Characterization of transients formed in aqueous solutions of substituted alkyl sulfides: a pulse radiolysis study

Abstract

The transient optical absorption band (λ_max= 340 nm) formed on reaction of OH radicals with substituted alkyl sulfides, S(CH₂CO₂R)₂, R = CH₃, C₂H₅, C₃H₇, C₄H₉ in neutral aqueous solutions has been assigned to the OH adduct. The yield, lifetime and molar absorption coefficient of this band is found to decrease with increasing chain length of R. The OH adduct of S(CH₂CO₂CH₃)₂ is able to undergo an electron transfer reaction with Br^–, I^– and SCN^–. in acidic solutions, dimer radical cations are formed at high solute concentration. The observed rate constant for the decay of dimer radical cations is deconvoluted to different processes and the deprotonation is found to be the rate-determining step. The yield and lifetime are found to decrease with increasing chain length of R. The high concentration of acid required for their formation is discussed. Cl^˙–₂ and SO^˙–₄ are able to undergo one-electron transfer reactions with S(CH₂CO₂CH₃)₂ with rate constants of 1.9 × 10⁹ and 1.4 × 10¹⁰ dm³ mol^–1 s^–1, respectively. The dimer radical cation is found to be a strong oxidizing agent and is able to oxidize Br^– with a rate constant of 2.2 × 10⁹ dm³ mol^–1 s^–1.