Kinetics and Mechanism of 2,2/-Bipyridyl Promoted Chromic Acid Oxidation of Ethanol and Propan-1-ol in Aqueous Micellar Media

ABSTRACT

In aqueous H2SO4 media Cr(VI) oxidation of ethanol and propan-1-ol to the corresponding aldehyde in presence and absence of 2,2´-Bipyridyl have been studied under the experimental conditions. Under the kinetic conditions, [alkanol]T >> [CrVI]T and [bipy]T >> [CrVI]T (subscript T stands for the total concentration) both the slower uncatalysed and faster catalysed (by heteroaromatic N- base i.e. bipy) paths go on. The monomeric species of Cr(VI) has been found to be kinetically active in absence of bipy where as in the heteroaromatic N-base catalysed path, the CrVI-bipy complexes have been found to be the active oxidants. Both the paths show first order dependence on [alcohol]T and Cr(VI)T. The uncatalysed path shows a second order dependence on [H+]. The heteroaromatic N-base catalysed path is first order in [bipy]T. These observations remain same in the presence of externally added surfactants. Sodium dodecyl sulphate (SDS) an anionic surfactant has been found to accelerate both the uncatalysed and bipy-catalysed paths while N-cetyl pyridinium chloride (CPC) a cationic surfactant shows rate retarding effect for both uncatalysed and bipy-catalysed paths. The observed micellar effects have been rationalized by considering the distribution of the reactants between the aqueous and micellar phases in terms of the proposed reaction mechanism.

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