Kinetics and mechanism of oxidation of hypophosphite by Waugh-type enneamolybdomanganate(IV) in perchloric acid

The reaction between hypophosphite and enneamolybdomanganate(IV) in perchloric acid was carried out under pseudo-first-order conditions keeping large excess of hypophosphite. The order in oxidant was found to be unity and that of hypophosphite was found to be less than unity. The reaction proceeds with prior formation of complex between the reactants followed by its rate determining decomposition. The accelerating effect of hydrogen ions on the reaction is due to the formation of active hexaprotonated oxidant species. The formation of the complex is supported by kinetic results and also by spectrophotometric study. The product of the reaction was found to be phosphitomolybdate, [H10(HP)Mo6O26]2−, which was confirmed by FTIR study and AAS analysis. The reaction involves direct two-electron transfer step without any free radical intervention. The effect of ionic strength, solvent polarity and the activation parameters were also in support of the mechanism proposed.

The reaction between enneamolybdomanganate(IV) and hypophosphite occurs through prior complex formation between the reactants followed by its rate determining decomposition. The phosphitomolybdate was the product of reaction characterized by AAS and FTIR analysis.Figure optionsDownload as PowerPoint slide