α-Phosphoryl sulfoxides. Part XII. The question of sulfinyl oxygen participation in the alkaline hydrolysis of α-phosphoryl sulfoxides

Abstract

The course of the alkaline hydrolysis of (diphenoxyphosphoryl)methyl p-tolyl sulfoxide (8) has been elucidated by a combination of 18O isotopic labelling and mass spectrometric analysis of the hydrolysis products. The hydrolysis of the sulfoxide 8 containing 18O in the sulfinyl group afforded the corresponding phosphonic acid 9, which, upon methylation with diazomethane, was converted into [methoxy(phenoxy)phosphoryl]methyl p-tolyl sulfoxide (10) also containing 18O in the sulfinyl group, as demonstrated by the EI- and CI-mass spectra. The hydrolysis of 8 in 18O-enriched water followed by methylation with diazomethane gave the sulfoxide 10 in which 18O was incorporated into the phosphonic ester moiety. These results do not support a two-step mechanism for the hydrolysis of α-phosphoryl sulfoxides involving participation of the neighbouring sulfinyl group and formation of a cyclic oxathiaphosphetane intermediate. The latter is most probably formed in the mass spectrometric fragmentation process of α-phosphoryl sulfoxides.