Kinetic and mechanistic investigation of Pd(II)-catalysed and Hg(II)-co-catalysed oxidation of d(+)melibiose by N-bromoacetamide in acidic medium

The kinetic and mechanistic study of homogeneously Pd(II)-catalysed and Hg(II)- co-catalysed oxidation of d(+)melibiose (mel) by N-bromoacetamide (NBA) in perchloric acid medium have been made at temperature 40 °C ± 0.1 °C. Kinetic results show first-order kinetics with respect to NBA at its low concentrations, tending to zero-order at its high concentrations. The oxidation rate is directly proportional to [Pd(II)] and [sugar], indicating first-order kinetics with respect to Pd(II) and sugar. Zero effect of Cl− and H+ ions throughout their variation have been noted. First-order kinetics with respect to Hg(II) at its low concentration tends to zero-order at its higher concentration. Addition of acetamide (NHA) decreases the first-order rate constant (k1) while the rate of reaction is not influenced by the change in ionic strength (μ) of the medium. The first-order rate constant decreases with an increase in dielectric constant of the medium. Arabinonic acid, lyxonic acid and formic acid were identified as oxidation products of the reaction. Various activation parameters including the entropy of activation were also calculated. A plausible mechanism conforming to kinetic data, spectrophotometric observations, reaction stoichiometry and product analysis has been proposed.

Graphical abstractKinetics and mechanism of oxidation of d(+)Melibiose by N-bromoacetamide in acidic medium using chloro-complex of Pd(II) as homogeneous catalyst have been studied at 40 °C ± 0.1 °C. The rate determining step of the reaction involves the formation of most reactive activated complex, , by the interaction of oppositely charged species, [PdCl4·S]2− and Hg2+. Figure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slide