Oscillations in the Permanganate Oxidation of Glycine in a Stirred Flow Reactor

Abstract

Oscillatory behavior is reported in the permanganate oxidation of glycine in the presence of Na2HPO4 in a stirred flow reactor. In near-neutral solutions, long-period sustained oscillations were recorded in the potential of a Pt electrode and in the light absorbance measured at λ = 418 and 545 nm, characteristic wavelengths for following the evolution of the intermediate [Mn(IV)] and reagent [MnO4(-) ] during the course of the reaction. No evidence of bistability was found. The chemical and physical backgrounds of the oscillatory phenomenon are discussed. In the oscillatory cycle, the positive feedback is attributed to the autocatalytic formation of a soluble Mn(IV) species, whereas the negative feedback arises from its removal from the solution in the form of solid MnO2. A simple model is suggested that qualitatively simulates the experimental observations in batch runs and the dynamics that appears in the flow system.