Electron spin resonance. Part 67. Oxidation of aliphatic sulphides and sulphoxides by the sulphate radical anion (SO ₄ – ˙) and of aliphatic radicals by the peroxydisulphate anion (S ₂ O ₈ ²– )

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].