Oxidation of vanillin by diperiodatocuprate(III) in aqueous alkaline medium: A kinetic and mechanistic study by stopped flow technique

The kinetics of oxidation of vanillin (VAN) by diperiodatocuprate (III) (DPC) in alkaline medium at a constant ionic strength of 0.50 mol dm(-3) was studied spectrophotometrically. The reaction between DPC and vanillin in alkaline medium exhibits 1 2 stoichiometry (vanillin DPC). The reaction is of first order in [DPC] and has less than unit order in both [VAN] and [alkali]. Intervention of free radicals was observed in the reaction. Increase in periodate concentration decreases the rate. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate(III)-vanillin complex, which decomposes slowly in a rate-determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, and MS studies. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. (c) 2007 Wiley Periodicals, Inc.