Thermochromism of 1,2,5-triphenylphosphole and the formation of 1,1,2,2-tetrachloro-1,2-diphenylethane from α,α,α-trichlorotoluene

Abstract

On boiling a yellow solution of 1,2,5-triphenylphosphole in carbon tetrachloride the colour changes to red, reverting to yellow on cooling. This reversible colour change has been conducted in the presence of various additives in an attempt to determine the cause of the colour change. Boiling 1,2,5-triphenylphosphole in α,α,α-trichlorotoluene similarly showed a colour change and gave a coupling product of the solvent, 1,1,2,2-tetrachloro-1-2-diphenylethane. From this evidence and related synthetic, nmr, and esr experiments it is proposed that the colour change of the former system arises from the incipient formation of a phosphole-trichloromethide salt with carbon tetrachloride. With trichlorotoluene the phosphole undergoes more substantive formation of dichlorophenylmethide and possibly chloride salts which undergo further reaction to the observed coupling product.