Crown Ether Solutions Research Articles

Role of anions in radiation-induced transformations of 18-crown-6 complexes with barium salts: simulating the effects of extraction mechanism on radiation stability of macrocyclic extractants

Complexes of 18-crown-6 with BaCl2, Ba(NO3)2 and Ba(NTf2)2 salts were synthesized and irradiated with X-rays to simulate the radiation degradation of a macrocyclic component of extractants based on crown ether solutions in commonly used solvents. Structures and post-irradiation transformations of radical products stabilized in these complexes at 77 K were studied using EPR spectroscopy, and the mechanism of their formation and decay was proposed. Differences in ionization potentials of the macrocycle and the anions and reactivity of the intermediates generated from the anions are of importance for radiation stability of the studied compounds. The nitrate-anions was demonstrated to protect 18C6 from destruction whereas Cl− and bis(trifluoromethylsulfonyl)imide-anions can impair the radiation stability of the macrocycle. The results of the present study offer an opportunity to predict the radiation stability of the crown ether extractants and their applicability for liquid radioactive waste reprocessing.

Extraction of cesium by crown ethers in the presence of activating additives

Extraction of cesium by solutions of crown ethers in organic solvents from neutral and acidic solutions in the presence of various activating additives was studied. The highest distribution coefficients of cesium (DCs) are observed for the extraction from neutral solutions using a new additive of lithium bis(trifluoromethylsulfonyl)imide. The influence of the crown ether structure, solvent type, acid type and concentration, and amount of activating additive on DCs was studied.

Liquid–liquid extraction and quantitative determination of tungsten(VI) using macrocyclic reagent (DB-18-C-6) as a thiocyanate complex [WO (SCN)5]2−

In recent years, the extraction using crown ethers has reached a resounding success in different scientific and technical fields. In this work, the authors report the results of the main steps of extraction and determination (proportioning) of the tungsten ion (VI) using a chloroformed solution of crown ether. The dibenzo–18–C-6(2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadeca-2,11-diene according to the IUPAC systematic nomenclature). The identification and quantification of W(VI) using the absorption spectrum, the influence of the necessary reagents, the needed acidity level for complete extraction and complexation of W(VI) using a crown ether, and the influence of multivalent metal ions were examined, considering that the sensitivity, selectivity, and detection limits have been determined. This system obeys Beer’s law in the range of 0.18–18.3 μg cm−3of tungsten with a molar absorption of 1.6 × 104 mol−1 cm−1 at 415nm and the detection, quantification limits were, respectively, equal to 0.7–1.8 μg cm−3. The developed method was applied for the extraction of W(VI) in the high speed steel (HSS): HS2–9-1–8 containing 2% W, 9% Mo, 1% V, and 8% Co.

Chiral separation of amino-alcohols using extractant impregnated resins

The performance of extractant impregnated resin (EIR) technology for chiral separation of amino-alcohols has been investigated. Phenylglycinol was selected as an archetype model enantiomer and azophenolic crown ether was used as a versatile enantioselective extractant. 1-Phenyloctane was selected as a suitable solvent for this application because of its very low solubility in water. The extraction system was first evaluated by liquid–liquid equilibrium experiments. It was shown that crown ether dissolved in 1-phenyloctane has an intrinsic selectivity of 11.5. However, due to very low solubility of phenylglycinol in 1-phenyloctane, the overall capacity of the crown ether solution in 1-phenyloctane is limited. The extractant solution was immobilized in macroporous polypropylene particles. Competitive sorption isotherms were obtained from batch experiments and successfully described with a predictive model based on the complexation constants and partitioning ratios, either obtained from literature or from independent experiments. The equilibrium selectivity of these EIRs approaches the intrinsic selectivity for low phenylglycinol concentrations. The dynamic behaviour and stability of the system were examined in column experiments. Breakthrough profiles as well as the elution curves of the R enantiomer are less sharp than those of the S enantiomer proving that the R enantiomer is strongly retained on the column. Separation of phenylglycinol enantiomers is favoured by using lower feed flow rates. The column was regenerated by water with only atmospheric carbon dioxide dissolved which proved to be sufficient. After several cycles the breakthrough profiles remain unchanged suggesting that these EIRs will be sufficiently stable.

Selective Interactions of Crown Ethers with Fluosilicic Complex Acids

.One of priority goals of supramolecular chemistryis revealing selective interactions of crown ethers( hosts ) with guest species, resulting in stabiliza-tion of unstable guest species in the form of stablecrystalline inclusion compounds [7, 8]. In this connec-tion, we examined the possibility of selective syn-thesis of crystalline supramolecular complexes ofcrown ethers with fluosilicic complex acids from solu-tions of crown ethers in aqueous HF under the condi-tions of spontaneous formation of fluosilicic acid.We found that evaporation of solutions of 1,4,7,-10,13,16-hexaoxacyclooctadecane (18C6) and

Complex formation of crown ethers with cations in the water-organic solvent mixtures. Part V. Thermodynamic of interactions of Na + ion with 15-crown-5-ether in the mixtures of water with N,N-dimethylformamide at 298.15 K

The equilibrium constants of complex formation of 15-crown-5-ether with sodium iodide have been determined by conductivity measurements in the mixtures of water with N,N-dimethylformamide-water-sodium iodide system have been measured at 298.15 K. The N,N-dimethylformamide at 298.15 K. Standard enthalpies of solution of crown ether in the thermodynamic functions of complex formation of 15-crown-5-ether with sodium iodide are discussed. The complex formation in this mixed solvent depends on the enthalpic effect. The linear enthalpy-entropy relationship for complex formation is presented. The transfer enthalpy of the complex from pure N,N-dimethylformamide to the examined mixtures were calculated and discussed.

Thermodynamics of interactions of Na + ion with 15-crown-5 ether in the mixtures of water with dimethylsulfoxide at 298.15 K

Standard enthalpies of solution of crown ether (15-crown-5 ether) in the dimethylsulfoxide-water-sodium iodide system have been measured at 298.15 K. The equilibrium constants of complex formation of 15-crown-5 with sodium iodide have been determined by the 13C NMR chemical shift of 15-crown-5 ether and by conductivity measurements at various molar ratios of 15-crown-5 ether and sodium iodide in the mixtures of water with dimethylsulfoxide at 298.15 K. The thermodynamic functions of 15-crown-5 ether complex formation with sodium iodide were calculated. The linear enthalpy-entropy relationship for complex formation was discussed. The enthalpies of transfer of the complex from pure dimethylsulfoxide to the examined mixtures were calculated and discussed.

Complexes of Crown Ethers with Diaminomaleodinitrile

1,2-Diaminomaleodinitrile (HCN tetramer) is usu-ally considered as one of the key steps of chemicalevolution [1 4] on the pathway of transformation ofhydrogen cyanide into amino acids and heterocycles[4 6]. According to [7, 8], in simulation of biochem-ical processes, it is important to reveal noncovalentinteractions of relatively small molecules with cavity-containing structures, in particular, with crown ethers.The goal of this work was to examine the possibil-ity of preparing crystalline molecular complexes ofcrown ethers with 1,2-diaminomaleodinitrile and toreveal the selectivity of such host guest interactions.We found that spontaneous evaporation of solventsfrom solutions of crown ethers [benzo-15-crown-5,I;18-crown-6,II; benzo-18-crown-6,III; mixture ofcis,syn,cis (IV) and cis,anti,cis (V) isomers of dicyclo-hexano-18-crown-6] with 1,2-diaminomaleodinitrileVI results in crystalllization of molecular complexesVII X.

The studies of viscosity behaviour in aqueous 18-crown-6 solutions at 25°C

Abstract The viscosities of aqueous solutions of 18-crown-6 (0.04 – 0.24 M) have been measured at 25°C. The relative viscosities, in the studied concentration range, can be fitted well with the relation η = 1 + Bc + Dc2. The viscosity B-coefficient and D-coefficient are found to be high when compared with those reported for other simple non-electrolyte solutes. These results are interpreted in terms of hydrophobic hydration and occupation of crown ether cavities by water molecules, leading to the formation of a spherical entity (brownon), slipping through the hydrophobic hydration sheath. The analysis of the data shows that ⋍ 5 water molecules are embedded in the crown ether cavity. The structural interactions may involve stacking type equilibria stabilized by co-operative interactions amongst the water molecules in the cavity of one crown ether molecule with those of the other crown ether molecule. Preliminary results of the viscosity measurements of the 0.24 M aqueous 18C6 solutions involving varied amounts of the salt, KBr are also reported. The viscosity B-coefficient for KBr in aqueous crown ether solutions is found to be almost similar to that found in the aqueous solutions. However, the A-coefficient (a measure of ion-ion interactions) cannot be interpreted unambiguously.

Crown ether activation of cross-linked subtilisin Carlsberg crystals in organic solvents

The activity of cross-linked subtilisin Carlsberg crystals in the catalysis of peptide bond formation can be significantly enhanced by pretreatment of the enzyme crystals with crown ethers. Soaking of the enzyme crystals in a solution of crown ether in acetonitrile followed by evaporation of the solvent results in an up to 13 times enhanced enzymatic activity. The effects of crown ether treatment under various conditions gives support for the hypothesis that removal of bound water molecules from the active site during the drying process is the origin of the observed enzyme activation.

RING-SIZE AND SUBSTTTUENT EFFECTS IN THE SOLVENT EXTRACTION OF ALKALI METAL NITRATES BY CROWN ETHERS IN 1,2-DICHLOROETHANE AND 1 -OCTANOL

ABSTRACT The extraction of alkali metal nitrate salts by solutions of crown ethers in each of the two diluents 1,2-dichlorethane and 1-octanol has been surveyed. The crown ethers include 18-crown-6, 21-crown-7, and 24-crown-8 ethers bearing cyclohexano, benzo, t-alkylbenzo, and/or furano substitutents. The extraction efficiencies of the different crown ethers are examined in terms of ring-size, substituent, and solvent effects. Partition ratios for the crown ethers between water and either 1,2-dichloroethane or 1-octanol are discussed. The extraction selectivities, expressed as the separation factor for cesium over sodium, are examined in relation to crown ether structure.

Desorption of crown ether–alkali metal ion complexes in liquid secondary ion mass spectrometry (LSIMS)

The liquid secondary ion mass spectra of crown ether solutions containing an equimolar mixture of alkali halides display large differences in the relative abundances of the crown ether–cation complexes formed, depending on various desorption yields. The results presented here show that from dilute solutions of samples, the less solvated ion species lead to better sensitivities. At higher concentrations, the matrix hydrophilicity plays an important role by discriminating between the mixed complexes in favour of those possessing both a surface activity and limited interactions with the solvent. The desorption of other ions is delayed by a slower desolvation, thus increasing the ion pairing by recombination with the anions present. This leads to an ion signal suppression in the case of strongly solvated complexes (lithium complexes) or anions (chlorides). Use of hydrophobic matrices limits considerably the solvation energy of the dissolved complexes thus reducing the discrimination between the complexes towards the desorption process. Provided that an appropriate choice of matrix, counteranion and other experimental parameters has been made, the desorption of crown ether-alkali cations does not suffer from any discriminatory effect.

Evidence for the direct desorption of crown ether—metal ion complexes in liquid secondary ionization mass spectrometry

The liquid secondary ionization mass spectra of crown ether solutions and crown ether solutions containing alkali metal cations were generated. Cesium cations acted as both the primary ion beam and as a competing gas—selvedge-phase reactant. The data suggest that crown ether complexes formed in the condensed phase survive intact the fast ion bombarding event and the transition into the gas phase. The data further suggest that crown ether complexes formed in the condensed phase predominate in the ion spectrum over the corresponding complexes formed in the selvedge.

Excess enthalpies and apparent molar volumes of aqueous solutions of crown ethers and cryptand(222) at 25�C

The enthalpies of dilution and densities of aqueous solutions of 12-crown-4, 15-crown-5, 18-crown-6, 1,10-diaza-18-crown-6 and cryptand (222) were measured at 25°C. The excess enthalpies and enthalpic coefficients of solute-solute interactions were calculated by the McMillan-Mayer theory formalism. Values for the apparent molar volumes at infinite dilution were determined by extrapolation. The contributions of the-CH2CH2O-group to values of h2 and to the limiting partial molar volume were calculated for the series of crown ethers studied. It is concluded that the hydrophobic hydration and the hydrophobic solute-solute interaction are predominant in the solutions investigated.

Nuclear magnetic relaxation of atomic neon-21 in liquid solution

The investigation of magnetic relaxation of noble gas nuclei in liquid solutions is a relatively new and promising field of interest in NMR. The reason for this interest lies in the fact that noble gas nuclei may serve as very informative probes for their surroundings, since they are uncharged and inert. So far, these relaxation studies have been restricted to xenon and krypton. In the present work we report first relaxation measurements on 2’Ne. The natural noble gas xenon contains two isotopes, 13’Xe (I = $ ) and 129Xe (I = f ). It has experimentally been shown that 13’Xe relaxes by the electric-field-gradient- quadrupole interaction (QF interaction) (1, 2). This quadrupole relaxation of 13’Xe has also been investigated in detail by MD computer simulation techniques (3). Ex- perimental relaxation time measurements on both i3’Xe and ‘29Xe have been per- formed in more than 60 different solutions and also in many aqueous solutions of dia- and paramagnetic salts, aqueous mixtures of organic solvents, and solutions of crown ethers (4). The relaxation behavior of both xenon nuclides has also been com- pared in isotropic and anisotropic liquids (5). Two independent studies (4,5) revealed that 129Xe is relaxed by the spin-rotation interaction. in 1987 one of the present authors reported the first 83Kr (I = 4 ) relaxation data in liquid solutions and it could be shown that the 83Kr relaxation behavior is of quadrupolar nature and is thus similar to 13’Xe relaxation (6). From a comparison of 83Kr and 13’Xe chemical-shift values it could be concluded that the diamagnetic shielding of the noble gas atoms is dom- inating the chemical shift of the nuclei (6). This result has also been obtained by Diehl and co-workers ( 7) by comparison of 2’Ne and i31Xe shifts in solutions. In the following we will present our results of the first T, measurements on 2’Ne of atomic neon dissolved in several liquids and we will give a comparison of these results with the corresponding 13’Xe data. For the measurements we used neon gas in which the isotope 2’Ne was enriched to 96.7% (IC Chemikalien, Munich, Germany). The different liquids which we used as solvents for the neon gas were of c.p. grade and have been freed from oxygen. The samples used for the measurements were saturated solutions under a gas pressure of 30-40 bar. The concentration of neon gas in the different liquids varied from 0.01 to 0.05 mol/liter depending on the respective solubility. The solutions under pressure were kept in thick-walled Duran glass tubes. The outer diameter of the tubes was 0.9

Solvated electrons, and not potassium (K-) anions, the initial products of dissolution of potassium by solutions of crown ethers

Les electrons solvates et les complexes crown cationiques de potassium sont les produits initiaux. Etude cinetique. Mecanisme de reaction. Stabilite des solutions de potassium. Produits de decomposition

Vapor-liquid equilibrium of aqueous crown ether solutions

The activity of water in crown ether solutions has been obtained at 298,313 and 333 K over a wide range of concentrations. A minimum in the activity coefficient of water is observed. The minimum becomes more pronounced with decreasing temperature.

Fast atom bombardment of crown ether/cation complexes in solution: Inferences on mechanisms of energy transfer

Mechanisms of energy transfer leading to the mass spectrometric detection of ionized species during fast atom bombardment are discussed. These mechanisms may be of an equilibrium or non-equilibrium nature but consideration of either mechanism suggests that the observed mass spectral peak heights for desorbed ionic species should be proportional to the concentrations of these species in solution. Solutions of crown-ethers with added metallic salts provide a means for testing this deduction. Under fast atom bombardment, a wide range of metal ions has been found to desorb as crown ether/cations and the technique affords a sensitive means of detecting metal ions in solution. The variation in concentration of a crown ether/cation complex in solution at normal temperatures with different molar ratios of crown ether to added metal salt is reflected accurately by the accompanying changes in mass spectral peak heights of the crown ether/cations. From the mass spectral data, it seems possible that quantitative determination of crown ether/metal salt stability constants can be effected simply. Methods for extracting such information are discussed.

Removal of sodium-24 by chromatographic extraction with a Kieselguhr column and a crown ether solution

Sodium-24 was readily removed from aqueous solutions by a chromatographic process based on an isotopic exchange reaction. The reaction was carried out with a granular Kieselguhr column and a chloroform solution of crown ether-sodium picrate. The process took about 1 h and can be utilized in neutron activation analysis of many elements, Cl, Br, Sc, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Ru, In, Sn, Ce and W. It cannot be used, however, for alkali and alkaline earth elements. The amount of /sup 24/Na in a treated sample was 10/sup -2/ of the original amount. The Compton background was reduced in the range of ..gamma..-ray energy after the removal of sodium-24. 3 figures, 3 tables.

Preparation of reactor-produced carrier-free 18F-fluoride as the potassium 18-crown-6 complex for synthesis of labelled organic compounds

An anion exchange and distillation procedure is described for preparing reactor-produced carrier-free 18F as K 18F complexed with 18-crown-6 in acetonitrile for subsequent syntheses of labelled organic compounds. The reaction sequence 6Li( n, t) 4He− 16O( t. n) 18F produced yields of approximately 250 mCi of 18F per hour per gram of 96% enriched 6Li, as 6LiOH·H 2O target, in a reactor thermal neutron flux of 3 × 10 13 n cm −2s −1. Yields of tritium-free carrier-free 18F dissolved in the crown ether solution typically reach 85 ± 5% within the 20–30 min required for the radiochemical procedure