Kinetics of catalytic activities of micro amount of Ir(III) in oxidation of D(-) Galactose by N-bromosuccinimide in acidic homogeneous medium

Abstract

It has been investigated how iridium(III) catalyses the oxidation of D(-)Galactose by N-bromosuccinimide (NBS) in an aqueous perchloric acid solution at 308 K. NBS kinetics is first-order, while galactose kinetics is zero-order. As a function of [Ir(III)], the reactions demonstrate first order at lower [Ir(III)] and zero-order behaviour at higher [Ir(III)]. On the rate of oxidation, inverse fractional-order has been reported in [H⁺], [Cl^-] and [succinimide]. There is no difference in the rate of oxidation with changes in the ionic strength of the medium or with the addition of Hg(OAc)₂ (a Br-ion scavenger). Galactonic acid has been identified as the major oxidation product of the process. It is possible to compute the activation parameters by utilizing the rate constants observed at four distinct temperature levels. For the sake of this research, it is hypothesised that HOBr and [IrCl₅H₂O]^2-are both reactive species oxidants (i.e. NBS) as well as catalysts. It is very probable that the reaction mechanism for the oxidation of galactose by NBS is supported by current kinetic data, reaction stoichiometry, and product analysis.