Conductimetric and potentiometric investigation of effect of acidity on formation of homoconjugates in acetonitrile solvent

Abstract

In the present work, 11 aromatic and nine aliphatic carboxylic acids, namely benzoic, 2-nitrobenzoic, 3-nitrobenzoic, 4-nitrobenzoic, 2,4-dinitrobenzoic, 3,5-dinitrobenzoic, 2-aminobenzoic, 3-aminobenzoic, 4-aminobenzoic, o-phthalic, salicylic, formic, acetic, monochloroacetic, dichloroacetic, trichloroacetic, propionic, n-butyric, caprylic, and myristic acids, were titrated conductimetrically and potentiometrically with triethylamine in acetonitrile solvent, under a nitrogen atmosphere, at 25 °C. Closer investigation of the conductimetric titration curves of these acids showed that the acidity of an acid, rather than the basicity of its conjugate base, plays a major part in the formation of homoconjugate ions, at least in acetonitrile solvent. If the acid is strong enough, there is a maximum before the experimental end point at about the half-neutralization point. To determine the minimum strength for an acid to show this maximum before the end point, all acids were also titrated potentiometrically. It was found that those acids which have half-neutralization potentials over −85 mV give a strong homoconjugation reaction and show a maximum before the experimental end point. Moreover, the acids that show maxima before the experimental end point in the conductimetric titration also show rather well-shaped potentiometric titration curves. Keywords: nonaqueous media, conductimetric titrations, potentiometric titrations, titration in acetonitrile, acidity and homoconjugation.