Pd(II) catalysed and Hg(II) co-catalysed oxidation of D-arabinose and D-ribose by N-bromoacetamide in perchloric acid medium: A kinetic and mechanistic study

Abstract

The kinetics and mechanism of the homogeneollsly Pd(II) catalysed oxidation of D-arabinose (Arb) and D-ribose (Rib) by N-bromoacetamide (NBA) in perchloric acid medium, using mercuric acetate as scavenger for Br ions as well as co-catalyst have been investigated in the temperature range 308-323 K. The kinetic results exhibit first order kinetics at low [NBA] and [sugars] (Arb and Rib), tend towards zero-order at high [NBA] and [sugars]. The oxidation rate is directly proportional to [Pd(II)], while inverse fractional order in each of [H⁺] , [Cl^-] and [acetamide] is observed. A positive effect on the rate of the reaction has been found on the successive addition of [Hg(OAc)₂], whereas change in the ionic strength (μ) of the medium does not influence the reaction rate. Formic acid and D-erythronic acid for the oxidation of both Arb and Rib have been identified as main oxidation products of the reactions. The various activation parameters have also been evaluated. A plausible mechanism involving reaction stoichiometry, product analysis has also been proposed.