Pulse radiolysis investigations on electron-transfer reactions in aqueous solutions of substituted alkyl sulfides

Abstract

The transient optical absorption band (λmax= 345 nm, t½= 4.0 µs, Iµ= 2.6 × 103 dm3 mol–1 cm–1) formed on pulse radiolysis of N2O-saturated dilute neutral aqueous solutions of dimethyl 3,3′-thiodipropionate (DTDP) is assigned to an ˙OH-adduct. The rate constant for the reaction of ˙OH radicals has been determined to be 1.4 × 1010 dm3 mol–1 s–1. At higher solute concentrations the ˙OH-adduct is converted to sulfur-centred dimer radical cations (λmax= 510 nm, Iµ= 4.9 × 103 dm3 mol–1 cm–1, t½= 14.0 µs). In acidic solutions, only dimer radical cations are formed. In neutral aqueous solutions of 3,3′-thiodipropanol (TDP)˙OH radicals are able to bring about one-electron oxidation, forming intramolecular radical cations with p-orbital overlap between the oxidized sulfur and oxygen (λmax= 420 nm, t½= 17 µs, Iµ= 2.6 × 103 dm3 mol–1 cm–1). In acidic solutions, sulfur-centred dimer radical cations are formed (λmax= 510 nm, t½= 12 µs, Iµ= 6.3 × 103 dm3 mol–1 cm–1). In the presence of halide ions, the oxidized sulfur in DTDP and TDP stabilizes by formation of an S∴X type species.