SOLVENT-EXTRACTION OF SODIUM AND POTASSIUM-IONS BY DICARBOXYLATED CALIX[4]ARENES

The extraction of sodium and potassium ions by methyl-26,28-dimethoxy- 5,11,17,23-tetra-tert-butyl calix[4]arene ((LH2)-H-I) in chloroform sh ows the formation of (MLH)-H-I and M2LI complexes (M = Na, K). In 1,2- dichloroethane, the (MLH)-H-I species are formed in the acidic pH rang e, while only the Na2LI species is found at high pH values. The corres ponding extraction equilibrium constants K-11 (M) and K-21 (M) have be en evaluated and show a selectivity in favour of Na+ as compared to K, whatever the nature of the complexes. In chloroform, this selectivit y is much more pronounced considering the 2:1 complexes: K-11(Na)/K-11 (K)much less than K-21(Na)/K-21(K). The coexistence of 1:1 and 2:1 met al:ligand complexes is also shown in the extraction of sodium in 1,2-d ichloroethane by the -26,28-dimethoxyethoxy-5,11,17,23-tetra-tert-buty l calix[4]arene ((LH2)-H-II), locked in the cone conformation. Structu ral data of the complexes are discussed on the basis of H-1-NMR spectr a. In particular, for (LH2)-H-I, a conformational change from cone to partial cone upon metal complexation has been evidenced for the comple xes (KLH)-H-I, K2LI and Na2LI.