SOLVOLYSIS OF PHOSPHONIUM COMPOUNDS CONTAINING A THIOPHENOXY GROUP LINKED TO PHOSPHORUS

A kinetic study of the solvolysis of six alkylphenyl thiophenoxyphosph onium chlorides in 50% water/methanol is reported. The rates of solvol ysis, where thiophenol and phosphine oxides are formed, are little inf luenced by the substituents linked to phosphorus. The present findings are in sharp contrast to the 10(4) higher rate of the alkaline decomp osition of tetraphenyl as compared to trialkylphenyl phosphonium salts , where phenyl is the leaving group. Further, the rate of solvolysis o f the cyclic phenyl thiophenoxyphospholanium salt, is nearly identical to the rate of the corresponding dialkylphenyl thiophenoxyphosphonium compound. Calculation of the activation parameters of the solvolysis of thiophenoxyphosphonium compounds shows that the underlying reaction forces, expressed as activation energies and entropies, are strongly influenced by the substituents. The results suggest that the thiopheno xy group is expelled from the pentacovalent, trigonal bipyramidal reac tion intermediate, before pseudorotation of the substituents linked to phosphorus takes place.