GB586442A - Improvements in or relating to the isolation of an isomeric form of benzene hexachloride - Google Patents

Abstract

To obtain from crude benzene hexachloride a composition containing an enhanced proportion of the g -isomer to a -isomer and suitable for the manufacture of pesticidal compositions, the material (obtainable by treating benzene with chlorine at ordinary or elevated temperature while irradiating actinically, discontinuing the chlorination while unchanged benzene is still present, and flashing off unchanged benzene with hot water) is treated with a solvent comprising at least one normally liquid homologue of benzene. The amount of the solvent being sufficient to dissolve the g -isomer and to leave a substantial proportion of the a -isomer undissolved. Advantageously, the solvent is composed of one or more homologues of benzene containing in the molecule not more than 9 carbon atoms. Specified solvents are: toluene, o-, m-, and p-xylenes, commercial xylene, mesitylene, cumene, and pseudocumene. When toluene or commercial xylene is used, it may be mixed with 10 to 20 per cent by weight of the mixture of a pentane or a petrol ether fraction. The extraction may suitably be performed in the cold with an amount of toluene or commercial xylene of about half the weight of the crude benzene hexachloride. Advantageously the desired product is isolated from the extract by adding thereto, in amount sufficient to precipitate the product, a liquid, e.g. a pentane or a petrol ether fraction, which is miscible with the solvent and which has at most a low solvent power for the g -isomer. In examples: (1) crude benzene hexachloride (obtained by passing chlorine into benzene at 50 DEG C. under actinic radiations, stirring the resultant solution with a large volume of water at 76 to 78 DEG C. and filtering off the product, drying and grinding) is agitated for 2 hours in the cold with commercial xylene, the reaction mixture is filtered and the filtrate is treated with more xylene before being evaporated to obtain substantially all the g -isomer; (2) ground benzene hexachloride obtained as in (1) is agitated for 2 hours in the cold with toluene and the extract is treated as in (1) to obtain a solid containing substantially all the g -isomer; (3) crude benzene hexachloride is agitated for 1 hr. in the cold with toluene forming a slurry which is filtered and the filtrate is evaporated to obtain a solution from which substantially pure g -isomer is crystallised, further quantities of solid containing g -isomer being obtained by adding petrol-ether. Specifications 573,689, 586,434 and 586,464 are referred to.