MARTIN B. HOCKING and TREVOR A. SMYTH. Can. J. Chem. 60, 138 (1982). 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 a,a,a-trichlorotoluene similarly showed a colour change and gave a coupling product of the solvent, 1, I ,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 phospholetrichloromethide 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. MARTIN B. HOCKING et TREVOR A. SMYTH. Can. J. Chem. 60, 138 (1982). Une solution de triphenyl-l,2,5-phosphole dans le tetrachlorure de carbone portee a ebullition devient rouge, et la couleur passe du rouge au jaune lors du refroidissement. On a realise ce changement reversible de couleur en presence de plusieurs additifs dans le but d'en determiner la cause. Le triphenyl-l,2,5-phosphole dans le trichloro-a,a,a-toluene porte a ebullition presente les m h e s caracteristiques et donne un produit de couplage avec le solvant; le tetrachloro-1,1,2,2 diphenyl-l,2-ethane. A partir de ces observations et apartir des experiences de synthese, de rmn et de rpe, on propose que le changement de couleur du premier systeme provient de la formation d'un sel phosphole-trichloromethylure par reaction avec le tetrachlorure de carbone. Dans le cas du trichlorotoluene. le phosphole conduit a la formation plus appreciable de dichlorophenylmethylure et eventuellement de chlorures qui, par des reactions subsequentes, conduisent au produit de couplage observe.[Traduit par le journal] Introduction Thermochromism, or a reversible colour change obtained on heating (or cooling) a substance from room temperature, has been relatively recently reviewed (1-3). More recently than these summaries and related to this study, the thermochromism demonstrated by solutions of highly arylated pyr-