GB618994A - Improvements in or relating to the purification of benzene hexachloride - Google Patents

Abstract

Benzene hexachloride is treated with aqueous methanol or aqueous ethanol so as to remove all the delta isomer present without removing any substantial proportion of the gamma isomer. p Room temperatures and alcohols containing from 10 to 30 per cent by weight of water are preferred. The benzene hexachloride used may first be substantially freed from alpha and beta isomers by treatment with ethanol or methanol. The benzene hexachloride obtained may be further purified by treatment with non-aqueous solvents. The delta isomer is recovered from the aqueous-alcohol solution by precipitation with water with subsequent recrystallisation from, e.g. carbon tetrachloride. A table is given of the relative solubilities of the gamma and delta isomers in aqueous-methanol and aqueous-ethanol solutions of varying compositions. In examples: (1) benzene hexachloride obtained by chlorinating benzene with chlorine, whilst irradiating with a mercury arc lamp is treated with aqueous-methanol the proportion of methanol to water being 80 to 20 and (2) the benzene hexachloride obtained as in (1) is extracted with methanol and the extract, after removal of solvent, treated with aqueous-methanol the proportion of methanol to water being 73 to 27. Specifications 573,689, 573,693, 586,439 and 586,442 are referred to.