Reactivity of Superoxide Ion with Thioamides in Dimethyl Sulfoxide

Article abstract of DOI:10.1021/jo00245a007

The first step in the reaction of O2^radical- with thioamides (thiobenzamide, thionicotinamide, thioisonicotinamide, 2-ethyl-4-pyridinethiocarboxamide , thioacetamide, and thioacetanilide) in dimethyl sulfoxide is nucleophilic addition.Subsequent reaction of the initially formed peroxythiolate anion with a second O2^radical- yields O2 and the peroxythiolate dianion; the latter undergoes nucleophilic addition with a second thioamide to give, after cleavage, 2RC(S^-) = NH + HOOH.The overall stoichiometry is one O2^radical- per thioamide.The formed thioamide anion and O2 slowly react to form the corresponding nitrile (RC<*>N), polysulfides, and a second HOOH.The rates of reaction for the primary step have been evaluated via rotated ring-disk voltammetry under pseudo-first-order conditions; the apparent second-order rate constants range from 115 +/- 15 M^-1 s^-1 for thioacetamide to (6 +/- 1) x 10³ M^-1 s^-1 for thioacetanilide in dimethyl sulfoxide at 25 deg C.