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.     

Fundamental equilibrium analysis on the ion-pair extraction of dibenzo-18-crown-6 complex of alkali metal ions with picrate ion into 1,2-dichloroethane

The ion-pair extraction equilibria of dibenzo-18-crown-6 (DB18C6) complexes of Na⁺, K⁺, Rb⁺ and Cs⁺ (M⁺) with picrate ion (Pic⁻) into 1,2-dichloroethane (1,2-DCE) have been studied at 25.0°C. In the case of the Rb⁺ and Cs⁺ systems, the extraction results were interpreted by taking into consideration the formation of a (DB18C6)₂ -M⁺ complex in 1,2-DCE. The thermodynamic constants of extraction, , and ion-pair formation in 1,2-DCE, , of ion pairs of the DB18C6-M⁺ complexes with Pic⁻ were determined. By using the distribution coefficient of M⁺·Pic⁻ the thermodynamic formation constants of the DB18C6-M⁺ complexes in 1,2-DCE, , were evaluated. Consequently the component equilibrium constants of the ion-pair extraction were completely determined and a contribution of these constants to the difference of value was discussed. The value in 1,2-DCE is quite high compared with that in solvating solvents and log decreases linearly with increasing Gutmann donor number of solvents.     

Solvent extraction separation of thorium as picrate complex with 18-crown-6

Thorium was quantitatively extracted from 0.04M picric acid with 0.065M of 18-crown-6 at pH 2.0–3.5. It was stripped from organic phase with 0.5M nitric acid and was determined spectrophotometrically at 655 nm as its Arsenazo-III complex. Thorium was separated from mixture containing cerium, uranium, zirconium, hafnium, yttrium and lead in complex mixtures. The method was extended for the analysis of thorium in monazite.     

Thermodynamic properties of the solvent extraction of ion pairs of metal chelate cations with some anions

Thermodynamic quantities were determined for the extraction of ion pairs of tris(1,10-phenanthroline)iron(II) and tris(2,2'-bipyridine)iron(II) chelate cations with halide, pseudohalide and polythionate anions from aqueous phase into nitrobenzene. Ion pairs with larger anions have more negative enthalpy changes with higher extractability. No clear trend was observed for the entropy changes. Linear relationships were observed between the free energy changes and the reciprocal radii of monovalent counter anions.     

1H NMR and spectrophotometric study of alkaline metal ion complexes with N-dansyl aza-18-crown-6

Formation of complexes of A18C6-Dns and metal cations (Ca²⁺, Sr²⁺, Ba²⁺ and Mg²⁺) in acetonitrile has been studied by NMR, absorption and fluorescence spectroscopy and PM5 semi-empirical methods. A18C6-Dns forms stable complexes with Ca²⁺, Sr²⁺ and Ba²⁺ cations. The stability constants of various complexes are determined by different methods and their structures are visualised by the PM5 semi-empirical calculations.     

Potentiometric study of complexation of phenylaza-15-crown-5, 4-nitrobenzo-15-crown-5 and dibenzopyridino-18-crown-6 and other derivative of 18-crowns-6 with Na+ ion in methanol

The complexation reaction of phenylaza-15-crown-5, and 4-nitrobenzo-15-crown-5, benzo-15-crown-5 and dibenzopyrdino-18-crwon-6, dibenzo-18-crown-6,dicyclohexyl-18-crown-6(cis and trans), and 18-crown-6 with Na⁺ ion in methanol have been studied by potentiometric method. The Na⁺ ion-selective electrode has been used both as indicator and reference electrode. The stoichiometry and stability constants of complexes of these crown ethers with sodium ion were evaluated by MINIQUAD program. The major trend of stability of resulting complexes of these macrocycle with Na⁺ ion varied in the order DCY18C6 > DB18C6 > 18C6 > DBPY18C6 > phenylaza-15C5 > benzo-15C5 > 4-nitrobenzo-15C5. The obtained results in particular stability constant of complexes of DBPY18C6, phenylaza-15C5 and 4-nitrobenzo-15C5 with sodium ion in comparison with other crowns ether are novel, and interesting.     

An NMR study of the stoichiometry and stability of lithium ion complexes with 12-crown-4, 15-crown-5 an 18-crown-6 in binary Acetonitrile-Nitrobenzene mixtures

Proton NMR spectroscopy was used to study the complexation reaction between lithium ion and 12-crown-4, 15-crown-5 and 18-crown-6 in a number of binary acetonitrile-nitrobenzene mixtures. In all cases the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average¹H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of acetonitrile in the mixed solvent. It was found that, in all solvent mixtures used, 15-crown-5 forms the most stable complex with Li⁺ ion in the series.     

Effect of the 18-crown-6 and benzo-18-crown-6 on the solvent extraction and separation of lanthanide(III) ions with 8-hydroxyquinoline

The synergistic solvent extraction of 13 lanthanides with mixtures of 8-hydroxyquinoline (HQ) and the crown ethers (S) 18-crown-6 (18C6) or benzo-18-crown-6 (B18C6) in 1,2-dichloroethane has been studied. The composition of the extracted species has been determined as LnQ₃ · S. The values of the equilibrium constant and separation factor have been calculated. Here, the effect of the synergistic agent (18C6 or B18C6) on the extraction process is discussed.     

Structures of 18-crown-6, 15-crown-5 and their metal complexes in methanol solution as studied by Raman spectroscopy

Raman spectra of 18-crown-6, 15-crown-5, and their complexes with Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺ and Ba²⁺ have been investigated in methanol solution. Normal coordinate calculations are presented for the D_3d⁻ and C_i-symmetric structures of 18-crown-6. Analysis of the Raman spectra gives information on the ring conformations of the crown ethers and the stoichiometry of complexation. The uncomplexed ethers adopt diverse conformational states in methanol at room temperature, the D_3d state being the most stable in 18-crown-6 and various states equally stable in 15-crown-5. Most of the cations form 1:1 or 2:1 crown—metal complexes depending on the cation size relative to the hole size of crown. Exceptionally, Cs⁺ forms both 1:1 and 2:1 complexes with 18-crown-6. The ring structures in complexes of 18-crown-6 are not much distorted from the D_3d one, though the distortion is rather large in the 2:1 Cs²⁺ and 1:1 Ca⁺ complexes. Complexes of 15-crown-5 exhibit for types of ring structure depending on the size and charge of the cation. These structures are likely to involve distortion from the gauche or gauche′ conformation about the CC bonds and various conformation about the CO bonds.     

Temperature study of the intramolecular interactions in 15-crown-5 and 18-crown-6

The Raman CH stretching spectra of 15-crown-5 and 18-crown-6 in water solution are studied in the temperature interval 5–80°C. The method of Fourier deconvolution is applied to resolve the overlapped bands in the complex isotropic and anisotropic spectra. The intramolecular coupling constants and the unperturbed CH stretching frequency are calculated for all studied temperatures. The temperature dependencies are discussed in comparison with the temperature dependencies for 12-crown-4 obtained previously.     

Solvent extraction of strontium picrate from water into nitrobenzene in the presence of benzo-15-crown-5

From extraction experiments with 85Sr as a tracer, the extraction constant corresponding to the equilibrium Sr²⁺(aq) + 2A^- (aq) + 2L (nb) Û SrL₂ ^,2+ (nb) 2A^- (nb) in the two-phase water-nitrobenzene system (A^- = picrate, L = benzo-15-crown-5; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex     

Electrochemical study of 18-crown-6-Tl+ complexes in binary solvent mixtures

Summary The formation constants,K _S, of the 18-crown-6 complex with thallium(I) ion were studied by polarographic measurements in binary mixtures of acetonitrile, acetone, tetrahydrofuran, and dimethylsulfoxide with water, as a function of the solvent mole fraction. In all the cases, the variation of the stability constant can be described by the empirical relation logK _S=a[(–1)/(2+1)]+b where stands for relative permittivity of a given mixture anda andb mark the regression coefficients. The values ofa calculated for four series of binary mixtures showed correlation with the Gutmann donor numbers of the neat organic solvents which form the mixture.On leave from the Department of Chemistry, Jingzhou Teacher's College, Jingzhou, Hubei, China     

Spectrophotometric study of interaction of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone with diaza-18-crown-6 and diaza-15-crown-5 in acetonitrile and chloroform solutions

Interactions of diaza-18-crown-6 and diaza-15-crown-5, as electron donors, with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), as an electron acceptor, have been investigated spectrophotometrically in acetonitrile and chloroform solutions. The results indicated immediate formation of an electron donor-electron acceptor complex DA: [reaction in text] which is followed by two relatively slow consecutive reactions: [reaction in text]. The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance time data to appropriate equations. The formation constants of the resulting DA complexes have also been determined. The influences of both the azacrown's structure and the solvent properties on the formation of DA complexes and the rates of subsequent reactions are discussed.     

The solvent extraction of alkali metal picrates with 4,13-N,N'-dibenzyl-4,13-diaza-18-crown-6

Extraction of alkali metal picrates with N,N'-dibenzyl-18-crown-6 was carried out, with dichloromethane as water-immiscible solvent, as a function [ligand]/[metal cation]. The extractability of metal picrates (Li(+), Na(+), K(+), Rb(+), Cs(+)) was evaluated as a function of [L]/[M(+)]. The extractability of complex cation-picrate ion pairs decreases in this sequence: Li(+)>Rb(+)>Cs(+)>K(+)>Na(+). The overall extraction equilibrium constants (K(ex)) for complexes of N,N'-dibenzyl-18-crown-6 with alkali metal picrates between dichloromethane and water have been determined at 25 degrees C. The values of the extraction constants (logK(ex)) were determined to be 10.05, 6.83, 7.12, 7.83, 6.73 for Li(+), Na(+), K(+), Rb(+) and Cs(+) compounds, respectively. DB186 shows almost 2-fold extractability against Li(+) compared to the other metal picrates, whereas it shows no obvious extractability difference amongst the other metal cations when [L]/[M(+)] is 0.2-1. However, an increasing extractability is observed for Cs(+) when [L]/[M(+)] [1].     

二环己基-18-冠-6异构体A与铀的萃取配合物的结构研究

二环己基-18-冠-6-异构体Δ(dcc)在盐酸体系中萃取UO2Cl2和UCl4时, 形成的配合物晶体的组成分别为(C20H36O6.H3O)2UO2Cl4.2C6H6(1)和(C20H36O6.H3O)2UCl6(2). 结构分析证实, 在1和2中, U(VI)和U(IV)均未与冠醚直接配位, 而是分别形成配阴离子四氯铀铣(II)和六氯化铀(II). 而配阳离子均由冠醚环的三个氧原子与H3^+O以较强的氢键键合, 将H3O^+稳定于冠醚环中, 成为配阳离子dcc.H3O^+. 由静电吸收及Van der Waals力形成稳定的晶体.     

Synergistic extraction of uranyl ion with acylpyrazolones and dicyclohexano-18-crown-6

Synergistic extraction of uranyl ion with acylpyrazolones such as 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5 (HPMTFP, pKa=2.7), 1-phenyl-3-methyl-4-acetylpyrazolone (HPMAP, pKa=3.8) or 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (HPMBP, pKa=4.2) in combination with dicyclohexano-18-crown-6 (DC-18-C6) has been studied at various fixed temperatures. The results indicate that the equilibrium constants of the organic phase addition reaction, log Ks, at 30°C are almost constant, viz., 2.72, 2.69 and 2.84, respectively, for the above three systems. The similarity and low log Ks values with DC-18-C6 as compared with TBP systems with these pyrazolones appears to arise due to the limitation to the approach of the large crown ether molecule in bonding with the uranyl chelate. This is in contrast to the fact that the relative basicities of the two donors (equilibrium constant for nitric acid uptake) are comparable. Thermodynamic data for chelate extraction with HPMTFP evaluated by the temperature coefficient method indicates that a hydrated chelate is extracted into the organic phase. Also, the organic phase addition reaction with DC-18-C6 is stabilized by exothermic enthalpy change, the entropy change counteracting in all the three cases.     

Synthesis of bis-benzo-15-crown-5 and bis-benzo-18-crown-6-ethers

Bis-crown ethers with benzo-15-crown-5 and benzo-18-crown-6 moieties bridged by different length of polyethylene ethers have been successfully synthesized.