GB655686A - Process of preparing benzene hexachloride - Google Patents

Abstract

Technically pure g -isomer of benzene hexachloride is prepared by crystallization of solutions over-saturated with a , b and g isomers, in a process in which a benzene solution saturated with a , b and g isomers at atmospheric temperature is boiled to evaporate part of the benzene, the boiling being interrupted before a stage is reached corresponding to saturation with isomers other than a , b and g , and the solution is then gradually cooled without undue stirring so that only the g -isomer crystallizes, which is preferably separated by filtration or continuous decantation. The saturated solution which is the starting-material may be obtained either by treating crude benzene hexachloride with such a quantity of benzene at room temperature that a saturated solution of a , b and g isomers is produced, from which solid a - and b -isomers are separated, or by the additive chlorination of benzene until crystals appear, when a portion of the benzene is evaporated, the solution cooled to e.g. 20 DEG C., and the solid a - and b -isomers separated. A crude solid benzene hexachloride may also be produced by mixing the a - and b -isomers with the mother-liquor from the final g -isomer crystallization and then evaporating all the benzene. An example is given of the process in which the initial benzene solution of isomers is obtained by chlorination of benzene. Specification 619,677 is referred to. The Specification as open to inspection under Sect. 91 is not restricted to the use of benzene as solvent, it being stated that other known solvents may be used. This subject-matter does not appear in the Specification as accepted.