Mechanisms of peroxide decomposition: an electron paramagnetic resonance study of the reaction of the peroxomonosulphate anion (HOOSO ? 3 ) with CuI. A marked contrast in behaviour with that of TiIII and FeII

Abstract

EPR spectroscopy has been employed in conjunction with a continuous-flow system to show that CuI(produced from the rapid reaction of CuII with TiIII) reacts rapidly with the peroxomonosulphate anion (k≈ 2 × 104 dm3 mol–1 s–1 at pH 2 and 20 °C) to give the hydroxyl radical (HO˙) which is trapped via its addition to alkenes. In contrast, FeII and TiIII react with HOOSO–3 predominantly to give the sulphate radical-anion (SO˙–4). It is argued that with CuI the reaction shows characteristics of an outer-sphere electron-transfer process, whereas in the inner-sphere reaction of FeII and TiIII the reaction is facilitated by attack of the hydroxyl oxygen atom on the smaller, more highly charged metal ions.