SOLVENT-EXTRACTION OF ALKALINE-EARTH IONS BY DICARBOXYLATED CALIX[4]ARENES

The extraction of the alkaline-earth metal ions by dimethoxy-5,11,17,2 3-tetra-tert-butylcalix[4]arene ((LH2)-H-I) and oxyethoxy-5,11,17,23-t etra-tert-butylcalix[4]arene ((LH2)-H-II) in 1,2-dichloroethane is sho wn to be pH dependent. The analysis of the extraction equilibrium resu lts indicates that the extraction process takes place via the formatio n of (ML2H2)-H-I (M2+ = Ca2+, Sr2+ and Ba2+), (ML2H2)-H-II (M2+ = Ca2 and Sr2+) and MLII (M2+ = Ba2+) complexes. Both ligands show a high s electivity for calcium. The existence of the ML2H2 complexes is suppor ted by H-1-NME and FAB(+) experiments on the corresponding Ca2+ comple xes. H-1-NMR investigations show that the calcium ion is located outsi de the calixarene cavity. Competitive extraction of Mg, Ca, Sr and Ba suggests the formation of mixed complexes. (C) 1998 Elsevier Science L td. All rights reserved.