Thermodynamic study of solvent extraction of monovalent metal picrates with benzo-18-crown-6 into chloroform

Thermodynamic parameters (H _ex ⁰ and S _ex ⁰ ) for the overall extractions of monovalent metal (Na, K, Rb, and Tl) picrates with benzo-18-crown-6 (B18C6), and those (H _D,L ⁰ and S _D,L ⁰ ) for the distribution of B18C6 were determined between chloroform and water. All the extracted B18C6 complexes were l:1:1 complexes (B18C6:metal ion: picrate anion). The H _ex ⁰ and S _ex ⁰ values for all the metals are negative. Every extraction of the metal picrate with B18C6 is completely enthalpy driven. The H _D,L ⁰ and S _D,L ⁰ values of B18C6 are both positive, and the partition of B18C6 is entirely entropy driven. Enthalpy (H _ex,ip ⁰ ) and entropy changes (S _ex,ip ⁰ ) for ion-pair extractions of B18C6-metal ion complexes with picrate anions were calculated. All the H _ex,ip ⁰ and S _ex,ip ⁰ values are negative, and the ion-pair extractions are completely enthalpy driven.     

Hydration of complexes of 18-crown-6 with potassium nitrate or potassium picrate in the polymer phase

Adsorption of water vapor by granular polymer based on dibenzo-18-crown-6 and containing potassium nitrate or potassium picrate in the polymer phase was studied by the isopiestic method at 298 K. The adsorption of water vapor is described by isotherms corresponding (according to BDDT classification) to polymolecular absorption with a high adsorptive potential. In terms of the Aranovich model of polymolecular absorption, the monolayer capacity and differential heat of adsorption were calculated, and the stoichiometry of hydration of the potassium nitrate and potassium picrate complexes with immobilized crown ether was estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1940–1942, October, 1998.     

Extraction of Sodium and Potassium Perchlorates with Dibenzo-18-crown-6 into Various Organic Solvents. Quantitative Elucidation of Anion Effects on the Extraction-Ability and -Selectivity

The constants for overall extraction into various diluents of low dielectric constants (K_ex) and aqueous ion-pair formation (K_MLA) of dibenzo-18-crown-6 (DB18C6)–sodium and potassium perchlorate 1:1:1 complexes (MLA) were determined at 25°C. The K_ex value was analyzed by the four underlying equilibrium constants. The K_MLA values were determined by applying our established method to this DB18C6/alkali metal perchlorate extraction system. The K_M(DB18C6)A value of the perchlorate is much greater for K⁺ than for Na⁺, and is much smaller than that of the picrate. The K_MLA value makes a negative contribution to the extractability of DB18C6 for MClO₄, whereas the value of the MLA distribution-constant does a major one. The partition behavior of M(DB18C6)ClO₄ obeys the regular solution theory. However, the M(DB18C6)ClO₄ complexes in the diluent of high dipole moment somewhat undergo the dipole–dipole interaction. DB18C6 always shows high extraction selectivity for KClO₄ over NaClO₄, which is governed largely by the much greater K_MLA value for K⁺ than for Na⁺. The K⁺ extraction-selectivity of DB18C6 over Na⁺ for perchlorate ions is comparable to that for picrate ions. By comparing this perchlorate system with the picrate one, the anion effects on the extraction-efficiency and -selectivity of DB18C6 for Na⁺ and K⁺ was discussed in terms of the fundamental equilibrium constants.     

Extraction of Alkali Metal (Na—Cs) Picrates with Dibenzo-18-crown-6 into Various Organic Solvents. Elucidation of Fundamental Equilibria which Govern the Extraction-Ability and -Selectivity

In order to quantitatively investigate effects of the size, the structuralrigidity, and the lipophilicity of dibenzo-18-crown-6 (DB18C6) on itsextraction-ability and -selectivity for alkali metal ions, constants of theoverall extraction (Kex), the distribution for various diluents of lowdielectric constants (K_D,MLA), and the aqueous ion-pairformation (K_MLA) of DB18C6-alkali metal (Na-—Cs) picrate 1:1:1 complexes were determined at 25°C; the partition constants of DB18C6 itself were also measured at 25°C. The log K_MLA of Na, K, Rb, and Cs are -0.14 ± 0.11, 1.30 ± 0.10, 1.00 ± 0.09, and 0.24 ± 0.11, respectively. The partition behavior of DB18C6 and its1:1:1 complexes with the alkali metal picrates can be clearly explained byregular solution theory, except for chloroform. The molar volumes andsolubility parameters of DB18C6 and the 1:1:1 complexes were determined.A relation between molar volumes of the complexes and K_MLAis discussed. The magnitude of Kex is largely determined by that ofK_D,MLA. For every diluent, the extraction selectivity of DB18C6increases in the order Na > Cs > Rb > K. The K extraction-selectivity of DB18C6 over Na is the highest among all the combinations of the two neighboring alkali metals in the periodic table. The extraction-ability and -selectivity for the alkalimetal picrates and their change with the diluent of DB18C6 were completely elucidated by the four fundamental equilibria and regular solution theory.     

Extraction of Alkali Metal (Li, Na, K) Picrates with Benzo-15-crown-5 into Various Organic Solvents. Elucidation of Fundamental Equilibria Determining the Extraction-ability and -selectivity

To quantitatively elucidate the effects of the benzo group on the extraction-selectively and -ability of benzo-15-crown-5 (B15C5)for alkali metal ions, the constants of the overall extraction (K_ex), thedistribution for various diluents having low dielectric constants (K_D,MLA), and the aqueousion-pair formation (K_MLA) of B15C5-alkali metal (Li, Na, K) picrate 1:1:1 complexes (MLA) weredetermined at 25 °C. The partition constants of B15C5were also measured at 25 °C. The log K_MLA values for Li⁺, Na⁺, and K⁺ are -0.32 ± 0.22, 2.66 ± 0.19, and 0.71 ± 0.47, respectively. In going from 15-crown-5 (15C5) to B15C5, the benzo group considerably decreasesthe K_MLA value for the same alkali metal ion. The distributionbehavior of B15C5 and its 1:1:1 complexes with the alkali metal picrates closely obeys regularsolution theory, omitting chloroform. Molar volumes and solubility parameters of B15C5and the 1:1:1 complexes were determined. For every diluent, the K_ex valuefor B15C5 increases in the order Li⁺ < K⁺ < Na⁺. K_D,MLA makes anunfavorable contribution to the Na⁺ extraction-selectivity of B15C5 because of the smallest molar volume of the Na(B15C5)A complex. The Na⁺ extraction-selectivity of B15C5 is determined completely by much the highest K_Na(B15C5)A value.The extraction-ability and -selectivity of B15C5 for the alkali metal picrates are compared with those of 15C5on the basis of the underlying equilibrium constants.