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

The course of the alkaline hydrolysis of (diphenoxyphosphoryl)methyl p-toly l sulfoxide (8) has been elucidated by a combination of O-18 isotopic label ling and mass spectrometric analysis of the hydrolysis products. The hydrol ysis of the sulfoxide 8 containing O-18 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 (1 0) also containing O-18 in the sulfinyl group, as demonstrated by the EI- a nd CI-mass spectra. The hydrolysis of 8 in O-18-enriched water followed by methylation with diazomethane gave the sulfoxide 10 in which O-18 was incor porated into the phosphonic ester moiety. These results do not support a tw o-step mechanism for the hydrolysis of alpha -phosphoryl sulfoxides involvi ng participation of the neighbouring sulfinyl group and formation of a cycl ic oxathiaphosphetane intermediate. The latter is most probably formed in t he mass spectrometric fragmentation process of alpha -phosphoryl sulfoxides .