Dynamics of cetyltrimethylammonium bromide mediated reaction of phenylsulfinylacetic acid with Cr(VI): Treatment of pseudo-phase models

Abstract

micellar effect % Hammett correlation % Piszkiewicz cooperative model KR nema The influence of cetyltrimethylammonium bromide, CTon the oxidative decarboxylation of phenylsulfinylacetic acid, PSAA and several meta- and para-substituted PSAAs by Cr(VI) was investigated in 95 % H2O-5 % CH3CN medium. The rate profile displayed a peculiar trend with an initial rate increase at low [CTAB] followed by sharp rate inhibition at higher [CTAB]. The initial rate acceleration can be explained by strong binding of SO42- on the positively charged micellar surface. The specific partitioning of PSAA in micellar phase by hydrophobic interaction and the oxidizing species, HCrO3+ in aqueous phase by electrostatic repulsion accounted the rate retardation at higher [CTAB]. The Hammett plot with different substituted PSAAs showed an excellent correlation affording negative ? value which supports the proposed mechanism involving a sulfonium cation intermediate formation. The obtained ? value in CTmedium is found to be slightly lower than that in aqueous medium. The quantitative analysis of rate data for the inhibition shown by CTwas performed using Menger-Portnoy and Piszkiewicz pseudo-phase models. The binding constant for PSAA with micelle was evaluated from Piszkiewicz cooperative model.

Dynamics of CTAB micelle mediated reaction of fuchsin degradation in alkaline medium

“…Since n > 1, it indicates positive cooperativity which implies that binding of the first molecule of the substrate allows for the binding of subsequent molecules. Furthermore, the value of n is far than the aggregation number (20-100) of the surfactants which indicate the formation of catalytically productive sub-micellar aggregates [15]. The linear plot supports the positive cooperativity between fuchsin and micelle to form reactive micelles which indicates that the substrate, fuchsin molecules are included into the micellar phase.…”

Picolinic acid promoted oxidative decarboxylation of phenylsulfinylacetic acid by Cr(VI)

“…Though phenylsulfinylacetic acid (PSAA) is a versatile compound finding utility in pharmaceutical and synthetic fields [20][21][22][23][24][25][26], literature survey clearly reveals that there is no systematic mechanistic study on the oxidation of PSAA except our recent publications [27][28][29][30][31]. Hence, in continuation of our work it is decided to carry out a systematic investigation on the PA promoted Cr(VI) reaction with PSAA with a view to proposing a suitable mechanistic path.…”

A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non‐linear Hammett

“…In recent years, much attention has been paid to the chemistry of sulfur‐centred radicals and radical cations because of their importance as intermediates in organic synthesis, environmental and biological studies. As these intermediates are reported in most of the sulfoxidation reactions, and there is no systematic mechanistic study on the oxidation of phenylsulfinylacetic acid (PSAA) in the literature except our recent publications, a systematic mechanistic investigation on the reaction between biologically active iron(III) polypyridyl complexes and therapeutically active PSAA is undertaken in the present work. On the basis of the observed spectral, kinetic, thermodynamic and substituent effects a suitable mechanistic path is proposed.…”