Extraction of Monocarboxylic Acids with Trioctylamine: Equilibria and Correlation of Apparent Reactive Equilibrium Constant

This is the authors' abstract. We don't add key points for this paper.

Liquid−liquid equilibria for aqueous solutions of carboxylic acids, namely formic, acetic, propionic, butyric, valeric, monochloroacetic, dichloroacetic, trichloroacetic, glyoxylic, glycolic, and lactic acids, with trioctylamine (TOA) in various diluents, including 1-octanol, chloroform, methyl isobutyl ketone (MIBK), tetrachloromethane, and hexane, were determined at various TOA concentrations. The loading of TOA for a given carboxylic acid depends on the nature of the solute; the hydrophobicity and p K a of the acid; and the nature of solvent, diluent type, and TOA concentration, which can be expressed by the specific basicity of TOA (p K ‘ a,B ), and increases with increasing acidity and hydrophobicity of the acid. The strength of solvation of the complex by the diluent for the acids studied decreases in the order 1-octanol ⩾ chloroform > MIBK > tetrachloromethane > hexane. An equilibrium model is presented that employs the mass action law and is used to determine model parameters and apparent extraction equilibrium constants ( K 11 ). The apparent extraction equilibrium constants depend on the hydrophobicity and acidity of the carboxylic acid, as well as the specific basicity of TOA, and the quantitative correlation of log K 11 is obtained using log P, p K a, and p K ‘ a,B .