Kinetics and mechanism of oxidation of 6-deoxyhexoses by sodium N-bromobenzenesulphonamide in alkaline medium

The kinetics of oxidation of three sugars, L-fucose, D-fucose and L-rhamnose by sodium N-bromobenzenesulphonamide (bromamine-B) has been studied in alkaline medium at 308 K. The reaction is first order with respect to the oxidant], sugar] and HO-] The added halide ions, the reaction product benzenesulphonamide (BSA) and the variation of ionic strength have no influence on the reaction rate. The dielectric effect is negative. The rate increased in D2O medium, the inverse solvent isotope effect, k(obs) (D2O)/k(obs) (H2O) is found to be congruent to 2. Proton inventory studies were made in H2O-D2O mixtures. The reactions were studied at various temperatures (298-318 K). The activation parameters were computed from the Arrhenius plots. An isokinetic relation is observed with beta = 342 K indicating the enthalpy of activation as the rate-controlling factor. A mechanism involving an enediol anion (E-) of the sugar reacts with the oxidant in the rate determining step has been proposed