Stabilities in water and Gibbs free energies of transfer from water to nonaqueous solvents of alkali metal ion complexes with 1,2-bis[2-(2-methoxyethoxy)ethoxy]benzene (acyclic polyether)

Abstract

Stability constants of 1:1 complexes, ML⁺ (M⁺ and L being a univalent metal ion and a ligand, respectively), of Na⁺ and K⁺ with 1,2-bis[2-(2-methoxyethoxy)ethoxy]benzene (AC · B18C6), a linear counterpart of benzo-18-crown-6 (B18C6), were determined in water at 25°C by conductometry. The stability of ML⁺ is lower for AC · B18C6 than for B18C6 because of the macrocyclic effect, and AC · B18C6 is selective for Na⁺ in contrast to B18C6. Also determined were Gibbs free energies of transfer (ΔG_H2O→S^°) from water to nonaqueous solvent S (S=acetonitrile, propylene carbonate and methanol) of AC · B18C6 and B18C6 at 25°C through measurements of the distribution constants between tetradecane and the polar solvent. From these data as well as the literature values of K_ML in the nonaqueous solvents and of ΔG_H2O→S^° of M⁺, the ΔG_H2O→S^° values of ML⁺ complexes of the alkali-metal ions with AC · B18C6 and B18C6 were calculated. The ΔG_H2O→S^° values of M⁺ are positive but those of ML⁺ and L are negative in all the systems. This indicates that, although the M⁺ ions are more soluble in water than in the nonaqueous solvents, when the M⁺ forms a complex with the lipophilic L, the complex becomes more soluble in the nonaqueous solvent than in water. The lipophilicity of AC · B18C6 is higher than that of B18C6, but the reverse holds for the ML⁺ complexes. It was concluded that AC · B18C6 shields the M⁺ ions less effectively in the complexes from the surrounding solvents than B18C6.

References

1. B. G. Cox and H. Schneider, in Coordination and Transport Properties of Macrocyclic Compounds in Solution, Elsevier, Amsterdam, 1992, p. 81.
2. Y. Takeda, R. Kohno, Y. Kudo and N. Fukada, Bull. Chem. Soc. Jpn., 1989, 62, 999.
3. Y. Takeda, S. Sakamoto, N. Ohashi and N. Fukada, Bull. Chem. Soc. Jpn., 1988, 61, 2707.
4. Y. Takeda, Bull. Chem. Soc. Jpn., 1983, 56, 866.
5. Y. Takeda, H. Yano, M. Ishibashi and H. Isozumi, Bull. Chem. Soc. Jpn., 1980, 53, 72.
6. Y. Takeda and H. Yano, Bull. Chem. Soc. Jpn., 1980, 53, 1720.
7. Y. Takeda, in Cation Binding by Macrocycles, ed. Y. Inoue and G. W. Gokel, Marcel Dekker, New York, 1991, p. 133.
8. G. Chaput, G. Jeminet and J. Juillard, Can. J. Chem., 1975, 53, 2240.
9. Y. Takeda, Y. Ohyagi and S. Akabori, Bull. Chem. Soc. Jpn., 1984, 57, 3381.
10. Y. Takeda and T. Kimura, J. Inclusion Phenom., 1991, 11, 159.
11. A. F. M. Barton, Chem. Rev., 1975, 75, 731.
12. Y. Takeda, T. Kimura, S. Ochiai, S. Yajima, Y. Kudo, M. Ouchi and T. Hakushi, J. Chem. Soc., Faraday Trans., 1995, 91, 4079.
13. I. M. Kolthoff and M. K. Chantooni Jr., Anal. Chem., 1980, 52, 1039.
14. Y. Marcus, Pure Appl. Chem., 1983, 55, 977.
15. M. K. Chantooni Jr. and I. M. Kolthoff, Proc. Natl. Acad. Sci. USA, 1981, 78, 7245.
16. D. R. Rosseinsky, Chem. Rev., 1965, 65, 467.