Kinetics and mechanism of the oxidation of the sulphite ion by the Mn(III)–cydta complex ion

Abstract

The reinvestigated oxidation of S(IV), HSO3−/SO32−ions, by [Mn(cydta)(OH)]− confirmed that S(IV) is oxidized in two parallel paths; the order with respect to [S(IV)] is one in one of the paths and two in the other. The nature of the dependence of the rate on [H+] is also confirmed. However, the rapid scan of the reaction mixture and measurement of the initial absorbance of the reaction mixture at different wavelengths at the beginning of the reaction suggest an outer-sphere mechanism. The rate parameters are of the same order as obtained in known reactions of an outer-sphere mechanism and this mechanism is further supported by the Marcus cross relation. Keywords: kinetics, outer-sphere mechanism, [Mn(cydta)]−, SO32−.