Influence of sodium dodecyl sulfate/TritonX-100 micelles on the oxidation of D-fructose by chromic acid in presence of HClO4

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 HClO4. 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 (NH4Br, NaBr, LiBr), and the inhibition order Na+ > Li+ > NH4+ is explained on the basis of electrostatic considerations. The rate constant (k(m)), binding constants (K-S and K-F), and corresponding activation parameters (E-a, DeltaH(not equal) and DeltaS(not equal)) have been evaluated and discussed. The order of reactivities of different sugars is found as: D-fructose > D-arabinose > D-xylose > D-glucose. (C) 2002 Elsevier Science Ltd. All rights reserved.