KINECTIC AND MECHANISTIC INVESTIGATION OF OXIDATION OF D(+)RIBOSE BY POTASSIUM IODATE IN PRESENCE OF Rh(III) AS CATALYST IN ALKALINE MEDIUM

摘要

The kinetics of Rh(III)-catalysed oxidation of D(+)ribose by potassium iodate in alkaline medium has been studied at 40°C. The reaction exhibits first-order kinetics with respect to [Rh(III)] and [D(+)ribose], The order of reaction was found to be unity at low concentrations of potassium iodate and OH~- which tends to zero-order at their higher concentrations. It was found that dielectric constant of the medium and ionic strength had no effects on the rate of reaction. There is nil effect of [Cl~-] on the rate of oxidation. The reaction has been studied at four different temperatures and observed rate constant values were utilised to calculate activation energy and other activation parameters.The species, [RhCl_3(H_2O)_2OH]~- and IO_3 are postulated as the main reactive species of Rh(III) chloride and potassium iodate, respectively in alkaline medium. Sodium salts of erythronic acid and formic acid were identified as the main oxidation products of the reaction. On the basis of kinetic results, spectroscopic information and activation parameters, a suitable mechanism for the oxidation of D(+)ribose has been proposed and rate law has been derived.