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.
Evidence is also presented that radicals formed by the addition of both HO˙ and SO˙–4 to alkenes (˙CR1R2CR3R4Y, Y = OH, OSO–3) are readily oxidized by HOOSO–3(k≈ 105 dm3 mol–1 s–1), a reaction which leads to the formation of SO˙–4.
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