Uncatalyzed and Ruthenium(III) Catalyzed Oxidation of Aspartame by Potassium Permanganate in Aqueous Alkaline Medium: A Comparative Kinetic Study

Abstract

The reaction kinetics and mechanism of the oxidation of aspartame by permanganate ion in the absence and presence of ruthenium(III) in alkaline media has been studied spectrophotometrically at 298 K and at a constant ionic strength of 1.10 mol·dm−3. The uncatalyzed and catalyzed reaction has a stoichiometry, 1:2 (aspartame: $$ {\text{MnO}}_{4}^{ - } $$ ). The oxidation products, $$ {\text{MnO}}_{4}^{2 - } $$ and 6-benzyl-3-hydroxy-3-methylpiperazine-2,5-dione were characterized by spectral studies. The order with respect to $$ {\text{MnO}}_{4}^{ - } $$ concentration was unity and that of aspartame was less than unity in the uncatalyzed and catalyzed reactions. The alkali KOH concentration was varied and it was found that as the KOH concentration increased, the rate increased with less than unit order in either the absence or presence of catalyst. The order with respect to ruthenium(III) concentration was unity. The species [Ru(H2O)5OH]2+ was found to be the active species of ruthenium(III). The effect of ionic strength and solvent polarity were studied. Based on experimental results suitable mechanisms were proposed. Activation parameters and thermodynamic quantities were determined and discussed.