Determination of extraction constant, true partition coefficient and formation constant of ion-pair complexes of quaternary ammonium salts, tetrabutylammonium bromide and isopropamide iodide.with some organic anions by a solvent extraction technique

Abstract

A new method of determining the extraction constant ( K e, the true partition coefficient (TPC) and the formation constant ( K f) of ion-pairs, was developed by the solvent extraction technique. K e and TPC were estimated from the reciprocals of the intercept and the slope of the regression line obtained by plotting B T W APC − dA vs B B T W dA APC − dA + A T W + B T W in the following equation. B T W APC − dA = 1 K e + B B T W dA APC − dA + A T W + B T W x 1 TPC where [A T W] and [B T W] are the total concentrations of the cationic compound A and that of the anionic compound B in the aqueous phase respectively, APC is the apparent partition coefficient of A, dA is the partition coefficient of cation A +. K f, which is expressed by K e/TPC, was then calculated. These constants were determined for the ion-pair extraction of tetrabutylammonium bromide and isopropamide iodide with 4 organic anions, i.e. benzoic acid, p-toluenesulfonic acid, salicylic acid and taurodeoxycholic acid. This new method might be applicable to other ion-pairs without further assumptions except that the molar ratio of the ion-pair formation be 1 : 1.