GB686354A - Process for fractionating commercial hexachlorocyclohexane especially to obtain the ª†-isomer - Google Patents

Abstract

Crude hexachlorocyclohexane is mixed with methanol to form a paste and to dissolve the d - and e -isomers, the liquid extract is expressed from the paste by filtration with pressure, and the solid residue is extracted with methanol to dissolve the g -isomer and leave the a - and b -isomers substantially undissolved, the g -isomer being recovered by crystallization after concentrating the extract. The methanol used in the pasting operation may be at a low temperature, e.g. ice-cold, in order to enhance the difference in solubilities between the d - and e -isomers and the g -isomer. The pasting operation may also be performed in two or more steps, extract from the preceding stage being reactivated with fresh methanol and used to re-extract the solid residue of that stage. The mother liquor from the recovery of the g -isomer may be evaporated to dryness to give a residue containing 60 per cent of the g -isomer. A graph is provided which indicates the points in the process when all the a - and e -isomers have been removed and when only d - and b -isomers remain the portion in between these points representing the extraction of the g -isomer. In an example methanol 150 c.c.s. is mixed at 0 DEG C. with crude hexachlorocyclohexane (500 gms.), stood for 20 minutes, filtered, methanol 50 c.c.s. added to the extract and the resulting liquid used to re-extract the solid residue, methanol (800 c.c.s.) is added at ordinary temperature to the solid residue from the second extraction, the mixture stirred for 50 minutes, filtered, and the filtrate concentrated by the removal of one quarter of its volume to yield pure g -isomer (35 gms.) on cooling, the mother liquor yielding an isomeric mixture containing 60 per cent of the g -isomer on evaporation to dryness.