Chloramphenicol’s oxidation by metallic oxidant potassium permanganate in an acidic medium: Kinetic and thermodynamic investigation

Abstract

The kinetics and mechanism of the oxidation of chloramphenicol by potassium permanganate have been examined in acidic media under pseudo first order conditions. The reaction was monitored iodometrically at a constant temperature of 308 K by adjusting the amounts of chloramphenicol, permanganate, sulfuric acid, and sodium perchlorate. The rate of oxidation increases with increasing concentrations of chloramphenicol, potassium permanganate, and hydrogen ions, but ionic strength displays no influence on the reaction rate. The substrate dependency exhibits a minor saturation tendency at increased chloramphenicol concentration, suggesting the production of an intermediate substrate–oxidant complex prior to the rate-determining phase. Activation parameters were estimated from Arrhenius and Eyring plots. The modest activation enthalpy, ∆ H # = 42.483 KJ mol −1 and substantial negative entropy of activation, ∆ S # = -136.57 J K −1 mol −1 are consistent with the creation of a highly organized activated complex during the oxidation process. A feasible process involving protonation of permanganate to generate the active oxidizing species, followed by complex formation with chloramphenicol and a delayed electron-transfer breakdown step, has been proposed. The derived rate law satisfactorily explains the observed kinetic behavior of the system. The present study provides fundamental kinetic and mechanistic information on the oxidation of chloramphenicol by potassium permanganate in acidic medium. These findings may serve as a basis for future investigations aimed at evaluating the applicability of permanganate-based oxidation processes for pharmaceutical removal under environmentally relevant conditions.