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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Institution: | (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(SH
2 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 SH
2 Ovalue of a crown ether wereobtained. The SH
2 Ovalues of the 19C6–alkali metal ion complexes(SH
2 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 SH
2 O (ML+) islarger than the correspondinglog SH
2 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 SH
2 O (ML+) is also greater thanthe correspondinglog SH
2 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 SH
2 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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