Stabilities in Polar Nonaqueous Solvents and Transfer Activity Coefficients from Water to Nonaqueous Solvents of 19-Crown-6-Alkali Metal Ion Complexes |
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Authors: | Yasuyuki Takeda Yusuke Mochizuki Yasumasa Matsuzaki Shoichi Katsuta |
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Affiliation: | (1) Department of Chemistry, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan |
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Abstract: | Formation constants of 1 : 1 19-crown-6(19C6) complexes with alkali metal ions weredetermined conductometrically at 25 °Cin acetonitrile(AN), propylene carbonate (PC), methanol, DMF, andDMSO. 19C6 always forms the most stable complex withK+. The selectivity order of 19C6 forheavy alkali metal ions isK+ > Rb+ > Cs+.The selectivity for Na+ varies withthe solvent; that for Li+ is the second lowest(AN, DMSO) or the lowest (PC). Transfer activity coefficients(SH2 O) of19C6 from water to the nonaqueous solvents (S) weremeasured at 25 °C. The contributions of a methylenegroup and an ether oxygen atom to thelog SH2 Ovalue of a crown ether wereobtained. The SH2 Ovalues of the 19C6–alkali metal ion complexes(SH2 O (ML+)) werecalculated, M+ and L denoting an alkali metal ionand a crown ether, respectively. For AN, PC, andCH3OH, although the M+ ion is more stronglysolvated by water than by AN, PC, or CH3OH, thelog SH2 O (ML+) islarger than the correspondinglog SH2 O (L)expect for the case of M+ = Li+.The higher lipophilicity of the19C6 complex ion is attributed to an enforcement ofthe hydrogen-bonded structure of water for the complexion caused by the greatly decreased hydrogen bondingbetween ether oxygen atoms and water uponcomplexation. For DMF and DMSO, thelog SH2 O (ML+) is also greater thanthe correspondinglog SH2 O (L).It was concluded from thisfinding that the unexpectedly lowest stability of the19C6 complex ion in water is due to the hydrogenbonding between 19C6 and water. The stabilities and thelog SH2 Oof 19C6–alkali metal ion complexes were compared with those of 18C6complexes. |
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Keywords: | stability constants transfer activity coefficients from water additivity functional group contributions 19-crown-6 18-crown-6 alkali metal ions complexes polar nonaqueous solvents conductometry |
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