Kinetics of ruthenium(III)-catalysed oxidation of paracetamol by diperiodatonickelate(IV) in aqueous alkaline medium (stopped flow technique)

The kinetics of ruthenium(III)-catalysed oxidation of paracetamol by diperiodatonickelate(IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 1.0 mol dm−3 was studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 1:2 stoichiometry (DPN:paracetamol). The reaction shows first order dependence on [DPN] and [ruthenium(III)] and (apparent) less than unit order in both [paracetamol] and [alkali] under the experimental conditions. However, the order in [paracetamol] and [alkali] changes from first order to zero order as the concentrations change from lower to higher concentrations. Addition of periodate has a retarding effect on the reaction. The effects of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The main products were identified by spot test, IR and NMR. A mechanism involving the monoperiodatonickelate(IV) (MPN) as the reactive species of the oxidant has been proposed. The active species of ruthenium(III) is understood as [Ru(H2O)5OH]2+. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.