Oxidation of ketorolac by permanganate in aqueous alkali: a thermodynamics and mechanistic study

Oxidation of ketorolac, a non-steroidal anti-inflammatory drug, by permanganate in alkaline medium at a constant ionic strength of 0.1 mol dm(-3) has been studied spectrophotometrically at 526 nm. The reaction was studied over a wide range of experimental conditions which shows that the rate of the reaction is enhanced by increase in [OH-], temperature, and reductant concentrations. Reaction between MnO4 (-) and ketorolac in alkaline medium exhibits 2:1 stoichiometry (MnO4 (-):ketorolac). Kinetic results show a first-order dependency on [MnO4 (-)] and apparently less than unit order in both ketorolac and alkali concentrations. Initial addition of reaction product did not affect the rate. A plausible mechanism involving the formation of intermediate complex has been proposed, leading to the rate law. Rate constant of slow step and equilibrium constants involved in different steps of the mechanism are calculated, k = 3.3 x 10(-2) s(-1), K (1) = 68.8 dm(3) mol(-1), and K (2) = 69.4 dm(3) mol(-1), respectively. Activation parameters with respect to overall reaction are computed to be E (a) = 15.5 kJ mol(-1), a dagger H (not equal) = 13 kJ mol(-1), a dagger S (not equal) = -244.5 J K-1 mol(-1), a dagger G (not equal) = 86.4 kJ mol(-1), and log A = 0.03. Thermodynamic quantities were also evaluated which have supported the proposed mechanism.