Extraction of europium trifluoromethanesulfonate into nitrobenzene in the presence of some electroneutral calixarene ligands

From extraction experiments and γ-activity measurements, the extraction constants corresponding to the general equilibrium Eu3+(aq) + 3 A−(nb) + L(nb) ⇔ EuL3+(nb) + A−(nb) taking place in the two-phase water–nitrobenzene system (\( {\text{A}}^{ - } = {\text{CF}}_{3} {\text{SO}}_{3}^{ - } \); L = tetrakis(2-ethoxyethoxy)-tetra-p-tert-butylcalix[4]arene (1), tetraethyl p-tert-butylcalix[4]arene tetraacetate (2), p-tert-butylcalix[4]arene-tetrakis(N,N-diethylacetamide) (3), hexaethyl p-tert-butylcalix[6]arene hexaacetate (4), p-tert-butylcalix[6]arene-hexakis(N,N-diethylacetamide) (5); aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the EuL3+ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the series of 2 < 4 < 1 < 5 < 3.