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

Abstract

The transient optical absorption band (λ _max= 345 nm, t_1/2= 4.0 µ s, ε = 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 (λ _max= 510 nm, ε = 4.9 × 10³ dm³ mol^-1 cm^-1, t_1/2= 14.0 µ s). 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 (λ _max= 420 nm, t_1/2= 17 µ s, ε = 2.6 × 10³ dm³ mol^-1 cm^-1). In acidic solutions, sulfur-centred dimer radical cations are formed (λ _max= 510 nm, t_1/2= 12 µ s, ε = 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.