Kinetics and mechanism of the oxidation of lower oxyacids of phosphorous by morpholinium chlorochromate

Oxidation of lower oxyacids of phosphorous by morpholinium chlorochromate (MCC) in dimethylsulfoxide (DMSO) leads to the formation of corresponding oxyacids with phosphorous in a higher oxidation state. The reaction exhibits 1 : 1 stoichiometry. The reaction is first order with respect to MCC and the oxyacids. The reaction does not induce polymerization of acrylonitrile. Reactions are catalysed by hydrogen :ions. The hydrogen-ion dependence has the form : k(obs) = a + b[H+]. The oxidation of deuteriated phosphinic (DPA) and phosphorous acids (DPPA) exhibited a substantial primary kinetic isotope effect. The oxidation was studied in nineteen different organic solvents. The solvent effects were analysed in terms of Taft's and Swain's multiparametric equations. The effect of solvent indicates the solvent polarity plays a major role in the process. It has been shown that the pentacoordinated tautomer of the phosphorous oxyacid is the reactive reductant and it has been concluded that tricoordinated forms of phosphorous oxyacids does not participate in the oxidation process. A mechanism involving transfer of a hydride ion in the rate-determining step has been proposed.