Extraction constants of ion-pairs

Assignment of extraction constants to individual ions and solvents

Abstract

It is assumed that the extraction constant, K_ex, for the ion-pair extraction systems is made up of three independent constants (individual extraction constants), K_e, K_a and K_s, in accordance with the equation:
log K_ex=logK_e+logK_a+log K_s
where the subscripts c, a, and s denote cation, anion, and solvent, respectively. Log K values for several cations, anions, and solvents were calculated from experimental values of log K_ex by tentatively assigning the log K values 1.0 and 0.0 to perchlorate and benzene, respectively, as reference values. The cations, anions and the solvents studied were Co (III) complexes of three 2-(2-pyridylazo)-5-diethylaminophenols, perchlorate and three anionic surfactants, and benzene, toluene, and chlorobenzene. The above equation is shown to be useful in estimating the unknown value of K_ex from the constants assigned to each ion and the solvent.