GB743913A - Improvements in or relating to the production of hexachlorocyclohexane - Google Patents

Abstract

Benzen is chlorinated in admixture with methyl chloride, methylene chloride, chloroform, 1:1-dichloroethane or ethylene dichloride, or mixtures of these at - 40 DEG C. to + 40 DEG C. in actinic light, the intensity of light and the rate or introduction of chlorine being adjusted to maintain the concentration of free chlorine in the mixture at not more than 5 per cent by weight of the total, and between limits shown on the accompanying Figure, to give a product having a high content of gamma isomer. Tables are given of a series of batch experiments carried out with methylene chloride, ethylene dichloride, chloroform and 1:1-dichloroethane at temperatures of - 25 DEG C. to + 25 DEG C., the free chlorine concentrations differing at selected temperatures and the quantity of gamma isomer being estimated at such points. The maximum gamma product content for a particular temperature and solvent was obtained from the paraboloid graphs, and the free chlorine concentrations as upper and lower limits corresponding to a gamma content of 90 per cent of the maximum plotted against temperature gave a <PICT:0743913/IV(a)/1> graph of approximately 2 straight lines using a logarithmic scale for the chlorine content, from which the desired limits for free chlorine concentration for any particular temperature may be determined. Actinic light is provided by mercury arc lamps, the intensity being varied to give the desired concentration of free chlorine. A further example describes 5 batches of a chlorination process in methylene chloride at - 25 DEG C. with free chlorine maintained at 0.05 per cent to 0.3 per cent continued until 28 per cent of the benzene had been converted to hexachloride, to give high yields of the gamma product. Specifications 653,364 and 678,577 are referred to.