GB730915A - Improvements in or relating to the production of ª†-benzene hexachloride - Google Patents

Abstract

Benzene hexachloride containing at least 95 per cent of the gamma isomer is obtained by dissolving a crude mixture containing gamma benzene hexachloride and its isomers in a lower alcohol containing 1-6 carbon atoms, e.g. methanol, the boiling-point of which is raised above the normal atmospheric by raising the pressure and/or by adding a substance which increases the boiling-point of the solvent without impairing its dissolving power, saturating the solvent with the crude benzene hexachloride mixture at a temperature above the normal boiling-point and cooling, suitably to 40-50 DEG C., to crystallize the gamma isomer. Suitable substances which may be added to increase the boiling-point of the solvent include hydrocarbons, aromatic compounds, halogenated hydrocarbons, halogenated aromatic compounds, phenols, phenolic ethers, cyclic ketones, terpenes and esters of aliphatic or cyclic acids, particularly those substances which have a low vapour pressure and favourable cryoscopic properties, e.g. low molecular weight, low vapour pressure compared with the solvent, inability to form low-boiling azeotropes with the solvent and chemical inertness. The process may be carried out semi-continuously by using the mother-liquor from a previous crystallization as the solvent for a fresh quantity of crude benzene hexachloride. The amount of delta isomer present in the crude benzene hexachloride should preferably be kept below 5 per cent. In examples gamma benzene hexachloride is obtained from crude benzene hexachloride according to the invention by crystallizing from (1) methanol containing trichlorobenzene; (2) methanol containing decahydronaphthalene; (3) methanol containing xylene; (4) methanol containing cyclohexanone; and (5) methanol under superatmospheric pressure.