Combined effect of promoter and surfactant on the chromium(VI) oxidation of D-ribose in aqueous media at room temperature

<p>Effect of polypyridine derivatives on chromium(VI) oxidation of D-ribose in aqueous media was studied spectrophotometrically. The oxidized product D-erythrose was detected by paper chromatography. The promoters 1,10-phenanthroline, 2,2΄-bipyridine, 2-picolinic acid, and 2,3-dipicolinic acid accelerated the oxidation, whereas isomeric 4,7-phenanthroline, 4,4΄-bipyridine, 4-picolinic acid, and 2,6-dipicolinic acid did not influence the oxidation. Formation of Cr(VI)-promoter complex was identified through fluorescence spectroscopy. Rate constants depended on promoter concentration. SDS and TX-100 enhanced the D-ribose oxidation, while CPC retarded the reaction. Location of D-ribose inside micelles was observed through ¹H NMR. DLS study showed that the relative size of SDS and TX-100 micelles expanded in presence of chromium(VI).</p

Influence of Chain Length and Concentration-Dependent Morphological Switching on Oxidation of Aromatic Alcohols in a Micellar Environment

Catalytic oxidation of benzyl alcohol (BA), p-chlorobenzyl alcohol (p-ClBA) and p-anisyl alcohol (p-OMeBA) in aqueous media has been investigated in the presence of two cationic surfactants, viz. cetylpyridinium chloride (CPCl) and dodecylpyridinium chloride (DPCl). The chromium(VI)-governed oxidations of such aromatic compounds exhibit an unusual kinetics depending upon the concentration of CPCl and DPCl. Both the cationic surfactants catalyzed the oxidations at lower concentrations while retardation was noticed at higher concentrations. The catalytic and inhibitory functions of both the surfactants at the sub- and postmicellar levels have been enlightened based on the kinetic CMC (critical micellization concentration). The chain length of the two surfactants influences the kinetic profiles of the oxidation processes. Herein, the π–π interaction and the cation−π interaction play important roles in the solubilization process and therefore encourage the reaction rate. These strong interactions result in a maximum 12-fold catalytic enhancement for the oxidation of p-anisyl alcohol in the CPCl micellar environment, while the inhibitory effect of CPCl and DPCl on the oxidation kinetics have been analyzed based on the dilution effect. The morphological alteration of aggregates during the oxidation aids the interpretation of the inhibitory activity of both micelles produced by CPCl and/or DPCl. Berezin’s model has been employed to reveal the inhibition caused by cationic micelles. Morphological alteration of both the cationic surfactants from spherical-to-cylindrical shape at variable concentrations in the absence and presence of substrate was supported by SAXS (small-angle X-ray scattering), TEM (transmission electron microscopy), and FE-SEM (field emission scanning electron microscopy) analysis