Synergistic extraction of americium(III) with 2-thenoyltrifluoroacetone and crown ethers

Extracton, of Am³⁺ in benzene with 2-thenoyltrifluoroacetone (HTTA) and crown ethers (CEs) such as 15-crown-5, 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, dicyclohexano-24-crown-8, and dibenzo-24-crown-8 was investigated. Synergistic effect by CE was observed regardless of the kind of CE examined. The extracted species was found to be Am(TTA)₃(CE), and adduct formation constants between Am(TTA)₃ and CE in the organic phase were determined. The sequence of constant could not be explained only by basicity of CE and the steric effect of CE should be taken into account to elucidate the adduct complex formation.     

Ion-pair extraction of tetravalent plutonium from hydrochloric acid medium using crown ethers

Ion-pair extraction behaviour of plutonium (IV) from varying concentrations of HCl solution was studied employing crown ethers (benzo-l5-crown-5 (B15C5), 18-crown-6, (18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6, (DC18C6), dibenzo-24-crown-8 (DB24C8) and dicyclohexano-24-crown-8 (DCH24C8)) in nitrobenzene as the extractant. Ammonium metavanidate was used as the holding oxidant in the aqueous phase and the conditions necessary for the quantitative extraction of the tetravalent ion were found. The co-extraction of species of the type [HL⁺].[HPu(Cl) ₆ ^– ] and [HL⁺]2·[Pu(Cl) ₆ ^2– ] as ion-pairs (where L represents the crown ether) is suggested.     

Development of a dispersive liquid–liquid microextraction method for determination of palladium in water samples using dicyclohexano-18- crown-6 as extracting agent

A new separation procedure for determination of palladium using dispersive liquid–liquid microextraction with dicyclohexano-18-crown-6 as complexing reagent was developed. In this method, potassium–dicyclohexano-18-crown-6 was used as a hydrophobic complex for the microextraction of palladium as PdCl₄ ^2? complex ion. The main factors affecting DLLME efficiency, such as type and volume of extractant and disperser solvent, concentration of chelating reagent, concentration of KCl and pH were optimized. Under the optimal conditions, the limit of detection for palladium was 16.0 ng mL^?1 with enrichment factor of 138. The present method was applied to the determination of palladium in water samples with satisfactory analytical results. The method was simple, rapid, cost efficient and sensitive for the extraction and preconcentration of palladium.     

Conductance Study of the Thermodynamics of Tl+ ion Complexes with Different 18-Membered Crown Ethers in Binary Dimethylformamide-Acetonitrile Mixtures

A conductance study of the interactionbetween Tl⁺ ion and 18-crown-6 (18C6),dicyclohexano-18-crown-6 (DC18C6), benzo-18-crown-6(B18C6), diaza-18-crown-6 (DA18C6),dibenzyldiaza-18-crown-6 (DBzDA18C6) andhexaaza-18-crown-6 (HA18C6) indimethylformamide-acetonitrile mixtures was carriedout at various temperatures. The formation constantsof the resulting 1 : 1 complexes were determined fromthe molar conductance-mole ratio data and found tovary in the order HA18C6 > DA18C6 > DBzDA18C6 >18C6 > DC18C6 > B18C6. The enthalpy and entropy ofthe complexation reactions were determined from thetemperature dependence of the formation constants.     

Lithium-7 NMR Study of Several Li+-Crown Ether Complexes in Binary Acetone-Nitrobenzene Mixtures

⁷Li NMR measurements were employed to monitor the stoichiometry andstability of Li⁺ ion complexes with 12-crown-4 (12C4), 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) l8-crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-18-crown-6 (DB18C6) in binary acetone-nitrobenzene mixtures of varying composition. In all cases studied, the variation of ⁷Li chemical shift with the crown/Li⁺ mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all solvent mixtures used, the stabilities of the resulting 1:1 complexes varied in the order15C5 > B15C5 > DC18C6 > 18C6 > 12C4 >DB18C6. It was found that,in the case of all complexes, an increase in the percentage of acetone in thesolvent mixtures significantly decreased the stability of the complexes.     

Dediazoniations of Arenediazonium Ions. Part XXI. Dediazoniation of Arenediazonium Ions Complexed with Crown Ethers

The evaluation of the dediazoniation kinetics of various m- and p-substituted benzenediazonium tetrafluoroborates in 1,2-dichloroethane at 50° in the presence of 18-crown-6, 21-crown-7 and dicyclohexano-24-crown-8 demonstrates that the rate constant for the dediazoniation within the complex (k₂) is smallest, and the equilibrium constant for complex formation (K) is largest for the complexes with 21-crown-7 (cf. Scheme 1). The logarithms of the equilibrium constants (K) for complex formation with each of the crown ethers studied correlate well with Hammett's substituent constants, σ, to give reaction constants ρ = 1.18–1.38. A linear correlation between the logarithms of the rate constants for the dediazoniation within the complex with those of the dediazoniation rate constants of uncomplexed diazonium ions (log k₂ vs. log.k₁), found for most substituted diazonium salts, indicates that the dediazoniation mechanism of the complexed diazonium ions is not significantly different from that of the free ions. For very electrophilic diazonium ions (p-Cl, m-CN), k₂ was much larger than expected on the basis of the linear log k₂ vs. log k₁ relationship. Analysis of the dediazoniation products showed that this was due to a change in mechanism from heterolytic to homolytic dediazoniation. The complexation rate of diazonium salts by crown ethers (k_c) is practically diffusion controlled and does not change much with the size of the crown ether. The decomplexation rate (k_d), however, is significantly lower for complexes with 21-crown-7, than for those with 18-crown-6 and dicyclohexano-24-crown-8, and is therefore the reason for the variations in the equilibrium constant (K) and thus for the fact that complexes of arenediazonium salts with 21-crown-7 are the most stable. The amounts of the N_α-N_β rearrangement, as well as those of the exchange of the ¹⁵N-labelled diazonio group with external nitrogen during dediazoniation of p-toluenediazonium salt were independent of the addition of crown ethers. A dediazoniation mechanism involving a charge transfer, as well as an insertion-type diazonium ion-crown ether complex is proposed. In this mechanism, dediazoniation of the insertion complex does not take place directly, but through the charge-transfer complex.     

Radiation-chemical synthesis of crown-containing poly(ethylene oxide) hydrogels. Swelling behavior and crown ether retention

Poly(ethylene oxide) hydrogels containing physically immobilized dicyclohexano-18-crown-6 (DCH18C6) were synthesized by radiation-chemical cross-linking. DCH18C6 concentration in initial polymer solution has insignificant effect on the gelation dose at the weight ratio of crown ether to polymer lower than 0.2. The higher molecular weight of PEO results in lower gelation dose and higher gel fraction. An increase in absorbed dose leads to a noticeable decrease in the swelling ratio corresponding to a denser hydrogel network. At the same time the absorbed dose in the range of 5–100 kGy has no pronounced effect on the DCH18C6 retention.     

NMR Spectra of Guest–Host Complexes of Boron and Silicon Fluorides with Crown Ethers in Nonaqueous Solutions

¹⁹F, ¹¹B, and ²⁹Si NMR spectroscopy was used to examine the behavior of the guest–host complexes (BF₃· H₂O)₂· 18-crown-6 · 2H₂O, (BF₃· H₂O)₂· DCH-6B, and (DCH-6A · H₃O)SiF₅in acetone (DCH-6B and DCH-6A are the cis-anti-cis- and cis-syn-cis-isomers of dicyclohexano-18-crown-6, respectively). It was shown that molecular boron fluoride complexes undergo partial solvolysis in acetone to yield BF₃· acetone as the main product; the ionic pentafluorosilicate complex does not experience significant solvolysis transformations.     

Studies of Activity Coefficients for Ternary Systems: Water + 18-Crown-6 + Alkali Chlorides at 298.15 K

Osmotic vapor pressure measurements have been carried out for three ternary systems, H₂O + 0.2 m 18-crown-6 + LiCl, H₂O + 0.2 m 18-crown-6 + NaCl and H₂O + 0.2 m 18-crown-6 + KCl at 298.15 K using vapor pressure osmometry. Water activities for each ternary system were measured and used to calculate the activity coefficients of 18-crown-6 (18C6) and its salts following the methodology developed by Robinson and Stokes for isopiestic measurements. In the concentration range studied, it was found that (in NaCl and KCl solutions) there is considerable lowering of activity coefficients of one component in the presence of other solutes that has been attributed to the formation of the complexed 18C6:Na⁺ (or 18C6:K⁺) species in solution. The Gibbs energies of transfer of alkali chlorides from water to aqueous 18C6 solutions and that of 18C6 from water to aqueous electrolyte solutions have been calculated. These were further used to evaluate the pair and triplet interaction parameters. The calculation of thermodynamic equilibrium constants using the pair interaction parameter, g _NE (i.e., the nonelectrolyte–electrolyte pair interaction) for the studied complexation of cations yields values which are in good agreement with those reported in literature obtained by using ion-selective potentiometry and calorimetry. The results are discussed in terms of water structural effects, complex formation, and hydrophobic interactions.     

Preparation and X-Ray Study of Inclusion Complexes of (4Z,5E)-Pyrimidine-2,4,5,6(1 H,3H)-Tetraone 4,5-Dioxime and the Product of Its Cyclization, (1,2,5)-Oxadiazolo(3,4-d)-Pyrimidine-5,7(4 H,6H)-Dione with Two 18-Membered Macrocycles

The novel dioxime, (4Z,5E)-pyrimidine-2,4,5,6(1H,3H)-tetraone 4,5-dioxime (H₂-PTD) was obtained by the interaction of 6-amino-5-nitrosopyrimidine-2,4(1H,3H)-dione with hydroxylamine hydrochloride. X-ray structural analysis determined the 4Z,5E-configuration of the corresponding monoanion, pyrimidine-2,6(1H,3H)-dione-4-iminole-5-iminolate in the inclusion complexes with diazonia-18-crown-6 (1,4,10,13-tetraoxa-7,16-diazoniacyclooctadecane) (H₂-DA18C6)²⁺ (complex (1), stoichiometry 2 : 1), and its ammonium salt in the complex with the cis-syn-cis isomer of dicyclohexano-18-crown-6(DCHA) (cis-syn-cis-2,5,8,15,18,21-hexaoxatricyclo (20.4.0.0^9,14)hexacosane) (complex (2), stoichiometry 1 : 1). X-ray data were also obtained for the complex of the product of (H₂-PTD) cyclization, (1,2,5)-oxadiazolo(3,4-d)pyrimidine-5,7(4H,6H)-dione (OPD) with diaqua diaza-18-crown-6 (complex (3), stoichiometry 2 : 2 : 1).In (1) the (H-PTD)^- anions are joined into dimers through the bifurcated OH...N and OH...O hydrogen bonds and alternate with diazonia-18-crown-6 cations in the chains sustained by the NH(crown) ... O and NH(crown) ...N interactions. The chains are further combined into the 3D network via NH...O(crown) hydrogen bonds. In (2) the self-complementarity of the (H-PTD)^- anions facilitates their assembly into the chain via OH...N, NH...O and OH...O interactions. The ammonium cations bridge each anion and the DCHA macrocycle with the formation of a ribbon developed along the [101] direction in the unit cell. Ternary complex (3) is built of the neutral species, diaza-18-crown-6, water molecules and dimers of OPD alternated in the chains and held together by OH...O and NH...O hydrogen bonds.     

PVC-based dicyclohexano-18-crown-6 sensor for La(III) ions

A new ion-selective electrode (ISE) based on dicyclohexano-18-crown-6 (DC18C6) as a neutral carrier is developed for lanthanum(III) ions. The electrode comprises of dicyclohexano-18-crown-6 (6%), PVC (33%), and ortho-nitrophenyl octyl ether (o-NPOE) (61%). The electrode shows a linear dynamic response in the concentration range of 10⁻⁶ to 10⁻¹ M with a Nernstian slope of 19 mV per decade and a detection limit as 5×10⁻⁷ M. It has a response time of <30 s and can be used for at least 5 months without any significant divergence in potentials. The selectivity coefficients for mono-, di-, and trivalent cations indicate good selectivity for La(III) ions over a large number of interfering cations. The sensor has been used as an indicator electrode in the potentiometric titrations of La(III) with EDTA. The membrane is successfully applied in partially non-aqueous medium. It can be used in the pH range 4-9.     

Conductance Study of Complexation of Lead Ions by Several 18-Membered Crown Ethers in Acetonitrile-Dimethyl Sulfoxide Mixtures Between 25 and 55°C

A conductance study of the interaction between Pb²⁺ ion and 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexyl-18-crown-6 (DC18C6), aza-18-crown-6 (A18C6), diaza-18-crown-6 (DAI8C6), dibenzopyridino-18-crown-6 (DBPy18C6), and dibenzyldiaza-18-crown-6 (DBzDA18C6) in acetonitrile–dimethyl sulfoxide mixtures was carried out at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance–mole ratio data and found to vary in the order DA18C6 > A18C6 > DBzDA18C6 > DC18C6 > 18C6 > B18C6 > DBPy18C6. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the resulting complexes are enthalpy stabilized, but entropy destabilized. A linear relationship is observed between log K _f of different complexes and mole fraction of acetonitrile in the solvent mixtures. The TS ⁰ vs. H ⁰ plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of an enthalpy–entropy compensation in the complexation reactions.     

New concept for the preparation of potassium sodides: the use of hexane as a non-polar solvent

NaK alloy in contact with 15-crown-5 hexane solution became potassium sodide K⁺(15-crown-5)₂Na⁻. After the evaporation of hexane the crystalline solid product was analyzed by X-ray diffraction and the lattice parameters were calculated. The potassium sodide thus obtained could be easily dissolved in tetrahydrofuran. A deep blue solution containing sodium anions and complexed potassium cations was formed with a very low concentration of solvated electrons, i.e. of the order of 10⁻⁷ M. Potassium anions were not detected in this case. A new crystalline potassium sodide K⁺(DCH-24-crown-8)₂Na⁻ was obtained using NaK alloy and dicyclohexano-24-crown-8 hexane solution.     

Separation of rhenium by extraction with crown ethers and flow-injection extraction—spectrophotometric determination with Brilliant Green

The extraction behavior of perrhenate with crown ethers was studied and methods for the separation and determination of rhenium were developed. The distribution ratio of perrhenate with dicyclohexano-18-crown-6 (DC18C6) increases with increases in the dielectric constant of organic solvents and in the potassium ion concentration of aqueous solution. The molar ratios of crown ether to KReO₄ in the extracted species are probably 1:1 for DC18C6, dibenzo-18-crown-6 and 18-crown-6 and 2:1 for benzo-15-crown-5 and 15-crown-5. Microgram amounts of rhenium were satisfactorily separated from large amounts of molbdenum(VI) by extraction with DC18C6 in 1,2-dichloroethane from 2 M potassium hydroxide solution containing tartrate and by back-extraction with sodium phosphate buffer solution after the addition of a twofold volume of hexane to the organic phase. Rhenium was determined by the flow-injection extraction-photometric method with Brilliant Green. Rhenium was satisfactory determined in molybdenite and other ore samples.     

Preconcentration of uranium(VI) by solid phase extraction onto dicyclohexano-18-crown-6 embedded benzophenone

Summary The preparation of a solid phase extractant (SPE), dicyclohexano-18-crown-6 embedded benzophenone, for preconcentration of uranium(VI) is described. The uranium(VI) can be quantitatively retained from 0.5 l solution on 1% dicyclohexano-18-crown-6 embedded benzophenone in the pH range 6.0-7.0, and then eluted with 5.0 ml of 1M HCl. Uranium(VI) content of the eluent was determined spectrophotometrically by Arsenazo III. Calibration graphs are rectilinear over the uranium(VI) concentration in the range of 0.004-0.4mg^.ml^-1. Five replicate determinations of 40mg of uranium(VI) present in 0.5 l sample gave a mean absorbance of 0.185 with a relative standard deviation of 2.45%. The detection limit corresponding to three times the standard deviation of the blank was found to be 2.0mg^.l^-1. The accuracy of the developed preconcentration procedure was tested by analyzing standard marine sediment reference material. The uranyl ion content of soils and sediments was estimated spectrophotometrically after the preconcentration procedure and compared to the results gained by standard inductively coupled plasma mass spectrometry (ICP-MS).     

Electrochemical behavior of nicotinamide using carbon paste electrode modified with macrocyclic compounds

The electrochemical behavior of nicotinamide was studied at a carbon paste electrode and the electrodes modified with macrocyclic compounds using voltammetric and impedance measurements. The electrodes so formed were able to bind nicotinamide ions chemically and gave better voltammetric responses than the unmodified ones. The macrocycles used as modifiers for the electrode preparation were 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, 1,4,7,10,13,16-hexathiacyclooctadecane (Hexathia), 1,4,7,10-tetratosyl-1,4,7,10-tetraazacyclododecane, 1,4,8,11-tetraazacyclooctadecane, c-Methylcalix[4]resorcenarene and calix[8]arene. Among these macrocyclic modified electrodes, hexathia showed more affinity towards nicotinamide and a 2.3-fold increase in voltammetric signal was obtained. Impedance measurement was used to confirm this enhancement observed on modified electrode. This increase in anodic peak current was then used for finding linear working range, which was 0.1–500 μg mL⁻¹ with a detection limit of 0.03 μg mL⁻¹ by DPV. Interference from other vitamins like thiamine HCl (Vit. B₁), riboflavin (Vit. B₂), pyridoxine HCl (Vit. B₆) cynocobamine (Vit. B₁₂), para-aminobenzoic acid (PABA) and ascorbic acid (Vit. C) was also studied. The modified electrode could be used for the simultaneous determination of riboflavin, nicotinamide and pyridoxine HCl. It has also been utilized for the analysis of nicotinamide in pharmaceutical preparations.     

Extraction of tetrafluoroborate with crown ethers and its application to silicate rock analysis

Summary The extraction behaviour of tetrafluoroborate with crown ethers was studied. A high distribution ratio of tetrafluoroborate is obtained by extraction with dicyclohexano-18-crown-6 (DC18C6) in an organic solvent of high dielectric constant from potassium fluoride solution. The molar ratios of crown ether to KBF₄ in the extracted species are probably 1:1 for DC18C6, dibenzo-18-crown-6 and 18-crown-6, and 2:1 for benzo-15-crown-5 and 15-crown-5. The flow-injection extraction-spectrophotometric determination of tetrafluoroborate with Brilliant Green was worked out. Many rock reference samples were analyzed for boron (1–150 ppm).     

<Superscript>133</Superscript>Cs NMR Study of Cs<Superscript>+</Superscript> Ion Complexes with Dibenzo-24-crown-8, Dicyclohexano-24-crown-8 and Dibenzo-30-crown-10 in Binary Acetonitrile-Nitromethane Mixtures

Complexation of the cesium ion with the macrocyclic ligands: dibenzo-24-crown-8 (DB24C8), dicyclohexano-24-crown-8 (DC24C8) and dibenzo-30-crown-10 (DB30C10) was studied in binary acetonitrile-nitromethane mixtures by ¹³³Cs NMR spectroscopy. The ¹³³Cs chemical shift data indicated that the cesium cation forms 1:1 cation:ligand complexes with DB24C8 and DB30C10 but forms 2:1, 1:1 and 1:2 cation:ligand complexes with DC24C8 in acetonitrile-nitromethane mixtures. The formation constants of the complexes were calculated from the computer fitting of the chemical shift mole ratio data. The results show that the complex formation constants with the Cs⁺ cation vary in the order DC24C8>DB24C8∼DB30C10. It was found that the stability of the resulting complexes increases with increasing nitromethane concentration in the solvent mixture.     

Separation of strontium from nuclear waste solutions by solvent extraction with crown ethers

The possibilities of strontium separation from medium activity waste (MAW) solutions have been investigated. MAW originates from the PUREX process and contains NaNO₃ and HNO₃ in a large excess. By solvent extraction with the crown ether dicyclohexano-18-crown-6 (DC-18-C-6) in 1,1,2,2-tetrachloroethane, separation is possible. The distribution ratio for Sr²⁺ depends on the concentration of HNO₃, NaNO₃ and Pb(NO₃)₂. The extraction system is employed in a continuous counter-current process. After use, the extraction agent can easily be regenerated by reextraction with pure water.     

Equilibrium Constant Studies for Complexation between Ammonium Ions and 18-Crown-6 in Aqueous Solutions at 298.15 K

Osmotic vapor pressure and density measurements have been carried out for binary aqueous and ternary aqueous solutions containing a fixed concentration of 18-crown-6 (0.2 mol⋅kg⁻¹) and ammonium chloride or ammonium bromide at 298.15 K. The concentration of the ammonium salts was varied between 0.02 to 0.5 mol⋅kg⁻¹. The measured water activities were used to obtain the activity coefficient of water and the mean molal activity coefficient of the ions in binary as well as ternary solutions. Using the method developed by Patil and Dagade reported earlier in this journal and the McMillan-Meyer pair and triplet Gibbs energy interaction parameters, the thermodynamic equilibrium constant (K) for the 18-crown-6:NH₄ ⁺ complexes were determined. It is observed that the nature and polarizability of anions play important roles in imparting stability to the complexed species. The log₁₀ K values for the 18-crown-6:NH₄ ⁺ complexed species are lower than for the complexes involving alkali metal ions such as K⁺. The volume of complexation for the studied systems obtained from the apparent molar volumes of ammonium halides in ternary solutions are positive and of smaller magnitude than those reported for complexation with alkali ions. The results are further discussed in terms of water structural effects, complex formation, the role of counter anions and hydrophobic interactions.