Kinetics and mechanism of oxidation of L-leucine by alkaline diperiodatocuprate(III) - A free radical intervention, deamination and decarboxylation

The kinetics of oxidation of L-leucine by diperiodatocuprate (III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm (-aEuro parts per thousand 3) was studied spectrophotometrically. The reaction between L-leucine and DPC in alkaline medium exhibits 1:4 stoichiometry (L-leucine: DPC). The reaction is of first order in [DPC] and has less than unit order in both [L-leucine] and [alkali]. However, the order in [L-leucine] and [alkali] changes from first order to zero order as their concentration increase. Intervention of free radicals was observed in the reaction. Increase in periodate concentration decreased the rate. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate (III) - L-leucine complex, which decomposed slowly in a rate-determining step followed by other fast steps to give the products. The main oxidative products were identified by spot test and GC-MS. The reaction constants involved in the different steps of the mechanism were calculated.