GB732129A - Improvements in or relating to separation of gamma benzene hexachloride - Google Patents

Abstract

Benzene hexachloride containing above 96 per cent of the gamma isomer is obtained by extracting the crude product of additive chlorination of benzene with an amount of cold methanol not less than half the weight of the isomer mixture, but such as to leave a substantial part of the mixture undissolved, concentrating the extract by removing 50 to 75 per cent of the methanol, cooling to 0 DEG to 30 DEG C. to crystallize a gamma fraction containing 80 to 90 per cent of the desired isomer, dissolving this fraction in at least 3 times, preferably 3 to 5 times, its weight of methanol, concentrating to give a methanol/benzene hexachloride ratio of between 1.25 : 1 and 2.5 : 1, preferably about 1.5 : 1, and cooling to a temperature of 0 DEG C. to 30 DEG C. to crystallize a p second high gamma isomer fraction having a purity of above 96 per cent. A preferred process giving a product containing over 99 per cent of gamma isomer comprises making the original extract using two parts by weight of methanol to one of benzene hexachloride, concentrating by removing 70 per cent of the methanol, cooling to 15 DEG C. to crystallize a fraction containing 80 to 85 per cent of gamma isomer, dissolving this fraction in methanol and concentrating as previously described, and finally cooling to 15 DEG to 30 DEG C. Examples are given. Specification 573,693 is referred to.