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Oxidation of Hypophosphite and Phosphite by Anderson‐Type Hexamolybdocobaltate(III) Anion
Author(s) -
Barge Jyoti N.,
Gokavi Gavisiddappa S.
Publication year - 2016
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20975
Subject(s) - chemistry , hypophosphite , protonation , dimer , aqueous solution , inorganic chemistry , ion , molybdate , electron transfer , reaction mechanism , inner sphere electron transfer , solvent , medicinal chemistry , photochemistry , organic chemistry , catalysis
The oxidation of hypophosphite and phosphite by the Anderson‐type hexamolybdocobaltate(III), [H 6 Co III Mo 6 O 24 ] 3− , anion was investigated at pH 2 and 1, respectively, in aqueous medium. The reaction is found to occur through an outer‐sphere mechanism with a prior weak complex formation between the reactants. Under the reaction conditions, the oxidant exists in the [H 5 Co III Mo 5 O 20 ] 2− , [H 6 Co III Mo 6 O 24 ] 3− , and [H 4 Co III 2 Mo 10 O 38 ] 6− (dimer) forms, and [H 5 Co III Mo 5 O 20 ] 2− is the active species. Inhibition of the reaction by the oxidant anion and added molybdate ion kinetically indicates existence of prior equilibria between various forms of the oxidant. Both hypophosphite and phosphite exists in their protonated forms. The reaction involves direct electron transfer from the phosphorus center to the anion‐generating free radicals in a rate‐determining step. The effect of ionic strength and change in the solvent polarity did not affect the rate of the reaction. A probable mechanism was proposed leading to a complicated rate law as a result of involvement of prior equilibria between various forms of the oxidant. The activation parameters were also determined and are in support of the proposed mechanism.