Mesolysis of an asymmetric diphenyldisulfide radical anion studied by γ -ray and pulsed-electron radiolyses.

Diaryldisulfides are known to undergo S-S bond cleavage upon one-electron reduction, which is called mesolysis of radical anions, to form the corresponding arylthiyl radical and anion. In this study, we prepared (4-cyanophenyl)(4'-methoxyphenyl)disulfide (MeOSSCN), and the mesolytic profiles were investigated by γ -ray and pulsed-electron radiolyses in 2-methyltetrahydrofuran. As a result of radiolysis of MeOSSCN at room and lower temperatures, the formation of the methoxythiyl radical was recognized upon mesolysis of the radical anion. This observation indicated that intramolecular electron transfer in the radical anion occurred, and the stepwise mechanism was operative after the attached electron occupied the antibonding σ*-orbital for promoting the S-S bond cleavage. According to the Arrhenius expression for the decay rates of the radical anion, the activation energy and frequency factor were determined. DFT calculations provided the bond dissociation energy and bond length for the S-S bond and charge distribution on the S atoms in the radical anion. The substituent effects on the mesolysis process are discussed.