GB637732A - Improvements in the production of gamma benzene hexachloride - Google Patents

Abstract

Gamma benzene hexachloride is obtained by the photo-chlorination of benzene fortified with normally precipitated benzene hexachloride, i.e. benzene hexachloride containing alpha and beta isomers, and substantially no gamma isomer, the precipitate obtained is filtered off and benzene hexachloride containing a high percentage of the gamma isomer is recovered from the filtrate. The precipitated hexachloride may then be added to a further batch of benzene and the process repeated. It is advantageous to employ blue filtered light and to add a small quantity, e.g. up to 10 per cent by weight, of chloroform. In examples: (1) benzene is treated in sunlight with chlorine gas at below 35 DEG C. until a weight increase of 20 per cent is obtained when after standing for twelve hours the precipitate is filtered off and benzene hexachloride containing a high percentage of the gamma isomer is recovered from the filtrate, the above precipitate is added to benzene containing 10 per cent of chloroform and the above chlorination process repeated with light filtered through a blue filter; in (2) thiophene free benzene with 7 1/2 per cent of chloroform is chlorinated with direct sunlight to obtain a 20 per cent weight increase when after standing overnight the precipitate is filtered off and added to a similar batch of thiophene free chloroform containing benzene and the chlorination process repeated at not above 35 DEG C., the gamma isomer being recovered from the various mother liquors and the precipitated a - and b -isomers added to fresh batches of benzene.