73745-98-9Relevant articles and documents
Micellar effect on the reaction of chromium(VI) oxidation of D-fructose in the presence and absence of picolinic acid in aqueous media: A kinetic study
Das, Asim K.,Roy, Aparna,Saha, Bidyut,Mohanty, Rajani K.,Das, Mahua
, p. 333 - 342 (2001)
The kinetics and mechanism of the Cr(VI) oxidation of D-fructose in the presence and absence of picolinic acid (PA) in aqueous acid media were studied under the conditions [D-fructose]T ?[Cr(VI)]T at different temperatures. Under the kinetic conditions, the monomeric species of Cr(VI) was found to be kinetically active in the absence of PA whereas in the PA-catalysed path, the Cr(VI)-PA complex was considered to be the active oxidant. In this path, the Cr(VI)-PA complex undergoes a nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition through glycol splitting leading to the lactone of C5-aldonic acid along with formaldehyde and the Cr(IV)-PA complex. The primary product formaldehyde undergoes further oxidation (in part) to form formic acid. Then the Cr(IV)-PA complex participates further in the oxidation of D-fructose and ultimately is converted into the inert Cr(III)-PA complex. In the uncatalysed path, the Cr(VI)-substrate ester experiences an acid-catalysed redox decomposition (2e transfer) in the rate-determining step giving rise to the products. The uncatalysed path shows a second-order dependence on [H+] whereas the PA catalysed path shows a fractional order in [H+]. Both paths show a first-order dependence on [D-fructose]T and [Cr(VI)]T. The PA-catalysed path is first order in [PA]T. All these patterns remain unaltered in the presence of externally added surfactants. The effects of a cationic surfactant, N-cetylpyridinium chloride (CPC), and an anionic surfactant, sodium dodecyl sulfate (SDS), on both the uncatalysed and PA-catalysed paths were studied. CPC inhibits both the uncatalysed and PA-catalysed paths whereas SDS catalyses the reactions. The observed micellar effects are explained by considering a distribution pattern of the reactants between the micellar and aqueous phases. The applicability of different kinetic models, e.g. the pseudo-phase ion-exchange model, the Menger-Portnoy model and the Piszkiewicz cooperative model, was tested to explain the observed micerllar effects. The effect of [surfactant]T on the activation parameters was explored to rationalize the micellar effect. Copyright
