Different channels of hydroxyl radical reaction with aryl sulfides: effect of the substituents

Abstract

In a neutral aqueous solution of (phenylthio)acetic acid, the hydroxyl radical is observed to react with a bimolecular rate constant of 7.2 × 10⁹ dm³ mol^-1 s^-1, and the transient absorption bands are assigned to ^•OH radical addition to benzene and sulfur with rough estimated values of 50 and 40%, respectively. The reaction of the ^•OH radical with diphenyl sulfide (k = 4.3 × 10⁸ dm³ mol^-1 s^-1) is observed to take place with the formation of the solute radical cation, OH-adduct at sulfur, and benzene with rough estimated values of 12, 28, and 60%, respectively. The transient absorption bands observed on reaction of the ^•OH radical, in neutral aqueous solution of 4-(methylthio)phenyl acetic acid, are assigned to solute radical cation (λ _max = 550 and 730 nm), OH-adduct at sulfur (λ _max = 360 nm), and addition at benzene (λ _max = 320 nm). The fraction of ^•OH radical reacting to form a solute radical cation is observed to increase with increasing concentration of acid, and in highly acidic solutions, the solute radical cation is the only transient species formed on reaction of ^•OH radical with these sulfides.