The Chemistry of Dyestuff. Intermediate Compounds. VI. Halogen Compounds.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)The chloro-derivatives of the aromatic compounds are in most cases easily obtained by the action of chlorine in presence of a catalyst. The most important catalytic agents are ferric chloride, aluminium chloride, molybdic chloride (MoCl₅) and iodine.

In the cold and dark the chlorination takes place mainly in the ring, at the boiling point and in sunlight the chlorination of homologues, e.g., toluene, occurs mainly in the side chain. These compounds are produced mostly for the manufacture of aldehydes and carboxylic acids.

The manufacture of caustic soda by electrolysis of salt has given a cheap supply of chlorine. This has increased the use of chloro-derivatives such as chloracetic acid, phosgene, chlorobenzaldehydes etc., and has enabled the use of chlorobenzidine etc., to be extended giving dyes of greater fastness.

Chloronaphthalene sulphonic acids may be employed for the preparation of naphthylamine sulphonic acids by means of ammonia in presence of copper salts. Chlorand brom-anthracene derivatives are also of importance for the production of alky1 and aryl derivatives of anthracene etc.

Chlorobenzene [] (B.P. 129°C.) is obtained by  action of chlorine upon benzene in presence of ferric chloride. The product is then fractionated.

By further chlorinatiori para-dichlorobenzene [] (M.P. 53°C.) is obtained, this compound is employed for the production of p-phenylene diamine by heating under pressure with ammonia in the presence of a copper salt.

Ortho chlorotoluene (B.P. 159°C.) and parachlorotoluene (B.P. 162°C., M.P. 7,4°C.) are obtained by chlorination of toluene in the cold in the presence of molybdic chloride (MoCl₅).

Benzyl chloride [] (B.P. 1 76 179°C.) is obtained by chlorination of toluene at the boil, in earthenware vessels, heated with a leaden steam pipe. The vapours are condensed and returned to the vessel. The chlorination is continued until a sample has the specific gravity of ri at 15°C. The product is then fractionated, some unchanged toluene and benzal chloride distil over.

Benzal chloride [] (B.P. 206°C.) is obtained by further chlorination until the specific gravity is about 1,20. The product is then rectified.

Benzotrichloride [] (B.P. 213°-214°C., Sp. Gr. 1.38) is obtained as a by-product in the production of benzal chloride.

a-Chloronaphthalene  [] (B.P. 252°C.) is obtained by chlorination of naphthalene at the boil in presence of ferric chloride. The product is then purified by distillation.

The dichloronaphthalenes 1.4, and 1.5, are obtained by chlorination in carbon disulphide solution below°C., traces of the 1.2, and 1.7 isomers are also present.

Tetrachloronaphthalene [] is obtained by action of chlorine upon naphthalene in shallow layers in the cold, the product is extracted with petrol to remove the dichloronaphthalenes.

A large number oi chloronaphthalene sulphonic acids is obtained by sulphonation of the chloronaphthalene derivatives.

Chlorophthalic anhydrides are obtained by the chlorination ot phthalic anhydride in fuming sulphuric acid solution.

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Three isomerides are obtained, the main compound being the 3.6-dichlorophthalic anhydride. The three isomerides may be separated by crystallisation of the zinc salt of the dichlorophthalic acid.

Tetrachlorophthalic acid and anhydride  [] are obtained by passing chlorine through a mixture of antimony chloride and phthalic anhydride heated to 200°C. When chlorine is no longer absorbed, the antimony pentachloride is distilled off, the residue may be either distilled, or well washed with water after cooling. The anhydride is insoluble in cold water (M.P. 252°C.).