Solvent Extraction of Several Anions with Tetrabutylammonium Ion into 1,2-Dichloroethane and Hydration of Anions in the Organic Phase

The partition equilibrium of tetrabutylammonium salts Bu4NX, where X− is N3−, NO3−, SCN−, ClO4−, and picrate ion, has been measured between water and 1,2-dichloroethane at 298 K. The distribution ratio of these salts can be explained in terms of the extraction of an ion pair (the extraction constant is defined as Kex = [Bu4N+X−]org/[Bu4N+]aq[X−]aqf±2) and the dissociation and dimerization of the ion pairs in the organic phase. The hydration number of the salt in the organic phase, nh, seems similar among dissociated, ion-paired, and dimerized species. The free energy of phase transfer corrected for the hydration effect in the organic phase, −RT(ln Kex−nh), may be correlated with the Gibbs free energy of hydration of the anions in the aqueous phase.