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Mechanism of the permanganate oxidation of unsaturated compounds. Part VI. Kinetic investigation of the oxidation of methylmaleic acid, methylfumaric acid, and dimethylmaleic acid
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1976
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Advanced Oxidation ProcessEngineeringOrganic ChemistryChemistryRedox BiologyDimethylmaleic AcidReaction IntermediateRedox ChemistryInorganic ChemistryBiochemistryRadical (Chemistry)Permanganate OxidationCatalysisKinetic InvestigationStopped-flow TechniqueMethylmaleic AcidNatural SciencesChemical KineticsRate Constants
The kinetics of the permanganate oxidation of methylmaleic (MMA), methylfumaric (MFA), and dimethylmaleic (DMA) acids have been studied by the stopped-flow technique in aqueous solution between pH 0.0 and 5.0. Manganese(III) has been detected as a short-lived intermediate in all cases. The reactions are first order with respect to both MnO4– and the substrate. The second-order rate constant depends strongly on the pH. The rate of interconversions of the acid, the mono-, and the di-anion is much higher than the rate of oxidation. The rate constants are, in the above order (at 25°C, in dm3 mol–1 s–1) : 150, 660, and 310 (MMA); 1 240, 370, and 98 (MFA); 240, 90, and 54 (DMA). Low activation enthalpies and high negative activation entropies are observed in all cases. The rate-determining step is the cis-attack of permanganate on the double bond, resulting in the formation of a short-lived, undetectable cyclic hypomanganate (MnO43–) ester. The relative reactivities reflect the influence of steric factors.