ISSN:
1573-1111
Keywords:
solvent extraction
;
constituent equilibria
;
ion-pair extraction constant
;
lariat 16-crown-5
;
uni- and bivalent metal picrates
;
side-arm effect
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The overall extraction constants (Kex) of uni- andbivalent metal picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5(L16C5) were determined between benzene and water at 25°C. TheKex values were analyzed into the constituent equilibriumconstants, i.e., the extraction constant of picric acid, the distributionconstant of the crown ether, the stability constant of the metalion–crown ether complex in water, and the ion-pair extraction constantof the complex cation with the picrate anion. The Kex valuedecreases in the orders Ag+ 〉 Na+ 〉Tl+ 〉 K+ 〉 Li+ andPb2+ 〉 Ba2+ 〉 Sr2+ for theuni- and bivalent metals, respectively, which are the same as those observedfor 16C5. The extraction selectivity was found to be governed by theselectivity of the ion-pair extraction of the L16C5–metal picratecomplex rather than by that of the complex formation in water. Theextraction ability of L16C5 is smaller for all the metals than that of 16C5,which is mostly attributed to the higher lipophilicity of L16C5. Differencesin the extraction selectivity between L16C5 and 16C5 were observed for thebivalent metals but little for the univalent metals. The side-arm effect onthe extraction selectivity was interpreted on the basis of the negativecorrelation between the effect on the complex stability constant in waterand that on the ion-pair extraction constant.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1007904302118
Permalink