Efficient divalent metal cation extractions with di-ionizable calix[4]arene-1,2-crown-4 compounds

Di-ionizable calix[4]arene-1,2-crown-4 ethers in the cone conformation were synthesized and their conformation and regioselectivity verified by NMR spectroscopy. These new ligands exhibited high Ba2+ selectivity in competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform. The selectivity order was Ba2+>>Sr2+>Ca2+>Mg2+ with Ba2+/Sr2+ selectivity exceeding 100. The ligands also exhibited high extraction ability for Pb2+ and for Hg2+ in single species extraction. With variation of proton-ionizable groups, which are oxyacetic acid moieties and N-(X)sulfonyl oxyacetamide units with X=methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, ‘tunable’ ligand acidity was obtained.