Oxidation of Pentoses by Sodium-N-bromo-P-toluene sulphonamide: A Kinetic and Mechanistic Study

Kinetics of oxidation of D-xylose, D-ribose, D-lyxose and L-arabinose by bromamine-T (sodium N-bromo-p-toluene sulphonamide, BAT) was studied in alkaline medium at 30 °C. The rate was zero-order in [BAT]0, but exhibited fractional order kinetics with respect to [sugar]0, and [HO−]0. The rates levelled off at higher [sugar]0, and [HO−]0. Stoichioaetry experiments have shown that the sugar was oxidised to the respective aldonic acid. Variation of ionic strength of medium and addition of the reaction products, p-toluenesulphonamide and Cl− ions have no effect on the rate. The rate increased with decrease in dielectric constant of the medium. Solvent isotope studies using Dg0 have shown that ks(DgO)/ ks.(HgO) = 1.36. The reaction has been studied at different temperatures and the overall activation parameters have been calculated. Activation parameters for the rate limiting step were determined from Michaelis-Menton type plots. A mechanism in which formation of the enediol anion of the sugar is the rate limiting step is proposed.