Kinetics of the oxidation of hypophosphite, deuteriohypophosphite, phosphite and neutralized phenyl phosphonous acid by tris(pyridine-2-carboxylato)manganese(III) in picolinate-picolinic acid buffer medium

Hypophosphite, deuteriohypophosphite, phosphite and neutralized phenyl phos phonous acid are oxidized by tris(pyridine-2-carboxylato)manganese(III) in Na(pic)-picH [where Na(pic) = sodium salt of picolinic acid and picH = pico linic acid] buffer in the 4.63-5.45 pH range. All the reactions appear to f ollow the same mechanistic pathway in which the substrate initially forms a 1:1 intermediate complex with the oxidant. The complex then breaks down in the rate-determining step to give a free radical intermediate which subseq uently reacts with another molecule of oxidant to give the products. A deut erium isotope effect of k(H)/k(D) = 4.26 at 313 K, was observed in the oxid ation of hypophosphite indicating that proton removal from phosphorus takes place in the rate-determining step. A mechanism consistent with the experi mental observations has been proposed.