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_½= 4.0 µs, 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_½= 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 (λ_max= 420 nm, t_½= 17 µs, ε= 2.6 × 10³ dm³ mol^–1 cm^–1). In acidic solutions, sulfur-centred dimer radical cations are formed (λ_max= 510 nm, t_½= 12 µs, 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.