Solvent extraction of univalent and bivalent metal picrates with 1,2-bis[2-(2-methoxyethoxy)ethoxy] benzene (noncyclic crown ether) into CHCl3

Abstract

The overall extraction equilibrium constants, Kex, of 1:1:m complexes of 1,2-bis[2-(2-methoxyethoxy)ethoxyjbenzene (AC · B18C6) with uni- and bivalent metal picrates, MA m were determined at 25°C between CHCl3 and water, and thereby the ion-pair complex-formation constants,K MLA,o, of AC · B18C6 with the univalent metal picrates in CHCl3 were calculated. The AC · B18C6 is an open-chain analog of benzo-18-crown-6 (B18C6). The equilibrium constants of AC · B18C6 were compared with those of B18C6. Kex sequences of AC · B18C6 for uni- and bivalent metals are Tl+ > K+ > Rb+ > Cs+ > Na+ > Li+ and Pb2+ > Ba2+ > Sr2+, respectively. The same extraction-selectivity was observed for B18C6, but the extractability of AC · B18C6 for the same cation is much lower than that of B18C6; the extraction selectivity of AC · B18C6 for alkali metals is lower than that of B18C6. TheK MLA,o sequence of AC · B18C6 is K+ > Rb+ > Tl+ > Cs+ ≌ Na+, which is consistent with that of B18C6. ButK MLA,o of AC · B18C6 is much smaller than the correspondingK MLA,o of B18C6; the selectivity of AC · B18C6 among alkali metal picrates in CHCl3 is lower than that of BI8C6. This reflects the difference in the structures between AC · B18C6 (acyclic and flexible) and B18C6 (cyclic and rigid).