12) Di- and Trinaphthyl-methane Derivatives . .681

(13) Acenaphthene ....... 682

(14) Hydro-naphthalene Derivatives. — (A) Dihydro-deri-

vatives. (B) Tetrahydro-derivatives. (C) Hexa-, Octo-, Deca-, and Dodeca-hydro-naphthalenes . 683

3. Phenanthrene Group. — Halogen Nitro-, Oxy-, and Amido-Phen-

anthrenes. Carboxylic Acids. Hydro - phenanthrenes. Betene. Chrysene. Picene. Pyrene. Triphenylene . .687

4. Fluorene Group. — Fluorene. Retene, Chrysene, and Picene.

Fluorene. Phenyl-fluorene. Diphenylene-ketone. Fluor- enone. Fluoranthene ....... 695

5. Anthracene Group. — Anthracene. Alkylic Anthracenes. Sub-

stituted Anthracenes. Oxy-anthracenes. Anthranol. Anthrone. Anthra-hydroquinone. Oxanthrone. Carboxylic Acids. Hydro-anthracene. Dihydro-anthranol. Anthra- quinone. Alizarin. Purpurin. Emodin. Dianthraquinoyl. Pyranthrone. Benzanthrone . . . .710

6. Glycosides or Glucosides and Pentosides. — Sinigrin. Sinalbin.

Arbutin. Salicin. Populin. Gein. Gaultherin. Coni- ferin. Syringin. Phlorizin. .£sculin. Daphnin. Fraxin. Indin. Saponarin. Digitalin. Saponin. Convolvulin. Jalapin. Polygonin. Amygdalin. Naringin. Hesperidin. Quercitrin. Frangulin. Aloin . . . . . . 719

7. Bitter Principles. — Cantharidin. Anemonin. Picro-toxin.

Picrotin. Santonin. Artemisin ..... 724

8. Natural Dyes. — Brasilin. Hematoxylin. Carthamin. Curcumin.

Lichen Dyes. Carminic Acid. Kermessic Acid . . 725

A TEXT-BOOK

OF

ORGANIC CHEMISTRY

II. CARBOCYCLIC COMPOUNDS

The methane derivatives, or acyclic carbon compounds, with open carbon chains, dealt with in the first volume of this work, are here followed by organic compounds with closed carbon chains, or carbon rings, and these compounds I call by the name of Carbocydic Com- X>ounds. In contrast with these we have, e.g., the azocycUc compounds with a ring consisting only of nitrogen atoms, such as nitrogen hydride, and its derivatives. The carbocydic compounds are also called isocydic compounds, but the latter expression is too comprehensive, since it denotes compounds containing a ring consisting of a number of atoms, of any dement. Iii contradistinction to isocydic compounds we have the heterocyclic compounds, in which the atoms of several different dements take part in the formation of the ring.

The fundamental carbocydic hydrocarbons are those with a carbon ring consisting of from three to nine methylene groups. They are isomeric with the olefins, with an equal number of carbon atoms. They are designated either as polymethylenes, in accordance with the number of methylene groups which they contain ; or by prefixing an *' R " or " R." to the names of the normal olefins with which they are isomeric (" ring olefins ") ; or, according to the Geneva resolu- tions, by the names of the normal paraffins containing an equal number of carbon atoms with the word *' cydo-" prefixed (cyclo-paraffins). The first and third of these designations are to be preferred.

CH s. Trimethylene [Cyclopropane] *^CHj

Tetramethylene [Cydobutane] * *

CHj—— Cxij

Qxj CH V

Pentamethylene [Cyclopentane] ' /-xr* y^^«

Hexamethylene [Cyclohexane] cjj'— Ch!^H* Heptamethylene [Cydoheptane] * * ^ "NcH,

Octomcthylcne [Cydooctane] ch'--Ch!Zch!Zch*

Nonomethylcne [Cydononane] dj*— Ch!^hU-Ch!^^"' VOL. II. B

2 ORGANIC CHEMISTRY

Hexamethylene is also called hexahydrobenzol, and heptamethylene, suberane. For the nomenclature of ring substances see also B. 29, 587.

As the paraffins are followed by olefins and diolefins, so the cyclo- paraffins are followed by cyclo-olefin, cyclo-diolefin, and cyclo- triolefin.

Among the carbocyclic structures a special significance attaches to benzol (benzene), the fundamental hydrocarbon of the so-called aromatic substances or benzol derivatives, the most numerous class of organic compounds. If, in accordance with A. Kekul6, we assume in benzol a ring of six carbon atoms linked together in alternate single and double Unking — an assumption 'which the author prefers — ^benzol is a cyclo-triolefin :

Benzol [CyclohexatriCn] CH^^2 ^SV^.

By the addition of hydrogen it is possible to convert benzol into hexahydrobenzol, hexamethjdenc, and cyclo-hexane. A constantly increasing number of transformation products of aromatic compounds are becoming known, which can be referred to dihydro- or tetrsiiydro- benzol (cyclo-hexadiene and cyclo-hexene), and which, together with the hexamethylene or hexahydrobenzol derivatives, are termed *' hydro- aromatic compounds." To tliese belong many natural products, especially those of the terpene and camphor series. If this system were rigidly followed, every cyclo-paraffin system would be associated with the corresponding cyclo-olefin system having the same number of carbon atoms. But the treatment of the hydro-aromatic substances presupposes a knowledge of the aromatic substances, to such an extent that it is better to deal first with the latter. We there- fore treat first of the tri-, tetra-, penta-, hepta-, octo-, and nono- carbocyclic compounds, and afterwards of the hexacarbocyclic compounds.

In many ways the aromatic substances show a peculiar behaviour, different from that of the aliphatic compounds. But the hydro- aromatic compounds, as well as the other known polycarbocyclic compounds, approach in their chemical properties the saturated aUphatic substances, or the unsaturated ones, if there are any double- linked pairs of carbon atoms in the ring. These compounds are there- fore called aHphatic cycUc, or aUcycUc saturated, and imsaturated, compounds, to distinguish them from the aromatic compounds (B. 22, 769).

The study of the carbocyclic compounds has shown that the tri- and tetramethylene ring is more easily split than the more stable pentamethylene or hexamethylene ring, while hepta- and octomethy- lene rings are formed with greater dif&culty, and can usually be easily transformed into rings of a smaller number of carbon atoms.

We have met similar phenomena in the formation of some hetero- cyclic derivatives of aliphatic substances, e,g, the lactones, lactames, and dicarboxylic anhydrides (Vol. I.). In the case of the oxy-acids we indicated a scheme of the space-configuration of carbon chains, designed to explain the rare formation of a- and j3-lactones, in com- parison with the ease with which y- and 8-lactones are produced. An attempt at explaining the different stabilities of the tri-, tetra-, penta-.

METHODS OF RING FORMATION 3

and hexamethylene rings is made in the tensi(m theory of A. v. Baeyer (B. 18, 2278; 28, 1275). This theory proceeds from the following assumption : — " The four valencies of the carbon atom act in directions joining the centre of a sphere with the comers of an inscribed regular tetrahedron, and therefore form angles of 109® 28' with each otiier." These four lines are called axes.

" The direction of attraction can undergo a deflection, but this is accompanied by a tension, increasing with the amount of the latter." The assumption of valency forces acting at an angle is excluded, the amount of deflection being proportional to the tension. " In ethylene the direction of attraction is equally deflected, for both valencies of each carbon atom, until the directions have become parallel. In ethylene the angle of deflection is ^(109*' 28') =54® 44'. In trimethy- lene, which may be figured as an equilateral triangle, tiie angle between the axes must be 60**, and the deflection of each must be Kiog** 28'— 60®) =24^ 44'."

In the same way we obtain the following deflections :

Tetramethylene ^(109*' 28'— 90"*) = 9"* 44' Pentamethylene i(i09*' 28'— 108**) = o*' 44' Hexamethylene 4(109'' 28'— 120**) =— 5** 16'

HeptamethyleneJ(i09'*26'— 128*'34')=— 9*^33' Octomethylene J(io9** 28'— 135°) =— 12^51' Nonomethylene ^(109** 28'— 140*') =—15** 16'

This supposes, of course, that the carbon atoms all lie in the same plane, viz. the plane of the ring.

In dimethylene or ethylene the greatest deflection of the direction of action of both valencies has taken place. It has the greatest tension and is the loosest ring, which is easily spUt up by chlorine, bromine, hydrobromic acid, and iodine. Trimethylene reacts with much greater difficulty. Tetra-, penta-, and hexamelJiylene rings no longer behave Uke unsaturated compounds, and are very stable in the presence of halogens, hydrohalogen acids, and potassium permanganate. In harmony witii these views, the determination of the heats of combustion of the simplest cyclo-paraffins showed a considerable decrease from tri- to hexamethylene (B. 25, 496). According to Baeyer 's tension theory, the pentamethylene ring should form even more easily than the hexamethylene ring — a conclusion which led to successful attempts to prepare pentamethylene derivatives (B. 28, 655).

Methods of Ring Formation in Cyclo-paraffin Bodies.

Special importance is attached to the methods by which open carbon chains are converted into closed carbon chains. In accordance with the definition of nuclear syntheses as reactions in which previously unlinked carbon atoms are linked together (Vol. I.), every transforma- tion of an open carbon chain into a closed one must be regarded as a nuclear synthesis. And indeed it is by well-known nuclear synthesis methods applied to suitable aUphatic substances that the closing of rings with formation of cyclo-paraffin bodies has been carried out. The facts in question, already mentioned in divers places in Vol. I., con- stitute the transition reactions joining the class of paraffins with that

4 ORGANIC CHEMISTRY

of cyclo-paraffins. The most important items may be briefly enumerated.

I. Cyelo-parafflns themselves are produced by the action of sodium or zinc upon dibromo-substituted paraffins, the hydrobromic acid esters of the glycols :

i

■\CH,B I CH,— CHjBr "XCH,— CH,Br | CH,— CH,— CH,Br

^xi/CH, icH,— CHCH, i ^„ /CHr-CHCH. ICH,— CH,— CH,

"\CH, CHg— CH,

nCHj— Cxij CHj— CHj— ^Hj

a-Monobromine derivatives of the glutaric acid series yield tri- methylene-carboxyUc acids even when treated with alcoholic potash.

2. Intramoleeidar pinaeone formation. — Besides secondary alcohols, the reduction of the ketones yields ditertiary glycols, the pinacones. On reducing diacetyl-pentane we obtain besides an aliphatic disecondary glycol a ditertiary glycol, a cyclic pinaeone :

^„ /CH,— CH,— CH{OH)CH8

^„ /CHf-CH,— CO.CH, -^ — "^ "XCHg— CH,— CH{OH)CH8

• \CH,— CH,— CO.CH, ^ (, jj /CH,— CH,— C(0H)CH3

■ \CH,— CH,— C(OH)CHg

3. CyeUo syntheses with the aid of metallorganle compounds. — By

treating the di-magnesium compound of the i, 5-dibromo-pentane with acetic ester we obtain methyl-cyclo-hexanol. Carbonic acid reacts with the formation of cyclo-hexanone :

^„/CH,— CH,\po^^2!_rw /CH,.CH,.MgBr CH^COOCH, /CH,— CH,\p/OH

^"\CH,-CH,/ ^^ ^"* \CH,.CH,.MgBr ^ ^**^\CH.-^H./ ^XCH,

The synthesis of a tertiary alcohol from a magnesium alkyl iodide and a ketone proceeds intramolecularly in the action of magnesium upon S-aceto-butyl iodide :

CH,.CH,I Mg CH,.CH,\p /OMgl

CH,.CH,.C0CH3 CH,.CH,/ Xch,

4^. Intramolecular aceto-acetic ester condensation. — When sodium acts upon adipinic acid ester there is intramolecular condensation cor- responding to the formation of acetic ester, and a cyclic j3-ketone- carboxylic ester is formed :

CH,— CHg--COOC,H, CH,— CH^-- — COOC,H,

CH,— CH,— COOCtH, -AH.oh'* CH,— CHjXo

The same behaviour is shown by the esters of the pimelinic acids, which yield jS-ketone acid esters with six-membered ring chains.

46. Oxalo-acetic ester condensation. — The action of oxalic ester and glutaric acid ester upon sodium ethylate produces diketo-penta- methylene-carboxylic ester :

rx2 /CH,CO,C,H, COOCjHj ^ ^^ yCHCCO.CtH,)— CO

" \CH,CO,C,H, COOCjH, "\CH(CO,C,H,)— Co

Similar reactions are shown by j3-substituted glutaric acid ester, acetone-dicarboxyUc acid ester, methyl-ethyl-ketone, dibenzyl-ketone, etc., with oxalic ester and sodium ethylate.

METHODS OF RING FORMATION 5

4c. Intramoleeular formaflon of jS-dlketones. — y-acetyl-butyric acid ester is condensed by sodium ethylate to diketo-hexamethylene :

CH,— CO— CH, CH«— CO— CH,

CHg— CHg— COOCjH, CH,— CH,-CO

With the same treatment the c- and f-ketonic acid esters yield extra* cyclic /3-diketones of the pentamethylene and hexamethylene series.

5. Cyelie syntheses with malonie add esters, aeetie aeid esters, eto. — ^T^ough the action of alkylene bromides upon sodium malonie acid esters we obtain cyclo-paraffin acid esters (W. H. Perkin, jun.).

The reaction takes place in three phases :

CH,Br j,^C,„(,„. ^ CH,CH(CO.C,H,),+NaBr

CH,.CH(CO,C,H,), + NaHC(CO,C,H5), « CHj.CNa(CO,C,Hj), CHjBr

-NaBr I <^H.Br +CH,(CO,C,H,), *^JJ«)>C(CO,C,H,),

eH.<CH.Br aNaHC(CO,c.H>),_^ CH.<^H;>C(CO.C.H.).

By introducing the bromination products of oleiin-mono- and olefin- dicarboxyUc acid esters in the place of alkylene bromides, this reaction has been used for preparing numerous trimethylene derivatives. Cyano-acetic ester biehaves like malonie ester (C. 1899, II. 36, 824).

If sodium aceto-acetic ester acts upon i, 4-dibromo-n-pentane, I, 2-methyl-acetyl-pentamethylene-carboxylic acid ester is produced:

/CH,

CH,.CHBiCH3 CHNa.CO,C,H, CH,.CH \ /CO,C,Hj CH,CO,C,H, CH,.CH,.Br "^^CO.CHa "CH,.CH,/ NCOCH, "^COCH, +2NaBr

From I, 5-dibromo-pentane we correspondingly obtain a-acetyl-hexa- methylene-carboxyhc ester (B. 21, 742 ; 40, 3943).

6. From the di-sodium compounds of alkylene-dimalonic esters iodine or bromine extracts the sodium with the formation of a ring, just as iodine converts the sodium aceto-acetic ester into diaceto- succinic ester, and mono-sodium malonie ester into dimalonic ester. From the cydo-parafiBn-tetracarboxylic acids thus produced we may obtain cyclo-paraffin-dicarboxylic acids by splitting of! 2CO, (W. H. Perkin, jun.).

Tri, tetra-, penta-, hepta-, octo-, and nonocarbocyclic compounds :

CH /CNa(CO,C,H,), rxx /C(CO,C,H5)g ^w /CHCO,H

•\CNa(CO,C,H,), "XCCCOtCtH,), •\CHC0,H

CH^-CNa(CO,C,HJ, CH^— C(CO,C,H,), CH,— CHCO.H

CHf-CNa(CO,C,H,), CHg— C(CO,C,Hj), * CH,— tHCO,H

CH^ ^^••^N*(^^»^«^*)«— >CH /CH,-C(CO,C,H,), ™ /CHr-CHCO,H ^CH,.CNa(CO,C,HJ, •\CHr-C(CO,C,HJ, •\CH,— CHCO,H

7. Cyelie ketone formation. — As the calcium salts of the paraffin- monocarboxylic acids during distillation 3deld open ketones, so the

ORGANIC CHEMISTRY

calcium salts of some higher normal paraffin-dicarboxylic acids yield during dry distillation cyclic ketones (J. Wislicenus) :

CH,— CHg—CO,\^ CH,— CHa— CO,/ ,CH, — CH,\qq CH,— CH,/

^jj /CHg-CH,-CO.\^ CH,— CH,--CH^-CO,\^

■^ y^TT ^*TT /^/^ X i^TT /^XT /^"WT />^N /

NcHr-CH,— COj/ ^ ' rw /^^« — C^t\po

CHj— CHj— CHg— CO,/ CH j(— CH J— CH,\ p ^ CH,— CHg— CH^/ ^„ /CH,— CH,— CIV-CO,\^ CH,— CH,— CH,— CHg— CO,\^ '\CH,— CH,— CH^-CO,/ I CH,— CHg— CH,— CH,— CO,/

CHy'^^r-<^Hg— CH,\^Q nCH,— Cxi,— CH,/

JL CH,— CH,— — CHg— — Cxl,\p|-v CHg— — CH,— CH,— CH, /

7fl. During distillation at ordinary pressures the anhydrides of adipinic and pimelinic acids and their alkyl substitution products split into CO, and cyclic ketones (H. G. Blanc; see Vol. I.).

8. Allphatie dlazo-eompoiinds, like diazo-methane (Vol. I.) and diazo-acetic ester, add themselves to olefin-mono- and -dicarboxyUc esters with the formation of cydic azo-compounds or pyrazolin com- pounds, which, by splitting off nitrogen, pass easily into trimethylene- carboxylic acids (E. Buchner) :

N=N CHCO,R

\/ +11 CO,RCH CH,

N=N CHCO,R

\/ +11 CH, CHCOjR

N=N— CHCO,R_j,^

CO,RCH

dn-i:

H.

>CO,RCH< I

/

CHCOjR

\

N=N— CHCO,R _N,

ch/i

CH, CHCO,R

CH, CHCO,R ^CHCO,R

Cp. also the condensation of benzol with diazo-acetic ester to isophenyl-acetic or norcaradiene-carboxylic ester.

I.— TRI-, TETRA-, PENTA-, HEPTA-, OCTO- AND NONO-

CARBOCYCLIC COMPOUNDS

A number of natural products are closely related to these groups of carbocyclic compounds : carone, eucarvone, pinene, camphor, tropin, ecgonin, pseudo-pelletierin, etc. This group of bodies, there- fore, has lately grown in scientific and practical interest.

We may here first give a summary of the physical properties of the simplest cyclo-paraffins (B. 40, 3981) :

Name.	Melting-point.	Boiling-point.	Sp. G. at 4*.	Refractive Index for D Line.
Cyclopropane Cyclobutane Cyclopentane Cydohexane Cycloheptane Cyclooctane Cyclononane	1 1 1	Gaseous Liquid + 6-4'* ~I2* + 11-5° • *	Approx. — 35*» II°-I2° 49^ Si** US'* i45-3°-i48° 170°-! 72°	• • 0-7038 07635 07934 0-8275 0-850 o785(?)	■ • 1-37520 1-40855 1-4266 I 4452 I 1-44777 1-4328

The molecular refractions determined from the densities and refractive indices indicated agree with those calculated from theory

TRIMETHYLENE GROUP 7

(see Vol. I., Introduction). It follows that in the cyclo-paraffins the fonnation of rings has no influence upon the molecular refraction.

A. Trimethylene Group. Trimethylene {cyclopropane) axjV/^^i is an easily condensible gas.

It is obtained from trimethylene bromide with the aid of sodium (Freund, 1882), or of alcohol and zinc dust (B. 20, R. 706 ; /. pr, Ch, 2, 7, 512). It may combine with bromine, especially in the presence of HBr acid, whereby chiefly trimethylene bromide CH,Br.CH,CH.Br is produced, or with hydriodic acid, forming n-propyl iodide, but it does so with greater difficulty than propylene. At a red heat it transforms itself into propylene (B. 29, 1297 » C. 1899, I. 925, II. 287). In the presence of finely divided nickel, hydrogen reduces it to propane already at 80"* (B. 40, 4459). MnKO solution does not oxidise tri- methylene in the cold (B. 21, 1282).

Concerning the difference in the heats of formation of trimethylene and propylene, see C. 1899, II. 801.

Methyl-trimethylene, b.p. 4'' (B. 28, 22 ; C. 1902, I. 1277) ; 1, l-Dimethyl-trimethylene b.p. 21^ (C. 1899, I. 254; 1900, II. 1069) ; 1,1,2- and 1, 2, 3-Trimethyl-trimethylene (B. 84, 2856); Vinyl-

CH,.

trimethylene I ^chch=ch, b.p. 40**, D 073, are produced in a

peculiar reaction by the action of alcohol and zinc dust on the tetra-

bromate of penta-erythrite (see Vol. I.) ; by MnKO it is oxidised to

CH,v CHOH

glycol I ycK/^ \ , which, by further oxidation with dilute

HNO3, 3delds a-oxy-glutaric acid ; with Br it forms a dibromide, whidi, on treating with lead oxide, yields keto-pentamethylene (B. 29, R. 780 ; C. 1897, II. 696 ; also C. 1898, II. 475, footnote) ; with NjOj it gives a pseudo-nitrosite, m.p. 145°, from which on reduction, besides diamine C5H8(NH,)2, b.p. i8o**-i85°, cyclo-butanone is formed (B. 41, 915). Concerning another interpretation of vinyl-trimethylene, see B. 40, 3884.

CHjv /CH3

Dimethyl-methylene-trimettaylene I /^'^^ (?)» b.p. yo'^-yi'*,

is produced from dimethyl-trimethylene-carbinol on boiling with acetic anhydride (C. 1905, II. 403 ; 1909, I. 1859).

Monoehloro-trimettaylene, b.p. 43"" (B. 24, R. 637).

Diehloro-trimethylene, b.p. 74"^ (B. 25, 1954).

Amino-trlmethylene (CjHgJNHg, b.p. 49^ from trimethylene- carboxylic amide with KOBr (C. 1901, II. 579). Miscible with water in all proportions. Smells Uke propylamine. With nitrous acid it yields allyl alcohol, with spUtting of the ring (C. 1905, I. 1704).

Trimethylene-methylamine (C,H5)CH,NH2, b.p. 86^ from tri- methylene-carboxylic nitrile by reduction. Gives with nitrous acid trimethylene-carbinol and cyclo-butanol, with expansion of the ring

(B. 40, 4393)

Trlmethyl-carbinol (C8H5)CH20H, by the reduction of trimethylene- carboxyUc ester with Na and alcohol (B. 40, 4397). With concentrated HBr it passes into i, 3-dibromo-butane (C. 1908, 1. 818),

8 ORGANIC CHEMISTRY

Trimethylene-ethyl-earblnol, b.p. 14''.

Trimethylene-isopropyl-carbinol, b.p. 151''.

These two are obtained by reduction of the corresponding ketones.

Trimethylene - dimethyl - carbinol (C,H5)C(CH8)jOH, by treating Mg(CH3)I with acetyl-trimethylene or trimethylene-carboxylic ester; chloride, b.p. 132** ; bromide, b.p. 152®. By oxalic acid it is isomerised, with splitting of the ring, to dimethyl - tetramethylene oxide

Ch!JISi.*>^ (^- ^' 3887).

Trimethylene-dlethyl-carblnol (C,H5)C(C,H5),OH, b.p. 158*.

Trlmethylene-methyl-ethyl-carblnol (C,H5)C(CHs) (CgHOOH, b.p. 141** (C. 1909, I. 1859).

CH

Trlmettaylene-aldehyde I *)>ch.cho. b.p. 98"*, by oxidation of

trimethylene-carbinol with chromic acid.

Acetyl-trimethylene ^^"^ch.coch,. b.p. 113*' :

1. From aceto-propyl-bromide with ejection of HBr by KOH (C. 1898, II. 474).

2. From acetyl-trimethylene-carboxylic acid by heating.

3. By the action of Hg(CH3)I upon trimethylene cyanide. The three-ring is split up by mineral acids. For homologous ketones see C. 1909, I. 1859.

Trimethylene-earboxyllc acids (A. 284, 197) are obtained by the general methods of ring formation 5, 6, and by method 8, which only leads to trimethylene-derivatives (p. 6). From those trimethylene- polycarboxylic acids which contain two carboxyls bound with one carbon atom, we obtain the carboxylic acids poorer in carboxyl by splitting off CO,. Certain peculiar phenomena of isomerism (cis- and trans-forms) are attributed to the position of the carboxyls on the same side, or on different sides, of the trimethylene plane, as in the case of the isomerisms of the tri-thio-aldehydes (Vol. I.).

Trimethylene-carboxylic add CjHgCOaH, m.p. 18**, b.p. iSs"*, is isomeric with crotonic acid. The trimethylene ring is split by bromine with formation of a, y-dibromo-butyric acid (C. 1909, II. 1130). Its nitrite, b.p. 118**, has been obtained by distilling y-chloro-butyro-nitrile over KOH ; ethyl ester, b.p. 134**; chloride, b.p. 121°; amide, m.p. 124*' (C. 1901, II. 579 ; 1902, I. 913).

CH coon

Trans - phenyl - trimethylene - carboxylic acid c«h,ch<j[

m.p. 105**, has been obtained by method 8, by addition of diazo-acetic ester to styrol {q.v.). It was successfully disintegrated to cis-trans- trimethylene-i, 2-dicarboxylic acid.

2, 2 - Dimethyl - trimethylene - carboxyUc acid (CHj.c/^^^^^^,

b.p. 100**, smells strong^ of butyric acid. The ester, b.p. 90**, is formed by separation of HBr from the 3, 3-dimethyl-y-bromo-but3nic acid ester (C. 1907, II. 897).

Trimethylene-1, 1-dlcarboxyllc acid {vinaconic acid) ^!!*^(COtH).,

m.p. 140° (see method 5, p. 5). With HBr this passes mto brom- ethyl-malonic acid CH(CO£H)2BrCHjCH2. It also takes up bromine

TRIMETHYLENE GROUP 9

(B. 18, 3314), but is not affected by HNOj, MnK04, or nascent hydrogen (B. 88» 704 ; 28, 8). With Na-malonic ester the ester of vinaconic acid condenses to butane-tetracarboxylic ester, and thus behaves quite like- a, ^-olefin-carboxylic ester (see Vol. I. and B. 28, R. 464). Con- cerning the constitution of vinaconic acid and the homologous methyl- vinaconic acid, see A. 294, 89.

1, l-Cyano-trimethylene-earboxylic aeid, m.p. 149'', from sodium- cyan-acetic ester and ethylene bromide (C. 1899, II- 824).

Aeetyl-trimethylene-earboxylie ester ^2"S^<^^^S?*tx » ^P- ^95°'

from sodium-aceto-acetic ester and ethylene bromide (B. 17, 1440).

Trimetliylene-1, 2-dicarboxylie aeid is known in two isomeric forms, distinguished as cis- and cis-trans- or trans- forms (A. 246, 128) :

COjH CO,H CO,H H

C C C C

ft\CH,/fi ft\CH^CO,H

r-cis- form. F-cis-trans- form.

Cls-trimethylene-1, 2 - diearboxylie aeid, m.p. 139''; anhydride, m.p. 59**, is obtained from tr-i, 2-tri- and -i, 2-tetracarboxylic acid by heating. Cis-trans-trimethylene-i, 2-dicarboxylic acid, m.p. 175*, from monobromo-glutaric add ester with alcohoUc caustic potash (C. 1900, 1. 284). It has been separated into two optically active com- ponents by means of its quinine salt, Uke the cis-trans-trimethylene- 1, 2, 3-tricarboxylic acid described below (B. 88, 3112). Its methyl ester, b.p. about 210**, is obtained from acryl-diazo-acetic ester by method 8, brides glutaconic acid ester ; and from fuinaric acid ester with diazo- methane (B. 27, 1888 ; 28, R. 290).

Cis - phenyl - trans - 2, 8 - trimethylene - diearboxylie aeid

C,H,Ch/ , m.p. 175** ; anhydride, m.p. 134** ; from a-bromo-

benzylidene-bis-malonic ester with alcoholic ammonia, or by adding diazo-acetic ester to cinnamic-acid ester (B. 86, 3774 ; /. pr, Ch., 2, 75, 490).

Trimethylene-1, 2-triearboxyUe aeid ch,((^^^^^*, m.p. i%f, by

disintegration. Its ethyl ester, b.p. 276**, from a,p-dibromo-propionic- acid ester (B. 17, 1187), and from a-brom-acrylic ester with Na-malonic- acid ester by method 3 (B. 20, R. 140, 258).

Sym. trimethylene-1, 2, 3-triearboxylie aeid co,hch/^||^^^«^, cis-

form, m.p. 150^-153*' ; cis-trans-form, m.p. 220** ; anhydride, m.p. 187**, b.p. 265**. The cis-acid is obtained from the i, 2, 3-tetracarboxylic add (B. 17, 1652), the cis- trans-acid from fumaric-acid-diazo-acetic ester (B. 28, 2583). The latter acid is also obtained from the oxidation of isophenyl-acetic or norcaradiene-carboxylic acid (B. 27, 868).

Trimetliylene-1, 2-tetraearboxylie aeid ^^tx^ico'ni' Passes at 200**

into the anhydride of the cis-i, 2-dicarboxyhc acid. Its ethyl ester, m.p. 43^ b.p.j, 187°, is obtained from method 6 (B. 28, R. 241).

Trimethylene-1, 2, 8-tetraearboxylie aeid (COtH)tC\§Hco*H P^^^^ at gs'^-ioo*' into cis-i, 2, 3-tricarboxylic acid. Its ethyl ester.

10 ORGANIC CHEMISTRY

b.p. 246°, from dibromo-succinic ester by method 5. The cis-i, 2,- trans-i, 3 acid decomposes at igS^^-igS® (B. 28, R. 290).

1, l-bimethyl-trimethylen6-2, 3-diearboxylie acid, caronic acid

(CH8),C<; ^2^^'tj' trans-form, m.p. 213**, passes on heating with acetic

anhydride into the cis-form, m.p. 176**. The anhydride of the cis-form melts at 55°. The caronic acids are obtained by oxidation with Mn04K from carone (see Terpene ketones), which therefore contains a trimethylene ring. Synthetically, the caronic acids have been obtained from a-bromo-pp-dimethyl-glutaric-acid ester with alcoholic potash (C. 1899, I. 522). By heating with HBr the caronic acids are easily transformed into terebinic acid {q.v.). On heating aai-dibromo-pp- dimethyl-glutaric ester with alcoholic potash we obtain etho-oxy-

caronic acid (CH,)tC<(^5So^H^^'^' "^'P' ^^^"^ ^^' ^^^^' "' ^^^)-

1, 2-Dimethyl-trim6thylene-29 8-diearbozylie aeid, m.p. 154'', is

identified with the acid the ester of which is obtained with PCI5 from

oxy-trimethyl-succinic ester (C. 1908, I. 627).

The 1, l-dialkyI-2, 8-dieyano-trimethylene-2, 8-dicarboxylie acids

have been obtained in considerable numbers in the form of imides of

the general formula o /C\A/ri,j\_r»o/^^ ' ^^^"^ ^® corresponding dialkyl-dicyano-bromo-glutarimides (C. 1899, II. 439 ; 1901, I. 57). Trlmetliylenc-tricyano-tricarboxyllo-acid ester roSc(cn)/^coor'

m.p. 119°, is formed by the action of bromine or iodine upon sodium- cyano-acetic ester in ether ; on saponification it jaelds trimethylene- tetra- and then -i, 2, 3-tricarboxylic acid (B. 38, 2979).

Metliyl-eyclo-propene-dicarbozylio acid ^^^^\§!ro*H)' ^'^' ^^^''' see B. 26, 750.

B. Tetramethylene Group.

For obtaining tetramethylene compounds the ring formation methods i, 5, and 6 are used.

Tetrametliyleno-oyclo-butane ^jj!I^h ' ^'^' ^^°-^^''' ^4^ 07038, is obtained by reducing cydo-butene with Ni and H at loo** ; at higher temperatures butane is also produced, with splitting of the ring. It possesses a very feeble odour, and bums with a luminous flame. In the cold it is stable in the presence of bromine and concentrated HI.

Metliyl-tetramethylene cJJ'Zch^^' ^P* 39''-42^ method i, p. 4. Cyelo-butene aC'Zch' ^^^y condensible gas of b.p. i-s^'-a*',

D4® 0733, generated together with A^'^-butadiene during dry distilla- tion of cyclo-butyl-trimethyl-ammonium hydroxide. Adds bromine, forming i, 2-dibromo-cyclo-butane, b.p.24 69°, m.p. —2°, which, with KOH, splits off HBr and passes into bromo-cydo-huUne, This is an oil of penetrating odour, b.p. 92**, which oxidises to succinic acid. With bromo-cyclo-butene as a starting-point, a number of bromo-substitution products of cyclo-butane have been prepared. Thus it combines with HBr to 1, 1-dibromo-cyeIo-butane (I.), b.p. 158**, and with Br to 1, 1, 2- tribromo-cyelo-butane (II.), b.p.j, 109"*. This gives, with alcoholic

TETRAMETHYLENE GROUP ii

KOH, if 2-dIbromo-eyelo-butene (III.)* b.p. iss'', distinguished by a great faculty for polymerisation. With KMn04 it oxidises to succinic add, and combines with Br to form 1, 2-tetra-bromo-eyolo-butane (IV.), m.p. 126^, which, on further bromination, yields pentabromo-eyelo- bQtane C4H,Brg, b.p.^, i75''-i85'', and hezabromo-eyelo-butane CgH^Br^, m.p. 186-5°, which is remarkable for its ease of crystallisation

(B. 40, 3979)-

(I.) (II.) (III.) (IV.)

^>

CH,— CBr ^CHr-CBr, CHt— CBr, ^CH^— CBr ^CH^-CBr,

CH,— CH ^ CHg— CH, CH^— CHBr ^ CH,— CBr ^ CH,— CBr,

The name dimethyl-fnethylene'tetramethylene p„' ^~ ^ ^'*, b.p.

loo^^-ioa**, is given to the hydrocarbon generated from the bromide of dimethyl-tetramethylene-carbinol by splitting off HBr. On reduction with HI it passes into i, 3-dimethyl-pentamethylene.

Oxy-tetramethylene, cyclo - hutanol C4H7OH, b.p. 123°, from anddo-tetramethylene by the action of HNOg, and by electrolysis of potassium tetramethylene-carboxylate (B. 40, 2594, 4962).

Amido-tetramethylene C4H7.NH2, b.p. Si'', arises from the amide of tetramethylene-carboxylic acid with bromine and an alkali (B. 40, 4745).

Tetramethylene - methylamlne ch'ch^^*^^'' ^P* ^^^''' ^^ reduction of tetramethylene-cyanide, gives, with HNOj, a mixture of tetramethylene-earbinol C4H7.CH2OH, and oyelo-pentanol CgHs.OH.

Tetramethylene-oarbinol C4H7.CH2OH, b.p. 142**, by reduction of tetramethylene-carboxylic ester with Na and alcohol ; bromide, b.p.

i37'-i39'(B.40,4959).

Tetramethylene-methyl-carbinol C4H7.CH(OH)CH„ b.p. 144'', by

reduction of tetramethylene-methyl-ketone.

Tetramethylene-dimethyl- and diethyl-earbinol, b.p. 147° and iSS"" respectively, by the action of Mg(CH3)I and Mg(C2H5)I on tetramethy- lene-carboxylic ester (C. 1905, II. 761 ; 1908, II. 1342).

Tetramethylone-diethyl-glycol [C4H7C(OH)C2H5]2, m.p. 95^ by reduction of tetramethylene-ethyl-ketone.

Keto-tetramethylene-eyclo-butanone ch'— ch ' ^P* 9^**' ^0^ 0-9548, generated (i) by action of bromine and alkali on a-bromo- tetramethylene-carboxylic amyl ; (2) during boiling of i, i-dibromo- butane with lead oxide and water. Nitric acid oxidises it to succinic add (C. 1908, I. 123).

Tetramethylene-methyl- and ethyl-ketone, b.p. 135'' and 145'', from the carboxyl chloride with zinc alkylene (B. 25, R. 371), or from the amide with Mg(CH8)I (B. 41, 2431).

Di-tetramethylene-ketone (C4H7)2CO, b.p. 205'', from the calcium salt of carboxylic acid.

Dimethyl- and diethyl-tetpamethyleno-ketone ^'^•^h Hchc h '

m.p. 45**-i20** and i6o°-i65®. This constitution is ascribed to substances obtained during distillation of Ba salts of aaj-dimethyl- and diethyl-glutaric acid (C. 1897, II. 342).

1, 8-Dimethyl-2, 4-dlketo-tetramethylene ^^coI^HCHa' ™P- ^35°>

12 ORGANIC CHEMISTRY

by saponification and rejection of CO, from the corresponding car- boxylic-acid ester, on boiling with bartya water.

1, 1, 8, 8-TetramethyI-2, 4rdlketo-tetramethylene ^^^'^'co^Iccch.)/

m.p. 116**, obtained by rejection of HCl from iso-butyryl chloride. Also by action of molecular silver on bromo-iso-butyryl bromide. In both cases we must assume the formation of dimethyl-ketene (see Vol. L), which easily polymerises to tetramethyl-2, 4-diketo-tetramethylene. Its odour recalls both menthol and camphor, and it has the great volatility of these compounds.

Dioxime» m.p. 281'' (B. 89, 970).

Tetramethylene-earbozyllo aeid C4H7CO2H, b.p. 194"^, smells like the fatty acids, and is generated from i, i-dicarboxylic acid ; on reduction by HI it jaelds n-valerianic acid, with splitting of the ring (C. 1908, II. 1342). Ethyl ester, b.p. 160*^ ; chloride, b.p. 142° ; anhydride, b.p. 160*' ; amide, m.p. 130** ; nitrite, b.p. 150** (B. 21, 2692 ; C. 1899, 11. 824).

Tetramethylene-ly 1-diearboxylio aeid melts at iss"", passing into monocarboxylic acid. Its ethyl ester, b.p. 224**, by method 5, p. 5 ; nitrile ester, b.p. 214®, from trimethylene bromide, and sodium cyan- acetic ester (C. 1899, II. 824 ; 1905, II. 761).

Cl8*tetramethylene-ly 2-dicarboxylie acid, m.p. 137'', from tetra- carboxylic acid. Anhydride, m.p. 77**, b.p. 271** (B. 26, 2243). Heating with HCl to 190° produces the trans-acid, m.p. 131'' (B. 27, R. 734). By bromination with Br and P, i, 2-dibromo-tetramethylene-dicarboxylic acid is produced ; and its ester, on treating with alcohol and KI, passes

pxT ceo H

into the ester of cyclo-butene-dicarboxylic acid /^h*— Cco!h* ^'^' ^7^°'

The latter easily yields an anhydride (/. Ch. Soc. 66, 950).

Tetramefhylene-1, 8-dioarboxylie acid, cis-form, m.p. 136'' ; anhy- dride, m.p. 51**; trans-form, m.p. 171°, have been obtained from the products of the action of formaldehyde upon malonic ester, and from a-chloro-propionic-acid ester, with the aid of Na alcoholate (C. 1898, II. 29). Also produced by boiling p-methoxy-methyl-malonic ester with concentrated HCl with the loss of two molecules of methyl alcohol, by saponification, and COj-rejection, from the tetra-carbo- ester first formed (C. 1909, I. 152) :

CH,0— CHtf— CH(COOR)t CH,— C(COOR),

(ROCO),CH— CH,— OCH3 (ROCO),C CH,

Tetramethylene-1, 2-tetraearboxylie aoid, m.p. i45°-i5o'', by trans- formation into cis-i, 2-dicarboxylic acid. Its ester is formed by method 6, p. .

Diacetyl-tetramethylene-diearboxylie ester by method 6, p. 5 (B. 19, 2048).

Keto-tetramethylene-triearbo-esters, such as :

CO— CHCOOR CO— c/^^ CO— c/^!?!*^

II II \COOR I iXCOOR

ROCOCH— C<['p5l„ ROCOCH— C<^^„ ROCOCH c/^^^

\COOR \COOR ^COOR

are formed by condensation of Na-malonic esters, or methyl and ethyl

TETRAMETHYLENE GROUP 13

malonic esters, with citraconic ester in alcoholic solution, in which process probably the tetracarboxyUc esters first formed with open chains undergo cycUc aceto-acetic ester condensation. By saponi- fication with HCl two carbox-ethyl groups are spHt off the above substances, and the following i-keto-tetramethylene-3-carboxylic acids are formed (B. 38, 3751) :

CO CH, CO CHCHs CO CHC,H,

^««-<SoH ^««-^<c?OH ^««-<c?OH

1, 8 - Dimethyl - 2, 4 - diketo - tetramethylene - earboxylic ester

CH3 CO~C— COOCjHj. m.p. I33°-I35°, has been obtained by the action

CHgCH— CO

of concentrated sulphuric acid upon sym. dimethyl-acetone-dicar- boxyhc ester. By alkalies the ring is easUy spUt again (B. 40, 1604). Diethyl - diketo - tetramethylene - dicarboxylic ester,

Co-C^-COOC,H, ^ II3°-II6^ is identified with the

C,HftOCOC CO > fo o

C,Ha

dimeric ethyl-ketene-carboxylic ester. During distillation at ordinary pressures it is depolymerised. Anilin also spUts the molecule, forming ethyl-malonic-ester aniUde (B. 42, 4908).

Tetramethylene-l,8-dlglyoxylic aeid ^^•^^^JJ,Ch!co.co,h' '^'^' 240**, produced by condensation of tartaric acid and paraformaldehyde with concentrated H2SO4. Decomposes into ethylene and oxalic acid by heating with alkalies, and, on further heating with HjSO^, it passes into a dilactone (B. 29, 2273).

By polymerisation of olefin and acetylene earboxylic acids, we sometimes obtain substances with a f our-membered carbon ring :

Diphenyl - tetramethylene - dicarboxylic acid, a-truxillic acid,

C SchIJhcooh' ""P- ^75'. forms from cinnamic acid (q.v.) by

illumination (B. 85, 2908, 4128), and is found among the subsidiary alkaloids of cocatn {q.v.). By distillation it again decomposes into two molecules of cinnamic acid.

Diphenyl - tetrene - dicarboxylic acid c'h*C~Ccooh' ^'^' ^^9^'

formed by polymerisation of phenyl-propiolic acid, on heating, or with POClg ; easily forms an anhydride or imide (B. 85, 1407).

Pinic acid c^t^CH qcH,), ^ norpinic acid co,h.ch .C(CH,),

CH,.CHCH,C0,H ^ CH,.CHCO,H

are disintegration products of pinene (see Terpenes), in which a tetra- methylene ring, the so-called piceane ring, is assumed.

C. Pentacarbocyclic Compounds.

The number of known pentacarbocyclic compounds is much greater than that of the tri- and tetracarbocyclic compounds. They are derived partly from cyclo-pentane or pentamethylene, partly from cyclo-pentene. Cyclo-pentadiene is found in the inital products of raw benzene, as obtained from coal-tar. Pentamethylenes, and hexa-

14 ORGANIC CHEMISTRY

methylenes, have also been obtained from the naphthenes of Caucasian petroleum ; and hexamethylenes are partially transformed into the isomeric pentamethylene derivatives by heating alone, or with HI under pressure (cp. A. 824» i, etc.). Cyclo-pentane and its progeny have been obtained, not only by the methods of ring s}aithesis specified on pp. 4, 5, and 6, but also from hexacarbocydic ring ortho- (Uketones by intramolecular atomic displacement (see Chloro-diketo- pentamethylene): This last reaction will be met with again in dealing with the disintegration of aromatic substances. In the same manner some remarkable pentamethylene derivatives have been obtained from hexa-oxy-benzol : croconic acid and leuconic acid, which are dealt with below under hexa-oxy-benzol.

Camphor, which is easily converted into aromatic substances, and which contains a five-membered carbon ring, the so-called " campho- ceanic ring," gives in different reactions pentamethylene derivatives, e.g, camphorphorone, camphoric acid, campholenic acid, campholytic acid, etc. Camphor and its cycUc transformation products are dealt with in connection with the terpenes among the hydro-aromatic compoimds, after the benzol derivatives.

I. Hydrocarbons. — Pentamethylene, R - penUne, cyclopentane

<CH •— CH ch'— CH*' ^'P* 5^**' ^^^^ pentamethylene iodide by reduction.

Methyl-pentamethylene, b.p. 70*^, contained in the so-called hexa- naphthene from Caucasian petroleimi (C. 1898, II. 412, 576) ; formed synthetically from i, 5-dibromhexane, also from methyl-cyclopenta- none, as well as tert.-methyl-cyclopentanol (C. 1899, I. 1211 ; B. 85, 2686). 1, 2-Methyl-ethyl-6yclopentane, b.p. 124''. 1, 8-Dimethyl- pentamethylene, b.p. 93°, from the corresponding ketone, is optically inactive ; but from the iodide of the i, 3-dimethyl-tert.-cyclopentanol by reduction an optically active i, 3-dimethyl-cyclopentane, b.p. 91°, Md I•78^ and also from i, 3 -ethyl -methyl -cyclopentanol 1, 8-Methyl-etliyl-oyclopentane, b.p. 121'', [a]D 4-34''> is obtained (B. 85, 2678). 1, 2-Diphenyl-pentamethylene, m.p. 47"", and 1, 2, 8, 4- Tetraphenyl-pentamethylene from anhydro-aceton- and anhydrodi- benzyl-ketone-benzile (C. 1901, II. 407, 1310). Triphenyl-metbyl- and Triphenyl-dimethyl-pentamethylene from the corresponding cychc pina- cones (C. 1903, I. 568).

Dipentamethenyl, dicyclopentyl C^H^-CgH,, b.p. 190'', from penta- methenyl bromide with Na (C. 1899, II. 367).

Cyclopentene <^H^^j^ Zch'' ^P* 45**' ^^^ pentamethylene iodide

or bromide with potash, or from cyclopentanol with P2O5 (C. 1899, II* 367), yields with ozone an ozonide CgHgOj, which in water decom- poses, forming glutardialdehyde (B. 41, 1701). Perchloro-eyclopentene CjClg, m.p. 41°, b.p. 283**, from hexachloro-cyclopentenone with PCI5

(B. 28, 2214). Methyl-cyelopentene ^^xchZch^^' ^P' 7^'*' f"^^"* 59'07*', from 3-methyl-cyclopentanol by means of zinc chloride or oxalic acid, also from the iodide with KOH. By oxidation it is spUt into a-methyl-glutaric acid, which, together with the optical activity, proves the formula assmned (B. 26, 775 ; 35, 2491). Isomeric with

the methyl-cyelopentene istheMethylene-oyelopentane S2*'^2* y<^ «CH,.

PENTACARBOCYCLIC COMPOUNDS 15

b.p. 78^-81**, a liquid of penetrating odour, produced from cyclopentene- acetic acid by rejection of COj; niiroso-chloride, m.p. 81®. Gives a glycol, m.p. 40**, by oxidation with Mn04K, and also cyclopentanone (A. 847, 325). Similarly, 1 - Methyl - 8 - methylene - cyelopentane

""^^IT^S'^H.CH, has been obtained from methyl-cyclopentene-

acetic acid. By oxidation it is split into i, 3-methyl-cyclopentanone (B. 84, 3950 ; C. 1902, I. 1222). Like methyl-cyclopentene, it is optically active. In comparison with the corresponding saturated hydrocarbons, the strong optical activity of the unsaturated hydro- carbons with five-membered rings is very remarkable.

Ethylidene-cyclopentane ^2""^^'V ' ^^c^' b.p. II4^ Isopropyl-

idene-eyelopentane S!J"^!!'')cc<f^^, b.p. 136**, from cyclopentene-

isobutyric acid, with displacement of the double linking. By alcoholic sulphuric acid it is isomerised to AMsopropyl-cyclopentene (A. 858,

307).

Cyelopentadiene, pentol (cp. B. 22, 916) CH,<^^j^^^|[||, b.p. 41 ^

an initial product in obtaining raw benzene from coal-tar, is a colour- less liquid, violently attacked by both acids and alkaUes. It reduces ammoniacal silver solution. It soon polymerises, at ordinary tem- peratures, to a bimolecular compound, Dieyclopentadiene (€5110)2, b.p.35 88**, which at 170° boils with partial re-formation of cyelopenta- diene. It is much more stable than the monomolecular compoimd, and resembles the terpenes in its behaviour (B. 89, 1492 ; C. 1906, II. 1403). On heating under pressure, both the simple and the dimeric cyelopentadiene are transformed into a higher-molecular polymer, which again can be split to simple cyelopentadiene (B. 85, 4151).

The H atoms of the CHg group of cyelopentadiene have reaction capacities similar to those contained in the group .CO.CHj.CO (see Vol. I.). With K in benzene solution it yields the highly reactive potassium-cyclopentadiene, which absorbs CO2 with formation of a potassium salt of the bi-cyclopentadiene-carboxylic acid (C5H5. COOH)^, m.p. 210°, and dimethyl ester, m.p. 85**. With oxalic ester cyelopentadiene in the presence of sodiinn ethylate it condenses to cyclo- pentadiene-oxalic ester CgHj.COCOOCgHj ; with NjOs an isonitro-<ieri- vative is formed. With aldehydes and ketones, under the influence of Na alcoholate, coloured hydrocarbons are formed, which, referred to the

hypothetical simplest representation rw— ch/^"^^^'' ^^ termed

fidvenes: Dimethyl-fulvene C5H4 : C(CH8)2, b.p. 46^ Methyl-ethyl- fulvene C5H4 : C(CH8)C2H5, b.p. 185°, orange-coloured oils ; Diphenyl- dilvene C5H4 : C(CjH5)2, deep-red prisms, m.p. 82**. Further fulvenes, see A. 848, i. Like cyelopentadiene itself, the fulvenes absorb the oxygen of the air, and form peroxides, e,g, [C5H4 : C(CH8)2]04 (B. 88, 666; 84,68,2933).

Cyelopentadiene unites with the quinones in molecular proportions to form stable compounds, hke cyclopentadiene-quinone CnHioOg, greenish-yellow flakes of m.p. 78° (A. 848, 31). With i or 2 molecules of the halogen hydrides and the halogens cyelopentadiene jdelds addition products like : monochloro-cyclopentene C5H7CI, b.p.^o 50° \ trichloro-

i6 ORGANIC CHEMISTRY

cyclopentane C5H7CI3, b.p. 196°; tetrachloro-cyclopentane C^H^Cl^, b.p.i5 94°. Monochloro-cyclopentene gives with anilin anilino-cyclo- pentene C5H7.NC5H10, b.p.„ 94*'-96** (B. 88, 3348). By adding 2Br to the conjugate double hnks of cyclopentadiene (Thiele), two stereo-

isomeric i-4-dibromides are generated ^xx— CHBrx ^' * ^^^ ^^^ and a liquid one, which, on oxidation, yield two stereo-isomeric ooi- dibromo-glutaric acids (A. 814, 296). Methyl-ethyl-cyclopentadienc, see below.

1, 2, 4-Triphenyl- and 1, 2, 8, 4-Tetraphenyl-oyclopentadien6, m.p. 149** and 177°, as well as triphenyl-methyl- and triphenyl-dimethyl- cyclopentadiene, m.p. 163® and 128°, are obtained from the corre- sponding cyclic pmacones by splitting off 2H2O (C. 1898, II. 924 ;

1903. I. 568 ; B. 86, 933).

2. Alcohols. — Cyelopentanol CjH^OH, b.p. 139**; chloride, b.p. 115** ; bromide, b.p. 137** ; iodide, b.p." 164° ; amine, b.p. 107*" (A. 276,

322). 8-Methyl-cycIopentanol hoch/^J|^«;^;;^^^, b.p.ia49^ amine.

b.p.i2 42** (B. 25, 3519 ; 26, 775). Both alcohols are obtained by the reduction of the corresponding ketones.

2-Methyl-oyelopentanol, b.p. 148'', from methyl-cyclopentenone. I- or tert.-methyl-cyclopentanol, m.p. 30°, b.p. 136**, from the corre- sponding amine, b.p. 144**, obtained by reduction from the nitrification product of methyl-pentamethylene ; also from cyclopentanone with CHjMgl, as well as by direct synthesis from 8-aceto-butyl-iodide with Mg (p. 4, and B. 86, 2684 ; C. 1899, 1. 1212).

1, 8-Dimethyl-tert.-cyelopentanoI, b.p.94 89"", from i-methyl-3- cyclopentanone with CH^Mgl (B. 34, 3950).

Pentamethylend-glycol C5H8(OH)2, m.p. 49"*, b.p.^ 127**, from the dibromide of the cyclopentene (C. 1899, II- 3^7)- A further number of glycols of the pentamethylene series have been obtained by intra- molecular pinacone formation (p. 4) by reduction from the i, 5-di- ketones (see C. 1901, II. 406 ; 1903, 1. 588).

Pentamethylene-carbinol C5H9CH2OH, b.p. 162'', from cyclo- pentyl-magnesium chloride and trioxy-methylene. Also by the action of HNO2 on pentamethylend-methylamine C5H,CH2NH2, b.p. 139''- 145°, besides the cyclohexanol {q,v.) produced by a pecuUar ring expansion (A. 868, 325 ; B. 41, 2629).

1-Isopropyl-cyelopentane-l, 6-diol ^h^h /^^^^""^^^^KcS' m.p. 62°, b.p. 14 108**, produced by action of CHjMgl upon a-oxy-cyclo- pentane-carboxylic ester. On heating with dilute SO4H2 or oxalic acid, the pinacone undergoes the pinacolin transformation with extraordinary facility, 2, 2-dimethyl-cyclohexanone being formed with displacement of a methylene group and expansion of the ring (A. 876, 152).

CHg— CH,/ ^ ^ 'XCHg

. CH /CH,— CO \p/CH.

3. Ring-Ketones. — ^The cyclic ketones obtained from calcium salts and the anhydrides of adipinic acid and the alkyl-adipinic acids by methods 7 and 7a, p. 6, formed the starting material for the prepara-

PENTACARBOCYCLIC COMPOUNDS 17

tion of the corresponding alcohols, from which later the saturated, and unsaturated, pentacarbocyclic hydrocarbons were obtained. The oximes of these ketones yield on treatment with concentrated S04H^ S-lactames by Beckmann's transformation (see Vol. I.).

Adipln-ketone [cyclopentanone], keio-pentamethylene ^^ch^Z^h*'

b.p. 130**, is found in the wood acids (B. 81, 1885), and is also generated from 2-keto-pentamethylene-carboxylic ester by ketone splitting. It smells Uke peppermint, and yields n-glutaric acid on oxidation. Oxime, m.p. 120** (A. 275, 312). Heating with acetic anhydride to 180° gives, with partial enolisation, cyclopetUenol acetate, b.p. I56°-I58®. With benzaldeh3'de, adipin-ketone condenses easily to a mono- or dibenzal compound QHjCH : (Cfflfi) and CeHgCH : (C5H4O) : CHCeHg (B. 29, 1601, 1836 ; 86, 1499 ; C. 1908, I. 637). With HNO, we get di-iso-nitroso-cyclopentanone HON : (C5H4O) : NOH, m.p. 215° (C. 1909, II. 1549). By sodium ethylate two and three molecules of the cydopentanone are condensed, forming cyclopentane-pentanone (CjHgO) : (CgHg), b.p.i, 118°, and cyclodipentane-pentanone (CgHg) : (C5H4O) : (CjHg), m.p. 77^ b.p.^ 190** (B. 29, 2962). 8-Methyl-eyelo-

pentanone ^ch!I5h ' ^'^' ^^2°, is opticaUy active, [a] 135-9**

(B. 85, 2489), and smells Uke camphorphorone {q,v.), which belongs to the cyclopentenones, but is only dealt with in connection with camphor. The oxime of methyl-cyclopentanone is spUt up by PjOj to the nitrile of hexylenic acid CjH^CN, with p-methyl-pyridine as a by-product (C. 1899, II. 947). Cp. the similar behaviour of other cycUc ketones.

A 2-MethyI-eyolopentanone, which also boils at 142 ''-144'', has been obtained from a-methyl-adipinic acid (B. 29, R. 11 15). 2, 5-Dimethyl- eyelopentanone, b.p. 146°, from cuii-dimethyl-adipinic acid (B. 29,403). 2, 8y S-Trlmethyl-eyclopentanone from a, p, p-trimethyl-adipinic acid is related to camphoric add (B. 83, 54). A large number of other homologues of cydopentanone have been prepared by method 7«, p. 6, from the anhydrides of the alkylated adipinic adds (C. 1908, II. 776).

1, 8.DimethyI-4, 6-diphenyl-cyclopentanone cS;chZS(CI^)^^^' m.v. I22^ by reduction of dimethyl-anhydro-acetone-benzile with HI and P. As an intermediate product we obtain 1, 8-Dimethyl- 4, 5-dlphenyl-AMyelopentenone, m.p. 122'' (C. 1905, 1. 172).

Metliyl-eyelopentenone ^h^.c^^J^;;;;;^^', b.p. I57^ in wood oil. Oxime, m.p. 128** (B. 27, 1538).

Phenyl-eyelopentenone ^•^•^cH^o*' ^'^' ^'*°' ^^™ phenacyl- acetone (q.v.) with dilute NaOH. Oxime, m.p. 147** (B. 41, 194). Vl9henf]reyelopmUnolone,anhydrO'acetonebenzile^^

•m.p. 149^, from benzile (q.v.) and acetone. By condensation with other ketones, such as methyl-ethyl-ketone and dibenzyl-ketone, several more such ketone alcohols, of the cydopentene series, have been formed; from benzile and laevuUnic acid (Vol. I.) we obtain similarly a D^henyl-eyelopentenolone-aeette acid or anhydro-benzile-lsevulinic add (C. 1899, II. 1051 ; 1901, II. 1310 ; 1903, I. 569). An isomeric VOL, 11. c

i8 ORGANIC CHEMISTRY

diphenyl-cyclopentenolone S'S'^'^T^^ Vo. m.p. 176°. is ob-

Of rlf C = C ((J Ji) /

tained by the action of concentrated SO4H2 upon dibenzal-acetone, which is oxidised by potassium permanganate to benzile, and desyl- acetic acid (j.v.)- With HI both isomeric compounds are reduced to 1, 2-Diphenyl-eyeIopentane (B. 87, 1133).

Hexaehloro-eyclopentenones ^J'J^J/^^* "^-P- 28^, b.p.go 156"*, and

CCI CCl')^^^' m.p. 92 ^ b.p.75 I48^ by oxidation with CrOj, from the

corresponding a-oxy-acids, obtained from benzene derivatives, like o-amido-phenol and pyro-catechin (B. 24, 926 ; 25, 2697). For the action of NH, upon these ketones, see C. 1898, 1. 607.

1, 2-Diketo-pentamethyIen6 ^qI^h*^^^" ^'^' ^^^' produced by ketone splitting of the i, 2-diketo-pentamethylene-3, 5-dicarboxylic ester. The diketone has acid qualities. In accordance with the

desmotropic formula of a Cyelopentenolone ^S)h^ =ch*/^^^*' ^^ forms

salts and reacts with acetyl chloride, benzoyl chloride, and phenyl cyanate (B. 35, 3201),

Chlorine easily acts upon diketo-pentamethylene, with formation of 3-Ghloro-l, 2-dik6to-pentamethylene, m.p. 139*". Chlorinated 1,2- diketo-pentamethylenes are also formed in a manner analogous to the chlorinated cyclopentenones, from benzoyl derivatives, Uke phenol, and chloranilic acid. From potassium chloranilate with chlorine and water

we obtain : ^o CHCl/'^^' ^'^' ^^^"^ ^^' ^^' ^'^^^' ^^^^^6 ^^^^ resorcin, Tetrachloro-dlketo-R-pentene ^XI^o/ ^^■' ^'^' 7^*"' ^P-t?

148°, was obtained (B. 24, 916 ; 25, 2225).

The primary disintegration products of the benzene derivatives serving as basic products in these reactions are often chlorinated ketonic acids. Thus,in the last case,from resorcin the acid CClj.CO.CCl : CCICCI2 COOH, perchlor-acetyl-crotonic acid, in which the ring completion to the keto-pentamethylenes is then carried out by heating with con- centrated sulphuric acid (B. 26, 513). In a similar manner it has been found possible to convert the )S, 8-dibromo-laevulinic acid CHjBr.COCHBr.CHj.COOH by means of fuming sulphuric acid

mto two : Dibromo-diketo-R-pentene n >pHBr, m.p. 99°, and

CH— CO ^

\cBr,. m.p. 137'' (A. 294, 183).

CH— CQ/

Methyl-trlketo-pentamethylene CQ<fg(^^»)-^g, m.p. II8^ from

oxalic ester, and methyl-ethyl-ketone, by method 46 (p. 4) (B. 89,

1336).

By analogy, we have from dibenzyl-ketone : Diphenyl-triketo-pentam ethylene, oxalyl-dibenzyl-ketone

^^\ChIc hIIIco' "^'P* ^^^^* ^^ heatmg, it transposes itself into isoxaJyl-(fibenzyl-ketone, the lactone of an acyclic acid (B. 27, 1353 ; A. 284, 245).

PENTACARBOCYCLIC COMPOUNDS 19

Pentaketo-pentamethylene is the leuconic acid {q,v,) produced by oxidation of croconic acid {q.v,). Both compounds are dealt with among the oxy-benzo-quinones in connection with rhodizonic acid.

4. Aldehydes and Extra-cyclic Ketones. — Cydopentane-alde- liyde C5H9CHO, an oil with a penetrating odour, resembling valeralde- hyde, has been obtained by the action of dilute SO4H2 on methylene- cyclopentane-glycol {q,v,), Semlcarbazone, m.p. 123''.

A'-Pyolopentenaldehyde ^|^I^j|][ ^.cho, an unstable liquid, smell- ing like benzaldehyde, formed easily by condensation of the dialdehyde of adipinic add (Vol. I.). Also from the nitroso-chloride of methylene- cyclopentane by rejection of HCl and splitting of the initially formed oxime with dilute acids.

l-Metliyl-2-aeetyl-pentamethyl6n6 C5H8{CH8)(COCHs), b.p. 170°, from its carboxylic acid.

Aeetyl-A'-cyelopentene ^^^^ /^-^^^^ t).p. i73°-i74°, smeUs

distinctly of benzaldehyde. Its oxime, m.p. 91**, is generated by HCl rejection from the nitroso-chloride of ethylidene-cyclopentane.

l-Metliyl-2-ac6tyl-A^-eyclopentene ^^«~^i?^^^c.cocH,. b.p. 191^.

Oxime, m.p. 85**, generated from the c-diketonane by Na ethylate. Oxidised with MnO.K it yields y-acetyl-butyric acid. The inter- mediate formation of a i, 6-diketone is also, probably, a step in the formation of :

Pentamethyl. acetyl. eyclopentene ^^;^^^—ycH,. b.p. 2I0'*-230^ by reduction of the mesityl oxide (Vol. I. ; C. 1897, II. 579). Concerning similar ring completions of i, 6-diketones to eyclopentene denvatives, see C. 1899, I. 21 ; 1909, I. 119).

1-Aeetyl-cyelopentanone ch'IS^^^^^^^' ^P-s 75°' ^^ method ¥» P- 5> from €-keto-oenanthyUc acid. By heating with alcoholic Na ethylate the ring is easily spUt again (C. 1909, II. 119).

By attaching cyclopentanone to benzal - aceto - phenone, by ?^^ ^^ alcoholic caustic soda we obtain the diketone

5. Carboxylic Acids.— CycIopentane^Murbozylic acid, b.p. 214°, ^ells of sweat ; 2-Methyl-cyclop6ntaneH5arlK)xyll6 acid, b.p. 219°; 2, 6- iMmetliyl-cyclopentane-carboxylic acid, three stereo-isomeric forms: °»-P- 75**-77°» m.p. 26*'-3o^ and m.p. 49^-50^ :

^;,^HCOOK ^;^^^>CHCOOH g::SS>CHC0OH.

These acids have been obtained from the cyclic malonic esters :

C^gl^COOK, ^f^^^lCOOK,. J|5;:™S>C<COOR,.

obtained from the corresponding alkylene dibromides by method «> (p. s)

(B. 26, 2246 ; 27, 1228 ; 84, 2565). ^ '

Cyclopentane-carboxylic acid has been prepared from the chloro-

20 ORGANIC CHEMISTRY

cyclopentane with Mg and COg, and from the corresponding a-oxy-acid. TTie 2-methyl-cyclopentane-carboxylic acid has been obtained from the corresponding a-acetyl-carboxylic acid.

S-Metlqrl-eyelopentane-earbozylie acid, b.p.xs iid"", [ajo —5*89'', from the iodide of 3-methyl-cyclopentanol with Mg and COj (B. 85, 2690). Isomeric with this is cyclopentane-acetic acid C^H^.CHjCOOH, by disint^ration of the condensation product of iodo-cyclopentane with Na-malonic ester (B. 29, 1907).

CycIopentane-1, 2-dlearboxyllo aeid is known in two modifications. The cis-form forms an anhydride, and is generated by heating the cyclopentane-i, 2-tetracarboxylic acid obtained by method 6 (p. 5), or from trimethylene bromide with sodium-malonic ester (B. 18, 3246 ; C. 1901, II. 1264).

1, 3 - Cyclopentane - tetracarboxyUc acid, produced in a similar manner, yields, on heating, Cb-eyelopentane-l, 8-diearboxylle aeid, m.p. 121° (anhydride, m.p. 161°), which on heating with HCl is partly trans- posed into the trans-acid, m.p. 88° (C. 1898, II. 770).

Pyclopentane-1, 2, 4-triearboxylic aeid CbH7(COOH}3 is obtained by the splitting of i, 2, 4-cyclopentane-hexacarboxyUc ester, which is formed by method 6 (p. 5), by the action of Br upon pentane-i, 3, 5- hexacarboxylic ester (C. 1900, I. 802).

Cyelopentene-earboxylie aeid C5H7.COOH, m.p. 120"^, from the corresponding aldehyde with AgjO (C. 1898, II. 761).

Cyelopentene-1, 2-dlearboxylie aeid ch«<(chJZccooh' ^'^' ^7^""' from aaj-dibromo-pimelinic acid by the action of Na alcoholate (see also p. 5). Also from i, 2-dibromo-cyclopentane-i, 2-dicarboxyUc acid, obtained by .bromination of cyclopentane-dicarboxylic acid, by treat- ment with alcohol, and KI. The acid easily adds 2Br ; by melting with potash it is disintegrated to adipinic acid (B. 28, 655).

Bb-eyelopentadiene-earbozylie aeid was mentioned above in connec- tion with cyclopentadiene.

Cyclopentane-acetic add CsH^CHjCOOH, b.p. 226*'-230*', has been obtained by transposition of cyclopentanol-acetic ester with HBr and reduction of the compound produced. Amide, m.p. 145° (A. 858, 304).

Severed a; )S-unsaturated acids are obtained by rejection of water from the oxy-acids dealt with below.

Cyolopentene-aeetle aeid (CgHg) : CHCOOH, m.p. 52°, b.p.„ 128°- 130**; Methyl-eyelopentene-aeetie aeid (CHjCgH,) : CHCOOH, b.p.^

128** ; Cyelopentene-proplonie aeid (C,h j : c<(^^jj, m.p. Io8^

On dry distillation these acids expel COg and pass into cyclopentene- hydrocarbons with semicyclic double linking; see Methylene-cyclo- pentane (A. 865, 273 ; C. 1902, I. 1222). By nuclear synthesis from laevulinic ester with Na alcoholate a Methyl-eyelopentadiene-earboxyl-

proploDie add cH.<g§««J~^«H^cjj^c J^ ^^ ^^^ °»'*^*"^' *^'^^

at 218*" gives off COg, and melts, forming at first methyl-cyclo- pentadiene-propionic acid C5H^(CH8)(CHgCHgCOOH), m.p. 65°, and then methyl-ethyl-cyclopentadiene C5H4(CHg)(CH8CH8), b.p. 135**. These substances resemble 6yclopentadiene in tlieir behaviour (B. 86, 944).

PENTACARBOCYCLIC COMPOUNDS 21

Camphorie aeid, i-methyI-2-dimethyl-cyclopentane-i, 3-dicarbo- xylic acid, is dealt with under camphor (g,v.).

6. Alcohol - carboxylic Acids. — a-Ozy-eycIopentane-earbozylie

••'^ Ch*I^h'/^^OH^' ^'^' ^^^**' *^^"^ cyclopentanone CyH and HCl (A. 275, 333), jaelds by reduction pentamethylene-carboxylic acid.

l-Methyl-a-amldo-eyelopentane-carboxylle aeld CH,.CBH8(NHt) COOH, m.p. 299"" (B. 89, 1728). Hezaehloro-a-oxy-eyolopentene-

earboxyUe add cci*^ca*^^OH^' «^^^*^ ^^^ chlorinated cyclo-

hexene-i, 2-diketone with NaCO, or sodium acetate. On heating it passes into an isomeric acid (B. 28, 824). Both acids, boiled with water, jdeld perchloro-indone {q,v,) (A. 272, 243). Triohloro-eyelo-

pentene-dloxy-earboxyUe aeid ^^!Z^^*yK^^' ^Y the action of

chlorine on alkaline phenol solution (B. 22, 2827).

1, l-Cyelopentonol aeid ester ^S::ch:><?S.cooch.' ^P" '^5"- 107°, by condensation of cyclopentanone and bromacetic ester by means of zinc. In the same manner we obtain 8-Methyl-l, 1-cyeIo-* pentanol-aeetlo ester C5H7(OH)(CHaCOOC2H5), b.p.^ 90^-92°; 1,1- Cyelopentanol-proplonie ester CsHg(0H)CH(CH8)C00CsHs ; 1, 1- Cyelopentanol-bobutyrie ester C5H8(OH)C(CH8)2COOCj|H5, b-p.^ 108^-

7. Ketone-carboxyucAcids. — 2-Keto-pentamethylene-earbozylic

«»tor ^!!*-^]?^^^'^^ Vo, from adipinic ester by method 4a, p. 4 ; this

ester may be r^arded as a carbocyclic derivative of aceto-acetic ester, and shows its typical reactions (Vol. I.). With Na alcoholate and methyl iodide it yields l-Methyl-2-keto-pentamethylene-carboxylic ester, b.p.j^ 108°, and by ketone sphtting, keto-pentamethylene. By acid splitting, adipinic acid is r^enerated. With amyl nitrite and Na ethylate, a-oximido-adipinic ester is produced.

4-Methyl-2-keto-pentamethylene-earboxylie ester from )3-methyl- adipinic ester (A. 817, 27, etc. ; C. 1908, I. 1169).

Keto-pentamethylene-8, 4rdIearboxyUe acid ^^<^ch' Chco H' ^P* 189^, by condensation of aconitic ester and Na-malonic ester, and subsequent disintegration (B. 26, 373).

Keto-pentametliylene-2, 3-dicarboxyUc ester c«t<(cH^HCOOC H^ b.p.18 166**, obtained from butane-i, 2, 4-tricarboxylic ester by method 4^ (p. 4). On saponification it expels CO,, and passes into :

Keto-pentamethylene-3-carboxylic aeid, ^Hi<(^"Il!cH*cooH' ^'^' 65** (C. 1908, II. 1781).

A Phenyl-keto-pentamethylene-dicarboxylie aeid has been prepared by condensation of 2 - phenyl - 1, 3, 4 - butane - tricarboxylic ester (A. 816, 219).

A Trlmethyl-keto-pentamethylene-diearboxylie ester, obtained from dimethyl-butane-tricarboxyhc ester by condensation with Na and methyl iodide, possibly contains an atomic group similar to that of camphoric acid (C. 1900, II. 332).

22 ORGANIC CHEMISTRY

l-Imino-2-cyaiio-cyclopentan6 ch'Zch^^/'^ '"^^' ^'^' ^4^*"' P^^' duced by intramolecular condensation of adipinic dinitrile with Na ethylate. Similarly, 2-Imino-8-cyano-cyclopentane-l-earboxylic ester

CHirCH(ColR)^^"^^* ^'^' ^^^*^'' ^^ obtained by the action of sodium cyanacetic ester upon i, i-cyano-trimethylene-carboxylic ester where an intermediate production of aoi-di-cyanadipinic ester must be assumed. On treatment with acids we obtain in succession : 3-Cyano-2-keto^entamethylene-earbozylieester» b.p. ^g iy2''-i 74"^, Cyano-

eyolopentanone ^h'Z!ch^^/^^^' ^'^' ^^9**' ^^^' finally, cyclopentanone (C. 1909, II. 14).

Several i, 2-diketo-pentamethylene-carboxylic acids have been obtained by method 46 (p. 4), by condensation of oxalic ester with esters of the glutaric acid series, and similar acids, e,g. l9 2-Diketo-

pentamethyIene.8.5-dlcarboxyUc ester cochSco'r!)^^^* (®- *^* 3206), and the corresponding methylated and phenylated ester in the 4-position. Some interest attaches to the ester of 4, 4-DimethyI-

1, 2-diketo-pentamethylene-8. 5-dlearboxylie aeid S ch(CO*H))'^^^^^*' which has been made to pass in succession into apocamphoric acid, and dimethyl-pentamethylene-dicarboxylic acid, by replacement of the keto-oxygen atoms by hydrogen (A. 868, 126).

By similar syntheses we obtain from oxalic and tricarbullyUc ester : 1,2- Dlketo - pentamethylene - 8, 4, 5 - triearboxylic ester ; from oxaUc acid acetone-dicarboxyUc ester : 1, 2, 4-Triketo-pentamethy- lene-8, 5-diearboxylie ester (C. 1897, II. 892 ; B. 29, R. 1117).

2 - Methyl - 1 - aeetyl - pentamethylene - earboxylie aeid

S!*.Ch1^)^^COOR ' o^t^e^ by °^^*o^ 5 (p. 5). is an extracylic ketone-carboxylic ester (B. 21, 742).

A special group is formed by some substances, in which a five- membered ring includes a three-membered ring, the so-called bicyclo- pentanes. By condensation of oaj-dibromo-p-dimethyl-glutaric ester with Na-malonic ester a dimUhyl-keto-hicyclopentane-iricarhoxylic ester is formed, through the intermediary of a Dimethyl-trimethylene- diearbo-malonie ester :

COOR COOR COOR /rw \ r/<^HBr .r.ry V p/C CH(COOR), . .prr X p/C CH.COOR

COOR COOR COOR

The tricarboxylic ester is changed by successive rejection of 2COOR into Dimethyl-keto-bieyelopentane-di-and-monocarboxylie acid

acid the trimethylene ring is broken up with formation of 2-Dimethyl- 4-keto-pentamethylene-carboxylie aeid (B. 85, 2126 ; B. 42, 2770).

D. Heptacarboeyclic Compounds.

These substances have lately acquired additional importance through their relations with alkaloids and terpenes, as weU as the

HEPTACARBOCYCLIC COMPOUNDS 23

so-called isophenyl-acetic acid. The frequently easy transformation of heptacarbocycUc compounds into benzene derivatives is worthy of note. Synthetically, most of the suberane derivatives have been obtained by starting from suberone (cp. A. 276, 356).

Suberane, heptamethylene, cycloheptane ^5* r2''^2"^^Ht» b-P- II7^

generated by reduction of suberyl bromide or iodide. By bromine and Al bromide suberane is converted into penta-bromo-toiuol (y.v.) ; by heating with HI, into methyl-cyclohexane and hexa-hydro-toluol (B. 27. R. 47).

Ethyl-saberane C7H18.C2H5, b.p. 163**, from zinc ethyl and suberyl bromide. Two molecules of suberyl bromide and sodium yield di- suberyl C7H13.C7H13, b.p. 291** (A. 827, 70).

Snberene, cycloheptene ^h ch'ch'/^^*' ^P' ^^'^''' obtained from suberyl iodide with alcoholic potash. Also from suberylamine by treatment with suberyl-trimethyl-ammonium hydroxide, and distillation of the latter (A. 817, 218). Combines with Br to form a dibromide.

Ai-Methyl-suberene ch' CH* CH /^^^' ^P" ^38^ from methyl- suberol on heating with potassium bisulphate. On oxidation with Hn04K it yields €-acetyl-capronic acid. Nitroso-chloride, m.p. 106° (A. 845, 139). Isomeric with this hydrocarbon is :

Methylene-cyeloheptane ^2**^2'f 2" y^ ^^^*» b.p. I39^ obtained by

distillation of suberene-acetic acid. Nitroso-chloride, m.p. 81**; Mn04K oxidises to glycol (QHia) : C(0H)CH20H, m.p. 50°, which, on further action, passes into oxy-suberane-carboxylic acid and into suberone (A. 345, 146).

Cycloheptadiene, heptamethylene - terpene, hydrO'tropilidene

^u * ^u"^2* y^^^i' b-P- ^21**, by distillation of the quaternary ammonium

bases generated by the complete methylation of the various amino- cydoheptenes (see below), produced partly by synthesis and partly by (Usintegration of tropin. Combines with Br to a i, 4-dibromide, which, on heating with quinolin, rejects 2HB and becomes :

Cyeloheptatriene, tropilidene ^^ \ c^^^«' ^-P- ^^6° (A- 317, 204) ;

the dibromide of the latter passes into benzyl bromide on heating to loo"* with HBr (B. 81, 1544).

Saberyl-alcohol, cycloheptanol, C7H13.OH, b.p. 184°, is formed besides suberyl-pinacone by reduction of suberone with Na and alcohol ; by strong reduction with HI, suberyl-alcohol is converted into hexahydro-toluol (B. 80, 1216). Chloride, b.p. 174® ; bromide, b.p-to loi** » iodide, Djg 1-572. Suberylamine, QH^.NHj, b.p. 169**, by reduction of suberone oxime, or from suberane-carboxyl amide with KOBr (B. 26, R. 813 ; A. 817, 219).

Methyl-suberol (CeHi^) : C(0H)CH3, b.p. I83^-I85^ from suberone withMgCCH,)!.

Cyeloheptenol-ethyl ether, QHji.OCsHg, b.p. 174'', from suberene dibromide with alcoholic potash.

Saberyl-methylamine (C7Hi3).CH2NH2, b.p. I93**-I95^ from the

24 ORGANIC CHEMISTRY

amide of suberane-acetic acid with Br and alkali. Nitrous add gives suberyl-carbinol, and azealol (A. 858, 327).

A»-Am!no-cycloheptene ch'ch'ch'/^^'^^ ^'^' ^^^''' ^^^ ^*" cycloheptene-carboxylic amide with KOBr, yields on methylation Aa-dimethyl-amino-cycloheptene C7Hii.N(CH3)„ b.p. 188°. This is also produced from suberene dibromide with dimethylamine, and shows positive isomerism with the two methyl-tropanes interpreted as A'- and A*-dimethyl-amino-cycloheptene, produced by disin- tegration of the alkaloid tropin (A. 817, 204 seq,),

Suberone [cycloheptanone] ch!Zch!IIch'/^' ^P* ^^'*' ^^^^^ ^* peppermint. From distillation of Ca suberinate. Passes on oxidation into pimelinic acid. Condenses Uke adipin-ketone with benzaldehyde into a dibenzal form, m.p. 108® (B. 29, 1600). Suberone oxime C7Hi2(NOH), m.p. 23**, b.p. 230°, is transposed by concentrated H2SO4 into i-heptolactame (see Vol. I.) Semicarbazone, m.p. 164°.

A^-Methyl-suberenone ^*c^*q^)<^'^^» b.p. 2oo*'-205''. Its oxime

has been obtained from the nitroso-chloride of A*-methyl-suberene by rejection of HCl (A. 84f6, 145).

Suberane-aldehyde ^h' ch' ch!/^^"^^^' ^ °^ smelling strongly of benzaldehyde, from the glycol of methylene-cycloheptane by the action oi dilute H2SO4 (A. 8&, 149).

A^-Suberene-aldehyde ^!!*'^?!*'^2 V.CHO also smells strongly of

benzaldehyde. It has been obtained from the nitroso-chloride of methylene-suberane by willidrawal of HCl, and spUtting of the oxime thus generated witli acids. Silver oxide oxidises it to suberane- carboxyUc acid.

Suberane-oarboxylic aeid, cycMieptane-carboxylic acid, C^HisCOgH, b.p.15 139°. Amide, m.p. 195®, has been obtained synthetically from Suberane-1, 1-diearboxylle acid, the ester of which is formed to a sUght extent from hexamethylene bromide and Na-malonic ester {B. 27, R- 735)- Suberane-carboxyUc acid is also obtained from suberyl bromide with Mg and CO, in ether, and by reduction from the various cycloheptene, heptadiene, and heptatriene carboxylic acids. With Br and P it yields a-Bromo-suberane-carboxyllc aeid, m.p. 93"", which, by rejection of HBr, gives :

A^Cyeloheptene-earboxylie add C^HnCOOH, m.p. 52*^. Amide, m.p. 126°. This acid is also obtained, by heating with caustic alkali, from the isomeric A^CycIoheptene-carboxylie aoid, m.p. 19*" ; amide, m.p. 158''. Both acids have also been obtained, together with some other isomers, by the reduction of cycloheptatriene-carboxylic acids or their dihydrobromides (A. 817, 234).

Cycloheptadlene-earboxyllc aoid QH,.COOH, m.p. 78^ identical with hydro-tropiUdene-carboxylic acid, a disintegration product of hydro-ecgonidin {q.v.).

Cycloheptatriene - earboxylie acids, tropilidene - carboxylic adds, isophenyUacetic acids, C7H7.COOH : a, m.p. 71° (amide 129''); j3, m.p. 56° (amide 98**) ; y, liquid (amide 90**) ; 8, m.p. 32** (amide 125**). The isomerism of these acids is governed by the various positions of the

HEPTACARBOCYCLIC COMPOUNDS 25

three double linkages. With HBr they form mono-, di-, and even trihydrobromides, but on energetic treatment with HBr they are transposed into the dihydrobromide of p-ioluylic acid. They have been obtained : (i) by disint^ation of the alkaloid ecgonin, which therefore, like the related tropin, contains a seven-member carbon ring (B. 81, 2498) ; (2) by transposition of the pseudo-phenyl-acetic add or norcaradiene<arboxylic add (C. 1900, I. 811). The latter, generated from benzene and diazo-acetic ester (Vol. I.) by rejection

of N, has the formula chIchIch/^^^^^^' ^^^ represents the combination of a six-member ring with a trimethylene ring, and therefore a condensed nucleus such as is dealt with below. Similar combinations are probably also contained in the terpene-ketones carvone (q.v.) and eucarvone (q.v.), of which the latter passes by reduction into dihydro-eucarvone, which should be regarded as methyl-gem- dimethyl^ydoheptenone CH,Ch/^^^^»3JTO, ^g 3^^ ^^^^

1 - Ozy - suberane - esrboxylie aold, suberyl^gfycoUc acid, C7H1, (OH)CO,H+JH,0, melts anhydrously at 79^ From suberone with HCy and HCl; also from a-bromo-suberane-carboxylic acid with baryta water (B. 81, 2505). With PbO, it may be oxidised again completely to suberone {B. 81, 2507). With concentrated HCl or PQj it passes into chloro-suberanic acid, m.p. 43** (A. 211 117 • B. 81, 2004). » / '

a-Amido-saberane-earboxylie add C7Hi2(NHj,)COOH, m.p fan- hydrous) 306^-307" (B. 89, 1730). > P ^an

l-Oxy-suberane-aeetle aeld, cycloheptanol - acetic acid ^^">^\OT,COOH' ^^ ^^^ ^^ ^^ ^^^^ (methyl, b.p.„ 1410-145°; ethyl, b.p.u 134°) are obtained from suberone and brom-acetic esters witii Zn or Mg. On heating with potassium bisulphate, the esters split off Hj|0 and pass into esters of Suberylene - aeetle add C,H„> C=CHCOOH, b.p.„ 159°, which, on distillation at atmo- spheric pressure, decomposes into CO 2 and methylene-cycloheptane C,H„>C=CHj (H. 814, 156; B. 85, 2143). By transposition with halogen hydrides, oxy-suberane-acetic add yields bromo- and iodo- suberane-acetic add, m.p. 69° and 8I^ which by reduction pass into Suberane-aeetie aeid (C7Hi3)CH,COOH, b.p.^, 165^ Amide, m.p. 148° (A. 858, 301). *^ ^

E. Octocartx)cycllc Compounds.

The doubly unsaturated hydrocarbons of cydo-octane have latdv attracted particular interest on account of their relations to rubber Pseudo-pelletierin, the alkaloid dosdy rdated to tropin and tropinone also contains the eight-member carbon ring. It forms the basis for the majority of the compounds here to be described

CyolOHK^tene ^Jt^lIl^S:::^":' ™P- "-5'. b.p. r46o-i48o.

D4 0-849, I^as been obtained by reduction of j8-cyclo-octadiene with Ni and H.

A^'^-Oyelo-oetadiene ^^t— ck=ch— CH, , generated together with small quantities of an isomeric, bicyclic

I

26 ORGANIC CHEMISTRY

hydrocarbon during distillation of the quaternary ammonium base obtained by thorough methylation of N-methyl-granatanin, a reduction product of pseudo-pelletierin (q.v.) (cp. the analogous preparation of cycloheptadiene from tropane). The cyclo-octadiene is a mobile oil of penetrating odour, the vapour of which is poisonous. It polymerises with extraordinary facility even in the cold, and explosively on heating. This produces a cficyclo-octadiene (CgHi2)2, m.p. 114°, and a polycyclo- octadiene (CgHij)*! an amorphous mass with a m.p. above 300®. Ozone transforms the cyclo-octadiene into a di-ozonide CgHuOg, which, with water, decomposes with formation of succinic dialdehyde. With HBr it combines to form a dihydrobromide C8Hi4Brg, b.p.jj 150°, from which, by the action of caustic potash or quinolin, a p-Cyolo- octadleney b.p. 143°, is obtained, which is isomeric with the original compound. It has an agreeable odour and shows no tendency to poljrmerisation (B. 40, 957).

According to Harries, Para rubber is a polymerisation product of

rCHg.C CH,— CH,— CH 1

1, S-Dimeihyl-A^-^-cyelo-oetadiene II .It

L CH— CH,— CH,— C.CHaJx

is probably, therefore, also the intermediate product in the poly- merisation of isoprene (Vol. I.), which has lately acquired technical importance (B. 88, 3985).

As from suberinic acid we obtain suberone, so by distillation of cal-

cium azelainate we obtain Azelaone, cyclo-octanone /^h*— jCh!!Zch*~^h ' but only in small quantities. It is an oil with an odour closely resembling suberane, b.p. I95<^-I97*', m.p. 25°-26°. Semicarbazone, m.p. 85°. On oxidation with Mn04K the ketone 3aelds cork acid. By reduction with Na and alcohol it passes into the corresponding

alcohol called Azelaol S'ISh^I^h^IIch^^' ^'P' ^®^°' '^^^ ^^ ^^^ obtained by the action of nitrous acid upon suberyl-methylamine (B. 81, 1957 ; C. 1899, II. 182 ; A. 858, 328).

Tricyclo-oetane-, dimethyl-, and dlphenyl-tricyelo-octane are sup- posed to be represented by tiie hydrocarbons derived from the diolefin- carboxylic acids (vinyl-acrylic acid, sorbinic acid, and cinnamenyl- acrylic acid) on heating with baryta water, polymerisation, and rejection of COg (B. 40, 146), These formulae are, however, not yet sufficiently well established.

F. Nonocarbocydic Componnds*

Compounds with a ring of nine carbon atoms have only been obtained quite recently. But the physical data indicate that these substances are not yet obtainable in a state of purity.

08665, is obtained in minute quantities on distilling sebazinic acid with slaked lime. Semicarbazone, m.p. 105°. Na reduces it to:

Cydononanol cS1^h|I5h|IJhI/^^^^' ^^^ 97^-io5', which, through the corresponding iodide, can be transformed into :

Cyelononaneg|J^2|lSHl^H!/^^«' ^P' I7o°-I72^ D," 07733, the fundamental hydrocarbon of this series (B. 40, 3277, 3876).

BENZENE DERIVATIVES 27

IL-HEXACARBOCYCLIC COMPOUNDS

The chemistry of hexacarbocyclic compounds is incomparably greater and more richly developed than liie chemistry of the ring systems dealt with in the preceding chapter. Hexacarbocyclic compounds may be divided into three classes :

A. Mononuclear aromatic substances, or benzene derivatives.

B. Mononuclear hydro-aromatic substances. This class contains the terpene group and the camphor group.

C. Polynudear aromatic substances. The fundamental hydro- carbons of this group contain (a) several benzene nuclei connected direct or by aliphatic hydrocarbon residues ; or (6) two or more nuclei are so combined with one another that two carbon atoms are common to each (twin nuclei, condensed nuclei).

C.H. C.H./'^**' C.H,A"^'"» CH./^\C,H,

Diphenyl Diphenyl-methane Triphenyl-methane Tetraphenyl-methane

W*^ CjHsCH, C,H,CH C,H,C

I II III

CgH^CHf C(ii|CH CfHgC

Dibenzyl Stilbene Tolane

(6) C.H,/CH Vh J'jj*/CH, C„H, C,.H„

Indene Fluorene Naphthalin Anthracene, etc.

With each of these hydrocarbons numerous derivatives of all kinds may be associated, thus forming an unlimited field. Many of these bodies, especially naphthalin and its derivatives, give rise to hydro-compoimds. These are, however, not dealt with as a separate fourth class, but always in connection with the unhydrogenated derivatives of the hydrocarbons in question.

A. Mononuclear Aromatic Substances or Benzene Derivatives.

By the name " aromatic " compounds we designate substances which are mostly obtained from aromatic oils and resins, and which differ in general from the fatty bodies or methane derivatives by various peculiarities, especially a greater content of carbon and a well-marked ** aromatic " odour. Our theoretical conceptions con- cerning the constitution of these compounds are mainly derived from the benzene theory formulated in 1865 by Kekul^. It may be summarised in the following theses (cp. Kekul6, Lehrbuch der org, Chemie, ii. 493 ; A. 187, 129) :

1. " All aromatic compounds are derived from a nucleus consisting of six carbon atoms, the simplest combination of which is benzene CeHf. They are produced by the replacement of the H atoms by otiiier atoms or groups of atoms (side groups). They all show the specific benzene characteristics, contrasting with the methane derivatives, and should be called ' benzene derivatives.' "

2. " Benzene has a symmetrical constitution. Each carbon atom is joined to an H atom to a carbin group CH. As in the case of the polymethylene derivatives, no differences can be traced between the

28 ORGANIC CHEMISTRY

several C or H atoms, and isomerisms of derivatives are therefore only found in the case of two or more side groups."

3. " The structure of the benzene nucleus resembles the methane derivatives in that the six atoms, or CH group, are alternately bound by single and double links, thus making a closed ring-formed chain of six carbon atoms, according to the scheme :

\=/

0=0—^=0— c=*c or "~^ O—

I ^1 \ /

c— c

which can also be expressed by a regular hexagon. The fourth valence of the carbon atoms is attached in benzene to an H atom, and in its derivatives to other atomic groups."

Historical. — ^The first to invent a structural formula for an aromatic compound was Archibald Scott Couper, who in 1858, in his work on salicyUc acid (C./?. 46, 1107), represented it by the formula:

^Ic H

Mcz:? OH (^-«)

JO.

\ o

OH

In 1861 J. Loschmidt published a pamphlet called Chemische Studien (Wien, Ceroid), with new graphic formulae for 360 substances, among them being 180 aromatic compounds. Loschmidt charac- terises the aromatic adds as substances with incomplete nuclei, having incompletenesses in eight places. The simplest of these nuclei is Ce^^ for which he brings the six carbon atoms close together :

(Scheme 181 of Loschmidt)

thus obtaining a formula as contained in Couper's saUcylic acid formula. He figures the C atoms by means of circles touching where there is single binding, and intersecting where there is plural binding. He prefers, however, a " stratification " of the six C atoms to their

.xw-

Allyl V^A. /^ J Benzol nucleus

(Scheme 68) . ^ fljf}^ (Scheme 1 82) .

" condensation," and imagines the nucleus as a double allyl nucleus (scheme 182). For allyl, Loschmidt had considered the trimethylene formula (scheme 68). Loschmidt, however, left the question of nuclear constitution in suspense, his constructions being independent

BENZENE DERIVATIVES 29

of it. He says : " We assume for the nucleus Ce^^ the symbol 184 " — a larger circle — " and treat it as if it were a hexavalent element."

Loschmidt then gives graphic formulae for many benzene deriva- tives, some of which are given here :

C^vi (184). C,H, (186). CeHjOH (185). C^H^CHa (197).

Of these, 185 represents phenol, and 197 toluol.

Loschmidt had therefore already formed the first thesis of Kekul6's benzene theory. He says nothing about the equivalence of the six benzene H atoms. It was, in fact, excluded on the assumption that the benzene molecule consisted of two stratified allyl rings, since in scheme 182 the free valencies are unequally distributed, as shown by the points of scheme 181. Kekul^, on the other hand, places the structure of the nucleus into' the foreground, and derives from it the equivalence of the six H atoms and the explanation of the isomerism of the substi- tution products.

General Survey of the Benzene Dertvatives.

The benzene derivatives can be derived from the replacement of the H atoms of benzene in the same manner as the aliphatic substances are derived from methane. Benzene derivatives with side chains containing carbon may be built up from benzene and brought back to benzene by eliminating the side chains. Benzene derivatives differ from methane derivatives in the stability of the benzene nucleus. Thus oxidation usually stops short at the benzene nucleus, and so does reduction in general, leading finally, as a rule, to cyclohexane derivatives or hexahydro-benzene derivatives, without any splitting of the benzene ring. Reduction therefore connects benzene deriva- tives with cyclohexane derivatives (p. 2).

Those benzene derivatives which are solid at ordinary temperatures are often distinguished for their ease of crystaUisation, and this is a great aid to their experimental investigation.

The 1^ of benzene is easily replaced by the halogens and the groups nitro NO2 and sidpho SO,H :

Chlotx>-ben£ene . . C,H,a CcH4Clt CeHsClft C«C1«

Nitro-benzene . . C«HsNO| C,H«(NOa)| C,H,(NO|),

Benzol-8ulpho-acid . C,H,SO^H C,H4(S0^H)| C,H,(SO^H),

According as to whether one, two, three, or more H atoms of benzene are replaced, we distinguish mono-, di-, tri-, tetra-, penta-, or hexa- derivatives of benzene.

Specially characteristic for the benzene derivatives is the formation of nitro-bodies through the direct action of HNO3, whereas the aUphatic bodies are generally oxidised or decomposed by it.

Reduction of the nitro-bodies produces the amido-compounds :

Amido-benzene (aniline) CeH^NH, CeH4(NH,), CeH3(NHj)8.

30 ORGANIC CHEMISTRY

As intermediate products of reduction, we have the so-called azo- compounds, while the action of nitrous acid upon amido-compounds produces the diazo-compounds ; both classes of bodies are only excep- tionally present in the aliphatic series (Vol. I.).

On replacing the H in benzene by hydroxyl we obtain the phenols, comparable to the alcohols :

C,H,OH C,H4(OH), C,H3(OH),

Phenol (carbolic acid) Dioxy-benzol Trioxy-benzol.

Like the tertiary alcohols, the phenols contain the group C.OH linked to three C valences, and they cannot therefore form any corre- sponding aldehydes, ketones, or acids by oxidation.

The benzene nucleus weakens the basic properties of the amido- group and imparts acid properties to phenyl-hydroxyl. It possesses a more negative character than the residues of aliphatic hydrocarbons.

By the entry of monovalent paraffin, olefin, and acetylene residues, the so-called homologous benzene hydrocarbons are derived, both saturated and unsaturated :

CfHf CfHfCI^ CfH4(CH3)| CfHfCHg.CHj CgHfC^Hf, etc.

Benzolene Methyl-benzol Dimethyl-benzol Ethyl-benzol Pxopyl-benzol

(toluol) (xylol)

C^HjCH = CH, C,H,C =CH, etc.

Vinyl-benzol (styrol) Acetylene-benzol.

In these hydrocarbons the benzene nucleus preserves the specific properties of benzene. Its hydrogen is easily replaced by halogens and by the groups NOj and SOjH. But the side chains behave just like the hydrocarbons of the fatty series ; its hydrogen can be replaced by halogens, but not (through action of concentrated HNO3 or H2SO4) by the groups NOg or SOgH. According as to whether the halogens (or other groups) enter into the benzene residue or into the side chains, we obtain different isomers :

Chloro-toluol CeHiCLCHg Benzyl chloride C,H,.CH,Cl

Dichloro-toluol CcHsCli.CHo Chloro-benzyl chloride C^HfCl.CHtCl

Benzal chloride CcH,CHCl,.

The halogen atoms in the benzene residue are firmly held, and usually incapable of a double substitution, while the halogen atoms in the side chains act just as in the methane derivatives.

If in the side chains H is replaced by hydroxyl, we get the true alcohols of the benzene series :

C,H,.CH,OH C,H..CH,.CH,OH ^•^^^ch'.OH

Benzyl-alcohol Phenyl-ethyl-alcohol TolyUalcohol

the primary ones of which form aldehydes and acids by oxidation :

C,H,.CHO C,H,.CH,.CHb ^•^KciK)

Benzaldehyde Phenyl-acetaldehyde Tolyl-aldehyde.

The acids in which COOH is joined to the benzene nucleus may also be produced by direct introduction of carboxyl into the benzene, or by oxidation of the homologues of benzene :

ISOMERISM OF THE BENZENE DERIVATIVES 31

C,H,.CO,H ' C,H4(CO,H), C,H8(CO,H)8

Benzol-carboxylic add Benzol-dicarboxylic acid Benzol-tricarboxylic acid

^•<Sh C.H..CH..CO.H C.H,<g5)'

Toluylic acid Phenyl-acetic acid Mesitylenic acid.

In these acids, as well as the alcohols and aldehydes, the H of the benzene residue is also replaceable by halogens and by the groups NO,, SOjH, OH, etc.

In the above discussion benzene was regarded as the foundation. The various benzene derivatives with aUphatic side chains were all regarded as benzene substitution products. It is obvious that this view may be reversed. Then the benzene derivatives with a single side chain appear, e,g, as phenyl substitution products of the ahphatic substances, as exemphfied by the following terminology :

C,HcCH, Phcnyl-methane C,H,CH,CH,OH Phenyl-«thyl-alcohol

CfH^CCI, Phenyl-chloroform CjHjCHjCHO Phenyl-acctaldehyde

CjHjCH.OH Phenyl-methyl-alcohol C,H,CH,COOH Phenyl-acetic add

C,HsCOOH Phenyl-fonnic add Cja^CH^CHfiOtH. Phenyl-propionic acid.

Isomerism of the Benzene Derivatives.

Proof of the equivalence of the six H atoms of Benzene. — If in benzene one H atom is replaced by another atom or atomic group, any compound so obtained is only found in one modification ; there is but one chloro- benzene, one nitro-benzene, one amido-benzene, one toluol, one benzoic acid ; so the compounds

CeHfiCl CeH5.NO, C,H5.NH, C.HgCH, CeH^.COjH, etc.

are only known in one modification. The six H atoms of benzene are equivalent, Uke the four H atoms of methane (Vol. I.). Benzene has a symmetrical structure.

Historical. — ^The proof of the equivalence of the six hydrogen atoms of benzene was given in 1869 simultaneously and independently by W. Komer and A. Ladenburg (B. 2, 274, 1869 ; 7, 1684 ; 8, 1666).

I. Both investigators used the transformation of the three monoxy- benzoic acids into the same phenol, in order to prove the equivalence of the three positions taken by the carboxyl in benzene.

According to Korner, it follows from the reduction of the three monochloro-benzoic acids with Na amalgam to the same benzoic acid.

The equivalence of a fourth H atom follows, according to Laden- burg, from the transformation of phenol into bromo-benzol, and from this into benzoic acid. Ladenburg's proof of the equivalence of four H atoms of benzene may therefore be represented as follows :

a b c d e f

C, (OH) H H H H H

C, Br H H H H H

C, (CO,H) H H H H H

C, (CO,H) OH H H H H

C, (CO,H) H OH H H H

Ce (CO,H) H H OH H H

•> Phenol I Bromo-benzol I Benzoic acid t

I Ortho-oxy-benzoic acid Jl Meta-oxy-benzoic add — Para-oxy-benzoic acid —

Komer deduced the equivalence of the fourth H atom with the three H atoms replaced by carboxyl in the three monoxy- and the

d a	e H	f H
Br	H	H

32 ORGANIC CHEMISTRY

three monochloro-benzoic acids from the following facts : — ^Para-oxy- benzoic acid corresponds to para-nitraniline (Aippe), which is con- vertible into either paranitro-chloro- or paranitro-bromo-benzene.

Paranitro-chloro-benzene, by replacement of the nitro-group by Br, gives the same parabromo-chloro-benzene as is obtained on sub- stituting CI for the nitro-group in paranitro-bromo-benzene. Hence the two H atoms which are replaced in para-nitraniline by the nitro- and amido-group respectively, are equivalent, as are also the H atoms re- placed by hydroxyl and carboxyl respectively in para-oxy-benzoic acid.

abed e f

C« OH H H COtH H H Para-oxy-benzoic add

— C, NO, H H NH, H H Para-nitraniline

->Ce NO, H H a H H ► C, Br H H

->C, NO, H H Br H H ► C, Q H H

This proves the equivalence of four H atoms of benzene.

2. Each hydrogen atom of benzene has two pairs of H atoms arranged symmetrically with respect to it, i.e, so that the replacement of either of the two H atoms of a pair by the same atom or the same atomic group leads to the same compound.

Komer proves this s3nnMnetry as follows for two H atoms. The volatile nitro-phenol which is convertible into pyrocatediin, and there- fore belongs to the same series as salicylic acid, may, by replacing two H atoms by one Br atom and one nitro-group respectively, be converted into the same bromo-nitro-ortho-nitro-phenol as is obtained by intro- ducing two nitro-groups into ortho-bromo-phenol :

abcdef abcdel

C, OH NO, H H H H- — ^r qH NO, H NO, H Br C, OH Br H H H H---'^ * * '

b«f.

It is therefore clear that in phenol there are two H atoms sym- metrical to hydroxyl, and that it is immaterial which of them is repre- sented by bromine, and which by a nitro-group. But if this symmetry is established for one pair of H atoms, it is also established for the second pair, since the symmetry of the first pair is unthinkable without the symmetry of the second pair. Hence follows the equivalence of all the H atoms of benzene.

The symmetrical arrangement of two H-atom pairs in benzene can also be proved as follows. For one pair, b and /, this thesis follows from the formation of the same ortho-amido-benzoic acid out of two different nitro-bromo-benzoic acids, obtained by the nitration of meta- bromo-benzoic acid (Hiibner and Petermann, A. 149, 129 ; 222, iii ; Ladenburg, B. 2, 140) :

f H Meta-bromo-benzoic add

	a	bed	e
c	CO,H	H Br H	H
c.	CO,H	NO, Br H	H
c.	CO,H	H Br H	H
c.	CO,H	NH, H H	H
c	CO,H	H H H	H
	Hence ab sal.

H

NO,

H

v-Meta-bromo-ortho-nitro-bencoic acid* as-Meta-bromo-ortho-nitro-benzoic acid* Ortho-amido-benzoic acid

NH, Ortho-amido-benzoic add -<-

* The designations v and as are dealt with below in connection with the tri-derivatives.

ISOMERISM OF THE BENZENE DERIVATIVES 33

For the second pair the proof is furnished by the formation of the same meta-bromo-toluol from two bromine compounds (Wro- blewsky, A. 192, 213 ; 284, 154), in which bromine replaces two different H atoms, which therefore are S3mimetrical with the H atom replaced by the methyl group of toluol : ac=ae.

a b c d e f

C, CHs H H NH(COCH8) H H C, CHs H Br NHCCCXH,) H H

C, CH, H Br H H H

C, CO,H H Br H H H

a b c d e f

->C, CH, H Br NH(COCH8) NO,H,^

C, CHj H Br NH, H H - C, CHj H Br H NO, H

C, CH, H H H NH,H '

C, CH, H H H Br H '

By oxidation this bromo-toluol passes into the same meta-bromo- benzoic acid which above served as a basis for the proportion of w- and as-meta-brom-ortho-nitro-benzoic acid. Hence it follows that bromine in the last proof replaces two H atoms other than those re- placed by the amido-group in ortho-amido-benzoic acid, and that in benzene there are not one but two pairs of H atoms in symmetrical position with resp>ect to an H atom. This establishes the equivalence of the six pairs of H atoms. (See also Ladenburg, B. 10, 1218.)

For the second pair of H atoms the proof of S3mimetry may be given as follows. The ortho-amido-benzoic acid obtained in two ways (see above) may be converted into the same oxy-benzoic acid, viz. salicylic acid, which on nitrogenation gives two different mononitro-saUcylic acids. By heating the ethyl ethers of these two nitro-salicylic acids with ammonia the ethoxyl groups can be replaced by the amido- groups, and, from the nitro-amido-benzoic amides, the free nitro- amido-benzoic acids may be obtained, which with nitrous acid and alcohol are converted into the same nitro-benzoic acid. Since this nitro-benzoic acid, obtained from two different nitro-salicylic acids, yields a (meta) amido-benzoic acid different from the amido-benzoic add from which the salicylic acid was obtained, and since it jdelds a (meta) oxy-benzoic acid different from salicylic acid, it follows that there are two further H atoms sjniunetrically placed with respect to the H atom replaced by the COOH group :

a bcdef a bcde f

C, CO,H NH, H H H H « C, CO.H H H H H NH, , "C, CO,H OH H • H H H - C, CO.H H H H H OH I

C, CO,H OH NO, H H H

' C, CO,H NH, NO, H H H ♦ C, CO,H H H H NO, NH,

'X, CO.H H NO, H H H

C, CO.H H H H NO, OH

C, CO.H H H H NO, H

C, CO,H H NH, H H H « - C, CO.H H H H NH, H -C, CO,H H OH H H H « i C, CO.H H H H OH H

For the third oxy-benzoic acid, para-oxy-benzoic acid, only one position therefore remains, viz. the para position, which in benzene is only possible once.

The equivalence of the six H atoms has lately been proved by Nodting in a very simple manner (B. 87, 1027).

In amido-benzol or aniline the amido-group is easily replaced by bromine, and the latter by the CHj group with tiie aid of methyl iodide VOL. n. D

34

ORGANIC CHEMISTRY

and sodium- In the toluol thus produced the methyl group therefore takes up the same position as the amido-group does in aniline. From the toluol we obtain by nitrogenation three isomeric nitro-toluols, and from these by reduction Siree toluidins, which by acetylation, oxidation, and the elimination of the acetyl group can be transformed into three different amido-benzoic acids. These all jdeld, by rejection of CO 2, an amido-benzol identical with the initial product, which proves the equivalence of four H atoms :

1

abode C, NH, H H H H C, CHg H H H H C, CHs NH, H H H •C, CHa H NH, H H C, CHg H H NH,H

f

H^ H H- H~ H-

a be

— C, CO,H NH, H

— C, CO,H H H

— Ce CO,H H H

d e H H NH, H NH, H

f

H H H

a=b=c=d.

The proof of the second thesis (that one H atom has two other H atoms placed symmetrically to it) is based upon one of the nitro- toluols just referred to, in which the CH, group takes up position a. This, on reduction, jdelds a toluidin from which, by nitrogenation of its acetyl compound and saponification, four isomeric nitro-toluidins are obtained. By elimination of the amido-group these yield four nitro-toluols. Now, it is found that of these two are identical with each other and two with the initial nitro-toluol, which proves the symmetrical position of two pairs of H atoms :

i

a	b	c	d	e	f
C, CH,	NO,	H	H	H	H-e—
C, CH3	NH,	H	H	H	H
Cj CH3	NH,	H	H	H	NO,-
C, CH3	NH,	H	H	NO,	H a	b	c	d	e	1
C, CHb	NH,	NO,	H	H	H -►C, CH3	H	NO,	H	H	H
C, CHj	NH,	H	NO,	H	H ^C, CHj	H	H	NO,	H	H
				ab	=af i	3LC=ae.

The six H atoms of benzene are therefore equivalent, and, since there are two pairs of symmetrically placed H atoms to each single H atom, a di-substitution product of benzene can only occur in three isomeric modifications.

Principles of Location for Benzene Substitution Products. The equivalence of the six H atoms in benzene is expressed by the

hexagon diagram, in which the mutual linking of the C atoms may for the present be disregarded. It is obvious that of each bi-derivative

BENZENE SUBSTITUTION PRODUCTS 35

CgH^X, obtained by replacement of two H atoms three modifications are possible and that their isomerism depends upon tiie relative position of the two new groups entering the benzene scheme. This is called isomerism of position or geometrical isomerism (Vol.* I. p. 32). And in fact three modifications are known of most di-derivatives, but not more than three. Thus there are three

'^<z <=^Co. <^<S!: -^--^s.

Dioxy-benzols Bromo-nitro-benzols Diamido-benzols Nitro-phenols

P„/CO,H ^„/CH, p„/CO,H p„/CO,H

^•^<OH ^•^*\CH, ^•^•\CH, ^•^•\C0.H

Oxy-benzoic acids Dimethyl-benzols Tolnylic adds Phthalic acids, etc.

The three modifications of each of these compounds can be con- verted into the corresponding modifications of the others. If, therefore, we have determined the relative positions of the replacing atoms or atomic groups in the three modifications of one of these bodies, it is known for all the others, and they can be converted into the three modifications of the first body by straightforward reactions free from intramolecular atomic displacements. The relative positions of re- placing groups have been determined in the case of several di- substitution products, e,g, the three dibromo-benzols, the three diamido-benzols, and the three phthalic acids. In this way a basis has been obtained for arranging the other di-substitution products in three series, designated as ortho-, meta-, and ^ara-series respectively.

In the or^-compounds two adjoining H atoms are replaced. If the six H atoms of benzene are indicated by numbers or letters, and any one of them by i or a, we see that there are two ortho-positions : a, b=a, f, or i, 2=1, 6 ; 6 or 2 and / or 6 are symmetrical to a or i. Ilie fn«to-compounds are produced by replacement of the atoms a, c =a, e, or i, 3=1, 5, the positions c (3) and e (5) being symmetrical to a (i). The />ara-compounds are produced by replacing the H atoms a,d or I, 4. While, therefore, there are two equivalent places for the oriho- and meia-positions, viz. 2 and 6, 3 and 5 respectively, the para- position has only one location corresponding to i, viz. 4.

The location of the replacing groups in the di-derivatives is indi- cated by prefixing ortko-, meta-, and para- to the compounds, abbreviated into o, m, and p, or by prefixing the numbers [i, 2]-, [i, 3]-, [i, 4]- endosed in square brackets. The formulae are often represented by writing the benzene ring as a hexagon and attaching the atoms or atomic groups to its comers. Or, again, by introducing the location figures between the benzene residue and the substitution groups :

OH OH OH

H^OH ^^jpH H/^H ^j^^ojj V^^-CH/WO"

H^H -''•''MMOH' h<^Oh" • *^[3]0H' HyH-'^'^'^WOH

H H OH

Pyro-catechin Resorcin Hydroquinonc

a-Dioxy-benzol m-Dioxy-benzol p-Dioxy-benzol

[i , 2]-Dioxy-benzol [i , 3]-Dioxy-beiizol [i , 4]-Dioxy-beiizol .

36

ORGANIC CHEMISTRY

Among the principal representatives of the three isomeric series we may put the following :

Qrtho, [1, 2] MMa, [i, 3] Pua» [i, 4]

C,H4<f Salicylic acid Meta-oxy-bcnzoic acid Para-oxy-benzoic acid.

/CH,

C«H4

\CH,

Ortho-xylol

Iso-xylol

C,H4/^^»JJ PhthaUc acid IsophthaUc acid

Para-xylol. Terephthalic acid.

Location of the Di-derivatives.

The benzene hexagon indicates two chemically identical ortho- derivatives, two chemically identical meta-derivatives, and a single para-derivative, if we neglect the mutual linking of the six C atoms.

The first to indicate a way of experimentally determining the location of the substituents in benzene multiple-substitution products was W. Komer. In 1867 he propounded the opinion that a trioxy- benzol, obtained from any of the three isomeric dioxy-benzols, must necessarily be a i, 3, 4-trioxy-benzol (Bull. Acad, Roy. Belg. 2, 24, 166). As the transformation of dioxy- into trioxy-benzols was attended with difl&culties, Komer replaced the dioxy-benzols by dibromo- benzols, and for these he determined the absolute constitution, in 1874, by conversion into tribromo-benzols (Gazz. Chim. Ital. 4, 305). Komer nitrogenated the three dibromo-benzols. One of them gave two mononitro-dibromo-benzols ; the second, three more ; and the last, one, all different. These six mononitro-dibromo-benzols were then reduced to the corresponding mono-amido-dibromo-benzols, and afterwards transformed into the three tribromo-benzols. Komer showed that in this last transformation the first dibromo-benzol jaelded two different tribromo-benzols ; the second, three different ones ; and the third, only one tribromo-benzol. Komer concluded that the first dibromo-benzol had the two Br in the of^Ao-position, the second in the m^-position, and the third one in the ^ara-position. Thus the absolute position of the bromine atoms in the three tribromo-benzols was determined and the constitution of the six mononitro-benzols was cleared up. The following diagrams illustrate this argument. For the sake of clearness, the H atoms have been omitted.

Br

I I

KJ

Br

I I IjBr

Br

Uno.

Br

Br

\y

Br Br

Br

(^

NO, • Br

I I \/

Br

Br

NOj Br

Br /^Br

\y

Br

Br NO,

Br

Br /\

\/

Br

A

Br I I Br

Br

Br Br

/\

I I

Br Br /\

I

Br

Br

BENZENE DI-DERIVATIVES

37

What may be called a reversal of this argument is found in the process experimentally realised by P. Griers (B. 5, 192 ; 7, 1223).

There are six isomeidc diamido-benzoic acids, and the diamido- benzol M^rated by A? rejection of COj from two of these acids is the o-compo^^pi^^nich is generated from three of the six acids is the m-compound, a^^iat which is generated from the sixth add is the Compound.

NH

/\

I

NH, ^ NH.

NHt

CO,H

NH, NH,

IJnh, co,hI>^nh,

CO,H

NH,

Anh,

u

NH,

I

NH.

NH.

i^'C0,H NH, NH,

I I \/ NH,

The constitution of benzene derivatives containing side chains is produced by* transformation into benzol-carboxylic acids. For the three phthalic acids or benzol-dicarboxylic acids the constitution is determined by the following facts (B. 4, loi) :

The phthalic acid obtained by oxidation of naphthalin is the [i, 2]- or ortho-benzol-dicarboxylic acid. Naphthalin consists of two benzene nuclei having two C atoms in common in the ortho- positions.

By oxidation of nitro-naphthalin we obtain nitro-o-phthalic acid, which can be converted into phthalic acid ; on oxidising the amido- naphthalin obtained by reduction of nitro-naphthalin, we obtain o-phthalic acid, the oxidation destroying, first the one, and then the other, side of the naphthalin molecule. This determines the constitu- tion of both the naphthalin and of phthalic acid as an o-dicarboxylic acid of benzene :

H H

H./\./\.H

/

H

H H Naphthalin r^C^cH a

NO, -|/\,CO,H

NH, H tH,/\,/^H

H H

H

H~l/^CO,H H H

CO,H— |/\,H

CO,H J 'H H

a- Amido-naphthalin Benzol-o-dicarboxylic acid

Phthalic acid.

The so-called isophthalic acid is benzol - m - dicarboxylic acid, since it can be obtained by oxidation from isoxylol. Isoxylol is m-dimethyl-benzol, as shown by its formation from mesitylenic

38

ORGANIC CHEMISTRY

acid, the first oxidation product of mesitylene, or [i, 3, 5]-tri- methyl-benzol :

CH,

5 3

CH3

H^H

CH,

CO,H

H(^H

5 3

H

CH,

CHjs^CH,

H

Mesitylene Mesitylenic acid

[i.3»5]-Trimethyl- benzol

H

CO,H H|^H

\/ H

CH,

Isoxylol

[i,3]-Dimethy-

benzol

H<^CO,H

H

Isophthalic acid Beiizol-[i,3]-di- carboxylic add.

The proof that mesitylene is really [i, 3, 5]-trimethyl-benzol is due to Ladenburg, who showed that iJie three unreplaced H atoms of mesitylene are equivalent (A. 179, 174) :

a b

, C,(CH,), H H

. C.(CH,), NO, NO, .C.(CH,), NO, NH, ^ C,(CH,), NO, NHCOCH,

c H

H a b

H-> C,(CH,), NO, H H ^C,(CH,). NH, H

c H

H I C«(CHt). NO, NHCOCH, NO,iC,(CHJ, NHCOCH. H H a

4 C,(CH,). NO, NH, NOkiC,(CH,), NHCOCH. NO, H or C.(CH.), NHCOCH. i C.(CH.), NO, H N0,4rC,(CH.), NH, NO, H or ^C,(CH,), NH,

b»c asb a-BC

b H H

0

NO, NO,

The above scheme clearly illustrates the argument. Mesitylene gives dinitro-mesitylene, of which the NOj groups may replace the H atoms a and 6, and then in succession nitro-amido-, nitro-acetamido-, dinitro- acetamido-, dinitro-amido-, and dinitro-mesitylene, identical with the origin. Hence b and c are equivalent. The nitro-amido-mesitylene, in which we assume the NHj group at b, jaelds mono-nitro-, mono-amido-, mono-acetamido-, mono-acetamido-nitro-, and mono-amido-nitro- mesitylene, identical with the first nitro-amido-mesitylene obtained by reduction of dinitro-mesitylene. Hence a and 6 or a and c are equi- valent; but, since b and c are already proved to be equivalent, the equivalence of the three unreplaced H atoms of mesitylene is proved. Mesitylene is symmetrical; therefore its three methyl groups must occupy the positions [i, 3, 5].

For the third benzol-dicarboxylic acid, terephthalic acid, only the 1, 4-position remains, as may be proved as follows : — Terephthalic acid is derived from p-dimethyl-benzol, and this again from p-bromo- toluol (through methyl iodide and Na). Now, p-bromo-toluol yields, by oxidation, p-bromo-benzoic acid ; p-bromo-benzoic acid and p-oxy-benzoic acid belong to the same series, for p-oxy-benzoic acid originates in the same p-amido-benzoic acid through the diazo-com- pound, through which p-bromo-benzoic acid may also be obtained. But of p-oxy-benzoic acid we have already proved that its hydroxyl group represents an H atom symmetrical to no other H atom of benzene.

With the di-derivatives of benzene containing no carbon-bearing radicles as substituents, the three phthalic acids have a genetic relation. The three dinitro-benzols may be converted into nitro-amido-, bromo- nitro-, brom-amido-, and dibromo-benzols on the one hand, and into nitro-cyanic, nitro-carboxyhc, amido-carboxylic, cyano-carboxylic.

BENZENE DI-DERIVATIVES 39

and phthalic adds on the other hand, by reactions in which no intra- molecular atomic displacements are observed (B. 18, 1492, 1496).

»'<Z:-y-''^l -^<l°- -^«-C"- -^«-<£

A further proof is furnished by the derivatives of the three isomeric xylols. We have

from Metaxylol, 3 nitroxylols, xylidins, and xylenols from Orthoxylol, 2 nitroxylols, xylidins, and xylenols from Paraxylol, i nitroxylol.

from which the following positions may be ascertained :

1,4:

meta- or isoxylol and isophthalic acid orthoxylol and phthalic acid paraxylol and terephthalic acid.

(B. 18, 2687.)

That in the ortho-compounds two neighbouring C atoms of the benzene nucleus hold the side groups, is shown by their capacity for simple reactions, in which a union of the side chains gives rise to carbo- and, especially, hetero-cyclic condensation products (o-pheny- lene-diamine, o-amido-phenol, o-amido-thiophenol, o-amido-benzalde- hyde, o-phthalic acid, o-oxy-cinnamic acid, etc.). There are also crystallographic reasons for supposing that the m^/a-compounds stand between ortho- and />ara-compounds (Zeitschr. f, KrysL, 1879, 171 ; B. 18, R. 148).

The hexagon scheme of benzene, therefore, not only represents all the isomeric relations of benzene derivatives, but sheds light on their chemical and physical behaviour.

Isomerism of the Benzene Poly-substitution Products.

When three or more H atoms are replaced in benzene, three cases must be distinguished : — ^The substituents are equal or different. In the first case there are three possible isomers of the tri-derivatives, such as CeH8(CH8)3, with the positions

[i, 2, 3] [i, 2, 4] or [i, 3, 5].

They are termed

adjoining

[I, 2, 3]

unsymmetrical [i, 2, ^'

symmetrical

[i» 3, 5J

or V = vicinal

or a5=asymmetric

or s = symmetric tri-derivatives.

For the tetra-derivatives with four equal groups C|,H2X4 there are also three possible isomeric structures :

[I, 2, 3, 4] {i, 2, 4, 5] [I, 2, 3, 5]. V s as

40 ORGANIC CHEMISTRY

With five or six equal groups only one modification is possible ; there is but one pentachloro-benzol C^jHClj, and only one hexachloro- benzol C^Cl^.

If the substituent groups are unequal, the number of possible isomers is much greater ; it is easily derived from the hexagon scheme. Thus we have for the formula of dinitro-benzoic acid C0H3(NO2)2COOH six isomers :

[1,2,3] [1,2,4] [l»2, 5] [1,2,6] [1,3,4] [1,3.5].

assigning position i to the carboxyl group.

The constitution of the poly-substitution products of benzene is determined by their genetic relations to the di-substitution products of known structure.

Constitution of the Benzene Nucleus.

According to the benzene formula established by Kekul6 in 1865, six C atoms are alternately simply and doubly linked into a closed^ chain. This assumption gives a comprehensive picture of the whole behaviour of the benzene derivatives :

1. It illustrates the synthetic formation of the benzene derivatives, the condensed benzols, naphthalin, phenanthrene, etc. ; and is corro- borated by all recent syntheses, such as that of a-naphthol from phenyl-isocrotonic acid, etc. (see also B. 24, 31 17).

2. It agrees with the splitting reactions of the benzene nucleus.

3. It explains, in a simple manner, how the ortho-derivatives — on account of the neighbouring position of two side groups — are capable of forming anhydrides and numerous derivatives founded upon an ortho-condensation. The benzene formula also results clearly from the ring formation of quinolin (A. 280, i).

4. The existence of three bivalent linkings explains in a simple manner, without new hypotheses, the faculty for forming addition products possessed by the benzene derivatives (p. 45). Such additions do not, indeed, take place with the same ease as in the case of ethylene linkings, in the methane bodies ; but aliphatic olefin compoimds also show gradual differences in powers of addition (see Allyl alcohol, Vol. I.).

5. Several physical properties also indicate the existence, in benzene bodies, of double linkings similar to those found in ethylene derivatives. Thus, according to Briihl (B. 27, 1065), the refractivities show that in benzene derivatives there are three ethylene Unkings CH=CH (Vol. I.), but in naphthaUn five. The specific volumes of the benzene bodies also seem to speak for the existence of three double Unkings (Vol. I.).

Kekul6's benzene formula does not, however, completely express the symmetry of the benzene nucleus ; for it would indicate a differ- ence in the ortho-derivatives [i, 2] and [i, 6], and they would have to give rise to four di-derivatives each — unless we follow Kekul6 in assuming oscillations of neighbouring carbon atoms (A. 162, 86 ; B. 5, 463 ; A. 279, 195).

Perhaps, during the formation of an ortho-derivative, a displace- ment of the double linkings occurs when the substituting groups approach two single-linked C atoms, so that what is formed is always

CONSTITUTION OF THE BENZENE NUCLEUS

41

the di-derivative in which the substituent groups are attached to two doubly linked C atoms. This would explain the easier complete oxi- dation of the o-derivatives, in comparison with the corresponding m- and p-derivatives.

It cannot be denied that the prediction of the existence of two modifications of an ortho-substitution product instead of one con- stitutes a weakness of Kekul6's benzene formula. It must also be remarked that the many analogies between the ortho- and para- derivatives, in comparison with the meta-derivatives (see Quinone and Quinone derivatives), are not sufficiently expressed by this formula. Still, we give it preference, in comparison with other benzene formulae, because it gives a consistent view of the connection between aromatic and aliphatic compounds.

Among oth^r benzene schemes we may figure the diagonal scheme of Claus (A), the prismatic scheme of Ladenburg (B^, Bj, B3), and the centric scheme of Armstrong and von Baeyer (C).

A Bj B,

dam: Dfaigoiial schema

Ladenbuig: Prismatic flcbeme

AnnstroDg-Baeyer i Centric scheme.

According to formulae A and B there are no double linkings in the benzene nucleus. The existence of nine univalent links was supposed to be proved by the specific volume of the benzene compounds, and especially by their heats of combustion ("Theory of Heats of Formation," by J. Thomson, B. 13, 1808 ; 19, 2944). But, according to more recent investigations, the specific volumes rather indicate the existence of three double links in the benzene nucleus, and the conclusions derived from the heats of combustion do not appear to be irrefutable (Briihl, /. pr, Ch. 2, 49, 201).

The prismatic formula of Ladenburg " accounts for all the static conditions of benzene," and illustrates the isomerisms of the benzene derivatives. But it denies all double linkages such as are proved to exist in the partly reduced nuclei of the di- and tetrahydro-addition products ; it gives a spatial arrangement, of the four affinities of the carbon atoms, having no analogy among the methane bodies; and, according to its author, "it yields priority to Kekul6's scheme for all processes of formation and decomposition of benzene bodies" (B. 88, loio).

Although Claus's diagonal formula is consistent with isomeric relations, and allows of any para- and ortho-additions (B. 20, 1422 ; /. i>f. Ch. 2, 49, 505), it arranges the four C affinities without analogy, and assumes a peculiar central valency of a new kind.

Baeyer's new centric formula leaves the condition of the fourth C valency indefinite, simply assuming that it exerts a centrally directed pressure. In this way it returns to^Kekuld's scheme, which does not profess to explain the linking of the fourth valency (B. 28, 1272 ; 84, 2689 ; A. 269, 145 ; B. 24, R. 728).

42 ORGANIC CHEMISTRY

Thiele has lately made a different attempt to explain the required symmetry of the benzene nucleus. He assumes that, in orcfinary double Unkings, certain " residual valencies " remain, two of which mutually saturate each other when the double linkings adjoin. On assuming such a saturation of all the residual valencies of the three ethylene links, the six C atoms are seen to be linked by six " inactive " double links (A. 308» 213 ; 311, 194).

Some constitutional formulae for benzene are based upon stereo- chemical considerations, such as Thomson's octahedral formula (B. 19, 2944), and especially the benzene model of Sachse (B. 21, 2530 ; Z,f. physik. Ch, 11, 214; 23, 2062), as well as that of J. Losclunidt {Wien, Akad,^ Ber. 1890, vol. 99, ii. p. 20). For later discussions of the various stereo-chemical formulae, see B. 85, 526, 703 ; and C. 1902,

n. 350.

Benzene Ring Formations.

The nuclear synthesis reactions of aliphatic substances, in which benzene rings are formed, are important mainly as joining aliphatic and aromatic substances genetically. They will therefore be passed in review, before dealing vnth the various classes of bodies, in the same succession as that in which the initial bodies were dealt with in the aliphatic series (Vol. I.).

1. CH4, methane, conducted through an incandescent tube, gives benzene and other products.

2. 3CH=CH, acetylene, polymerises at a red heat to benzene.

3a. 3CH = C.CH8, allylene, polymerises in SO4H2 to [i, 3, 5]-W- methyl-benzol or mesitylene.

36. 3CHj.C~C.CH3, crotonylene, polymerises to hexamethyU benzoL

4. CCI4, perchloro-methane, and CCl2=CCl2, perchloro-ethylene, on passing through an incandescent tube, give perchloro-benzol ; see also perbromo-benzol.

5. 3CH=CBr, monobromo-acetylene, poljmierises to [i, 3, 5]-/ri- bromo^enzoL

6. CjHjgl, hexyl iodide, gives with CI iodide hexachloro-benzol ; with bromine, hexabromo-benzoL

7a. (CH8)aC : CH.CHa.CHjC(CH,) :CH.CHO, geraniol or citral, gives with potassium bisulphate [i, ^-isopropyl-toliwl or cymol,

7b. CHg.CHjCH :C(CH8)CH rCH.COCHj, from methyl-ethyl-acrolein and acetone, yields psetuLo-cumoL

7c. (CsH7).CH2CH : C(C8H7).CH : CH.CO.CHj, from 2 mol. isovaler- aldehyde and i mol. acetone, gives di-tsopropyUtoluol (B. 28, R. 608).

8a. 3CH8COCH3, acetone, gives with SO4H2 [i» 3» 5]'irimethyl-benzol or mesitylene,

86. 3CH3CO.CHaCHs, methyl-ethyl-ketone, gives [i, 3, 5]-/m%/- benzoL

8c. 3CH3CO.CH2CH2CH8, methyl-n-propyl-ketone, gives [i, 3, 5]-/n- n^opylr-benzoL

9. 6C0, carbon monoxide, combines with K on heating to potassium- hexaoxy-benzoL

10. 3CH3CH2CH2COCI, butyryl chloride, is condensed by AljCle into triethyl'phoroglucin.

BENZENE RING FORMATIONS 43

11. 3CHSC.CO2H, propioUc acid, poljanerises in sunlight to f 1, 3, $]-benzol-tricarboxylic acid or tritnssinic acid.

12. 3N02CH(CHO)2, nitro-malonic aldehyde, gives, on decomposi- tion of its Na salt, sym. irinitro-benzol.

13. NO,.CH(CHO)a, nitro-malonic aldehyde, and CH3COCH,, acetone, give p-nilro-phenol (B. 28, 2597 ; C. 1899, II. 609).

14. 3CH3.CO.CH=CHOH, oxymethylene-acetone or formyl-acetone, condenses easily to [i, 3, 5]'lriacetyl-benzol CeH3(COCH3),.

15a. 2CH8CO.CO.CH3, diacetyl, condenses with alkalies to p- xylo-quinone or [2, $]-4iniethyl'quin(me.

156. 2CH8.CO.CO.CH2CH3, acetyl-propionyl, gives duro-quinone or tetramethyl-quinone.

16. 3CH(OH)=CH.C02C2H5, oxymethylene-acetic ester or formyl- acetic ester, and their dimolecular condensation product, cumalinic acid, condense easily to esters of the [i, 3, ^ybenzoUiricarboxylic acid or trimesinic acid] this is also obtained from a mixture of formic and chloracetic acids with zinc (C. 1898, II. 472).

17. 4CH3COCO2H, p5a:o-traubenic acid, condenses on heating with NaHO with rejection of oxalic acid and water to methyl-dihydro- trimesinic acid, which passes easily into uvitinic acid with rejection of COj.

18. 2CHOCH2CH2COOH, j3-formyl-propionic acid, gives terephthalic acid or p-benzoUdicafboxylic acid,

19. 2CH3CO.CHNa.C02C2H5, sodium-acetic ester, and CHCI3, chloroform, combine to oxy^wvitinic ester or oxymethyl-isophihalic ester,

alsoobtained direct from methenyl-bisacetic ester CH/^^^(S?."?I?»15?5^

V C (C0|C||J1|) COCH3

with Na alcoholate.

20. 2ROCOCH : CH.CHjCOOR, glutaconic acid ester, unites under the action of sodium ethylate, with rejection of one molecule of alcohol, and acetic ester to form ^-oxy-isthphthdlic acid ester (B. 37, 2 117).

2 J CHaCiCH.CO.CH.COCHs dehydracetic acid, yields orcin or 3,5.

dioxy^luoL

22, 2CH8.CO.CH2.CO.CO2C2H5, acetone-oxalic ester, is condensed to oxy-toluylic acid ester,

23a. CH3.CH2CH : C(CH3).CH : C(C00R)2, ^om methyl - ethyl - acrolein and malonic ester, 5delds with Na alcoholate oxy-mesitylenic acid.

23b. (CH3)2 : CH.CH,.CH2.C(CH3) : CH.CH : C(C00R)2, citralidene- malonic ester, yields ^-isoamenyU^-^methyUsalicylic acid.

It is doubtful whether in the formation of mellithic add or benzol^ hexacarboxylic acid Q(C02H)3 by the oxidation of charcoal or graphite a synthesis occurs ; perhaps this reaction must be regarded as the transformation of a molecule consisting of twelve C atoms.

On again survejring the reactions by which aliphatic bodies are converted into benzene bodies by nuclear synthesis, we find that :

(i) Some saturated compounds, like methane and tetrachloro- meihane, yield the benzene ring by the action of heat {pyrogen- densation). Many benzene derivatives, like benzene and the methyl- benzols, simple amido- and oxy-benzols, are distinguished for their constancy at high temperatures (see Coal-tar).

(2) During percUaration of many aliphatic compounds the occur-

44 ORGANIC CHEMISTRY

rence of perchloro-benzol was observed. Hexyl iodide is transformed particularly easily into perchloro- and perbromo-benzol.

(3) A large number of aliphatic acetylene compounds containing a triply linked pair of C atoms, jaeld benzene derivatives by polymerisa- tion of three similar molecules. A difficult polymerisation is that of acetylene to benzene. Brom-acetylcne is much more easily poly- merised. Allylene and crotonylene require sulphuric acid, propiolic acid, and sunlight for aromatic polymerisation.

The other aliphatic compounds above referred to, which may condense themselves to aromatic substances {aromatic condensation) , contain carbon and oxygen in double linking. Many are ketones, or they contain the oxy-methylene group.

(4) A direct addition reaction is exemplified by the manner in which potassium hexa-oxy-benzol is formed from CO and K.

(5) Hydrolytic condensation is exemplified by the simple ring formation in the transition of citral or geranial and other high-mole- cular keto-olefins into cymol, pseudo-cumol, and di-isopropyl-toluol, as well as the condensation of di-hydro-acetic acid to orcin, with liberation of COj.

(6) The condensation of acetone, methyl-ethyl- and methyl-n- propyl-ketone to [i, 3, 5]-tri-alkyl-benzols is paralleled by condensation of butyryl chloride to tri-ethyl-phloroglucin, vdth a triple rejection of HCl ; also by the condensation of two molecules j3-formyl-propionic acid to terephthalic acid, with rejection of water and hydrogen.

(7) These condensations are related to the condensations of nitro- malonic-acid aldehyde, and the oxy^methylene compounds (12 to 16). Also to

(8) The condensation of the a-diketones to quinones ;

(9) Of acetone-oxalic acid to oxy-toluylic acid ; and

(10) The condensation of chloroform and sodium-acetic ester to oxy-uvitinic-acid ester, in which methenyl-bis-acetic ester can be assumed as an intermediate product.

(11) The formation of homologous salicylic acids from alkengli- dene-malonic esters with Na alcoholate is based upon an intramolecular aceto-acetic ester condensation.

There is also a peculiar condensation of p5n"o-traubenic acid to methyl-dihydro-trimesinic or uvitinic acid, in which oxalic acid is first split off.

These benzene formations are associated with several reactions leading to hydro-aromatic compounds having a dose relation to benzene derivatives. We may mention the following :

I. Sodium-malonic ester condenses to phloroglucin-dicarboxylic ester, formed from acetone-dicarboxylic ester and malonic ester (B. 29, R. 1 1 17). Sodium-acetonic-dicarboxylic ester condenses to dioxy-phenyl-dicarboxylic ester (B. 81, 2014 ; C. 1897, II. 741). All these condensation products are probably derivatives of hexa- hydro-benzol.

Cp. also the condensations of sodium-acetone-dicarboxylic ester with iodine to hydroquinone-tetracarboxylic ester (B. 80, 2569), with eth-oxy-methylene, aceto-acetic, and eth-oxy-methylene-malonic ester to oxy-trimesinic ester, and resorcin-tricarboxylic ester, respectively

(C. 1899, II. IOI8, I020),

BENZENE RING SPLITTINGS 45

2. Succinic acid ester condenses mth sodium to succinylo-succinic acid ester.

3. 1, 5-diketo-compounds, which contain, in the terminal place, besides a CO group, a CH, or CHgR group, condense to cyclic sddols, of the hexamethylene series, which easily pass into keto-tetra-hydro- benzene derivatives. Methylene-bis-aceto-acetic ester, a, y-diacetyl- glutaric ester, thus gives methyl-keto-tetramethylene-dicarboxylic ester. Similarly, with sodium etihiylate, the y-acetyl-butyric ester CH,CO.CH2.CH8.CH2.COOC2H5 yields dihydro-resorcin, which can, by a reversed process, pass into y-acetyl-butyric acid by splitting (cp. benzol ring splitting).

Some other methods of synthesising hydro-aromatic compounds were mentioned on pp. 4 and 5.

Benzene Ring Sputtings.

As already mentioned, the benzene derivatives are in general distinguished by the tenacity of the benzene ring. In order to split the benzene ring, suitable benzene derivatives are treated with reagents which, partly or wholly, dissolve the double links of the nucleus. The splitting is therefore always preceded by the formation of hydro- aromatic intermediate products, which, as a rule, could not be retained. Sometimes we obtain split products containing the six nuclear C atoms in the molecule as an open chain, in some cases pentacarbocydic compounds from hexacarbocyclic a-diketones.

Ring splittings were found most easily practicable in the case of phenols, amido-phenols, quinones, oxy-quinones, and phenol-carboxylic acids.

I. Splitting by feeble oxidation. — While strong oxidisers convert the benzene nucleus into CO,, formic acid, and oxalic acid, ozone is capable of producing a straightforward, and extremely clear, splitting of benzene. By addition of three molecules of ozone to the three double links of the benzene nucleus, we get, first, ozobenzol, or benzol-triozonide CeHg09, which is decomposed by water into three molecules of glyoxal (Harries) :

0-0

OCH \

OCH CHO

dH O

.0— «I CH OCH Cx*w

CKT 11+ 3H,0 « T + 3H,0,

X)— CH CH OCH CHO

CH O

/

OCH

This splitting furnishes one of the strongest supports for Kekul6's benzene formula. The homologous benzene hydrocarbons behave similarly.

Pyro-catechin or [i, 2]-dioxy-benzol CeH4[i,2](OH)2 and proto- catechuic acid or [3, 4]-dioxy-benzoic acid C02H[i]C6H8[3,4](OH)2 are oxidised to dioxy-tartaric acid (Kekule).

46 ORGANIC CHEMISTRY

Hydroquinone or [i, 4]-dioxy-benzol, and the quinone easily generated from this, are split up by silver peroxide into maleinic acid and CO 2 (R. Kempf) :

COH CO COOH

HC CH

HC CH HC

II I ► II II ► II + 2CO,

HC HC HC CH HC

doH CO COOH

Phenol CqHjjOH has been transformed by potassium permanganate solution into meso-tartaric acid (Dobner). Probably in this case also quinone is formed in the first instance, and then maleinic acid, which with MnO^K passes into meso-tartaric acid (see Vol. I.).

By oxidation of o-nitro-p-cresol vdth fuming sulphuric acid we obtain j3-acetyl-acrylic acid (Schultz and Low) :

O-CH. COCH.

HC CH HC

II I > II

HC CNO, HC

\^ \

C— OH COOH

2. Splitting by simultaneous chlorination and oxidation. — Benzene treated with potassium chlorate and sulphuric acid passes first into chlorinated quinone and then into trichloro-pheno-malic acid and j3-trichlor-acetyl-acrylic acid (see Vol. I.), which with baryta water decomposes into chloroform and maleic acid (Kekul^ and Strecker) :

CH CO CO,H CO,H

/V__ -,/\- — / — /

TC C

HC CH HC CH HC HC

II I ► Jl 11 ► II ► II +HCC1,

HC CH HC CCl HC CCL HC

\/ \/ \

CO CO CO,H

Benzene Monochloro- Trichloro-pheno-malic acid Maldc add. quinone i8-Trichlor-acetyl-acrylic

add

^i

From phenol, salicylic acid, or ortho-oxy-benzoic acid COOH[i]CgH^ [2]0H, and from gallic acid COOH[i]CeH2[2, 3, 4](OH)3, we obtain, by treatment with potassium chromate and HCl, iso-trichloro-glycerinic acid CCl3C(0H)2C00H (see Vol. I.).

Picric acid or [i, OH, 2, 4, 6]-trinitro-phenol, treated with bleaching powder, yields chloro-picrin (Vol. I.) ; with bromine, and lime water, bromo-picrin.

Specially illuminating are the methods of benzene spUtting worked out by Zincke. They consist in the formation of chlorinated R- hexene and R-hexylene-ketones, from suitable aromatic compoimds, and the spUtting of the former.

We shall give, in what follows, four examples, the first three of which start from the three dioxy-benzols, and the fourth from [i, 3, 5]- trioxy-benzol, or phloroglucin.

BENZENE RING SPLITTINGS 47

(i) Pyro-catechin or o-dioxy-benzol, treated with chlorine, passes into tetrachlor-ortho-quinone, and then into hexachlor-o-diketo-R- hexene. By merely heating in water the latter is converted into hexachloro-R-pentene-oxy-carboxylic acid, which may be oxidised by means of chromic acid to hexachloro-keto-R-pentene. With caustic soda the hexachloro-R-pentene-ketone spUts to form perchloro-vinyl- acrylic acid, which, on reduction, yields ethylidene-propionic acid (B. 27, 3364) :

cci cci ca cci cci ch,

^\^\^\ /\ /\ /\„

CCI CO CCI CO CCI \ /rnw CCI \ CCI CO,H CH CO,H CCI CO CCI, CO CCI, / \OH CCI, / CCI CH

CCI CCI, CCI, CCI, CCI, CH,

Tetra- Hexachlor- Hexachloro-R- Hexachloro- Perchloro- Ethylidene- chloro- o-diketo- pentene-oxy- keto- vinyl- propionic

qainone R-hexene carboxylic acid R-pentene acrylic acid acid.

(2) The spUtting up of hydroquinone is simpler. By the action of chlorine upon hydroquinone, or quinone, as well as of potassiimi chlorate and HCl upon phenol, we can easily obtain tetrachloro-para-quinone (chloranile), and from, this, by chlorination, hexachloro-para-diketo- R-hexene, which, with alcoholic potash, is broken up to perchlor-acroyl- acrylic acid. The latter, as well as hexachloro-para-diketo-R-hexene itself, are decomposed by aqueous soda into dichloro-maleic acid and trichlor-ethylene (A. 267, i) :

-»>

CO CO CO,H CO,H

CCI CCI CCI CCI, CCI CCI, CCI CCI,

II II — ^11 I — ^11 II — >\\ +11

CCI ca CCI CCI, CCI cci cci chci

\ / \ / \ / \

CO CO CO CO,H

Tetrachloro- Hexachloro- Perchlor-acroyl- Dichloro- Trichlor- p-quinone p-diketo- acrylic acid maleic acid ethylene.

R-hexene

(3) From resorcin, with chlorine and glacial acetic acid, we obtain pentachloro-resorcin, and, from the latter, heptachloro-resorcin. Both m-diketo-chlorides split up in cold water alone. The penta- chloro-compound becomes dichloro-acetyl-trichloro-crotonic acid, and the heptachloro-compound becomes, with chlorine and water, trichloro- acetyl-pentachloro-butyric acid. The dichloro-acetyl-trichloro-crotonic acid, boiled in water, yields dichloro-methyl-chloro-vinyl-o-diketone. The trichloro-acetyl-pentachloro-butyric acid, treated with alkalies, splits into chloroform and pentachloro-glutaric acid, as does trichloro- acetyl-acrylic acid. But on treating it with boiling water it passes into tetrachloro-diketo-R-pentene, which, with chlorine, is trans- foimed into perchloro-acetyl-acrylic chloride. The chloride, with water, yields the add itself, whidi again, on treatment with alkalies, decom- poses into^ chloroform and dichloro-maleic acid :

48

ORGANIC CHEMISTRY

C(OH)

/ %> CH CH

" 1 CH C(OH)

Resorcin

CO

a:i CCl,

*tl J CH CO

\ / CCl,

Pentachloro- resorcin

CO,H a:i CCljH

CH Co

\ / CCl,

Dichloro-

acetyl-

trichloro-

crotonic add

CO,H

/ CCl, CCl,

inciio "^CHao) ccl; ccl;

Hepta- Trichloro-acetyl- chloro- pentachloro- resorcin butyric acid

CO Ca, CCl,

CCIH CCljH

•II I + CO,

CH CO

\ / CO

Dichloro-methyl-

chloro-vinyl-

o-diketone.

CO,H

CCl,

+ CHCI3 HCl CO,H

ccl;

Pentachloro- Chloro- glutaric add form.

I

CO CCl, COCl CCI3 CO,H CO, CO,H

CCl CO -*-CCl to -►CCl CO->C

\/ \/ ^/ \/

^\ CCl CCl CCl

CI CO,H+HCCla

CCl

Tetrachloro- Perchloro- Perchloro- Dichloro-

diketo- acetyl-acrylic acetyl-acrylic maldc R-pentene chloride acid acid

Chloro- form.

(4) The behaviour of resorcin closely resembles that of phloroglucin or [i, 3, 5]-trioxy-benzol, as this passes vdth chlorine into hexachloro- [i, 3, 5]-triketo-R-hexene. The triketone, treated with chlorine and water, decomposes into octochloro-acetone, and, treated with methyl alcohol, into dichloro-malonic-dimethyl ester and sym. tetrachloro- acetone ; and, treated with ammonia, into three molecules dichloro- acetamide (B. 23, 1706) :

COjCH,

CCl,

CO,CHi

CC1,H + CO icijH

:h

C(OH)

/ \,

CH CI

» I

C(OH) C(OH)

\ ^ CH

Dichloro- sym. Tetra- Phloro- malonic chloro-acetone glucin ester

CO

/ \ CCl, CCl,

-►I I

CO CO

\ /

CCl, Hexachloro-

2C£I^OH

CO,

+ CCI3 CCI3

CO CO

\ /

CCl,

Octochloro- [i* 3* 5]-triketo- acetyl-acetone. acetamide. R-hexylene

►

CONH,

CHCl, Dichloro-

3NH,

In the four examples the splitting takes place between a CO group and a CCl 2 group of keto-chlorides. These reactions were first developed by Zincke in the naphthalin series, and used for spUtting up one of the naphthalin nuclei and for the transformation of naphthalin derivatives into indene derivatives. Later he extended the process to the above-mentioned phenols and other aromatic compounds. In a similar manner Hantzsch carried out the splitting up of phenol with

I-

BENZENE RING SPLITTINGS 49

chlorine in alkaline solution, and its transformation into cyclopentene derivatives (B. 22, 1238).

3. SplittiDg up by reduetton in alkaline soluttou. — This splitting occurs in

(i) The o-phenol-carboxylic acids during reduction with Na in amyl alcohol. As intermediate products of the reduction we may assume tetrahydro-acids and their transposition products — ^hydro-aromatic-o- ketone-carboxylic acids. The latter take up water and change into pimelinic acids ; salicylic acid yields almost quantitatively n-pimelinic acid ; while o-, m-, and p-cresotinic acids yield the three isomeric methyl-pimelinic acids (Einhom and WiUstatter, B. 28, R. 744) :

COOH COOH COOH COOH

C <i CH CH,

CH C.OH CHjCOH CH, CO CH,COOH

CH CH *^CH, CH, "^CH-CH, ^CH, CH,

CH CH, CH, CH,

This reaction has been transferred with equal success to the naph- thalin-o-oxycarboxylic acids (see NaphthaUn-ring spUttings).

(2) Resorcin gives, on reduction, dihydro-resorcin, which, during oxidation with potassimn permanganate, 3delds n-glutaric acid (Merling, A, 278, 32) ; heating for several hours with concentrated baryta solution to i5o**-i6o** splits up dihydro-resorcin to y-acetyl-butyric acid with addition of H^O (VorlSLnder, B. 28, 2348) :

C(OH) CO CO

/ \ / \ / \

CH CH CH, CH, CH,CHi

II J ►! I ►!

CH C(OH) CH, CO CH,COOH

\ -/ \ / \ /

CH CH; CH,

This reaction is reversible.

1. The Single-Nucleus Benzene Carbohydrates.

Benzene, phenef benzol, C^H^, m.p.+5-4**, b.p. 80-4°, is the funda- mental hydrocarbon of the aromatic substances. It is generated in the dry distillation of coal, and is therefore found in coal-tar, accom- panied by a body most closely resembling it in physical properties, viz. thiophene {q,v.) C4H4S, and numerous other compounds. Pure benzene is fonned by heating benzoic acid or benzol-polycarboxylic adds with lime. Synthetically, benzene may be produced from acety- lene by heating to high temperatures (Berthelot, 1870).

Benzene is produced from coal-tar by fractionation, and is separated

from thiophene (q.v,) by repeated shaking up with a little concentrated

sulphuric add, treatment with aluminium chloride, or heating with

chlorine sulphide, formaldehyde, or phthalic anhydride (B. 29, R. 1000,

VOL, H. • E

50 ORGANIC Chemistry

1152 ; C. 1902, II. 737 ; 1909, II. 666). Finally it is purified by squeezing off, after being crystallised in a freezing mixture.

Historical (B. 23, 1271). — Benzene was discovered by Faraday in 1825, in compressed illuminating gas prepared from oil. It was obtained in 1834 by Mitscherlich by distillation of benzoic acid with quicklime, and was discovered by A. W. Hofmann in 1845 in coal-tar.

Properties. — Benzene is a mobile liquid of an odour resembling ether, Dq 0-899, Dg© 0-8799. ^* bums with a luminous flame, mixes vdth absolute alcohol and ether, and dissolves resins and fats very easily, also many hydrocarbons capable of crystallisation with crystal benzene (see Triphenyl-methane). Sulphur, iodine, and phosphorus are also soluble in benzene.

Behaviour and Transformations. — (i) On conducting benzene through an incandescent tube it is partly changed into diphenyl CeHg.CjHg, and into diphenyl benzols CJtl^(C^}i^)2, and decomposes partly into acetylene. (2) On oxidising benzene with Mn peroxide and H2SO4 some benzoic acid is formed, obviously due to some diphenyl formed intermediately (A. 221, 234), also some o-phthalic acid ; but benzene is very stable against oxidisers. By silver peroxide in the presence of HNO3, or by manganic sulphate, it is oxidised to quinone (q.v.) (B. 38, 3963 ; C. 1908, I. 74). Benzene is split up by treatment with CIO3K and H2SO4, passing into trichloro-pheno-malic acid and jS-trichlor-acetyl-acrylic acid. On passing ozone through benzene for some time, a white amorphous mass is obtained, the so-called ozobenzol, a very explosive substance, of the formula C^Hfi^, decom- posed slowly by water with formation of glyoxal (B. 37, 3431). (3) By heating with HI to 26o°-28o** benzene is mostly isomerised into methyl-pentamethylene ; but benzene and hydrogen combine to hexahydro-benzol, on passing over finely divided nickel at 180^-200° (C. 1901, I. 817). (4) Chlorine and bromine act upon benzene both by addition and by substitution. (5) HNOg transforms it into nitro-benzol QHjNO^; and (6) H2SO4 into benzol-sulpho-acid CgHgSOaH. The last two compounds are prepared industrially on a large scale. With the help of Al2Cle and halogen alkyls, alkyl residues may be introduced into benzene; (7) With aidehydes, benzene is condensed by H2SO4 to higher aromatic hydrocarbons (see Diphenyl-methane and ethane).

Coal-Tar.

Dry distillation of coal also gives rise to many alkyl-benzols, and some higher condensed aromatic bodies like naphthalin CjoH,,, acenaphthene CigHjo, fluorene C13H10, anthracene and phenanthrene C14HJ0, fiuoranthene CigHjo, pyrene Ci^Hiq, and chrysene C18H12. They are contained in the *' coal-tar" obtained in great quantities in gas-works and coke-ovens. Besides illuminating gas and tar, ammonia water is formed, while coke remains in the retorts, forming a fuel richer in carbon than coal itself.

For the rapid and brilliant development of aromatic chemistry it has been of the greatest utility that the fundamental aromatic sub- stances have been made available to chemical investigation, in any

COAL-TAR 51

desired quantity, by the industry concerned. For, while the paraffins were unsuitable bases for the building up of aliphatic substances, the aromatic hydrocarbons, with their faculty for the most varied reactions, form not only the systematic but also the practical foundation for the chemistry of aromatic substances. Coal-tar, which contains these hydrocarbons, is the inexhaustible source for preparing nmnberless aromatic compounds, many of which have been most widely used as dyes, perfmnes, and medicines.

Working of Coal-Tar for Aromatie Hydroearbons. — Coal-tar, which, besides the aromatic hydrocarbons, contains aliphatic bodies, thiophene and its methylated derivatives, phenols, pyridin bases, and other compounds, is first distilled into three or four fractions :

1. Light oU (3 to 5 per cent.), Hghter than water, boils at 150°.

2. Middle oil (8 to 10 per cent.), about the density of water, boils at I50**-2IO^

3. Heavy oil (8 to 10 per cent.), heavier than water, boils at

2I0°-27O'*.

4. Oreen oil, or anthracene oil (16 to 20 per cent.), of a green colour, boils at 270*^-400*'.

5. Residue. — Ktch (about 60 per cent.).

For the benzene compounds only light oil is in question, which is freed from resins, olefins, pyridin bases, etc., by washing with sulphuric acid, and then from phenols by washing with caustic soda. It is then subjected to a carefid fractional distillation.

Besides benzene, the following benzene hydrocarbons occur in coal- tar : — ^Toluol or methyl-benzol, the three isomeric xylols or dimethyl- benzols ; ethyl-benzol, vinyl-benzol or styrol ; the three isomeric tri- methyl-benzols ; mesitylene, pseudo-cumol, hemi-mellithol, n-propyl- benzol, the three isomeric toluols, and durol or tetramethyl-benzol. Aromatic hydrocarbons are also found freely in Ugnite tar, to some extent in wood-tar oil, in slate-tar oil, and in rock-paraffin oil.

The bulk of the benzene and toluol of to-day is obtained from the coke-oven gases, which contain about 42 grammes per cubic metre, by treating the gases with coal-tar fractionings, of higher boiling- points, in spraying towers.

The winning of aromatic bodies by dry distillation should be con- sidered in connection with their formation by pyrogenic synthesis or Pyro-condensation, by conducting aliphatic bodies through incandescent tubes. In dry distillation the retort walls take the place of the tubes (cp. B. 29, 2691 ; 10, 853 ; 20, 660).

Alkyl-Benzols CftHjtt-e-

The first place among the formation processes of alkyl-benzols must be given to the reactions of nuclear synthesis (Vol. I?).

I. It has been repeatedly mentioned that various symmetrical trialkyl-benzols are formed by polymerisation of alkyl-acetylenes in the presence of sulphuric acid, just as benzene is produced by the polymerisation of acetylene.

AUylene sCHj.CsCH -^^ CeH3[i,3,5](CH3)8, mesitylene. For the alkyl-acetylenes we may substitute ketones, acetone, ethyl-methyl- ketone, and treat them witii sulphuric add.

52 ORGANIC CHEMISTRY

2. Much more general is the reaction discovered in 1864 by Fittig : action of Na upon a mixture of brominated benzene hydrocarbons in ether solution, with alkyl-bromides, and iodides (A. 129» 369 ; 131, 303 ; B. 21, 3185) :

C,H,Br +CHiI +2Na=C,H,CHa +NaI +NaBr C,H4Br.C,H, +C,H,1 4-2Na=C,H4<^^*2* +NaI +NaBr.

This reaction is a very valuable generalisation of Wiirtz's synthesis of the paraffins, by the action of sodium upon halogen alkyls (Vol. I.). A few drops of acetic ester promote the reaction, which is the smoother, the higher the molecular weight of the alkyl iodide.

3. The synthesis of tetramethyl-methane from acetone chloride, and zinc methyl (Vol. I.), corresponds to the synthesis of iso-propyl- benzol out of benzol chloride and zinc methyl (B. 13, 45), and of one amyl-benzol out of benzol chloride and zinc ethyl :

CeH5CHClj+Zn(C,H6),=CeH6CH(C3H5)a+ZnCl,.

4. Essentially limited to aromatic compounds, but in these of very general utility, is the so-called aluminium chloride synthesis discovered by Friedel and Crafts in 1877, and consisting in the action of alkyl-haloids upon benzene hydrocarbons in the presence of Al chloride.

In some cases the olefins react in the presence of HCl in a manner similar to the alkyl-haloids (C. 1907, II. 366).

Similar action is shown by zinc chloride, and especially iron chloride (cp. Nencki, B. 32, 2414). The Al chloride can sometimes be replaced by a mixture of sublimate and Al filings (see B. 35, 868). Here it is probable that the alkyl-haloids first form organic compounds, which then act upon the hydrocarbons (C. 1900, I. 756 ; B. 33, 815). In some cases intermediate products have been preserved. The reaction between benzene, ethyl chloride, and Al chloride seems to traverse the following phases :

2C,H, +3C,H,a + A1,C1,= A1,C1,.C,H3(C,H,)8.C,H, +3HCI Al,Cle.C,H,(C,H,),.C,H. +3C,H,a= Al,Cl,[CeH,(C,HJs],HCl +2HCI.

This reaction product on heating decomposes into triethyl-benzol, HCl, and the compound Al2Clt*C^ll^{CJH.^)^, which under the action of HCl can convert a fresh molecule of benzene into triethyl-benzol, so that one may alkylise a large quantity of benzene with very little Al chloride. Water decomposes the compoimd Al2Cle.CeH3(C2H5)3 in A1(0H)2, HCl, and triethyl-benzol (/. pr. Ch. 2, 72, 57). There is no difficulty about replacing all the H atoms of benzene by methyl and ethyl groups (B. 14, 2624 ; 16, 1745). Sometimes CSj acts favourably as a diluent (A. 235, 207 ; cp. B. 29, 2884) :

CHsCl+C^He ^^^^-> HCl-FCeHgCH, 2CH3Cl-FCeHe -^^^^ 2HCl+CeH4(CH3)3 6CH3Cl+CeH3 J^£l^^ 6HCl+Ce(CH3)e.

ALKYL-BENZOLS 53

Similar reactions with the benzene hydrocarbons are shown by very different halogen compounds, like chloroform, and the acid chlorides. Ethyl ether also acts, in the presence of AlgClg, upon benzene hydrocarbons with formation of poly-ethylated benzols (C. 1899, 11. 755).

Dtsintegration reactions, — 5. Curiously enough, Al chloride is as suitable for disint^rating the alkyl-benzols as it is for synthesising them. Under suitable conditions it is possible to detach, by means of Al chloride, the side chains from one molecule of a hydrocarbon, and introduce it into another molecule of the same hydrocarbon. In this process, certain positions of the alkyl groups are preferred, both in synthesis and in disintegration, as shown by the following scheme of reactions (Anschiitz and Immendorf, B. 18, 657) :

^ CACx. 4](CH,), ^ ^ C.H,[i. 3. 4, 6](CH,)4 >^

C.H.CH, ^ J C,H,[i. 3. 4](CH.). Z ^ t C.H(CH.).

\ ^^".^.....^"..^^^ ^^^^^^

C,H,[i. 3](CH,). C Z CA[i» 3. 4. 5](CH,)4

C.H.

^ C.H,[i. 3» 5](CH.). ^

C,(CH,),

In the case of butyl- and amyl-benzols an isomerisation of the alkyl radicles is easily effected by Al chloride (C. 1899, I. 776).

If bromine is made to act upon poly-alkalised benzols, in the presence of Al bromide, the longest side chain is split off, with bromination of the resultant products (C. 1899, I. 32).

6. Concentrated sulphuric acid acts similarly, both for synthesis and for disint^ration.

7. Dry distillation of a mixture of aromatic acids, with lime or soda-lime, iron filings being added to promote heat- conduction. In this case all carboxyls are split off and the ftmdamental hydrocarbons are formed :

Benzoic acid . C^HgCOjII > COj+C^He Benzol

Toluylic acid CKJC^HJCOja -> COa+CeH^CHa Toluol

Phthalic add . CeH4(C02H), -> 2C0a+C«He Benzol.

8, 9, and 10. Replacement of inorganic residues in substitution products by hydrogen :

8. Treatment of diazo-compounds with alcohol and alkaline stannous oxide solution (B. 22, 587). This reaction is particularly important for solving questions of constitution. The diazo-compounds are obtained from amido-compounds, and the latter from nitro-compounds, produced by the action of HNO3 upon hydrocarbons.

9. Treatment of sulpho-acids with superheated steam, and sulphuric add, concentrated HCl, or phosphoric acid, at 180°.

10. Heating of oxygen-containing derivatives, phenols, and ketones, with zinc dust (Baeyer, A. 140, 295) or HI and phosphorus. It is notable that in this reaction benzo-phenone CeH5.CO.CgH5 is easily reduced, but diphenyl-ether CgHg.O.CeHg not at all. A spedal facility is shown in the reduction of the ketones, on passing vapours, with hydrogen, over findy divided nickel at I90*'-I95° (C. 1905, I. 29).

11. Many alkyl-benzols, like propyl- and isopropyl-benzols, are best produced by reiduction of the corresponding olefin-benzols, like

54 ORGANIC CHEMISTRY

CeHgCH : CHCH, and CeH5C(CH8) : CH^ with Na and alcohol (B. 36, 621, 1628, 1632 ; 37, 1721).

Properties. — The benzene hydrocarbons are mostly volatile liquids, though some polymethyl-benzols (durol, penta- and hexamethyl- benzol, also hexa-ethyl-benzol) are solid at ordinary temperatures. They possess a peculiar, and not unpleasant, odour, and are insoluble in water, though soluble in alcohol and ether. They are themselves good solvents for many organic compounds, which may be precipitated from them by means of petrol ether.

Behaviour and Transformations. — i. With reducing agents, especi- ally when the vapours are conducted with hydrogen over finely divided nickel, the alkyl-benzols and benzene itself pass into hydro-cyclic hydrocarbons. HI produces a transposition of the six-membered into an isomeric five-membered hydrocarbon.

2. Of great importance is the behaviour of alkyl-benzols in oxida- tion. Dilute nitric acid, chromic acid mixture, potassium perman- ganate, or ferricyanide convert the side chains of the benzene homo- logues into COOH groups. The number of COOH groups produced, and their mutual positions, give information concerning the number and position of the alcohol radicles in the oxidised benzene carbo- hydrates. By careful oxidation, especially with Mn04K, intermediate products may be obtained, when the side chains are long, the oxidation taking place according to the same rules as in the fatty bodies (cp. aromatic carboxylic acids).

3. Chlorine and bromine, when cold, replace H atoms of the benzene nucleus, and on heating they replace the H atoms of the side chain (see Toluol).

4. Concentrated nitric acid yields nitro-compounds.

5. Concentrated sulphuric acid decomposes alkyl-benzols to sulphq- acids on heating, and, from these, the hydrocarbons can be formed again (by method 9). A process for separating out, and purifying, the benzols has been based upon this.

6. Under the action of ozone the alkyl-benzols, and benzene itself, yield explosive triozonides, which are decomposed by water, with forma- tion of aliphatic aldehydes (A. 343, 369).

7. With chromyl chloride CrOgClj the homologous benzols yield compounds, from which water forms aromatic alddiydes, and ketones (q.v.).

8. On heating toluol or xylols with sulphur, stilbene C^HjCH : CHCflHg is formed, or methylated stilbene, and further transformation products (C. 1903, I. 502).

Isomerism. — Of the first member of the series, toluol, the theory only allows of one modification, and this is the only one found. The six H atoms of benzene are equivalent.

Of xylol or dimethyl-benzol three isomers are possible, as it is a di-substitution product :

o-Xylol C.H.{g§g m-Xylol C.H.Igg^J^ p-Xylol C.H.{[;g.

With these three known xylols ethyl-benzol CgH^CgHg is isomeric.

Of bodies with the formula C9H121 eight isomers are possible, and these are all known : (i) three trimethyl-benzols ; (2) three ethyl-

ALKYL-BENZOLS

55

methyl-benzols ; (3) two propyl-benzols : n-propyl- and isopropyl- benzol.

The isomerisms are therefore determined by the position, number, homology, and isomerism of the alkyls entering the benzene in replace- ment of hydrogen.

Constitation. — Of the syntheses of the alkyl-benzols, Fittig's reaction (see above) is especially valuable, as regards conclusions respecting constitution, since, as far as we know, no intramolecular atomic dis- placements occur in it, the alkyls taking the places vacated by the halogen atom. Oxidation also helps in deciding about the number and position of the side chains.

The following table shows the most important alkyl-benzols :

Name.

Tolnol

Xylols, Dimethyl-benzols

o-Xylol .

m-XyloI, IsoKylol

p-Xylol . Ethyl-benzol Trimethyl-benzols

[i *2,3] = Hemimellithol

[1,2,4] =FMiido-ciimQl

[i*3*5]=Meiitylene . Methyl-ethyl-benzols

o- or [1.2]-

m- or [1,3]-

p- or [1.4]- n-Propyl-benzol . Isopropyl-benzol, Comol Tetramethyl-benzol

[i ,2,3,4] =Prehnitol •

[i.2.3.5]=Isodurol .

[i,2,4.5]=Durol Methyl-isopropyl-benzols

[1.2]-

[1,3]-

[i,4]=0yinol . Pentamethyl-benzol Hexamethyl-benzol Penta-ethyl-benzol Hexa-ethyl-benzol

Formula.

C(H|CH3 CeH4(CH8)a

CfHsCHfCHji C.H,{CH,),

C,H,(CH,){C,H

)

C8H5CHjCH,CH3

C.H,CH(CHg),

C,H.{CH,).

C,H«(CH,)[CH{CH,)J

C.H(CH,), C,(CH,), . C,H{C.H,). C,(C.H,),

M.p.

-28<

-54"

+ 15'

19'

53' 164''

129°

B.p.

Density.

1103'

142**

139*^ 138** 136"

175" 170**

164-5'

159" 159** 162*'

158.5° 153^

204° 196° 190*

175°

175''

175" 230"

264**

277" 298**

08708 (131 74**)

0*8932 (o* 0-8812 0-8801 0-8832

R

0-8694 (9-8/4'*)

0-8731 (16°) 08690 (20°) 0-8652 (21°) 0-8810 (0°) 0-8798 (0°)

0-8961 (o/4'»)

0-8723 (o**) 0-8582 (18°) 0-865

0-8985 (19'')

From this table it is seen that the position isomers of the same formula, e.g. the three xylols, have closely adjoining melting-points. In the dimethyl-benzols the o-compound boils at the highest tempera- ture. Then come the meta- and finally the para-compound ; but the p-compound has the highest melting-point. Of the tetramethyl- benzols, durol is solid at ordinary temperatures, also the pentamethyl-, hexamethyl-, and hexa ethyl-benzols.

The entry of a methyl group produces in the methyl-benzols an elevation of the boiling-point by about 24° to 30"* : cp. toluol, xylols, tri-, tetra-, penta-, and hexamethyl-benzols. Entry of CH3 into a side chain raises the boiUng-point by about 24° : cp. toluol, ethyl- benzol, and n-propyl-benzol.

56 ORGANIC CHEMISTRY

Toluol CgHjCHj, so called because it is obtained from the dry distillation of tolu balsam, is found in coal-tar in company with thio- tolene or methyl-thiophene (q»v.), and is very valuable industrially. It is formed according to the general methods :

(i) From bromo-benzol, methyl iodide, and sodium ;

(2) From benzene, methyl chloride, and Al chloride ;

(3) From the polymethyl-benzols and Al chloride ;

(4) From the three toluyUc acids, and the methyl-polycarboxylic acids, by distillation with lime, etc.

On reduction, toluol passes into hexahydro-toluol ; by oxidation with dilute HNO3, or chromic acid, into benzoic acid ; with chromyl chloride, CrOjClj, and water, or MnOj, CljOj, and sulphuric acid, into benz- aldehyde. On nitrogenation it gives o- and p-nitro-toluol ; on sulphur- ising it yields much p-toluol-sulpho-acid, besides a little o-acid.

Chlorine has a remarkable action upon toluol. At boiling-point only the hydrogen of the side chain is replaced, and we get :

Benzyl chloride CgHgCHjCl Benzal chloride CgHgCHClj Benzo-trichloride CeHgCClj.

In the cold, on the other hand, o- and p-chloro-toluol are generated, CeH4Cl.CH3. In the presence of iodine and SbClg chlorine only enters the nucleus, even at boiling-point (Beilstein and Geitner, A. 189, 311). But a little PCI5 facilitates entry into the side chain (A. 272, 150). The same effect is produced by sunlight.

Hydroearbons CgHiQ. — Ethyl-benzol is isomeric with the three di- methyl-benzols. Of the three xylols occurring in coal-tar, iso- or m- xylol is most abundant and technically important.

During oxidation with dilute HNOj, o- and p-xylol are oxidised to o-and p-toluylic acid, and the latter to o-and p-phthaUc acid respectively. Metaxylol is attacked with greater difficulty. Potassium permanganate also oxidises the three xylols to the corresponding toluylic acids, and finally to phthalic acids. H,S04 dissolves o- and m-xylol to xylol- sulphc-acids (B. 10, 1013 ; 14, 2625). On distilling raw xylol with steam, p-xylol passes over first.

0-Xylol is also formed from o-bromo-toluol, CHjI and sodium. Oxidised by Mn04K it passes into phthalic acid. Chromic acid bums it to COj and HjO, like many c-derivatives.

m-Xylol or bo-xyloL — ^The production of m-xylol from mesitylenic acid, by heating with lime, is theoretically important. This reaction genetically connects m-xylol with mesitylene, in which the [1,3,5]- position of the three methyl groups can be established. This proves the m-position for the toluyUc and phthaUc acids generated by oxidation of m-xylol.

Mesitylene Mesitylenic acid Isoxylol m-Toluylic acid Isophthalic acid

p-Xylol, by distillation of camphor with ZnClj, also from p-bromo- toluol and p-dibromo-benzol, CH3I and Na (B. 10, 1355) . On oxidation

ALKYL-BENZOLS 57

with dilute HNO3 it gives first p-toluylic acid, then terephthalic acid, and with CrOj terephthalic acid at once. In fuming sulphuric acid it decomiK)ses, forming a well-crystallising sulpho-acid.

Ethyl-benzol CgHgCHjCHj also occurs in coal-tar (B. 24, 1955). Produced from bromo-benzol, ethyl bromide, and sodium ; or benzol, ethyl bromide, and Al chloride (B. 22, 2662) ; also by reduction of st3n:ol CgH5CH=CH2. Dilute HNO3 and chromic acid oxidise it to benzoic acid. CrO^Clj produces phenyl-acetaldehyde CeHg.CHj.CHO.

Hydroearbons C9H12 — The isomerism of the eight compounds of this formula has already been pointed out above. For physical constants see table.

Mesltylene, symmetrical trimethyl-benzol, occurs in coal-tar, and in certain naphtha fractionals (C. 1901, I. 1002), and is prepared from acetone (Kane, 1837) or aliylene with concentrated sulphuric acid (cp. B. 29, 958, 2884). The proof of its symmetrical structure is of funda- mental importance for the location of the benzene substitution products. With dilute HNO3, mesitylene passes into mesitylenic and mesidinic acids, or into uvitinic and trimesinic acids :

[i]CO,H

[3]CO,H l[5]CO,H

f[i]CH3 r[i]CO.H /[i]CO,H

C.H3 { blCHa ► C,H, I blCHs ► C,H, ] [3]CO,H ► C,H,

I [5]CH3 I [5]CHs I [5]CH3

Mesitylene Mesitylenic acid Uvitinic acid Trimesinic acid.

Under the influence of ozone, mesitylene gives a triozonide, which is spUt by water with formation of methyl-glyoxal (A. 348,

370)-

Pseodo-eomol, [i, 3, ^ytrimethyl-benzol, is also contained in coal-tar.

It is separated from mesitylene by means of the less soluble sulpho- acid (B. 9, 258). Also formed from bromo-p-xylol, and 4-bromo-m- xylol, which determines its constitution.

Hemi-menithol, [1,2, sytrimethyl-benzol, occurs in coal-tar (B. 42, 3603) ; prepared from isodurylic acid CeH2(CH3)3COOH, and from 2-bromo-m-xylol with CH3I and Na.

The three ethyl-toluols have been obtained from the three bromo- toluols with ethyl halides and Na. All these isomers are found in coal-tar (B. 42, 3613).

p-Btbyl-tolaol, m.p. 162"*, has been obtained from p-methyl-styrol and from p-cresyl-ketone by reduction (B. 28, 2648 ; 86, 1637).

n-Propyl-benzol, from bromo-benzol, n-propyl bromide or iodide and Na ; from benzyl chloride and zinc ethyl ; from benzene, n-propyl bromide, and AlgClj at —2° (B. 24, 768) ; and from propenyl-benzol QHgCH : CHCHs with Na and alcohol (B. 86, 622). Also found in coal-tar.

Isopropyl-benzol, cumol, CeHgCH (€113)2, first obtained by distillation of cuminic acid (CH3)2CHCeH4COOH with lime. Synthetically from benzal chloride and Zn(CH^2 ; and from benzene, isopropyl chloride or bromide, and Al chloride. Since heat transposes n-propyl bromide, with AljCl^, into isopropyl bromide, the Al synthesis gives isopropyl- benzol even when n-propyl bromide is used, unless the process is conducted in the cold. Cumol is best prepared synthetically by the reduction of isopropenyl-benzol QH5C(CH3) : CHg with Na and alcohol

58 ORGANIC CHEMISTRY

(B. 35, 2640). In the animal body cumol is oxidised to propyl-phenol (B. 17, 2551).

In (he hydrocarbons 0,^^^ theory predicts 22 isomers:

C.H,(CH,). C.H,{CAj^ ^'"^IcIh* ^"«{cit' C.H..C.H. 3 isomers 6 isomers 3 isomers 6 isomers 4 isomers.

(a) Tetramethyl-benzols CeH2(CH3)4. — ^The three possible isomers are known :

Durol, [1,24,5]- or sym, tetramethyl-benzol, is found in coal-tar (B. 18, 3034). Prepared from 6-bromo-pseudo-cumol and 4, 6-dibromo- m-xylol ^dth CH3I and Na ; from toluol and pseudo-cumol with CH5CI and Al chloride (B. 85, 868) ; and from penta- and hexamethyl-benzol with AljCli,. On oxidation it passes into durylic acid and cumidinic acid, thus proving its constitution (B. 11, 31). Concentrated H2SO4 converts durol into hexamethyl-benzol and the sulpho-acids of prehnitol, pseudo-cumol, and isoxylol, which can be separated by means of their amides. Similar behaviour is shown by pentamethyl and penta-ethyl-benzols.

Isodurol, [i, 2, 3, 5]- or unsym. tetramethyh-benzol, from bromo- mesitylene, CH3I and Na (B. 27, 3441), which proves its constitution ; also from camphor and Zn chloride or iodide (B. 16, 2259). ^y oxida- tion it gives 3-isoduryUc acid (B. 15, 1853), and finally, mellophanic acid.

Prehnitol, [i, 2, 3, 4]- or v-tetramethyl-benzol, from 2-bromo-pseudo- cumol, and from 2, 4-dibromo-m-xylol, CH3I and Na (B. 21, 2821). Oxidised to prehnityUc acid CeH2(CH3)3COOH (B. 19, 1214), and prehnitic acid CeH3(COOH)4.

(6) Dimethyl-ethyl-benzols: [i, 2, 4], b.p. 189°, and [i, 3, 4], b.p. 184"*; [i, 4, 3], b.p. 185°, from camphor with ZnCl^ and iodine, and from the corresponding dimethyl-vinyl-benzols by reduction (B. 23, 988, 2349 » 86, 1637); [1,3,5], t).p. 185°, from acetone and methyl-ethyl-ketone with S04Ha (B. 18, 666 ; 25, 1533).

(c) Three diethyl-benzols oxidise first to ethyl-benzoic acids and then to phthaUc acids. p-Diethyl-benzol, b.p. 183°, has also been obtained from p-ethyl-styrol by reduction (B. 36, 1633).

(d) Methyl-n-propyl-benzols. — ^The most important is the p-com- pound, cymol. m-Methyl-isopropyl-benzol is found in light resin oil (A. 210, 10). Also generated on heating fenchone (q,v.) with phosphorus pentoxide (A. 275, 157). o-Methyl-isopropyl-benzol has been prepared from o-bromo-cumol with Na, and methyl iodide (B. 84, 1950).

Cymol, [1, 4]-meihyl'isopropyl'benzol (see Table, p. 55), found in Roman carraway oil from the seeds of Cuminum cymintim besides ciuninaldehyde, in the oil from the seeds of Cicuta virosa, in thyme oil, eucalyptus oil, and many other etheric oils. Prepared from thymol, carvacrol, or camphor with P2S5 (B. 16, 791, 2259) or P3O5 (A. 172, 307) ; from turpentine oil, and other terpenes, with withdrawal of 2H, by SO4H2 or iodine. We must note the formation of cymol on boiling cumin alcohol with zinc dust, and from citral. Synthetically, cymol is produced from p-brom-isopropyl-benzol, CH3I and Na, which fixes its constitution (B. 24, 439, 970, 1362). Cymol has a pleasant

HIGHER HOMOLOGUES OF TOLUOL 59

odour. The cymol-sulpho-salt of barium (CiQHi3S03)2Ba+3H20, crystallising in shiny scales, is characteristic.

By dilute HNO,, and chromic acid mixture, cymol is converted into paratoluylic acid and terephthalic acid ; but in the animal organism it is oxidised to cuminic acid, also on shaking up with NaHO and air. Mn04K yields p-oxy-isopropyl-benzoic acid (CHj)2C(OH)C5H4COOH. The action of concentrated HNOg upon c)anol, produces p-tolyl-methyl- ketone (B. 19, 588 ; 20, R. 373).

(e) Butyl-benzols : n-Butyl-benzol, b.p. 180''. Isobutyl-benzol, b.p. 167°. Sec-butyl-benzol, b.p. 174*", by reduction of sec.-butenyl- benzol C^UslC(Cn^) : CHCHj (C. 1900, L 591 ; B. 86, 2642). Tert.- butyl-benzol, b.p. 167°. The latter is not attacked by bromine in sunlight, in the cold (B. 23, 2412 ; 27, 1610).

Higher Homologues of Toluol.

We may mention the following :

Hydrocarbons Ci^Hie. — Pentamethyl - benzol and hexamethyl- benzol from toluol, xylol, mesitylene, CH5CI, and AljCle (B. 20, 896) . For behaviour with SO4H2 see Durol. [1, 3, 5]-piethyl-methyl-benzol, b.p. 200®, from a mixture of acetone and methyl-ethyl-ketone, with sulphuric acid. [1, 2, 4, 5]-Trimethyl-ethyl-benzol, ethyCpseud(H>umol, b.p. 207° (B. 25, 1530 ; 86, 1641). Ethyl-mesitylene, b.p. 208'' (B. 29, 2459 ; 36, 1642). [1, 3]-Methyl-tert.-butyl-benzoI, b.p. 185*^-187**, occurs in resin essence, the distillation product of fir resin ; prepared from toluol, isobutyl bromide, and AljClf. Its trinitro-derivative forms artificial musk (B. 27, 1606). The isomeric p-tert-butyl-toluol, b.p. 190°, is obtained from toluol and isobutyl alcohol with fuming sul- phuric acid (C. 1898, L 450). Amyl-benzols, see C. 1899, L 776 ; B. 85, 2644.

Hydrocarbons CijHjg. — Hexamethyl-benzol, by polymerisation of crotonylene with SO4H2 ; by heating xylidin chloride with methyl alcohol to 300** ; also by analogy with durol. Insoluble in SO4H2, as it cannot form a sulpho-acid. Potassium permanganate oxidised it to benzol-hexacarboxyUc acid C^{COOYi)^, mellithic acid. p-Di-n- propyl-benzol, b.p. 219°, from p-dibromo-benzol, and p-n-Propyl- bopropyl-benzol, b.p. 212°, from cumyl chloride ClCH2.CflH4CH(CH8)2 with Zn(C2H5)2. These bodies both yield n-propyl-benzoic acid, isomeric with cuminic acid, on oxidation with HNO3. Propyl- mesitylene, b.p. 221'' (B. 29, 2459) ; Isobutyl-mesitylene, b.p. 228'' ; Iso-amyl-mesi^lene, b.p. 241°, by reduction of the corresponding acyl-mesitylenes (B. 37, 1715).

[l,3,5]-Triethyl-benzol, b.p. 218'', from ethyl-methyl-ketone with sulphuric acid ; from benzene, ethyl chloride, and Al2Cl« we obtain, besides the sym. form, the as- or [i, 2, 4]-triethyl-benzol, b.p. 218®, which can be separated from the former by the greater stabiUty of its sulpho-acid, against phosphoric acid, and can also be obtained by reduction of diethyl- vinyl-benzol (/. pr. ' Ch. 2, 65, 394 ; B. 36, 1634). [1, 2, 3, 4]-Tetraethyl-benzol, b.p. 251 ''. [1, 2, 4, 5]-TetraethyI- benzol, m.p. +13'', b.p. 250'' (B. 86, 1635). Pentaethyl-benzoL Hexaethyl-benzol from C^Hf, CjHgBr or ether and MjZ\^ (B. 16, 1745 ; 21. 2819). Optically active Hexyl-benzols CeH5CH2CH2CH(CH8)CaH5,

6o ORGANIC CHEMISTRY

b.p. 220^, and CeH5CH(CH)8.CH2.CH(CH8)„ b.p. I97^ s. B. 87, 654, 2308. Active p-Isopropyl-hexyl-benzol CJr{^.C^HJClI^.CH^,CK(CU^), CjHj, b.p. 265^ (B. 88, 2313). HeptyWenzol CeH5CH(CH8)CH, CH2C(CH8)2 (B. 86, 2645). Tert.-p-butyl-ethyl-benzol, b.p. 209°, from p-butyl-aceto-phenone (C. 1905, I. 29). Tert.-p-dibutyl-beiUEOl, m.p. 76°, b.p. 236** (C. 1904, II. 1112).

By Fittig's method the following mono- and di-alkyl-benzols with long side chain were obtained from bromo-benzol and bromo-toluol : — n-Oetyl-benzol, b.p. 262''. Cetyl-benzol CeHg.CieHjj, m.p. 27**, b.p.^ 230°. o-Methyl-eetyl-benzoi, m.p. 8'*-9**, b.p.^g 239"*. m-Methyl-eetyl- benzol, m.p. io**-i2°, b.p.^j 237"*. p-Methyl-eetyl-benzol, m.p. 27°, b.p.15 240°. Oeto-deeyl-benzol, m.p. 36°, b.p.jj 249° (B. 21, 3182).

2. Halogen Derivatives of the Benzene Hydrocarbons.

A. Halogen Substitution Products of Benzene.

As a cyclic triolefin, benzene, in sunlight, adds six atoms CI or Br, thus forming benzene hexachloride and benzene hexabromide— bodies which, as derivatives of cyclohexane, are treated later in con- nection with hexahydro-benzol. But the H atoms attached to the benzene nucleus are also easily replaced by chlorine and bromine, more easily than the H atoms of the paraffins.

Properties and Behaviour. — ^The halogen benzols are partly colour- less liquids, partly colourless crystalline compounds. They have a feeble, but not unpleasant, odour. They are not soluble in water, but easily in other solvents, and volatihse without decomposition. Of the dihalogen benzols the para-compounds are soUd, at ordinary temperatures. They melt at higher temperatures than the ortho- and meta-compounds, but boil at lower temperatures.

There is a remarkably close attachment of the halogen atoms to the benzene nucleus. They do not make a double decomposition (or only with great difficidty) with alkaline hydroxides, ammonia, potassium cyanide, etc. (B. 18, 335 ; 20, R. 712) ; but metals Uke Mg, Na, and Cu extract halogens, especially from benzol bromides and iodides. This is of importance for the synthesis of homologous benzene hydrocarbons. There is a notable facility of reaction of chloro-, bromo-, and iodo-benzol with piperidin, forming phenyl-piperidin ; prolonged heating with dimethyl-amine leads to dimethyl-aniline (B. 21, 2279 ; C. 1898, II. 478). Small quantities of powdered copper, or copper salts, which act catalytically, greatly favour the transformation with ammonia, and amines (C. 1909, 1. 475 ; B. 40,4541). Sodium amalgam in alcoholic solution, HI (C. 1898, II. 422 ; /. pr, Ch, 2, 65, 564), and phosphorus, as well as Ni and H at 270° (C. 1904, I. 720), reduce the halogen benzols to benzene.

nuoro-benzols are formed from benzol-diazo-piperididene by adding hydrofluoric acid (Wallach, A. 248, 221)

CeH5N=N— NC5Hio+2HFl=C^HeFl+N,+NH.C5Hio.HFl.

They are formed from the benzol-diazonium chlorides, sulphates, and fluorides {q,v,) by decomposition with aqueous solutions of HF (C. 1898, 1. 1224 ; 1900, 1. 145 ; 1905, 1. 1230).

HALOGEN SUBSTITUTION PRODUCTS OF BENZENE 6i

Fluoro-benxol CeHgF, m.p.— 41-2°, b.p. 85°, D*^ 1-0236, has also been obtained by heating fluoro-benzoic acid with HCl.

p-Diflaoro-benzol CeH4[i,4]F2, b.p. 88°, D iii.

Chloro-benzob. — Modes of formation : — (i) Free chlorine acts but slowly upon benzene. Its action is assisted by I, MoCl5,VCl4 (C. 1904, I. 87), FeClj (C. 1899, II. 287), or AlClj. Chlorination can also be accompli^ed with PbCl4.2NH4Cl (C. 1903, 1. 283, 570).

(2) The hydroxyl group of the phenols is chlorinated with difficulty by PCI5 ; in the nitro-phenols this replacement is easier.

(3) A very important process for forming chloro-benzols, and aromatic halogen derivatives generally, is based upon the transforma- tions of the so-called diazo-compounds, obtained from amido-com- pounds, the reduction products of nitro-compounds. These reactions involve no atomic displacement, the chlorine taking the place pre- viously occupied by the diazo-, amido-, or nitro-group.

Benzol-diazoiilam-ehlorideC9N5N2Cl=C4H5Cl-fN2.

If, therefore, in the di- and poly-substitution products the consti- tution of one of these bodies is known, the constitution of the others is determined.

Name.	Formula.	M.p.	B.p.	D.
Monochloro-benzol .	C^HjCl	-45"	132*	I 128 (o«)
[i, 2]-(o)-Dichloro-beii2ol .	C,H4C1,	■ •	i8o«
If 3]-(m)-Dichloro-benzol .	• •	« •	172*'
1, 4]-(p)-Dichloro-benzol . [i, 2, 3j-fv)-Trichloro-ben2ol	• •	+53^	172®	•
C,H,C1,	I6«	2l8«
i, 2, 4 -(as)-Trichloro-benzol	• •	63*^	213**
I, 3, 5]-(8)-Trichloro-benzol	• •	54"	2o8«
[i. 2f 3» 4]-(v)-Tctrachloro-benzol	C,H,Cl4	46^	254"
[i, 2, 3, 5]-fas)-Tctrachloro-benzol	■ •	50^	246"
i» 2, 4, 5]-(s)-Tetracliloro-benzol Pentachloro-benzol .	• •	137"	244"
C,HC1,	86**	276*
Hexachloro-benzol .	C.C1.	226*»	326«

In the chlorination of chloro-benzol, p-dichloro-benzol is mostly formed, with but Uttle o-dichloro-benzol (B. 29, R. 648) ; p-dichloro- bi^zol is also obtained from p-quinone (q.v,) with PCI5. Further chlorination of o-, m-, and p-dichloro-benzol 5delds 1,2,4-trichloro- and 1,2,4, 5-tetrachloro-benzol (^- ^905» II- 1528). Characteristic, for the dichloro-benzols, is their behaviour on nitrogenation :

o-Dicbloro-benzol gives [x, 2]-dichloro-4-nitro-beii2ol, m.p. 43"

m-Dicbloro-benzol „ [i, 3]-dichloro-4-nitro-be]ixol, „ 32*

p-Dicbloro-benzol „ [i, 4]-dicbloro-3-mtro-beii2ol, „ 55".

Hezaehloro-benzol (Juhn's " chlorocarbon ") has also been obtained by the thorough chlorination of many alkyl-benzols, and other benzene derivatives (B. 29, 875). It is also formed on conducting CHClj or CjCl4 through an incandescent tube.

Bromo-benxols have been obtained in a manner quite similar to the chloro substitution products, i.e. (i) by direct substitution, through bromine carriers, like Al bromide (B. 10, 971) or a mixture of sidphur bromide and HNOa (B. 88, 2883 ; C. 1901, II. 750) ; (2) from phenolene ; (3) from diazo-compounds (q.v.).

ORGANIC CHEMISTRY

Name.	'Fonnula i	M.p.	B.p.	1 D.
	1 ;C.H,Br
I. a -(o)-Dibromo-iK-niol		+ 7-8° •	224'
1,4 -(pj-Dibrtimo-beniol	1	89-	219°
>.*. 3 -{vl-Tribromo-beniol	|c,H,Br,	87'
1, 3, 4 -(as)-Tribromo-beniol
1,2.3 4>(v)-Tetrabromo-ben«il C,H^,
l.'.3.5i-(as)-Tetrabroino-benKil'
I, 2, 4, 5]-(a)-Tetrabromo-belliol !	;2^:		, (B. 28. 191)
	|C,Br,	S'S"

Of the dibromo-benzols we obtain on bromination of benzene with heat chiefly the p-compounds, more rarely the o-compounds (B. 10, 1345)- Characteristic of the dibromo-benzols, as of the dichloro- benzols, is their behaviour on nitrogenatlon.

The generation of tribromo-benzols from the three dibromo-benzols has been used for constitution determinations of all these bodies (Komer). Hexabromo-benzol is generated by heating CBrj to 300°.

Chloro-bromo-beniols, see C. 1899, 1. 835 ; II. 959.

lodo-benzols are obtained (i) by heating benzene, iodine, and HI to 200° (Kekul^). The action is represented by the equation (A. 187, 161) :

5C,H,+4l+IO.H=5C,H,I=3H,0.

{2) By treating benzene with a mixture of I,S, and HNO, (B. 33, 2875 ; C. 1901, II. 750).

(3) More usually, iodo-benzols are prepared from the corresponding amido-com pounds with the help of the diazo-com pounds (^.i'.).

{4) Bromo-benzol may be transformed to iodo-benzol by changing it in ether solution to phenyl-magnesium bromide, and then treating with iodine (C. 1903, I, 318) :

CH,Br-=_-	»CH.MgBr— il-	■* C,H.I+MgBrI.
Name.	Formula.	M.p.	B.p.
	C,H,I	-30"	i88*
I, 2 -(o)-Di-io do- benzol	.			286-
1, 3 -{m)-Di-iodo- benzol			40"
1,2 3 -(v)-Tii-iodo-benjoI		C,H.^
1, 2, 4 -(asj-Tri-iodo-benzol			91-4° •
I. 3. 5 -(s)-Tri-iodo-benzol			I84-4"
I. 2. 3. 4]-(v)-Tetra-iodo-beii2ol .			B.84,T343; C. 1901. II. 535
		148"
1. 2. 4, ■i]-(5)-Tetta-ioi]o-beoK»l .
	C,HI,
Heu-iodo-beiuol	C.I.	I40°-iso''

Hex8-lodo-beiusol C,I, forms during thorough iodination of benzol- carboxylic acids (benzoic acid, terephthalic acid) with iodine and

HALOGEN SUBSTITUTION PRODUCTS OF BENZENE 63

fuming sulphuric acid. It forms reddish-brown needles which melt and decompose at I40°-I50** (B. 29, 1631).

1, 8» 5-Tri-lodo-2-ehloro-benzol (C. 1907, 1. 632). About Bromo-iodo- benzols (B. 29, 1405 ; C. 1899, II. 371). 1, 3, 5-Trl-iodo-2, 4, 6-tribromo- benxols CeBrgl,, m.p. 322'' (C. 1898, II. 972).

Iodide ehlorides ; lodoso-benzol ; lodo-benzol ; DiphenyModonium hydroxide. — ^The iodo-benzols and their homologues, by the action of chlorine or substances easily liberating chlorine, are transformed into iodide - chlorides, e,g. phenyl iodide -chloride C^HglClg (Willgerodt, 1886). These contain chlorine bound to iodine, and may therefore be referred to iodine trichloride ICI3. The formation of these peculiar compounds is useful for the characterisation of iodinated benzene derivatives. The iodo-chlorides are easily changed into iodoso- benzols, and should be regarded as the chlor-anhydrides of the latter. From the iodoso-benzols we arrive through oxidation at the iodo- benzols, e.g, CjHglOj. From iodoso- and iodo-benzol we finally obtain the strongly basic diphenyl-iodonium hydroxide.

Phenyl-iodOH^hloride C^HbICIj, yellow needles, formed on conduct- ing chlorine through a solution of iodo-benzol in chloroform. By heating it is changed into p-iodo-chloro-benzol with hberation of chlorine (C. 1907, 1. 1198 ; II. 43). Shaken up with water and alkalies or other bases, it yields iodoso-benzol : • i/rj

C^H5lCl2-f2KOH=C^H5lO-MKr+H5,0.

Iodoso-benzol C^HjIO is an amorphous substance exploding about 210® ; treated with acidulated KI solution, it gives up its oxygen with liberation of the equivalent quantity of iodine :

CeHJO-f2KI+2CH8COOH=CeH5l-f2CH3COOK+2l+H20.

It has a basic character, and yields salts derivable from the hypo- thetical hydrate C«H5l(OH)2, like C«H5l(00CCH,)a ; we must there- fore regard C^HJCls as an iodoso-benzol chloride.

Iodo-benzol C^HglOj, by heating iodoso-benzol by itself, or by boiling in water :

2C.HJ0=CeHJ+CeHJ0. ;

also by oxidation of iodoso-benzol with hypochlorous acid, or treat- ment of phenyl-iodo-chloride with bleaching-powder solution (B. 29, 1567 ; cp. B. 83» 853). It is also formed direct from iodo-benzol by oxidation with K persulphate and concentrated H2SO4 (Caro's reagent, B. 88, 533), Iodo-benzol explodes at 227*^-230'*. It exhibits the behaviour of a super-oxide.

With concentrated HF, iodo-benzol yields benzoModo-fluoride C^HjIOFj, which with water regenerates iodo-benzol (B. 84, 2631).

Diphenyl-iodonium hydroxide (CeH5)2lOH is only known in aqueous solution. Generated by shaking up a mixture of iodoso- and iodo- benzol with moist silver oxide, according to the equation

C.HJO+C,HJO,+AgOH=(C.H5)J.OH-fIO,Ag.

Its iodide is formed on boiUng iodo-benzol with KI solution (B. 29, 2008). Diphenyl-iodonium hydroxide has a strong alkaUne reaction, and forms salts resembling those of thallium ; the carbonate and

64 ORGANIC CHEMISTRY

nitrate are very soluble. The chloride and bromide form white precipitates.

Diphenyl-iodonium iodide (C«H5)2l.I is polymeric with iodo-benzol. It forms yellow needles soluble in alcohol with difficulty. They melt at I75°-I76'*, forming iodo-benzol (V. Meyer, B. 27, 1592 ; 28, R. 80).

Fat-aromatic iodonium salts are obtained by transformation of acetylene-silver chloride with aromatic iodo-chlorides :

«C.H ja. +HCsCAg.AgCl =aHC : CCK j_^, ^^.H.! +,Aga.

Dieliloro-vinyl-phenyl-iodODium chloride, m.p. 174''. Bromide decomposes at 162°. The free base is unstable {A. 869, 132).

A number of homologous and substituted iodo-chlorides, iodoso- and iodo-benzols, and iodonium hydroxides have been prepared (see C. 1900, 1. 761 ; 1902, II. 1196 ; B. 84, 3406, 3666 ; 87, 1301 ; 89, 269).

B. Halogen Derivatives of the Alkyl-Benzol3.

Under the same conditions as in benzene itself, in the cold, in the presence of I, M0CI5, VCI4, FeCl,, sulphur bromide, and HNO, (B. 88, 2885), so in the alkyl-benzols the chlorine and bromine atoms enter almost solely into the benzene residue, and aromatic substitution products are formed. • Thus, toluol yields :

CeH^CHa ► CeH^CLCH, ► CeHjCljCHj, etc.

CeHjCH, ► CeH^BrCHa ► CeH^Br jCH,, etc.

But on conducting CI and Br through the boiling alkyl-benzols, hardly anything but the hydrogen of the side chain is replaced, and aUphatic substitution products are obtained. Thus, from toluol

CeHjCH, > C^HgCHaCl ► C^HjCHQ, ► CeHjCCla

Benzyl chloride Benzal chloride Benzo-trichloride

are obtained, corresponding to

CHjCHjCl ► CH3CHCI2 > CH3CCI,

Ethyl chloride EthyUdene chloride Methyl chloroform.

These are dealt with in connection with the corresponding oxygenated compounds :

C^HjCHjjOH ► C^HjCHO ► CeH^COgH

Benzyl alcohol Benzaldehyde Benzoic acid

into which they can be easily converted, and from which they can be obtained by means of PCI5.

In sunUght, CI and Br produce substitutions of the aUphatic side chains of the lower homologues, even when cold (B. 20, R. 530 ; cp. B. 85, 868). Isopropyl-benzol is transformed by CI, at boiUng-point, into p-chlorisopropyl-benzol (B. 26, R. 771). PClg also attacl^ the alkyles of the alkyl-benzols when hot. In this and many other reactions the presence of other substituents, in the benzene nucleus, exercises an impeding influence (C. 1898, I. 367, 1019).

HALOGEN DERIVATIVES OF THE ALKYL-BENZOLS 65

The two other methods for preparing the halogen derivatives of benzene, viz. the action of halogen phosphorus compounds upon oxy-benzols, and the transformation of the corresponding diazo-com- pounds, give alkyl-benzols, with substitution of halogens in the benzene residue. A substitution can take place both in the aromatic and the aliphatic residue of the same alkyl-benzol. The halogen atoms entering the side chain are always capable of reaction. They freely exchange for radicles, whereas the halogen atoms entering the benzene residue are very strongly bound. The aromatic monot^ogen derivatives of the aU^fl- benzols, especially the bromalkyl-benzols, are often used for bnilding up higher alkyl-benzols by Fittig's method. Of some importance for recognising the constitution is the oxidation of the side chains to carboxyl groups, which enables us also to determine the halogen atoms m the side chains.

With sodium amalgam in alcohohc solution, or with HI, the halogens are replaced by hydrogen.

Of the very numerous aromatic halt^en substitution products of this kind we may here enumerate the simplest representatives of the monohalogen toluols :

Name.	F.„^.	M.p.	B.p.
I, J -, a- Fluoro- toluol ,	CH,	i]C,H.	2]F		114° (C. 1906,11.	.830)
I. 3 -, m-FIuoro-toluol .	CH,	l]C,H,	3lF		"5°
I, 4 -, p-Flnoro-toluol .	ci4	.CH	jlF		116"
		iic:h:		-If-	156°
		■ cIh		150°
I. 4 -, p-Chloro-toluol .		.CH		+ 7°	i&3°
1, » -, o-Eromo-toluol .		.]C,H,	2]Br	-26°	181°
I, 3 -, m-Bromo-toluol .		.C,H	3]B<	-40°	183°
1. 4 -. p-Bromo- toluol .		■CH	+]Br	+3S'	184'
I, 2 -. o-Iodo-toluol	CH,	UC.h,			204"
I, 3 -. m-Iodo-toluol	CH.	.IC.H.	m		204°
I. 4]', p-lodo-toluol	CH,[,JC,H,	111	35°

0-, m-, and p-Fluoro-toluols have been prepared by the same methods as fluoro-benzol. On chlorinating or brominating toluol in the cold, or in the presence of iodine or FeClj, para- and ortho-com- pounds are produced, in nearly equal quantities. The p-chloro-toluol may be separated from the o-compound by heating to 150° with sulphuric acid, when the o-compound forms a stilpho-acid.

All the monochloro-, monobromo-, and mono-iodo- toluols may be obtained pure by decomposition of the diazo-compounds (q.v.) obtained from the three amido-toluols or toluidinenes. The o- and p-chloro- toluols are easily obtained from the corresponding toluidins. The m-bromo-toluol has also been obtained by brominatijig aceto-p- toluidin to m-brom-aceto-p-toluidin and then replacing the amido- group by hydrogen,

"ITie m-chloro-toluol has also been obtained from 3-methyl-Aj-

keto-R-hexene, easily prepared from methylene-diaceto-acetic ester.

In this process tetrEdiydro-m-dichloro-toluol is first prepared by

means of PCI,, and then "it splits into HCl and dihydro-m-chloro-toluol.

VOL. II. F

66

ORGANIC CHEMISTRY

Bromine withdraws two H atoms from this body, and m-chloro-toluol is formed (B. 27, 3019) :

C=

CH — CO

CH, -> C=CH — CClj

CH3 -> C=^CH — CCl

CHj— CHj— CHj CHj— OHj— Crij CHg— CH^— — CH

CHg ^C=CH— CCl CH =CH— CH

If we start from ethylidene-binaceto-acetic ester, we obtain [i, 3, 5]- chloro-m-xylol (B. 29, 310) ; and [i, 3, 6]-chloro-cymol has been similarly obtained from menthone or keto-hexahydro-p-cymol (B. 29,

314).

The iodoso- and iodo-compomids corresponding to p-iodo-toluol

are known (B. 26, 358 ; 27, 1903).

For the halogen toluols their transformation into solid nitro-halogen toluols, and their oxidation to the halogen benzoic acids of known constitution, are characteristic. Chromic acid oxidises the m- and p- halogen toluols to the corresponding carboxyUc acids, but it com- pletely bums up the o-halogen toluols. By boiling with dilute HNO3, by potassium permanganate or potassium ferricyanide, all the three isomers, including the ortho-compounds, are converted into carboxyhc acids.

Of aromatic di-halogen toluols with similar halogens six isomers are possible. The six isomeric dichloro-toluols are known (B. 29, R. 867). They are isomeric with benzal chloride C^HgCHClj, and the three chloro-benzyl chlorides C1C5H4CH2C1. For particulars of the higher chlorination products of toluol, see C. 1902, II. 1178 ; 1904, IL 1292, etc. The six isomeric dibromo-toluols and di-iodo-toluols have all been obtained (C. 1910, I. 525). Pentabromo-toluol is prepared from suberane and bromine. The six isomeric tribromo-xylols are all known (C. 1906, II. 1831).

The following table contains the easily prepared bromo-derivatives of polymethyl-benzols :

Name.	M.p.	B.p.
[i, 2, 4]-Bromo-o-xylol. ....	- 2**	214"
[i, 3, 4]-Bromo-m-xylol			• ■	203^
[i, 2, 4]-Bromo-p-xylol			+ 9°	200**
Tribromo-hemimellithol			245°	• •
[i, 2, 4, 3]-Monobromo-pseudocumol			• •	237'
'i» 2, 4, 3, 6]-Dibromo-p8eudocumol			64°	293**
Tribromo-pseudocumol			224°	• •
Monobromo-mesitylene					- I«	225°
Dibromo-mesitylene					+6o»	285**
Tribromo-mesitylene					224°	. •
Monobromo-prehnitol . Dibromo-prennitol					30**	265**
				210''	■ ■
Monobromo-isodurol					• •	253°
Dibromo-isodurol					209°	• •
Monobromo-durol					6i*»	262 *»
Dibromo-durol					IQQ''	317°
Bromo-pentamethyl-benzol					160°	289°

It is also remarkable that concentrated sulphuric acid can transfer bromine atoms instead of alkyl groups. It thus converts monobromo- durol first into dibromo-durol and then into lurol (B. 25, 1526).

NITROGEN DERIVATIVES OF BENZENE HYDROCARBONS 67

A number of iodinated alkyl-benzols have, like iodo-benzol itself, been prepared by means of sulphur iodide and HNO3 (^^ ^- ^9 2875)-

Concerning tie influence of alkyl groups in the " reverse substitu- tion " of iodine in iodinated benzols, see /. f>r. Ch. 2, 65, 564.

8. Hitrogen Derivattves of Beniene Qsrdroearbons in which the nitrogenated residue is connected with the benzene nucleus by nitrogen linking.

These compounds may be classified by the niunber of nitrogen atoms contained in the residues. The first class is formed by com- pounds in which the nitrogen group only contains one nitrogen atom. This is headed by the «»> o-compounds, so characteristic of the benzene derivatives in general, which form the bases for obtaining the succeed- ing groups. Then come the amiio-compounds, which comprise the generators of many coal-tar dyes and aromatic bodies of therapeutic importance. A link between both groups is formed by the nitroso- and the ^hydroxylamine compounds.

The second class is formed by the compounds in which the nitro- genated residue contains two or more N atoms mutually linked. Two N atoms are carried by the nUro-amines, the nitroso-P-hydroxyl- amines, the nitrosamines, the azoxy-compounds, the hydrazins, the dtazo- and the ozo-compounds. Three N atoms are carried by the nt^oso-hydrazins, the itazo-awirfo-compounds, and the azo-imido- compounds ; four N atoms by the <^*<wa-hydrazides or buzylene com- pounds, and the tetrazones ; five N atoms by the bis-diazo^amido- compounds ; and eight N atoms by the his-diazo-tetrazones or octtwnes.

Our knowledge of some of these classes of bodies has acquired the greatest importance, even for the chemistry of the inorganic nitrogen compounds. If we imagine these nineteen groups of aromatic nitrogen compounds derived from the inorganic nitrogen compounds obtained by replaang the aromatic residues by hydrogen, then out of the nineteen, only six occur free or in inorganic compoimds, and these are printed in heavy typ^ in the following list :

1. ^t^o-compounds . . derived from H.HOt

2. ^t^050-compounds . . „ „ H.NO

3. fi'Hydfoxylamine'Coxxi^Mnds . ,» H.NHOH

4. ilmufo-compounds . . ,, ,. HJIHt

5. NUro-amines HJTHJTOt

6. NUroso-$-hydroxylamines „ „ H.N(OH).NO

7. Nitrosamines „ „ H.NH.NO

8. Dioiro-compounds „ ,, H.N=N.OH

H.NH.NO or H.N(OH) • N

9. i4^a-compoands „ „ H.N=N.H

10. Azoxy-Qoxxrpoxmd^ . . „ „ H.N^- N.H

11. Hydrazins . . . . „ H.NHjra[«

12. NUroso-hydraxins . . „ ,. H.N(NO).NH,

13. Diajso-amido-componnds „ „ H.N=N.NH,

14. Diago-oxy-amido-^ompounds . „ „ H.N=N — NHOH

15. Diaxo^mido-compounds „ „ HJf^**

16. DiatO'hydrazO' or Buxylene com-

pounds ..... ,. H.N=N.NH.1SIH,

17. TBtroMOnes ...... ., H.NH.N=N.NH,

18. Bis-dioMO-amido-compoxxxids . .. „ H.N=N— NH— N=N.H

19. Bu-diaxO'tetragone or Octaxone „ ., H.N : N.NH.N : N.NH.N : NH.

68 ORGANIC CHEMISTRY

The first three groups will be dealt with in the succession shown, but the others will be arranged by their genetic rather than their systematic relations, as follows : — Nitroso-j3-hydroxylamines ; Amido- compounds ; Nitroso - amines ; Nitro - amines ; Diazo - compounds ; Diazo-amido-compounds ; Bis-diazo-amido-compounds ; Diazo-oxy- amido- and Azo-imido-compounds ; Azoxy- and Azo-compoimds ; Hydrazines ; Nitroso - hydrazines ; Tetrazones ; Diazo - hydrazo- or Buzylene compounds ; and Octazones.

I. Nitro-Derivatives of Benzene and the Alkyl-Benzgls.

Benzene and the alkyl-benzols which contain H atoms attached to the nucleus easily give nitro-derivatives under the action of nitric acid :

CeH^+NO,OH=CeH5N08+H30.

In these compounds of a more or less yellow colour the nitrogen of the nitro-group is directly Unked with a carbon atom, as in nitro- methane, for on reduction we obtain amido-compounds :

CeH5NO,+6H=CeH5NH8+2H20.

In the previous chapter it was stated that all the H atoms of ben- zene may be replaced by chlorine and bromine. This does not apply to the nitro-groups. The two first nitro-groups enter without diffi- culty, but the third encounters more resistance, and it has not been found possible to introduce more than three nitro-groups into a benzene derivative.

A mixture of one part HNOg and two parts H2SO4 acts more energetically than HNO3 alone, as the sulphuric acid withdraws water. Di- and trinitro-products are mostly obtained thus. A less complete nitrogenation is attained by first dissolving in glacial acetic acid and chloroform (B. 42, 4151).

The more alkyl groups are contained in a benzene hydrocarbon, the more easily it is nitrogenated. The production of nitro-phenols during such nitrogenation may be explained by assuming an addition of HNO3 to double links of the benzene ring, and the liberation of HNO2 on the one hand and H^O on the other (B. 24, R. 721 ; 42, 4152). Such unstable addition products may also be the cause of the dark- brown colouring at first observed during nitrogenation. On heating with dilute HNOj the nitro-group enters the aUphatic side chain. Such compounds are dealt with later in connection with the corresponding alcohols (B. 27, R. 193 ; C. 1899, I. 1237).

An admirable means of nitrogenation has been discovered in ben- zoyl and acetyl nitrate, suitable for some cases (B. 89, 3798 ; C. 1907, I. 1025). It avoids the generation of water which accompanies nitro- genation with HNOj :

C.H.+C.H6COON02=CeH,N02+CeH5COOH.

The action of AljCl^ upon the hydrocarbon mixed with ethyl nitrate can also produce nitro-compounds (C. 1908, II. 403).

From the aromatic amines obtained by reduction of the nitro-com- pounds the latter may be recovered through the intermediary of the diazo-compoimds, the nitrites of which yield nitro-bodies when treated with cuprous oxide. Nitro-bodies have also been obtained by direct

NITRO-DERIVATIVES OF BENZENE

69

oxidation from amines, e.g. nitro-benzol from aniline with K perman- ganate, in which process j3-phenyl-hydroxylamine and nitroso-benzol have been obtained as intermediate products (B. 82, 1675).

Properties and Behaviour. — ^The nitro-hydrocarbons are only slightly soluble in water, but they are soluble in concentrated HNO,, and are precipitated from this solution by water. They are easily dissolved in alcohol, ether, glacial acetic acid, etc. The nitro-products melt at rather a higher temperature than the corresponding bromine derivatives.

Of greater importance is the easy reduction of the nitro-compounds. As intermediate products of the reduction to amido-compounds the nitroso-compounds and the j8-phenyl-hydroxylamines have been re- tained. Both combine, under the influence of an alkali, to azoxy-com- pounds, which are further reduced to azo- and hydrazo-compounds. These genetic relations are represented by the scheme :

CeHjNO, ► CeH^NO

-> C.HsNHOH ► CjHjNH,

Nitroso-benzol /9-Phenyl-hydroxylainine Aniline

C,H,N,

Azoxy-benzol

C,H,N

C«H,N Azo-benzol

C,H,NH

C,H,NH Hydrazo-benzol .

During the electrolytic reduction of nitro-bodies dissolved in sul- phuric acid we obtain, besides amido-hydrocarbons, amido-phenols, by transposition of the unstable j8-phenyl-hydroxylamines (B. 29, R. 230). In HCl solution p-chloraniline is formed by a similar process (B. 29, 1894 ; C. 1907, I. 463).

About the electrolytic reduction of nitro-bodies, see also C.i 901, I. 105, 149 ; B. 38, 4006 ; A. 855, 175, etc.

The easy reduction of nitro-boddes to substances useful in the manufacture of coal-tar dyes has given them the position of im- portant and indispensable intermediate products.

By oxidation with alkaline K ferricyanide solution, the polynitro- benzols are easily converted into polynitro-phenols. Nitro-benzol, on heating with powdered caustic potash, yields o-nitro-phenol and azoxy-benzol ; m-nitro-toluol similarly yields m-nitro-o-cresol ; and m-dinitro-benzol yields 2, 4-dinitro-phenol (B. 82, 3486 ; 84,