Influence of micellar aggregates on oxidative degradation of β-cyclodextrin by alkaline permanganate: A kinetic and mechanistic study of inclusion complex

Abstract

Kinetics of MnO4−-β-cyclodextrin (BCD) redox reaction has been studied spectrophotometrically in presence of anionic surfactant micelles of sodium dodecyl sulfate (SDS) and cationic surfactant micelles of cetyltrimethylammonium bromide (CTAB) in alkaline medium. The rate of the reaction shows first order dependence on [MnO4−] and fractional order dependence on [BCD], [OH−] in the presence of both CTAB and SDS. Both the surfactants CTAB and SDS shows rate inhibition effects. Inhibition effect of CTAB was observed above critical micelle concentration (CMC) while that of SDS was observed below the CMC. Oxidised products were confirmed by FT-IR and 1H NMR spectral techniques. Reaction between SDS and BCD shows inclusion complex formation which was confirmed by conductivity measurements. The observed results were discussed in terms of Menger and Portnoy’s model for micellar inhibition. Activation parameters have been evaluated using Eyring equation. The effect of added salts (KCl, KBr, NaNO3 and Na2SO4) on the reaction has been studied. The effect of ionic strength and dielectric constant on the rate of reaction has been studied in the absence of surfactants. Probable reaction mechanism, in agreement with the observed kinetic results has been proposed and discussed.