A PULSE-RADIOLYSIS STUDY OF THE OH RADICAL-INDUCED AUTOXIDATION OF METHANESULFINIC ACID

Methanesulfinic acid, CH3SO2H, reacts with OH radicals at pH 7 forming CH3SO2 radicals with a rate constant k = (6.0 +/- 1.0) x 10(9) M(-1) s(-1). The CH3SO2 radical absorbs at 325 nm with an extinction coeffic ient of 900 +/- 100 M(-1) cm(-1) and disappears in a second order self -reaction with k = (1.0 +/- 0.2) x 10(9) M(-1) s(-1). This radical rea cts with oxygen, k = (1.2 +/- 0.3) x 10(9) M(-1) s(-1), forming a pero xy radical which absorbs in the UV below 300 nm. The peroxy radical re acts in turn with methanesulfinic acid reforming the CH3SO2 radical wh ereby a chain oxidation of sulfinic acid takes place. During the cours e of the chain oxidation a peroxyacid, presumably methaneperoxymonosul fonic acid, is formed and accumulated. This acid absorbs in the UV and eventually decays by reaction with excess methanesulfinic acid k = 5 x 10(3) M(-1) s(-1). The final product of the chain autoxidation is me thanesulfonic acid. The chain is very efficient and proceeds until eit her oxygen or methanesulfinic acid is exhausted. The mechanism is comp ared to the chain autoxidation of sulfite.