Browsing by Author "Udai Arvind"

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Acid–base equilibria and kinetics between triarylmethane dye carbinols and organic acids in apolar aprotic solvents: Relative basicities of dye carbinols in toluene
(1993) Susanta K. Sen Gupta; Udai Arvind
Equilibria and kinetics of acid–base reactions in toluene between a carboxylic acid (m‐toluic, salicylic acid) and a set of carbinol bases (derived from basic triarylmethane dyes) were studied spectrophotometrically. The results for the equilibrium and kinetic parameters were critically analysed. The rate constant of the forward step of the acid–carbinol base equilbrium was found to provide a suitable scale of basicities in toluene. The basicities of the dye carbinols chosen decrease in the order Ethyl Violet‐ >Crystal Violet‐ >Methyl Violet‐ ≈ Victoria Pure Blue BO‐ ≫ Brilliant Green‐ >Malachite Green–carbinol. This is fairly consistent with the order observed in water. A fairly good correlation between base strengths of the carbinols and σ R+ parameters of their para‐alkylamino substituents was obtained. Copyright © 1993 John Wiley & Sons, Ltd.
Equilibria and kinetics of reactions between carboxylic acids and the carbinol base of crystal violet in apolar aprotic solvents: Relative strengths of m- and o-substituted benzoic acids in toluene
(John Wiley and Sons Ltd, 1997) Susanta K. Sen Gupta; Udai Arvind
Equilibria and kinetics of proton-transfer reactions in toluene between a set of m- and o-substituted (methyl, methoxy, chloro, nitro and hydroxy) benzoic acids and the carbinol base (colourless) of Crystal Violet were studied spectrophotometrically. The data on equilibrium and kinetic parameters were critically analysed. The rate constant for the forward step of the acid-carbinol equilibrium was found to be an appropriate criterion for determining acidities in toluene. Toluene-phase acidities were found to be significantly more susceptible than aqueous-phase acidities to the structure of the substituents, particularly for the m-substituted acids. Quantitative analysis of the substituent effect on toluene-phase acidities using the Fujita-Nishioka model for the extended Hammett equation showed that the predominant factor contributing to the 'ortho effect' for benzoic acid-dye carbinol reactions in toluene is the proximity polar effect rather than the steric effect for most of the o-substituents © 1997 by John Wiley & Sons, Ltd.
General acid catalysis in benzoic acid-Crystal Violet carbinol base reactions in toluene
(2012) Susanta K. Sen Gupta; Sangeeta Mishra; V. Radha Rani; Udai Arvind
Kinetics of benzoic acid-dye carbinol base reactions in an apolar aprotic solvent exhibit a complex dependence on the concentration of the acid, indicating the occurrence of general acid catalysis, the acid playing the dual role of the substrate and the catalyst. The complex kinetic behavior observed for 23 ortho- and meta-substituted benzoic acids has been traced to overlapping participations of the monomer acid, hyperacidic open chain homoconjugated complex (dimeric and trimeric) acids, and nonreactive cyclic dimer and trimer acids. It has been found that although the degree of proton transfer in the transition state is 50-60% when the acid acts exclusively in the monomeric form, it gets enhanced to as high as more than 90% when the role of homoconjugated complex acids is taken into consideration. © 2012 Wiley Periodicals, Inc.