Interfacial catalytic influence of sodium lauryl sulphate in the oxidation of cyclic alcohols by Cr(VI)

Abstract

In the present work effort has been made to investigate the electron transfer mechanism for the oxidation of cyclopentanol of importance be Cr(VI) in presence and absence of surfactant (Sodium lauryl sulphate, SDS) and develop a kinetic model. The progress of the reaction was monitored spectrophotometrically by measuring the fall in absorbance of Cr(VI) at its λmax (wave-length of maximum absorbance). Under the conditions of [cyclopentanol] >≫ [Cr(VI)], the ln(Absorbance) vs time plots are obtained having constant slope value indicating the reaction exhibited a first order dependence with respect to Cr(VI). Unit order dependence of rate on [cyclopentanol], complex dependence on acid strength, nil effect of added salt (K2SO4) is what we observed while monitoring the progress of the reaction. The thermodynamic parameters like activation energy, enthalpy, entropy is computed by executing the reaction at 25, 30 and 35 0C. In presence of varying [SDS] it is observed that the rate marginally increases with increase in [SDS] until an optimum [SDS] which is around cmc and there after the rate decreases exponentially. In SDS medium partitioning of both the cationic Cr(IV) species and the substrate between water and micellar pseudo-phase is considered and accordingly Berezin et al. model is extended to explain the kinetic data. Based on all experimental findings a suitable kinetic model has been proposed for both aqueous and micellar phase reaction.