Mechanism of One-Electron Oxidation of β-, γ-, and δ-Hydroxyalkyl Sulfides. Catalysis through Intramolecular Proton Transfer and Sulfur−Oxygen Bond Formation

Abstract

The mechanism of photoinduced electron transfer between sulfur-containing alcohols and the 4-carboxybenzophenone (CB) triplet state in aqueous solution was investigated using laser flash photolysis and steady-state photolysis techniques. Bimolecular rate constants for quenching of the CB triplet state by five hydroxyalkyl sulfides, 2-(methylthio)ethanol (2-MTE), 2,2‘-dihydroxydiethyl sulfide (2,2‘-DHE), 3-(methylthio)propanol (3-MTP), 3,3‘-dihydroxydipropyl sulfide (3,3‘-DHP), and 4-(methylthio)butanol (4-MTB), with varying numbers of OH groups and varying locations with respect to the sulfur atom, were determined to be in the range (3.3−4.8) × 109 M-1 s-1 for neutral solutions. The intermediates identified were the CB ketyl radical anion (CB•-), the CB ketyl radical (CBH•), and intermolecularly (S∴S)-bonded radical cations. An additional absorption band at approximately 400 nm in the transient spectra for some of the hydroxyalkyl sulfides was assigned to the intramolecularly (•S−O)-bonded species (only f...