Ionic polymerisation as a means of end-point indication in non-aqueous thermometric titrimetry. Part VIII. Solvent effects in the determination of polyfunctional carboxylic acids and phenols

Abstract

A systematic study has been made of the effect of the solvent for the sample on the end-point sharpness and the reaction stoicheiometry in the catalytic thermometric titration of polyfunctional carboxylic acids and polyhydric phenols. Acrylonitrile was used as the end-point indicator.

The mechanisms proposed for the reactions involved in the neutralisation and indicator processes are based on the assumption that the titrants can exist as mixtures of ion pairs, solvent-separated ion pairs and free ions in the sample solution. It is suggested that the ratio of free ions to ions pairs is the factor that controls the reaction stoicheiometry, and the cation solvating power of the solvent is more important than the dielectric constant of the solution in influencing this ratio.

Solvent and titrant combinations are recommended for the determination of the total acidities of a range of benzene carboxylic acids, polyhydric phenols and hydroxybenzoic acids by the catalytic thermometric procedure.