Influence of sodium dodecyl sulfate/Triton X-100 micelles on the oxidation of D-fructose by chromic acid in presenic of HClO_4

摘要

The kinetics of oxidation of D-fructose by chromic acid in aqueous and aqueous surfactant (sodium dodecyl sulfate, SDS, and alkylphenyl polyethylenglykol, TX-100) media have been investigated in the presence of HClO_4. The reaction is acid catalyzed and is associated with an induction period which is dependent on [H~+], [surfactant] and temperature. The order of oxidation during induction under [D-fructose] > [chromic acid] conditions is fractional in each reagent in both media. The rate constant was found to increase with [Mn(II)]. A mechanism has been proposed for the reaction. The micelles produce a catalytic effect in the range of SDS and TX-100 concentrations used, and the effect is explained by means of the pseudo-phase mass-action model. In the presence of SDS, the reaction is inhibited by electrolytes (NH_4Br, NaBr, LiBr), and the inhibition order Na~+ > Li~+ > NH_4~+ is explained on the basis of electrostatic consideration. The rate constant (k_m), binding constants (K_S and K_F), and corresponding activation parameters (E_a, DELTAH~(dot = ) and DELTAS~(dot = )) have been evaluated and discussed. The order of reactivities of different sugars is found as: D-fructose > D-arabinoe > D-xylose approx = D-glucose.