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Previous studies of the effect of IL cation/anion hydrophobicity and the nature of the aqueous phase anion on the partitioning of alkali and alkaline earth cations between an acidic aqueous phase a...

Efforts to improve the TALSPEAK (Trivalent Actinide Lanthanide Separation with Phosphorus-Reagent Extraction from Aqueous Komplexes) Process have considered, among other options, the replacement of...

Extractant-loaded polysulfone (PS) capsules suitable for the separation and preconcentration of rare earth ions from acidic media have been prepared and characterized. Specifically, PS macro- and microcapsules have been impregnated with bis(2-ethylhexyl)phosphoric acid (HDEHP), and their performance in the extraction of europium (Eu3+) from nitric acid solution evaluated. The HDEHP-loaded microcapsules were found to exhibit sorption efficiency superior to those of analogous macrocapsules. Comparison to a conventional (i.e., commercial) extraction chromatographic (EXC) material (Ln•Resin), comprising HDEHP-loaded beads of poly(methyl methacrylate) (PMMA) of comparable size (50–100 µm), showed that the capacity of the HDEHP-loaded microcapsules for europium is ca. 2.5-fold greater than that of the conventional material. This larger capacity is the apparent result of both the higher extractant loading achievable with the microcapsules and an unexpected change in the complexation stoichiometry of europium by HDEHP upon extractant encapsulation. The microcapsule-based sorbent equaled or exceeded the performance of the commercial EXC material in other respects as well, most notably uptake kinetics and column efficiency, making it a promising alternative to established EXC resins.

A previously reported ion-exchange/extraction chromatographic scheme for the recovery of radiostrontium from urine for subsequent determination is systematically optimized to minimize reagent consu...

The partitioning of a number of organic compounds, including a series of n-alkanols and various simple, substituted benzene derivatives, between several hydrophobic (i.e., water-immiscible) deep eutectic solvents (HDESs) and water has been examined. The extent of extraction is shown to vary with the charge state of the molecule and the composition of the eutectic. In addition, the HDES–water distribution of a given solute is found to be directly proportional to (but typically less than) its partitioning in the octanol–water system, consistent with a significant role for solute hydrophobicity in the observed extraction behavior. Comparison of solute extraction into an HDES to that observed for other “unconventional” solvents (e.g., room-temperature ionic liquids and a soybean-derived oil) shows that hydrophobic deep eutectic solvents provide comparable or superior extraction efficiency.

The recent development of hydrophobic deep eutectic solvents (HDESs) has led to growing interest in these reagents as possible environmentally benign replacements for conventional organic media in a host of applications, among them metal ion separations by liquid-liquid extraction. To evaluate the potential utility of these novel solvents in this application, a systematic examination of the facilitated transfer of selected alkali and alkaline earth cations into representative HDESs from aqueous solution in the presence of a macrocyclic polyether (i.e., a crown ether) has been undertaken. Comparison of the results to those obtained for a series of oxygenated, aliphatic solvents (n-alcohols) and for several 1-alkyl-3-methylimidazolium-based ionic liquids (ILs) under the same conditions indicate that despite frequent suggestions that some HDESs resemble ILs, metal ion distribution in HDES-aqueous systems more closely mimics that seen for the alcohols. Metal ion partitioning in these systems appears less dependent on the water content of the organic phase and on structural variations in the solvent than is the case for either alcohols or ionic liquids, however. The implications of these results for the design and application of HDES-based extraction systems for metal ions are described.

Changes in the level of impregnation of an Amberchrom CG-71m support with bis(2-ethylhexyl)phosphoric acid (HDEHP) are shown to alter the column efficiency, peak tailing, and metal ion uptake capacity associated with the resulting extraction chromatographic resins. Optimum efficiency and minimum peak tailing are observed at intermediate levels (ca. 20% (w/w)) of support loading. Metal ion uptake capacity is reduced relative to a commercial (loaded to 40% (w/w)) resin under the same conditions, however. The utility of the improved efficiency arising from reduced support loading is illustrated in the separation of selected trivalent lanthanide ions, including Gd(III) and Eu(III), whose resolution is unsatisfactory using commercial extraction chromatographic materials.

The solvent extraction of metal ions came to prominence in the surge of interest in the production and processing of nuclear materials in conjunction with the Manhattan Project during the early 1940s. Metal ion separations have since come to constitute an essential component of numerous industrial processes and a primary step in many chemical analyses. For the last two decades, ionic liquids (ILs) have been evaluated as replacements for the molecular liquids normally used in solvent extraction. Various reports suggest that ILs may improve the performance and versatility of liquid-liquid extraction in metal ion separations. Many other studies, however, indicate that the participation of IL components in partitioning reactions between immiscible phases and certain of their physicochemical characteristics render their utility as direct replacements of molecular solvents questionable. In this chapter the use of ILs is described in the context of their properties and the approaches to their application as extraction solvents for metal ions, either alone or in combination with an extractant.

The high thermal stability typical of many room temperature ionic liquids (RTILs) is exploited as the basis of a method employing thermogravimetric analysis (TGA) for the determination of the solubility of various metal ion extractants in these solvents. The approach is simple, applicable to extractants lacking functional groups that would permit their ready quantification by other methods, and requires only small (mg) quantities of sample. These features of the method, along with its limitations, are illustrated by the determination of the solubility of representative examples of several common extractant families, including bis(2-ethylhexyl)phosphoric acid (HDEHP) and di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6), in a series of 1,3-dialkylimidazolium (Cnmim+)-based ionic liquids.

In the extraction of strontium nitrate from aqueous nitric acid solutions into a series of hydrophobic N-(1-hydroxyalkyl)-N’-alkylimidazolium bis[(trifluoromethyl)sulfonyl]imides by dicyclohexano-1...

Over the last two decades, extraction chromatography, a form of liquid chromatography employing as the stationary phase any of a variety of extractants in an appropriate organic solvent sorbed on a solid support, has emerged as an important tool for a number of analytical- and preparative-scale metal ion separations. Recent studies in which ionic liquids (ILs) have been evaluated as replacements for the molecular solvents normally used in liquid–liquid extraction suggest that an improvement in the performance of extraction chromatographic materials might be effected by the use of an IL as the basis for the stationary phase. In this report, approaches to the preparation of new sorbents incorporating ILs are described and the performance of the resultant materials in various metal ion separations is reviewed. In addition, promising areas for future work are identified.

Prior studies of metal ion partitioning between an acidic aqueous phase and an ionic liquid in the presence of a macrocyclic polyether have demonstrated that the overall partitioning is a composite of three distinct pathways: neutral complex/ion-pair extraction, exchange of a cationic metal-crown ether (CE) complex for the cationic constituent of the IL, and exchange of the metal ion for a hydronium ion in a CE-H3O+ complex formed during acid preconditioning of the IL. The obvious undesirability of the ion-exchange pathways, which can lead to substantial loss of the IL cation to the aqueous phase, has led to efforts to identify means by which these processes can be suppressed or eliminated. Prior work with N,N′-dialkylimidazolium and quaternary ammonium bis [(trifluoromethyl)sulfonyl]imides has shown that increasing the hydrophobicity of the IL cation can be an effective means of diminishing the contribution of ion-exchange. Work with the corresponding N-alkylpyridinium ILs, however, indicates that in certain instances, an increase in the hydrophobicity of the IL cation is accompanied by a marked increase in its propensity to self-associate, leading to the formation of micelles in the aqueous phase. The net effect is to diminish or even negate the expected beneficial effect of IL cation hydrophobicity in reducing the contribution of ion exchange to the overall metal ion partitioning process, adversely impacting the “greenness” of extraction processes employing these ILs.

Crown ether-loaded polysulfone (PS) capsules suitable for the separation and preconcentration of strontium from acidic nitrate media have been prepared and characterized. Specifically, PS macro- and microcapsules have been impregnated with the macrocyclic polyether di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6), either undiluted or as a solution in 1-octanol, and their performance in the extraction of strontium from nitric acid solution evaluated. The DtBuCH18C6-loaded microcapsules were found to exhibit strontium uptake efficiency significantly greater than that observed for the analogous macrocapsules, confirming earlier observations of a marked size-dependence of the behavior of extractant-loaded PS capsules. Comparison of the microcapsules to a commercial extraction chromatographic (EXC) material (Sr-resin) comprising DtBuCH18C6-loaded beads of poly(methyl methacrylate) (PMMA) of comparable size (50–100 μm), showed that the two materials exhibit similar strontium retention, uptake kinetics, and selectivity. The microcapsules provide higher column efficiencies, however, and when fully loaded with extractant, higher strontium ion uptake capacity.

Numerous factors have previously been shown to influence the mode of extraction of alkali and alkaline earth cations from an acidic aqueous phase into 1, 3-dialkylimidazolium-based ionic liquids (ILs) by a crown ether, among them the hydrophobicity of both the IL anion and cation. To determine if this observation is “generic” and thus, could provide the basis for guidelines for the rational design of ILs to be used as solvents in metal ion extraction, other families of ILs must be studied. A series of quaternary ammonium-based ILs have therefore been examined as solvents for the extraction of various metal ions from acidic nitrate- and chloride-containing aqueous phases by dicyclohexano-18-crown-6 (DCH18C6). Although the overall metal ion extraction behavior in these systems is similar to that observed for 1, 3-dialkylimidazolium-based ILs, significant differences in metal ion separation factors (e.g., αSr/Na) are observed under certain conditions, differences that may be sufficient to influence t...

Extraction chromatographic (EXC) resins incorporating an appropriate crown ether in an oxygenated organic solvent such as 1-octanol are well established as sorbents for the analytical-scale separation and preconcentration of radiostrontium from a variety of sample types. Recent solvent extraction studies employing crown ethers in various 1-alkyl-3-methylimidazolium-based (CnC1im+) room-temperature ionic liquids (RTILs) indicate that under certain conditions, distribution ratios (DSr) for strontium far in excess of those observed with conventional organic solvents are observed. To determine if this increase in liquid–liquid extraction efficiency will lead to improved strontium sorbents, several EXC resins and sol-gel glasses incorporating di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6) in either 1-decyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (C10C1imTf2N) or the related hydroxyalkyl-functionalized IL 1-(12-hydroxydodecyl)-3-butylimidazolium bis[(trifluoromethyl)sulfonyl]imide (C12OHC4im Tf2N) were prepared and characterized. Unexpectedly the performance of these materials was not uniformly better than that of a conventional EXC resin, an apparent result of the greater viscosity of the ionic liquids and the lower solubility of the crown ether in ILs versus conventional organic solvents.

The most commonly studied classes of ionic liquids (ILs) comprise relatively large and asymmetric heterocyclic cations (e.g., diakylimidazolium or N-alkylpyridinium) in combination with any of a wide variety of inorganic (e.g., BF4−, Cl−) or organic (e.g., bis[(trifluoromethyl- sulfonyl)imide], Tf2N−) anions. Recently it has been shown that ILs can also be formed by complexation reactions of metal cations (e.g., Li+, as its Tf2N− salt) with various neutral ligands (e.g., cyclohexano-15-crown-5 or alkylamines). Because the upper limit of the useful temperature range of any IL is governed by its thermal stability, and because the thermal stability of a neutral ligand (i.e., its propensity to either volatilize or decompose) is of obvious importance in determining that of an IL prepared from it, a systematic examination of the thermal properties of a series of macrocyclic polyethers of potential utility in the synthesis of new ILs has been undertaken. The results show that the temperature corresponding to the...

As part of a broader effort to determine the factors governing the relative contributions of ion-exchange processes and neutral complex/ion-pair partitioning in the extraction of metal ions into room-temperature ionic liquids by neutral extractants, the effect of ionic liquid (IL) anion on the extraction of alkali and alkaline earth cations by a crown ether from acidic nitrate and chloride media has been systematically examined. Results for a series of 1,3-dialkylimidazolium (C n mim + )-based ILs incorporating hexafluorophosphate ( PF 6 - ), bis[(trifluoromethyl)sulfonyl] imide ( Tf 2 N - ), or bis[(perfluoroethyl)sulfonyl]imide (BETI − ) as the counterion indicate that the choice of anion, in particular its hydrophobicity, can influence the balance among the various possible pathways for extraction, as well as both the extraction efficiency and selectivity. Overall, higher IL anion hydrophobicity is accompanied by a greater tendency toward ion exchange as the predominant mode of extraction. The effect upon extraction efficiency and selectivity is more complex, however, varying markedly with aqueous acidity.

A method has been developed for the rapid extraction of Sr-90 from the urine of individuals exposed to radiation in a terrorist attack. The method employs two chromatographic ion-exchange materials: Diphonix resin and Sr resin, both of which are commercially available. The Diphonix resin reduces the alkali ion concentrations below 10 mM, and the Sr resin concentrates and decontaminates strontium-90. Experimental and calculational data are given for a variety of test conditions. On the basis of these results, a flowsheet has been developed for the rapid concentration and extraction of Sr-90 from human urine samples for subsequent beta-counting.

A method has been developed for the isolation of strontium from human urine for subsequent determination in sample volumes as low as 5-20 mL. This method involves the acidification of the sample using methanesulfonic acid and its decolorization using charcoal, treatment of the filtrate with Diphonix(®) resin, and subsequent concentration of strontium on Sr resin. Data from retention model simulations provided the initial conditions which were then optimized by actual column separations. Diphonix(®) resin was shown to be effective at removing alkali metal ions from the urine matrix under conditions that retain higher valence ions. The suggested processing method provides 99% recovery of Sr(2+), a concentration factor of 50, and an expected per sample processing time of less than 1 h.

Measurements of the partitioning of various alkali and alkaline earth cations between solutions of hydrochloric acid and a series of 1,3-dialkylimidazolium-based ionic liquids (ILs) to which a crown ether has been added have revealed substantial differences in extraction behavior versus both conventional molecular solvents (e.g., 1-octanol) under the same conditions and the same ILs when nitric acid solutions are employed as the aqueous phase. These results can be rationalized by application of a three-path model for metal ion partitioning into ILs in the presence of a neutral extractant. Additionally, the results point to a significant role for anion hydration energy in determining the balance amongst the possible modes of partitioning and strongly suggest that ion exchange involving the cationic metal complex and the cationic constituent of the ionic liquid constitutes the "default" route for metal ion extraction in IL systems incorporating a neutral extractant.

Studies of the partitioning behavior of alkali and alkaline earth cations in systems comprising a nitric acid solution and an immiscible ionic liquid (IL) to which a crown ether has been added have established trends in the predominant mode by which these cations are transferred between phases. For a series of 1,3-dialkylimidazolium-based ILs, it is shown that the relative importance of cation exchange and neutral complex extraction to the overall ion transfer process can vary considerably with the hydrophobicity of the IL cation, the concentration of the aqueous acid, and the metal ion extracted. The overall trends observed display a simple correlation with charge density within each group of cations. Coupled with existing knowledge of ion partitioning into ILs, these results provide a framework by which variations in the extraction behavior of metal ions with changing conditions can be rationalized and the unique extraction selectivity exhibited by these systems can be exploited to develop improved systems for metal ion separations.

The extraction of trivalent lanthanides from an aqueous phase containing 1 M NaClO4 into the room temperature ionic liquid 1-butyl-3-methylimidazolium nonafluoro-1-butanesulfonate by the β-diketone extractant 2-thenoyltrifluoroacetone (Htta) was studied. Radiotracer distribution, absorption spectroscopy, time-resolved laser-induced fluorescence spectroscopy, and X-ray absorption fine structure measurements point to the extraction of multiple lanthanide species. At low extractant concentrations, fully hydrated aqua cations of the lanthanides are present in the ionic liquid phase. As the extractant concentration is increased 1:2 and 1:3 lanthanide:tta species are observed. In contrast, 1:4 Ln:tta complexes were observed in the extraction of lanthanides by Htta into 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

Modeling the transport and evaporation of multi-component liquids remains one of the most challenging problems in porous media studies. In this paper, slow isothermal evaporation of a non-dilute multi-component liquid mixture from a cylindrical porous wick made of sintered polymer beads is studied numerically and experimentally. Such wicks are used in several consumer products, such as air-fresheners and insect repellants, for dispensing volatile compounds into air. Since the evaporation rate is much smaller than the rate of capillary-pressure-driven liquid imbibition, the wick is considered fully-saturated while the evaporation from the wick top is modeled as a boundary effect. A volume-averaged model based on the work of Quintard and Whitaker is adapted to set the nonlinear species-transport equations inside the fully-saturated porous wick. Three numerical models with progressively increasing levels of complexity are employed to solve the governing equations in a one-dimensional domain representing the unidirectional, axial flow in a cylindrical wick. The Darcy velocity inside the wick is determined from evaporation rate at the wick-top, which in turn is a function of mole-fractions of all components at the liquid–air interface. Using the proposed numerical models, the evaporated liquid-mass and the composition of liquid mixture within the wick are predicted as functions of time. Results of the simulations are compared with experiments for a non-dilute mixture of decane, dodecane and hexadecane. Good agreement is observed for the three models, especially for the component concentration distributions along the wick, without the use of any fitting parameters. The evaporation rate is found to be a strong function of two model parameters: the porous-medium tortuosity and the air-film thickness at wick top.

Nuclear magnetic resonance (NMR) spectroscopy has been used to study hydrogen-bonding interactions between water, associated and dissociated acids (i.e., nitric and methanesulfonic acids), and the constituent ions of several water-immiscible room-temperature ionic liquids (ILs). In chloroform solutions also containing a crown ether (CE), water molecules strongly associate with the IL ions, and there is rapid proton exchange between these bound water molecules and hydronium associated with the CE. In neat ILs, the acids form clusters differing in their degree of association and ionization, and their interactions with the CEs are weak. The CE can either promote proton exchange between different clusters in IL solution when their association is weak or inhibit such exchange when the association is strong. Even strongly hydrophobic ILs are shown to readily extract nitric acid from aqueous solution, typically via the formation of a 1:1:1 {H(3)O(+)•CE}NO(3)(-) complex. In contrast, the extraction of methanesulfonic acid is less extensive and proceeds mainly by IL cation-hydronium ion exchange. The relationship of these protic equilibria to the practical application of hydrophobic ILs (e.g., in spent nuclear fuel reprocessing) is discussed.

Crown ethers (CEs) are macrocyclic ionophores used for the separation of strontium-90 from acidic nuclear waste streams. Room temperature ionic liquids (ILs) are presently being considered as replacements for traditional molecular solvents employed in such separations. It is desirable that the extraction efficacy obtained with such solvents should not deteriorate in the strong radiation fields generated by decaying radionuclides. This deterioration will depend on the extent of radiation damage to both the IL solvent and the CE solute. While radiation damage to ILs has been extensively studied, the issue of the radiation stability of crown ethers, particularly in an IL matrix, has not been adequately addressed. With this in mind, we have employed electron paramagnetic resonance (EPR) spectroscopy to study the formation of CE-related radicals in the radiolysis of selected CEs in ILs incorporating aromatic (imidazolium and pyridinium) cations. The crown ethers have been found to yield primarily hydrogen loss radicals, H atoms, and the formyl radical. In the low-dose regime, the relative yield of these radicals increases linearly with the mole fraction of the solute, suggesting negligible transfer of the excitation energy from the solvent to the solute; that is, the solvent has a "radioprotective" effect. The damage to the CE in the loading region of practical interest is relatively low. Under such conditions, the main chemical pathway leading to decreased extraction performance is protonation of the macrocycle. At high radiation doses, sufficient to increase the acidity of the IL solvent significantly, such proton complexes compete with the solvent cations as electron traps. In this regime, the CEs will rapidly degrade as the result of H abstraction from the CE ring by the released H atoms. Thus, the radiation dose to which a CE/IL system is exposed must be maintained at a level sufficiently low to avoid this regime.

An approach directed at rapid sequestration and disposal of technetium-99 from UREX (uranium extraction) liquid waste streams is presented. This stream is generated during reprocessing of light-water-reactor spent fuel to recycle the actinides and separate fission products for waste disposal. U and Tc are co-extracted from a nitric acid solution using tri-n-butylphosphate in dodecane, so that Tc(VII) is present in the strip solution after the actinide separations. The goal is to separate uranyl from the pertechnetate in this U-Tc stream and then sequester Tc in the metallic form. Our approach is based on reductive stripping of pertechnetate either from aqueous solution (for column extractions) or organic solvents (for liquid-liquid extractions). In both of these methods, metallic zinc in the presence of formic acid serves as a reducing agent, and 99Tc is recovered as a co-precipitate of Zn(II) hydroxide and hydrous Tc(IV) oxide, with a Zn:Tc ratio between 1:1 and 2:1 mol/mol. This solid residue can be red...

A laboratory experiment is described in which students compare two methods for the determination of the calcium content of commercial dietary supplement tablets. In a two-week sequence, the sample tablets are first analyzed via complexometric titration with ethylenediaminetetraacetic acid and then, following ion exchange of the calcium ion present for hydronium ion, by acid–base titration with sodium hydroxide. Upon completion of the laboratory work, students pool their data with classmates and perform a statistical analysis to determine whether the average values of the calcium content obtained by the two methods are equivalent. When taken together with such considerations as analysis time, accuracy, simplicity and ease of use, susceptibility to interference, and waste generation, these results enable the students to evaluate the relative merit of the two approaches to calcium determination. In so doing, they are introduced to an important aspect of “real-world” chemical analysis, namely, selection of th...

Hydrophobic ionic liquids (IL) have the potential to simplify certain separations by serving as both an extraction solvent and an electrolyte for subsequent electrochemical reductions. While IL-based solvents are known to be efficient media for metal ion extraction, separations employing these solvents are frequently complicated by the loss of constituent IL ions to the aqueous phase, resulting in deteriorating performance. In this study, we have examined the extraction of pertechnetate and related tetra-oxo anions from aqueous solutions into IL-based solvents incorporating tetraalkylphosphonium bis[(trifluoromethyl)sulfonyl]imide and a crown ether. In contrast to various previously studied IL-based cation extraction systems, facile anion extraction without significant transfer of the IL ions to the aqueous phase has been observed. In addition, the solvents exhibit high distribution ratios (100-500 for pertechnetate), significant electrical conductivity (>100 ?S/cm), and a wide (4 V) electrochemical window. The results suggest that these solvents may provide the basis for improved approaches to the extraction and recovery of a variety of anions.

An acidichromic silyl spiropyran was synthesized and covalently immobilized on the surface of mesoporous silica (SBA-15) through either post-modification or a co-condensation route. The integration of the spiropyran into the porous silica was probed by thermogravimetric analysis, nitrogen adsorption/desorption studies and UV-Vis optical spectroscopy. While the co-condensation route provides the higher spiropyran loading levels, it also leads to two different states of attachment. Both synthetic procedures favor the formation of the open, merocyanine form of the spiropyran within the framework, but this form can be readily switched from a protonated to a deprotonated state by treatment with buffered aqueous solutions. Preliminary evaluation of the metal ion sorption capabilities of the spiro-functionalized SBA-15 for selected monovalent, divalent, and trivalent metal ions indicates that the spiropyran-modified materials show modestly improved cation exchange characteristics versus the unfunctional...

Carbon dioxide has received significant attention as a potential environmentally benign medium to replace hazardous organic compounds, but is a relatively poor solvent. The addition of siloxane substituents provides an attractive and inexpensive means to solubilize a wide variety of compounds in CO2. By synthesizing and testing a family of gem-diphosphonate ligands that have been rendered CO2-philic by incorporation of a number of related, discrete dimethylsiloxane oligomers, we show that small variations in substituents have a significant effect on the CO2-philicity of the ligand. To our knowledge, this is the first systematic study of the effect of siloxane substituent size, branching, and position on the affinity of a ligand for CO2. In addition, we present a general approach to the preparation of novel gem-diphosphonate ligands.

The mode of partitioning of uranyl ion between nitrate-containing aqueous phases and various N,N'-dialkylimidazolium-based room-temperature ionic liquids (RTILs) in the presence of tri-n-butyl phosphate (TBP) is shown to change from an ion-exchange process to one involving extraction of a neutral uranyl-TBP-nitrato complex as the aqueous nitrate concentration is increased. Increasing the hydrophobicity of the RTIL cation eventually leads to nitrato complex extraction as the predominant mode of partitioning, regardless of nitrate concentration.

A novel extraction chromatographic resin for the separation and preconcentration of cesium from acidic nitrate media comprising an inert polymeric substrate impregnated with 1,3‐calix[4]bis‐o‐benzo‐crown‐6 (“BC6B”) in a chlorinated diluent is described. Cesium is shown to be both strongly and selectively retained by the resin at low (

The unique physicochemical properties of ionic liquids (ILs) and the relative ease with which these properties can be fine‐tuned by altering the cationic or anionic moieties comprising the IL have led to intense interest in their use as alternatives to conventional organic solvents in a wide range of synthetic, catalytic, and electrochemical applications. Recent work by a number of investigators has been directed at the application of ionic liquids in various separation processes, among them the liquid‐liquid extraction of metal ions. Although certain IL‐extractant combinations have been shown to yield metal ion extraction efficiencies far greater than those obtained with molecular organic solvents, other work suggests that the utility of ILs may be limited by solubilization losses and difficulty in recovering extracted metal ions. In this report, recent efforts to overcome these limitations are described, and progress both in achieving an improved understanding of the fundamental aspects of meta...

The predominant mode of strontium ion transfer from aqueous nitrate media into a series of 1-fluoroalkyl-3-methylimidazolium bis[(trifluoromethylsulfonyl)]imides containing dicyclohexano-18-crown-6 (DCH18C6) is shown to shift from cation exchange to strontium nitrato-crown ether complex partitioning as the length of the fluoroalkyl substituent is increased. Fluoroalkyl substituents are shown to be only slightly more effective than their non-fluorous analogs at inducing this shift. At the same time, the fluorinated ionic liquids (ILs) yield strontium distribution ratios as much as an order of magnitude lower than the corresponding 1-alkyl-3-methylimidazolium (Cnmim+) salts. Fluorous ILs thus appear to offer no compelling advantages over Cnmim+ ionic liquids as extraction solvents.

The determination of radiostrontium in biological and environmental samples generally requires its preliminary separation and preconcentration, both to remove radionuclides that may interfere with ...

Using a dynamic flow method, the supercritical carbon dioxide (SC‐CO2) solubilities of two series of symmetrically substituted alkylenediphosphonic acids, bearing 2‐ethylhexyl and 3‐trimethylsilyl‐1‐propyl ester groups, respectively, were determined as a function of the number of methylene groups separating the two phosphorus atoms. An even–odd effect, similar to that observed previously for the aggregation of these compounds in nonpolar diluents, was observed, with compounds that form more highly aggregated species in nonpolar diluents exhibiting lower solubility in SC‐CO2. Differences in the relative solubilities of analogous members of these series prompted the study of the SC‐CO2 solubilities of symmetrically substituted methylenediphosphonic acids bearing seven‐ and eight‐carbon ester groups of various degrees of branching to determine the relative importance of steric and electronic effects in determining SC‐CO2 solubilities. When molecular connectivity indices were used to quantify the ext...

Addition of an appropriate concentration of water to either 1-decyl-3-methylimidazolium bromide or its nitrate analog is shown to trigger the self-assembly of the ionic liquid (IL) and the concomitant formation of gel (“ionogel”) phases adopting a rich variety of structural motifs. Infrared and 1H nuclear magnetic resonance studies indicate that water addition disrupts hydrogen bonding between the imidazolium ring and the IL anion, and that gelation involves the partial replacement of these bonds with H-bonds between the anion and water. Using small angle X-ray scattering, the relationship of the water content and the nature of the IL anion to the mesoscopic structure of the ionogels has been determined. Of particular note is the observation that by adjustment of the ionogel composition (water content or anion), near-monodomain materials can be formed with either lamellar, 2-D hexagonal or 3-D cubic structures with tunable lattice dimensions.

The solid salts of the 1-ethyl-3-methylimidazolium and the 1-n-pentyl-3-methylimidazolium cations, abbreviated [C2mim]+ and [C5mim]+, respectively, of the Keggin heteropolyanion, α-[PW12O40]3−, were prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements of both [Cnmim]3[α-PW12O40] salts (for n=2 and 5) were performed in acetonitrile containing either tetra-n-butylammonium hexafluorophosphate, abbreviated TBAPF6, or the corresponding [Cnmim]BF4 ionic liquids (ILs) as electrolytes. The results are compared with the corresponding data obtained in the neat [Cnmim]BF4 ILs without addition of other electrolytes. The effects of countercation and supporting electrolyte on the voltammetry of the Keggin ion α-[PW12O40]3− are interpreted as resulting from an amalgamation of isomerization, ion-association, and redox processes. The combination of the unique solvent/electrolyte properties of ILs with the well-known electrochemistry of molecular polyoxometalates (POMs) like the Keggin anion leads to redox behavior that may have impact on the research and technology of catalytic and energy-storage phenomena.

Incorporation into a 20-crown-6 of a bulky substituent capable of impeding cation/anion access to one face of the crown ether cavity is shown to afford compounds exhibiting good extraction selectivity for potassium ion over both alkaline earth cations (Ca2+, Sr2+) and other alkali metal ions (Na+, Cs+), an apparent result of diminished flexibility of the crown ether cavity, inhibition of the formation of extractable “sandwich” complexes with large cations, and the destabilizing effect of forcing charge-neutralizing counter anions to approach from one face of the crown cavity.

Partially esterified alkylenediphosphonic acids were shown to be effective solvent extraction reagents for the removal of actinide cations from acidic aqueous solutions into conventional organic solvents. As a first step in an effort to design diphosphonic acid extractants that are soluble in supercritical carbon dioxide, we prepared and characterized a novel series of silyl-substituted alkylenediphosphonic acids. The aggregation of these extractants in toluene at 25°C was studied by vapor pressure osmometry. Their solvent extraction chemistry was investigated by employing radiotracers to determine the distribution ratios for selected metal ions between an acidic aqueous phase and an organic phase containing the diphosphonic acid extractant. To determine the effect of incorporating a silicon functionality into diphosphonic acids, the aggregation and solvent extraction properties of the silyl-substituted alkylenediphosphonic acids were compared with those of the conventional alkyl-substituted di(2-ethylhex...

The predominant mode of strontium ion transfer from acidic nitrate media into a series of 1-alkyl-3-methylimidazolium-based room-temperature ionic liquids containing dicyclohexano-18-crown-6 (DCH18C6) shifts from cation exchange to strontium nitrato-crown ether complex partitioning as the hydrophobicity of the ionic liquid cation is increased.

The synergistic extraction of alkaline earth (Ca2+, Sr2+, Ba2+ and Ra2+) and actinide (Am3+, UO2 2+ and Th4+) cations from aqueous nitric acid solutions by mixtures of P,P′-di(2-ethylhexyl) methylene-(H2DEH[MDP]), ethylene-(H2DEH[EDP]), and butylene-(H2DEH[BuDP]) diphosphonic acids and neutral extractants in o-xylene has been investigated. The cis-syn-cis and cis-anti-cis stereoisomers of dicyclohexano-18-crown-6 (DCH18C6), the unsubstituted 21-crown-7 (21C7) and dicyclohexano-21-crown-7 (DCH21C7) were used as neutral synergists of the crown ether type. For Am(III) synergistic effects were also investigated using neutral organophosphorus esters, such as, tri-n-butylphosphate (TBP), diamyl amylphosphonate (DA[AP]) and tri-n-octylphosphine oxide (TOPO) as co-extractants. In all systems investigated, no synergistic extraction enhancement was observed for actinide ions. For the alkaline earth cations, synergistic effects were only observed when mixtures of H2DEH[EDP] or H2DEH-[BuDP] with DCH18C6 were...

The silicon-substituted diphosphonic acid P,P′-di[3-(trimethyl-silyl)-1-propyl] methylenediphosphonic acid, H2DTMSP-[MDP], reacts with metal nitrates in methanol to form complexes M2(DTMSP[MDP])3 for M˭Fe, Eu and Yb and M(DTMSP[MDP])2 for M˭Th. The sodium salt, Na2-(DTMSP[MDP]), forms upon neutralization of H2DTMSP-[MDP] with NaOH. The calcium salt, Ca(DTMSP[MDP]), forms upon addition of the aqueous metal nitrate to an equivalent amount of the neutralized ligand in methanol. Elemental analysis, infrared spectroscopy and magnetic susceptibility measurements were used to characterize the compounds. Frequency shifts in the asymmetric and symmetric POO− stretching bands of the Fe, Eu, Yb and Th compounds indicate symmetrical coordination of the phosphonate groups through chelate and/or bridging interactions. The frequency difference between these stretching bands becomes smaller as the ionic potential (e/r) of the metal ion increases.

Chiral trans-anti-trans-dicyclohexano-18-crown-6 isomers are synthesized via a lipase-catalyzed reaction. The solid-state structure of the (S)-enantiomer is determined and compared with those reported for 18-crown-6 and trans-syn-trans-dicyclohexano-18-crown-6.

Stereospecific syntheses of the cis – trans -isomer of dicyclohexano-18-crown-6 allows the K + complexation behavior of all five dicyclohexano-18-crown-6 isomers to be compared.

In an ongoing effort to determine the relationship between structure and function in diphosphonic acids, the aggregation and solvent extraction chemistry of four novel silicon-substituted diphosphonic acids, P,P′-di[3-(trimethylsilyl)-1-propyl] propylene- (H2DTMSP[PrDP]), butylene- (H2DTMSP[BuDP]), pentylene- (H2DTMSP[PDP]), and hexylene diphosphonic acid (H2DTMSP[HDP]), were investigated. Vapor pressure osmometry indicates that H2DTMSP[PrDP] and H2DTMSP[PDP] are dimeric in toluene at 25°C, while H2DTMSP[BuDP] and H2DTMSP[HDP] are primarily trimeric and hexameric, respectively. The solvent extraction of selected alkaline earth cations (Ca, Sr, and Ba) and representative tri-, tetra-, and hexavalent actinides [Am(III), Th(IV), and U(VI)], from nitric acid solutions into o-xylene solutions of the ligands has been studied and compared to results reported previously for some analogous di(2-ethylhexyl)-substituted diphosphonic acids. Differences observed in the magnitude of distribution ratios, based on the nu...

The two trans stereoisomers of dicyclohexano-18-crown-6 are synthesized by a two-step method from cyclohexene oxide and the solid-state structure of the trans–syn–trans isomer is determined.