Divergent thermal behaviour of phenoxymethyl phenyl sulphoxide under gas and condensed-phase conditions

Abstract

A comparison is made between the behaviour of phenoxymethyl phenyl sulphoxide (2) under different thermolytic conditions. Passage of (2) through a quartz tube in the gas phase at 600 °C results in products which can be rationalised by assuming homolytic cleavage of the S–C bond and the generation of both the phenylsulphinyl (4) and phenoxymethyl (6) radicals which decompose by separate pathways to yield S-phenyl benzenethiosulphonate (3) and benzaldehyde, respectively. On the other hand, solution thermolysis of (2) in [²H₈]toluene at 110 °C leads to a facile S→O 1,2-shift and the formation of thermally stable phenoxymethyl benzenesulphenate (9) in quantitative yield. A bimolecular oxygen-transfer mechanism is proposed for the conversion of (2) into (9) which is rationalised in terms of a double (stabilising) anomeric effect brought about by the acetal group in (9). Cross-over experiments support the mechanism.