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

2468-2474The 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˃˃ [Ce(IV)]T ˃˃[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 process 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 process is acid catalysed and inhibited by [H2SO4-]. From the H2SO4- 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