Kinetics of oxidation of fumarate, acrylate, cinnamate, and maleate anions by hexavalent manganese has been studied in aqueous alkaline medium. The order in [oxidant] was unity while that in [substrate] was fractional. The order of reactivity of anions is fumarate -+ acrylate --f cinnamate + maleate. The reactions followed Michaelis-Menten kinetics suggesting the formation of a cyclic intermediate between Mn(V1) and the substrate followed by its disproportionation in a slow step. The equilibrium constant ( K ) for the preequilibrium step and the rate constant (k) for the slow disproportionation step have been calculated from the intercept and the slope values of the linear plot of l/kOb, versus l/[substrate]. Activation parameters are also presented and discussed. A convenient iodometric method is reported for the estimation of Mn(V1).

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