Electron spin resonance studies. Part 57. Alkane- and arene-sulphinate esters: an investigation of their photochemical decomposition and reactions with the t-butoxyl radical

Abstract

E.s.r. evidence is described for three modes of photolytic decomposition of sulphinate esters [XS(O)OR]. For some alkyl arenesulphinates (X =p-tolyl, R = alkyl) the arenesulphinyl radical (XSO·) is detected, evidently as a result of S–O bond fission; for some alkyl alkanesulphinates, photolysis apparently cleaves the O–R bond and alkane-sulphonyl radicals (XSO₂·;) are formed; for methyl phenylmethanesulphinate (X = PhCH₂, R = Me) the detection of the benzyl radical and MeOSO· suggests that the C–S bond has been broken.

It is suggested that the reaction between Bu^tO·(from di-t-butyl peroxide) and sulphinates usually involves attack at sulphur to give an intermediate sulphuranyloxyl radical XṠ(O)(OR)OBu^t. Evidence that this can undergo dealkylation derives from the detection of the benzyl radical in the reaction of PhCH₂S(O)OMe. On the other hand, the production of sulphonyl radicals (XSO₂· X = alkyl, aryl) from this intermediate may involve dealkoxylation and further reaction of the resulting t-butyl sulphinate ester.

Line-width variation in the e.s.r. spectrum of MeSO₂· at low temperature is attributed to the occurrence of restricted rotation about the C–S bond in a radical of pyramidal type.