ISSN:
1573-1111
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
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
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(SγH 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 SγH 2 Ovalue of a crown ether wereobtained. The SγH 2 Ovalues of the 19C6–alkali metal ion complexes(SγH 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 SγH 2 O (ML+) islarger than the correspondinglog SγH 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 SγH 2 O (ML+) is also greater thanthe correspondinglog SγH 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 SγH 2 Oof 19C6–alkali metal ion complexes were compared with those of 18C6complexes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1008144727454
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