Acid–base equilibria and kinetics between triarylmethane dye carbinols and organic acids in apolar aprotic solvents: Relative basicities of dye carbinols in toluene

Abstract

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.