Kinetic and mechanistic studies of Rh(III)-catalysed oxidation of D-xylose and L-sorbose by N-bromoacetamide in perchloric acid medium

Abstract

The kinetic and mechanistic studies of homogeneously Rh(III)-catalysed oxidation of D-xylose and L-sorbose by Nbromoacetamide (NBA) in perchloric acid medium were carried out at 40 °C. The reactions were first-order with respect to each of [NBA], [Rh(III)] and [H+] and zero-order in [sugar]. Variation of [Cl−] showed positive effect while variation of [Hg(OAc)2] showed negative effect on the rate of the reactions. Addition of acetamide (NHA) had a negative effect on the rate of the reaction. The rate of the reaction was unaffected by the change in ionic strength (μ) of the medium. Various activation parameters were calculated with the help of pseudo-first-order rate constant, k1, obtained at four different temperatures. The mechanisms involving RhCl4(H2O)2−, as reactive species of rhodium(III), and H2OBr+, as reactive species of NBA, are proposed which find support from the spectrophotometric evidence and activation parameters, especially the entropy of activation.