Proton transfer equilibria between o-substituted benzoic acids and the carbinol base of crystal violet in apolar aprotic solvents: Chemometric analysis of ortho effect

Abstract

Toluene-phase reaction equilibria between a set of o-substituted benzoic acids and crystal violet carbinol base producing a coloured ion-pair have been studied spectrophotometrically at 28±1°C. Chemometric analysis on the basis of both Charton's and Fujita-Nishioka's multiparameter approaches for o-substituent effects on the equilibrium constants show that proximity electronic effect of an o-substituent is the main intrinsic contribution to the anomalous ortho effect with its steric factor contributing merely a minor effect. However, in the aqueous phase the steric contribution becomes significant due to hydration induced substantial enhancement in the bulk of the -COOH group and the o-substituent.