Studies on kinetics and mechanism of iridium(III) catalysed cerium(IV) oxidation of D-mannitol and D-glucose in aqueous acid media

The kinetics and mechanism of Ce(IV) oxidation of D-mannitol and D-glucose in aqueous H2SO4 media in the presence and absence of Ir(III) have been studied and compared under the conditions, [S](T) much greater than[Ce(IV)](T)much greater than[Ir](T), where [S](T) gives the total substrate (D-mannitol or D-glucose) concentration and [Ir](T) denotes the total concentration of Ir(III) catalyst added. Ir(III) has been found to catalyse the title reactions very efficiently even at trace concentration (ca. 10(-6) to 10(-7) mol dm(-3)). Under the kinetic conditions, both the uncatalysed and catalysed reactions take place simultaneously. The overall proem shows a first order dependence on [Ce(IV)] and [S](T). The catalytic path is first order in [Ir](T). The catalytic path is suggested to involve the Ir(III)/Ir(IV) catalytic cycle. The proem is acid catalysed and inhibited by [HSO4-]. From the HSO4- dependence, both Ce(SO4)(2+) and Ce(SO4)(2) have been found kinetically active in D-mannitol oxidation while in D-glucose oxidation Ce(SO4)(2) is the main kinetically active species under comparable conditions. The different kinetic parameters for both the Ir(III) catalysed and uncatalysed paths have been estimated.