Kinetics and Mechanism of Oxidation of Phosphinic, Phenylphosphinic, and Phosphonic Acids by Pyridinium Chlorochromate.

Oxidation of the lower oxyacids of phosphorus by pyridinium chlorochromate (PCC) results in the formation of the corresponding higher oxyacids of phosphorus. The reaction is of first order with respect to PCC and the oxyacid. The reaction is catalyzed by hydrogen ions, kobs=a+b[H+]. The reaction exhibited a substantial primary kinetic isotope effect. The rates in 19 different organic solvents have been analyzed using Kamlet–Taft’s and Swain’s equations. It has been found that the cation-solvating power of the solvents plays a predominant role. It is proposed that the “inactive” tautomer of the phosphorus oxyacids is the reactive species. Transfer of a hydride ion from the P–H bond to PCC, in the rate-determining step, has been proposed.