Abstract
The ion-pair formation constant (KMLA0 in mol–1 dm3) for Li(B15C5)+ with a picrate ion (Pic–) in water was determined by potentiometry with a K+-selective electrode at 25˚C and an ionic strength of 0, where B15C5 denotes benzo-15-crown-5 ether. Using the concentration equilibrium constants, KMLA, estimated from this value, the extraction constants (mol–2 dm6 unit) of about ten diluents were re-calculated from previously reported extraction data. Also, the distribution constants of an ion-pair complex, Li(B15C5)Pic, between water and the diluents were re-estimated. A disagreement in the determined KMLA value between a solvent-extraction method and potentiometry was explained in terms of the Scatchard–Hildebrand equation; it came from the fact that the hydration of Li(I) in Li(B15C5)Pic was larger than that of free B15C5 in water. Then, the previously determined value by the former method was re-estimated using the potentiometric KMLA value.
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References and Notes
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The log Kex values for the NaPic-B15C5 system were revised by correcting activity coefficients in the data of Ref. 4. Then, the log KD,MLA values were estimated from the relation in the text. Their log Kex (I of the w-phase) and log KD,MLA values were: 3.637 ± 0.008 (0.022 mol dm–3) and 3.02 for DCM; 3.312 ± 0.012 (0.022) and 2.68 for CF; 3.760 ± 0.024 (0.021) and 2.63 for DCE; 3.089 ± 0.005 (0.022) and 0.67 for CBu; 3.204 ± 0.009 (0.022) and 1.32, 3.308 ± 0.015 (0.0063) and 1.37 for Bz; 3.179 ± 0.013 (0.022) and 1.06 for TE; 3.151 ± 0.005 (0.022) and 0.81 for mX; 3.629 ± 0.016 (0.022) and 1.93 for CB; 3.646 ± 0.008 (0.022) and 1.97 for BB; 3.738 ± 0.009 (0.022) and 2.06 for oDCB, respectively. Accordingly, the regression line was re¬calculated: log KD,MLA = (1.387 ± 0.114)log KD,L–(0.110 ± 0.158) with R = 0.97.
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This finding may come from the fact that the interaction of H2O with Na(15C5)Pic is somewhat smaller than that with K(15C5)Pic. See Ref. 4.
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Kudo, Y., Fujihara, R., Katsuta, S. et al. Hydration Effect on the Ion-pair Extraction of Lithium Picrate by Hydrophobic Benzo-15-crown-5 Ether into Various Less-polar Diluents. ANAL. SCI. 23, 1003–1006 (2007). https://doi.org/10.2116/analsci.23.1003
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DOI: https://doi.org/10.2116/analsci.23.1003