Permanganate partitioning in cationic micelles of cetyltrimethylammonium bromide: A kinetic study of D-fructose oxidation

The kinetics of oxidation Of D-fructose by permanganate was studied in cationic micelles of cetyltrimethyl ammonium bromide (CTAB), spectrophotometrically. An increase of [CTAB] led to an increase in the absorbance of the reaction mixture. The results indicate a very strong partitioning of the permanganate in favor of the micellar pseudo-phase. From the observed spectrophotometric data, CTAB-permanganate ion-pair formation constant (K-s) was calculated to be 2924 dm(3) mol(-1). The reaction is catalyzed by the CTAB micelles. The rate constant versus [CTAB] plot has a maximum at [CTAB] >= 40.0 x 10(-4) mol dm(-3). For [CTAB] well above the critical micelle concentration, the k(obs)-[CTAB] profile can be interpreted in terms of distribution of permanganate and D-fructose between water and the micelles. H2SO4 has inhibitory effect on the micellar catalysis. The redox reaction proceeds through the formation of water soluble colloidal MnO2 as an intermediate in less acidic medium. The effects of externally added manganese(II) and fluoride ion are complex. On the basis of the experimental findings, a suitable mechanism consistent with the observed kinetics has been proposed. (c) 2006 Elsevier B.V. All rights reserved.