Oxidation of Phosphorus Centers by Ferrate(VI): Spectral Observation of an Intermediate

The kinetics and mechanism for the oxidation of phosphite, hypophosphite, phenylphosphite, and trimethylphosphite by ferrate(VI) are reported. Hypophosphite is rapidly oxidized to phosphite which is slowly oxidized to phosphate, trimethylphosphite is oxidized to trimethylphosphate, and phenylphosphite is oxidized phenylphosphate. 18O induced shifts of the 31P NMR signals support oxygen transfer from ferrate(VI) to the phosphorus center during the oxidation process. Deuteration of the hydridic hydrogens in hypophosphite and phosphite resulted in significant kinetic isotope effects on the reaction rates. It is proposed that ferrate(VI) acts as a two-electron oxidant in conjunction with oxide transfer coupled with phosphorus hydrogen bond breaking for phosphite and hypophosphite and simple oxygen transfer for trimethylphosphite and phenylphosphite.