The crown ethers 18-crown-6 (18C6), dicyclohexano-18-crown-6 (DCH18C6), and 4,4‘-(5‘)-di-(tert-butylcyclohexano)-18-crown-6 (Dtb18C6) were dissolved in 1-alkyl-3-methylimidazolium hexafluorophosphate ([C n mim][PF6], n = 4, 6, 8) room-temperature ionic liquids (RTILs) and studied for the extraction of Na+, Cs+, and Sr2+ from aqueous solutions. In the absence of extractant, the distribution ratios for the metal ions indicate a strong preference for the aqueous phase. With the crown ethers as extractants in RTIL-based liquid/liquid separations, the resulting metal ion partitioning depends on the hydrophobicity of the crown ether and also on the composition of the aqueous phase (e.g., concentration of HNO3 vs Al(NO3)3). Aqueous solutions of HCl, Na3 citrate, NaNO3, and HNO3 (the latter at low concentrations) decrease the metal ion distribution ratios and also decrease the water content of the RTIL phase. High concentrations of HNO3 decompose PF6 - and increase both the water content and the water solubility of the RTIL phase. Highly hydrated salts such as Al(NO3)3 and LiNO3 salt out both the RTIL ions and the crown ethers; thus, when the aqueous phase contains Al(NO3)3, the trend more closely resembles traditional solvent extraction behavior where D Sr > D Cs and the most hydrophobic extracting phase produces the highest partitioning. When [C8mim][PF6] is used as the extracting phase, the metal ions can be loaded from Al(NO3)3 and stripped using water. Dtb18C6 forms 1:1 complexes with Cs+ and Sr2+ and also yields the highest distribution ratios out of the three crowns examined. In comparison to traditional solvent extraction behavior, the metal ion partitioning in these systems exhibits exceptional behavior and, in certain instances, suggests a complicated partitioning mechanism, which necessitates a more thorough understanding of RTILs as solvents before interpretation of the results.

Aqueous biphasic systems (ABSs) represent wholly aqueous systems that are safe, nontoxic, and nonflammable, and thus, they represent relatively environmentally benign extraction media. Such systems could be employed as alternatives to traditional aqueous-organic systems for the separation of, inter alia, small organic molecules, thus it is important to develop a fundamental understanding of these systems and the variables that govern solute partitioning within them. The partitioning of a series of neutral, substituted benzene compounds and neutral, aliphatic compounds in ABSs composed of different molecular weights of poly(ethylene glycol) (PEG-1000, 2000, and 3400) and formed as a result of the addition of different salt types [K 3 PO 4 , K 2 CO 3 , (NH 4 ) 2 SO 4 , Li 2 SO 4 , MnSO 4 , ZnSO 4 , and NaOH] has been examined. The results show that the distribution of organic solutes is a function only of the degree of phase divergence of the biphasic system as expressed by the difference in polymer concentration between the phases: ∆[poly-(ethylene glycol)], ∆[ethylene oxide monomers], or tie line length (∆PEG, ∆EO, or TLL, respectively). Solute partitioning depends only on the composition of the phase-forming components, PEG and salt. Using ideas taken from the study of critical phenomena, it can be shown that the composition of the phases is the result of the salting-out ability of the salt and the number of ethylene oxide monomers comprising the PEG. The salting-out strength of the salt (measured by its lyotropic number or position in the Hofmeister series) is related to its ability to lower the cloud point of the PEG solution. Hence, cosmotropic salts salt-out PEG, producing a series of nearly identical ABSs that, although differing in their overall concentrations of PEG and salt, are identical in terms of their lyotropic properties. This is an extraordinary simplification of a complex array of different ABSs to a single series of ABSs of graded lyotropy. Further comparison of solute partitioning in PEG/salt ABSs to partitioning in 1-octanol/water systems is discussed, and a greater similarity of solute distribution was found between different PEG/salt ABSs than between PEG/salt ABSs and 1-octanol/water.

Partition coefficients, as values of log P, between water and two room-temperature ionic liquids and between water and an aqueous biphasic system have been correlated with Abraham's solute descriptors to yield linear free energy relationships that can be used to predict further values of log P, to ascertain the solute properties that lead to increased or decreased log P values, and to characterize the partition systems. It is shown that, in all three of the systems, an increase in solute hydrogen-bond basicity leads to a decrease in log P and an increase in solute volume leads to an increase in log P. For the two ionic liquid systems, an increase in solute hydrogenbond acidity similarly decreases log P, but for the aqueous biphasic system, solute hydrogenbond acidity has no effect on log P. These effects are rather smaller than those observed in traditional water-solvent systems. However, the ionic liquids appear to have an increased affinity for polyaromatic hydrocarbons as compared to traditional organic solvents. Principal component analysis and nonlinear mapping show that the three unconventional partition systems are considerably different from conventional water-organic solvent systems. IntroductionA major contemporary industrial challenge is to continued manufacturing beneficial chemical products while eliminating or substantially reducing the detrimental environmental consequences of the processes adopted. The Montreal Protocol 1 identified the need to reevaluate chemical processes to take account of their environmental impact, especially with regard to the use of volatile organic solvents. In addition, some 90% of hazardous waste is aqueous in nature, 2 and thus, industry is reliant upon efficient separations from liquid media. To this end, liquid-liquid separations are widely applied in the chemical process industry. Typically, because of their immiscibility with water, volatile organic solvents are often employed in such processes. 3 Taken together, these issues suggest that the elimination of the use of flammable toxic and volatile organic solvents in separations processing represents a significant step in the creation of a sustainable industrial technology. 4 A number of different approaches to this problem have been identified, including solvent-free synthesis, the use of water as a solvent, 5 the use of supercritical fluids, 6 and the use of ionic liquids. Recently, roomtemperature ionic liquids (RTILs) have received worldwide attention 7,8 as replacements for organic solvents in catalysis, 9 synthesis, 10,11 and separations processes. 12,13 Room-temperature ionic liquids, in contrast to conventional ionic liquids such as molten sodium chloride, which are only liquids at temperatures above 800°C, represent ionic salts that are liquid at room temperature. Many RTILs are liquids over a wide temperature range, and RTILs with melting points as low as -96°C are known. The constituents of many RTILs (being ionic) are constrained by high Coulombic forces and thus exert practically no vapor pressure abo...

Echte Chemie: Spektroskopische und kristallographische Analysen bestätigen die chemische Reaktion von CO2 mit Carbenen in flüssigen 1,3‐Dialkylimidazoliumacetaten sowie die unterstützende Rolle des Acetations in diesen Reaktionen. Wenn CO2 durch [C2mim][OAc] geleitet wurde, konnte die Bildung des entsprechenden Imidazoliumcarboxylats, [C2mim+‐COO−], beobachtet werden.

Aqueous biphasic systems (ABSs) composed of poly(ethylene glycol) (PEG) and salt have been examined as potential environmentally benign solvents for liquid/liquid extraction. These systems might also represent an alternative to traditional solvent/water systems used in quantitative structure-activity relationships (QSARs). For the application and design of these systems, it is important to have a thorough understanding of the nature of the solvent and its interactions with the solute, and thus, PEG/salt ABSs have been characterized to this end by a variety of methods. The relative hydrophobicities of several PEG/salt ABSs composed of different molecular weights of PEG (1000, 2000, and 3400) and a variety of inorganic salts [K 3 PO 4 , K 2 CO 3 , (NH 4 ) 2 -SO 4 , Li 2 SO 4 , MnSO 4 , ZnSO 4 , and NaOH] were measured by the free energy of transfer of a methylene group ∆G CH 2 . These results indicate that the relative hydrophobicity of a PEG/salt ABS is a function of only the degree of phase divergence of the biphasic system as expressed by the difference in polymer concentration between the phases [delta poly(ethylene glycol) (∆PEG), delta ethylene oxide monomer (∆EO)] or the tie line length (TLL). The distributions of a wide range of solutes differing in structure and functionality were also measured in PEG/salt ABSs, and the results were compared to the corresponding 1-octanol/water partition coefficients. These data were used to develop a linear free energy relationship (LFER) based on Abraham's generalized solvation equation, enabling a direct comparison to be made between the solvent properties of PEG/salt ABSs and those of traditional solvent/water systems used, for example, in the determination of log P. Similar comparisons are also enabled with the properties of certain aqueous micellar systems.