Abstract
The kinetics of oxidation of beta-cyclodextrin in the presence of HClO4 by chromium(VI) has been studied spectrophotometrically under different experimental conditions. The reaction rate bears a first order dependence on [Cr(VI)] under pseudo-first order conditions, [beta-cyclodextrin] >> [Cr(VI)], in the presence of 1.39 mol dm(-3) perchloric acid. The reaction followed fractional order kinetics with respect to [beta-cyclodextrin]. The rate increased markedly with increasing [H+]. The inhibitory effect of manganese(II) has been ascribed to an one-step two-electron process in which chromium(IV) is formed as an intermediate. The energy (54 kJ mol(-1)), enthalpy (51 kJ mol(-1)) and entropy (-145 J K-1 mol(-1)) of activation have been calculated and discussed. One of the primary -OH group of alpha-D-glucopyranose unit of beta-cyclodextrin is responsible for oxidation. The net oxidation rate of beta-cyclodextrin, as measured by the consumption of [Cr(VI], is given as follows:
- d[Cr(VI)]/dt = k(1)K(es1)K(a1)[H+][beta-cyclodextrin] [Cr(VI)](T)/1+K-a1[H+]+K-es1 [beta-cyclodextrin]