GB586439A - Improvements in or relating to the production of benzene hexachloride isomers - Google Patents

Abstract

To obtain from crude benzene hexachloride a composition containing an enhanced proportion of g -isomer to a -isomer, the material (obtainable by chlorinating benzene 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 an aliphatic solvent therefor, other than methanol or ethanol, or with a cyclo-aliphatic solvent therefor containing a 6-carbon ring, the solvent being in such amount as to dissolve the g -isomer leaving a substantial proportion of the g -isomer undissolved, and if desired the solvent is then removed from the solution. Advantageously the composition is recovered from the extract as a precipitate by adding thereto a liquid which has a low solvent power for the g -isomer and which is miscible with the solvent. The aliphatic solvent may be a normally liquid chlorinated aliphatic hydrocarbon, e.g. chloroform, carbon tetrachloride, cis-dichloroethylene, trans-dichloroethylene, trichloroethylene, perchloroethylene, ethylidene chloride, ethylene dichloride, isobutyl chloride; or an esters of an aliphatic carboxylic acid, e.g. methyl acetate, ethyl acetate, n-butyl acetate, methyl trichloroacetate, methyl dichloroacetate, methyl propionate; and in either case the mixture of isomers may be recovered from the extract by mixing the latter with a pentane or a petrol ether fraction. The cycloaliphatic solvent may be cyclohexane, cyclohexene, cyclohexanol, cyclohexanone or decahydronaphthalene. Other specified solvents are: hydrocarbons: diesel oil, odourless distillate, kerosene, n-pentane, petrol ether, "white oil"; miscellaneous: diethyl carbonate, glacial acetic acid, acetone, acetonitrile, n-butyl bromide, diacetone alcohol, dimethyl acetal, ethyl ether, paraldehyde, carbon disulphide. In examples: (1) crude benzene hexachloride containing 12 per cent g -isomer and 70 per cent a -isomer (obtained by chlorinating benzene at 50 DEG C. under actinic radiations until a 20 per cent solution of the hexachlorides in benzene is formed and flashing off the excess benzene) is stirred with cyclohexane to obtain a solution containing 18 parts of solids of which 66 per cent are the g -isomer and from which the solvent is removed by evaporation; (2)-(6), crude benzene hexachloride, obtained as in (1), is: (2) deodorised by the method of Specification 586,464 and the product stirred with decahydronaphthalene to obtain a solution containing 18 parts of solids of which 66 per cent are the g -isomer; (3) stirred with tri-chloroethylene to obtain a solution containing 15 parts of solids of which 33 per cent are the g -isomer and the solvent is removed by evaporation; (4) refluxed with chloroform to obtain a solution containing substantially all the g -isomer, and the solution is concentrated to obtain the solid product; (5) stirred with glacial acetic acid to obtain a solution containing 23 parts of solids of which 21 per cent are g -isomer and the solids are precipitated by diluting with a large volume of water; (6) stirred with methyl acetate to form a slurry containing solid a -isomer, which is filtered and the filtrate is evaporated to obtain a solid containing 42 per cent of g -isomer. Specifications 573,689 and 573,693 also are referred to.