Spectral, Kinetic, and Theoretical Studies of Sulfur-Centered Reactive Intermediates Derived from Thioethers Containing an Acetyl Group

Abstract

The mechanism of the •OH-induced oxidation of S-ethylthioacetate (SETAc) and S-ethylthioacetone (SETA) was investigated in aqueous solution using pulse radiolysis and steady-state γ radiolysis combined with chromatographic and ESR techniques. For each compound, •OH radicals were added, as an initial step, to the sulfur moiety, forming hydroxysulfuranyl radicals. Their subsequent decomposition strongly depended on the availability of α- or β-positioned acetyl groups, pH, and the thioether concentration. For SETAc, which contains the α-positioned acetyl group, hydroxysulfuranyl radicals SETAc(>•S−OH) subsequently decay into secondary products, which do not include intermolecularly three-electron-bonded dimeric radical cations, even at high concentrations of SETAc. At low pH, these observations are rationalized in terms of the highly unstable nature of sulfur monomeric radical cations SETAc(>S+•) because of their rapid conversion via deprotonation to the α-(alkylthio)alkyl radicals H3C−•CH−S−C(O)−CH3 (λmax =...