The water-induced disproportionation of the electrogenerated superoxide ion (O 2 - ) in acetonitrile, dimethylformamide, and dimethyl sulfoxide media containing various concentrations of water as a Brønsted acid has been examined by UV−vis spectroscopy. Analysis of the kinetics as a function of O 2 - and water concentrations and of the measurement time demonstrated that the disproportionation of O 2 - by water in these media obeys a common mechanism: O 2 - + H 2 O ⇄ HO 2 • + OH - ( k 1, k -1 ) HO 2 • + O 2 - → HO 2 - + O 2 ( k 2 ) (HO 2 •, hydroperoxyl radical; HO 2 -, hydrogen peroxide anion). The solvent dependence of the obtained kinetic parameters of ( k 1 / k -1 ) k 2, k 1 and k -1 / k 2 is discussed in terms of the solvation of O 2 - and H 2 O as well as the effective acidities of H 2 O in different aprotic solvents.
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Che et al. (1996) studied this question.
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