Stabilities in Water and Transfer Activity Coefficients between Nonaqueous Solvents and Water of 1 : 1 Complexes of 15,15-Dimethyl-16-crown-5 with Metal Ions

Abstract

Abstract The stability constants of 1 : 1 complexes of 15,15-dimethyl-16-crown-5 (DM16C5) with Li+, Na+, K+, Ag+, Tl+, Sr2+, Ba2+, and Pb2+ and of 16-crown-5 (16C5) with Li+ have been determined by conductometry in water at 25 °C. The transfer activity coefficients (sγ H2O) of the alkali metal ion complexes between nonaqueous solvents (s: acetonitrile, propylene carbonate, and methanol) and water have been calculated. These values have been compared with the literature values for 16C5 and 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L16C5). In water, 16C5 and DM16C5 selectively complex Li+ over Na+ and K+. The complexing ability of DM16C5 for a given metal ion is generally lower than that of 16C5 and L16C5. The alkali metal ion complexes of all the crown ethers are much less stable in water than in s, and the selectivity and the substituent effects also depend upon the solvent. The sγ H2O values provide the following information: the alkali metal ion and the ether oxygen atoms are greatly dehydrated upon complexation in water; the dehydration is most drastic for Na+; the dehydration for Na+ is hindered by the methyl groups of DM16C5 and facilitated by the electron-donating side arm of L16C5. The solvent effects upon complexation are explained in terms of solute-solvent interactions.