Kinetics and mechanism of the oxidation of D-fructose by vanadium(V) in H2SO4 medium

The oxidative degradation of D-fructose by vanadium(V) in the presence of H2SO4 has an induction period followed by autoacceleration. The kinetics and mechanism of the induction period have been studied at constant ionic strength. The reaction was followed spectrophotometrically by measuring the changes in absorbance at 350nm. Evidence of induced polymerization of acrylonitrile and of reduction of mercuric chloride indicates that a free-radical mechanism operates during the course of reaction. Vanadium(V) is only reduced to vanadium(IV). The reaction is first and fractional order in [V(V)] and [D-fructose], respectively; but dependence on [H+] is complex, that is, - d[V(V)] / dt = k(1)K(es1)K(a1)[H+] [HSO4-][D-fructose][V(V)](T) / {(1/K-al[H+][HSO4-]) + 1 + K-es1[D-fructose]} At constant [H2SO4], sodium hydrogensulfate accelerates the reaction. The effect of added sodium sulfate on the H2SO4 and HSO4-catalyzed reaction is also reported. The activation parameters E-a = 118 kJ mol(-1), DeltaH(#) = 116 kJ mol(-1), DeltaS(#) = -301 JK(-1) mol(-1), and DeltaG(#) = 213 kJ mol(-1) are calculated and discussed. Reaction products are also examined, and it is concluded that oxidation of D-fructose by vanadium(V) involves consecutive one-electron abstraction steps. (C) 2003 Elsevier Ltd. All rights reserved.