Oxidation of 6-aminopenicillanic acid by an alkaline copper(III) periodate complex in the absence and presence of ruthenium(III) as a homogeneous catalyst

Abstract

The oxidation of 6-aminopenicillanic acid (6-APA) by diperiodatocuprate(III) (DPC) has been investigated both in the absence and presence of a ruthenium(III) catalyst in aqueous alkaline medium, at a constant ionic strength of 0.20 mol dm −3, spectrophotometrically. The stiochiometry was the same in both cases, i.e. [6-APA]/[DPC] = 1:2. In both the catalyzed and uncatalyzed reactions, the order of the reaction with respect to [DPC] was unity, while the order with respect to [6-APA] was <1 over the concentration range studied. The rate increased with an increase in [OH −] and decreased with an increase in [ IO 4 - ] in both cases. The order with respect to [Ru(III)] was unity. The oxidation products were identified by spectral analysis and suitable mechanisms were proposed. The reaction constants involved in the different steps of the reaction mechanisms were calculated for both cases. The catalytic constant ( K C ) was also calculated for the catalyzed reaction at different temperatures. The activation parameters with respect to the slow step of the mechanism and also the thermodynamic quantities were determined. Kinetic experiments suggest that [Cu(H 2IO 6)(H 2O) 2] is the reactive copper(III) species and [Ru(H 2O) 5OH] 2+ is the reactive Ru(III) species.