Oxidation of the lower phosphorus oxyacids by [C,H,NH] [CrO,F] results in the formation of corresponding oxyacids in the higher valence states. The reaction is first order with respect to the oxidant concentration. A Michaelis-Menten type kinetics was observed with respect to the substrate, indicating the formation of a complex in a pre-equilibrium. The formation constants and the rates of disproportionation of the complexes have been evaluated at different temperatures. The reaction exhibits a substantial primary kinetic isotope effect. The rates in 19 different organic solvents have been analysed using Kamlet-Taft and Swain equations. It has been found that the cation-solvating power of the solvents plays an important role. It is proposed that the 'inactive' tautomer of the phosphorus oxyacids is the reactive reductant, and that transfer of a hydride ion from the P-H bond to the oxidant in the rate-determining step occurs.The three lower oxyacids of phosphorus, viz. phosphinic (hypophosphorus) (1; R = H), phenylphosphinic (2; R = Ph), and phosphorous (3; R = OH), are known to exhibit tautomerism [reaction (l)]. 1,2 Generally, tautomer (A) is called the 'inactive' tautomer and (B) the 'active' one. The equilibrium constant, K,, has a value ca.Chromic acid4 oxidation of compound (2) has been reported to involve the 'active' form as the reactive species. In several oxidations, however, the participation of the 'inactive' form has been proposed, e.g. oxidation by permanganate and vanadium(v).6 Pyridinium fluorotrioxochromate(v1) is a versatile ~x i d a n t . ~We have previously reported its oxidation of alcohols and s ~l p h i d e s . ~ There seems to be no report on the oxidation of phosphorus compounds except on the synthetic aspects of oxidation of triphenylphosphine." In this paper we report the kinetics of oxidation of the three lower oxyacids of phosphorus by [C,H,NH][CrO3F] in dimethyl sulphoxide (dmso) as solvent. The mechanistic aspects are discussed.

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.

The kinetics of the oxidation of five vicinal diols, four other diols, and one of their monoethers by sodium Nbromobenzenesulphonamide have been studied. The vicinal diols yielded products arising out of glycol bond fission while other diols yielded hydroxycarbonyl compounds. The reaction is first order with respect to the diol and the oxidant. The oxidation of vicinal diols follows two mechanistic pathways, one acid-independent and another acid-dependent. The oxidation of the other diols shows a first-order dependence on hydrogen ion. The oxidation of [I ,I ,2,2-2H,]ethanediol showed the absence of a primary kinetic isotope effect. The values of solvent isotope effect, k( H,O)/k( D,O), at 303 K for the oxidation of ethanediol, propane-I ,3-diol, and 3-methoxybutan-I -01 are 2.24, 0.42, and 0.42, respectively. An acyclic mechanism involving glycol bond fission has been proposed for the vicinal diols. The other diols are oxidized by a hydride-transfer mechanism as are monohydric alcohols.We have recently reported 1 , 2 the kinetics and mechanism of the oxidation of alcohols by sodium N-bromobenzenesulphonamide (bromamine-B or BAB). It is known, however, that some oxidations of mono-and poly-hydric alcohols follow different mechanistic pathways, e.g. oxidations by lead(~v),~ periodic acid,4 and acid permanganate. Therefore, an investigation of the oxidation of diols by BAB in acid solution was undertaken. The mechanistic aspects are discussed here.

For Abstract see ChemInform Abstract in Full Text.

The oxidation of phosphinic, phenylphosphinic, and phosphorous acids by N-bromoacetamide (NBA) in acid solution, results in the formation of corresponding higher oxyacids of phosphorus. The reaction is first order with respect to NBA, second order in the oxyacid and inverse first in hydrogen ions. The oxidation of deuteriated phosphorus oxyacids showed the presence of a substantial primary kinetic isotope effect. The reaction failed to induce polymerization of acrylonitrile. Added acetamide has no effect on the reaction rate. It has been shown that the 'inactive' tautomer of the phosphorus oxyacids, RHP(O)OH, participates in the oxidation process. A rate-determining step involving transfer of a hydride ion from the P-H bond to the oxidant has been proposed.