Kinetics and Mechanism of Oxidation of L-proline by Trivalent Copper: A free radical intervention and decarboxylation

The kinetics of oxidation of L-proline by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm-3 was studied spectrophotometrically. The reaction between DPC and L-proline in alkaline medium exhibits 2:1 stoichiometry (DPC: L-Proline). The reaction is of first order in [DPC], less than unit order in [L-proline] and [alkali]. Periodate has no effect on the rate of reaction. The reaction rate increases with increase in ionic strength and decrease in solvent polarity of the medium. Effect of added products and ionic strength of the reaction medium have been investigated. The main products were identified by spot test and I.R spectra. A mechanism involving the DPC as the reactive species of the oxidant and a complex formation with L-proline has been proposed. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.