2 research outputs found
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 <sup>1</sup>H 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