Thiocarbonyl elimination from sulphenic systems. Part II. Elimination of benzenethiol from substituted diphenylmethyl phenyl disulphides

Abstract

Aryl diphenylmethyl disulphides undergo elimination of arenethiol to give thiobenzophenones by the action of sodium isopropoxide in isopropyl alcohol. The yield of thiobenzophenones varies with the nature of the substituents both on the diphenylmethyl and on the aryl moiety, being higher in the case of electron-attracting substituents. The second-order elimination rate constants at 20° allow one to estimate an approximate Hammett ρ value of +4 for diphenylmethyl substituents and of +2 for aryl substituents. A kinetic isotope effect, k_H/k_D, of 6·1 at 30° was measured for α-biphenyl-4-ylbenzyl 4-tolyl disulphide. Tritium exchange experiments carried out on this material showed no appreciable tritium intake by the unchanged material.

A concerted elimination mechanism is suggested and the geometry of the transition state is discussed. The results of thiocarbonyl elimination from aryl diphenylmethyl disulphides are compared with those of hydrogen cyanide elmination from diphenylmethyl thiocyanates.