Free-radical-induced oxidation of hydroxymethanesulfonate in aqueous solution Part 2A pulse and steady-state radiolysis study of oxygenated solutions

Abstract

At pH 4.0, the radical ˙CH(OH)SO3− formed by reaction of ˙OH with hydroxymethanesulfonate (HMS) reacts rapidly with oxygen to form the peroxyl radical, ˙OOCH(OH)SO3−, with k4 = (2.6 ± 0.3) × 109 d mol−1 s−1. This radical decays by a first-order process with k = 2.4 × 104 s−1 and Ea = (29 ± 1.2) kJ mol−1. The decay is by a split pathway, reactions (6) and (7), with k6 = 1.7 × 104 s−1 and k7 = 7.0×103 s−1. Reaction (6) involves direct elimination of HO2˙. Reaction (7) initially forms the formylperoxyl radical, but this is hydrolysed, reaction (8), to formic acid and HO2˙ with k8 = 2.46 × 103 s−1. ˙CH(OH)SO3− + O2 → ˙OOCH(OH)SO3− (4)˙OOCH(OH)SO3− → HO2˙ + CHOSO3− (6)˙OOCH(OH)SO3− → ˙OOCHO + HSO3− (7)˙OOCHO + H2O → ˙OOCH(OH)2 → HCOOH + HO2˙ (8)The yield of formate is compatible with this mechanism if it is assumed that the product of reaction (6), i.e. CHOSO3−, can also yield formic acid. Yields of SO42− have been determined and their origin is considered. At pH 7.0, the radical ˙CH(O-)SO3− reacts with oxygen to yield O2− with k11 = (1.6 ± 0.1) × 109 d mol−1 s−1. ˙CH(O−)SO3− + O2 → CHOSO3− + O2˙−(11)