Role of solute structure on the stability of the OH-adduct of substituted organic sulfides and its transformation to a radical cation

The sulfur-centered OH-adduct (λmax=360 nm) of 4-(methylthio)butanol transforms (k=1×106 s−1) to a sulfur-centered dimer radical cation (λmax=485 nm) in basic solution. The rate of transformation is accelerated in acidic solution and only the dimer radical cation is observed at pH=1. The transformation of the OH-adduct of 3-(methylthio)propanol is fast even in basic solution and only the intra-molecular radical (λmax=410 nm) is observed at pH>5 and the dimer radical cation (λmax=480 nm) at pH=1. The OH-adduct of 3,3′-thiodipropionamide (λmax=350 nm) undergoes transformation (k=1.4×105 s−1) to an intra-molecular radical cation (λmax=370 nm). The formation of the OH-adduct and its transformation to a solute radical cation could not be observed with 2-(methylthio)ethanol and 2,2′-thiodiethanamide.