Electron spin resonance. Part 67. Oxidation of aliphatic sulphides and sulphoxides by the sulphate radical anion (SO4–˙) and of aliphatic radicals by the peroxydisulphate anion (S2O82–)
Abstract
E.s.r. experiments employing in situ photolytic decomposition of the peroxydisulphate anion (S2O82–) have been carried out to study the reaction of SO4–˙ with aliphatic sulphides and sulphoxides. For the former, ‘dimer’ radical cations (R2SSR2+˙) are detected; these are evidently generated via direct one-electron oxidation of the sulphide (to give firstly R2S+˙). The more complex behaviour of the latter [involving, for example, the reaction of Me2S(O) to give ˙CH2S(O) Me (at low pH), Me˙, and MeSO2·] is interpreted in terms of the initial formation of an (undetected) radical cation R2S(O)+˙, subsequent competing reactions of which include deprotonation and hydration (followed by fragmentation).
Flow-system studies of the generation of radicals with ˙OH (from TiIII/H2O2) in the presence of S2O82– provide evidence that the latter is an effective oxidant for both unsubstituted and α-oxygen-substituted alkyl radicals. The rate of oxidation is increased by α-Me and α-OH or -OR groups [e.g. for Me˙ the rate constant is 3.3 ×104 dm3 mol–1 s–1; for ˙CH2OH, the value is 1.3 × 105 dm3 mol–1 s–1].