Kinetics of the oxidation of lactose by copper(II) complexed with bipyridyl in alkaline medium using chloro-complex of rhodium(III) in its nano-concentration range as homogeneous catalyst: a spectrophotometric study.

Kinetics of the oxidation of lactose by Cu(II) complexed with bipyridyl have been investigated at 40 °C for the first time spectrophotometrically using Rh(III) chloride as homogeneous catalyst in aqueous alkaline medium in its nano-concentration range. The order of reaction was found to be fractional positive-order, when the concentration of Rh(III) chloride was varied from 0.30×10(-9) M to 6.00×10(-9) M. The reaction shows fractional positive-order kinetics with respect to [lactose] and [OH(-)] and zeroth-order kinetics with respect to [Cu(II)]. The reaction also shows slight increase in the rate by decreasing dielectric constant of the medium and remains unaffected by the change in ionic strength of the medium. The reaction was carried out at four different temperatures and observed values of rate constants were utilized to calculate various activation parameters specially the entropy of activation (ΔS(#)). The species, [RhCl(3)(H(2)O)(2)OH](-), was postulated as the main reactive species of Rh(III) chloride for the oxidation of lactose by Cu(II) in alkaline medium. On the basis of kinetic and equivalence studies together with spectrophotometric information for the formation of a complex, [formula see text] the most appropriate mechanism for the aforesaid reaction has been proposed. Support to the proposed mechanism was also given by the observed activation parameters and multiple regression analysis. Sodium salts of formic acid, arabinonic acid and lyxonic acid were identified as the main oxidation products of the reaction under investigation.

Pd(II)-catalysed and Hg(II)-co-catalysed oxidation of D-glucose and D-fructose by N-bromoacetamide in the presence of perchloric acid: a kinetic and mechanistic study.

The kinetics of Pd(II)-catalysed and Hg(II)-co-catalysed oxidation of D-glucose (Glc) and D-fructose (Fru) by N-bromoacetamide (NBA) in the presence of perchloric acid using mercury(II) acetate as a scavenger for Br- ions have been studied. The results show first-order kinetics with respect to NBA at low concentrations, tending to zero order at high concentrations. First-order kinetics with respect to Pd(II) and inverse fractional order in Cl- ions throughout their variation have also been noted. The observed direct proportionality between the first-order rate constant (k1) and the reducing sugar concentration shows departure from the straight line only at very higher concentration of sugar. Addition of acetamide (NHA) decreases the first-order rate constant while the oxidation rate is not influenced by the change in the ionic strength (mu) of the medium. Variation of [Hg(OAc)2] shows a positive effect on the rate of reaction. The observed negative effect in H+ at lower concentrations tends to an insignificant effect at its higher concentrations. The first-order rate constant decreases with an increase in the dielectric constant of the medium. The various activation parameters have also been evaluated. The products of the reactions were identified as arabinonic acid and formic acid for both the hexoses. A plausible mechanism involving HOBr as the reactive oxidising species, Hg(II) as co-catalyst, and [PdCl3.S]-1 as the reactive Pd(II)-sugar complex in the rate-controlling step is proposed.