Kinetics and mechanism of Pd(II) catalysed oxidation of d-arabinose, d-xylose and d-galactose by N-bromosuccinimide in acidic solution

The kinetics of Pd(II) catalysed oxidation of Ara, Xyl and Gal by N-bromosuccinimide (NBS) in acidic medium has been studied using Hg(OAc)2 as a scavenger for the Br− ion. The reaction data show that first-order kinetics in each pentose and hexose at low concentrations tend to zero-order at high concentrations. First-order kinetics with respect to NBS and Pd(II) and inverse fractional order, i.e., decreasing effect of [H+] and [Cl−], were observed, whereas ionic strength, Hg(OAc)2 and succinimide did not influence the oxidation rate. Various activation parameters have been calculated and recorded. The corresponding acids, arabonic, xylonic and galactonic, were identified as the main oxidation products of the reactions. On the basis of the experimental findings, a suitable mechanism has been proposed.