Double Salt Ionic Liquids Research Articles

Dissolution of cellulose in imidazolium-based double salt ionic liquids

The dissolution of cellulose in double salt ionic liquids (DSILs) was studied in detail and compared with the dissolution in individual constituent ionic liquids (ILs). The DSILs, [C4mim](CH3CO2)xCl1-x (x is the mole fraction of the single component ILs), were synthesized using acetate and chloride salts of 1-butyl-3-methylimidazolium. These DSILs were then used for the investigation of the solubility of cellulose in the whole mole fraction range. Commercial cellulose (CC) powder, kraft pulp (KP), and prehydrolysis kraft pulp (PHKP) of jute were chosen as cellulose sources. The solubility of cellulose increased with an increasing temperature for [C4mim](CH3CO2)0.6Cl0.4 and with increasing amount of [C4mim]Cl in DSILs. The maximum solubility of CC powder was 32.8 wt% in [C4mim](CH3CO2)0.6Cl0.4 at 100 °C, while for KP and PHKP, solubilities were 30.1 and 30.5 wt%, respectively under the identical condition. Cellulose could be regenerated from the DSILs using water as an antisolvent. Structure, morphology, and thermal stability of the regenerated cellulosic materials were analyzed. DSILs could be recycled >99 % without a discernible change in structure. This work demonstrates that DSILs display enhanced solubility over ILs system and have potential as a chemical processing methodology.

Nanostructured ZnO with Tunable Morphology from Double-Salt Ionic Liquids as Soft Template.

ZnO nanostructures with tunable morphology were synthesized by the hydrothermal method from two ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate [C2mim]CH3CO2 and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim](CF3SO2)2N and their corresponding double-salt ILs (DSILs). ILs served as soft templates. DSILs were noted for the production of smaller particle size along with uniformity compared to their pure IL counterparts. A changeover of the shape of ZnO from nano-prism to a hexagonal disk-like structure was observed with the addition of [C2mim]CH3CO2 in the medium during synthesis while nano-dice- and rod-shaped particles were obtained from [C2mim](CF3SO2)2N. The effect of concentration of both ILs was explored for the variations of size and shape, and at high concentrations, the morphology was distinct and sharp with uniform size in each case. The synthesized products exhibited excellent phase (wurtzite) purity and polycrystalline nature. The smallest crystallite size was acquired from DSILs, indicating the advantageous effect of the dual anions. The selective adsorption effect of [C2mim]CH3CO2 on certain facets promoted the growth of ZnO clusters along the [1010] direction, while [C2mim](CF3SO2)2N favored the growth along the [0001] direction. Consequently, DSILs rendered interpenetrating hexagonal disks due to the combined action of the anions for controlling the shape. The band gap energies of the nanoparticles (NPs) were consistent with the distribution of size. Extremely strong red emission and negligible UV emission for the synthesized ZnO NPs demonstrate their potential in the advancement of optoelectronic devices.

Enhancing aromatics extraction by double salt ionic liquids: Rational screening‐validation and mechanistic insights

AbstractDespite offering remarkable advantages as solvents, double salt ionic liquids (DSILs) have been scarcely studied for extractive dearomatization from hydrocarbons as well as many other applications, thus urging a theoretical guidance method. In this work, a systematic framework combining the rational screening validation and mechanistic analysis is proposed for tailoring DSILs for the o‐xylene/n‐octane separation. From an initial pool of commercially available ionic liquids (ILs), key thermodynamic properties of paired DSILs are predicted by COSMO‐RS while their important physical properties are estimated from those of corresponding parent ILs (retrieved from experimental database or predicted by a deep learning model). Promising DSILs are tested by liquid–liquid equilibrium experiments, wherein the effect of ion ratio is also evaluated. The mechanism underlying the tunability of DSIL thermodynamic properties is disclosed by quantum chemistry calculation and molecular dynamics simulation. This work can be a valuable reference for guiding the design of DSILs for diverse applications.

Measurement and correlation for the electrical conductivity of double salt ionic liquids with triple ions

The neat ionic liquids 1-butyl-2,3-dimethylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C4C1C1im][NTf2]), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([C4C1C1im][BF4]), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate ([Deme][BF4]), N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis[(trifluoromethyl)sulfonyl]imide ([Deme][NTf2]) were used as parent ionic liquids to generate double salt ionic liquids (DSILs) with triple ions. The conductivity of DSILs [Deme]x[C4C1C1im](1-x)[NTf2], [Deme]x[C4C1C1im](1-x)[BF4], [C4C1C1im][NTf2]x[BF4](1-x) and [Deme][NTf2]x[BF4](1-x) were measured. There is a linear positive deviation for [Deme]x[C4C1C1im](1-x)[NTf2], [Deme]x[C4C1C1im](1-x)[BF4] and [C4C1C1im][NTf2]x[BF4](1-x), which indicates that most of the electrical conductivities of DSILs are greater than those of linear averages of the corresponding parent neat ionic liquids. The electrical conductivities of [Deme]x[C4C1C1im](1-x)[NTf2] and [Deme]x[C4C1C1im](1-x)[BF4] lie in the range of those of their corresponding parent neat ionic liquids. The electrical conductivity of [C4C1C1im][NTf2]x[BF4](1-x) rises with the concentration of [NTf2], and it has a maximum value at x = 0.9, which is larger than either of its parent neat ionic liquids. There is a linear negative deviation for [Deme][NTf2]x[BF4](1-x), which indicates that most of the electrical conductivities of the DSIL is less than that of linear average of the corresponding parent neat ionic liquids. The electrical conductivity of the DSIL lies between those of its parent neat ionic liquids and increases with the concentration of [NTf2]. The VTF equation and the Arrhenius equation were utilized to correlate the temperature dependence of DSILs, and VTF equation is more accurate than Arrhenius equation. The relationships between parameters of VTF equation and ion composition can be expressed by first-order Fourier equation. A transformed VTF equation based on VTF and Fourier equation was proposed to describe the combined effects of ion composition and temperature on the electrical conductivity. The experimental electrical conductivities of DSILs were correlated by the transformed VTF equation, and the correlation results agree well with experimental data.

Bifunctional Double-Salt Ionic Liquids Containing both 4-Chloro-2-Methylphenoxyacetate and l-Tryptophanate Anions with Herbicidal and Antimicrobial Activity.

The goal of this research was to obtain and characterize ionic liquids based on a bisammonium cation and both 4-chloro-2-methylphenoxyacetate (MCPA) and l-tryptophanate anions. The concept of including two structurally different anions was utilized to achieve improved biological activity, while crucial functional traits could be designed by modifying the cation. The synthesis process was efficient and resulted in high yields. Subsequent analyses (nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, and high-performance liquid chromatography (HPLC)) confirmed the chemical structure, purity, and molar ratio of ions in the obtained compounds. The described compounds are novel and have not been previously described in the literature. Evaluations of physicochemical properties indicated that the obtained double-salt ionic liquids (DSILs) exhibited high thermal stability, high solubility in water, and surface activity. A biological activity assessment using greenhouse tests revealed that the herbicidal efficiency of the studied DSILs was notably increased compared to the reference commercial herbicide (even by ∼50% in the case of oilseed rape), which could be attributed to their high wettability toward hydrophobic surfaces. The compounds also efficiently inhibited the growth of several microbial species, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)/minimum fungicidal concentration (MFC) values at the level of several μg·mL–1. The length of the spacer and alkyl substituent in the cation notably influenced the physicochemical and biological properties of the DSILs, which allowed us to design the structures of the obtained compounds in accordance with needs. The presented results confirm the high application potential of the described DSILs and provide a new and promising path for obtaining new and efficient plant-protection agents.

Double-salt ionic liquid derived facilitated transport membranes for ethylene/ethane separation

Ethylene/ethane separation is one of the key industrial gas separations which challenges the world because of their similar physical properties. Membrane separation technology holds great promise to replace or combine the currently energy-intensive cryogenic distillation to achieve effective ethylene purification. In this study, a series of double-salt ionic liquid derived facilitated transport membranes (DSIL-FTMs) were designed for the first time aiming at the highly effective ethylene/ethane separation, which were configured by incorporating ethylene transport carrier and double-salt ionic liquids (DSILs) into a robust Nylon support. DSILs are the liquid ionic compositions composing of more than one cation or anion, which offer an opportunity to enhance the design flexibility and structural regulation of the corresponding FTMs. The DSIL-FTMs exhibit good ethylene/ethane separation performance as well as high thermal stability and long-term durability, where the ethylene permeability is about 250 Barrer and ethylene/ethane selectivity reaches up to 67. The spectroscopic characterizations and structure-performance relationship investigation reveal that the excellent separation performances are attributed to the favorable rearrangement of cations and anions in the DSIL-FTMs, where the newly formed ion arrangement and cation-anion interactions of DSIL-FTMs favor the building of the compact membrane structure and obtainment of high carrier activity. This study opens a novel avenue to manipulate the physical-chemical properties of separation membrane by structural diversity of DSILs, and promotes the sustainable prosperity of FTMs for energy-intensive gas molecule separations.

Phase equilibria and volumetric and viscosity behavior of the aqueous double salt ionic liquid [EMIM][SCN]x[MeSO3](1-x)

Continuing our recent systematic studies on thermodynamic and thermophysical properties of binary aqueous ionic liquids (ILs), this work extends our investigations to aqueous double salt ionic liquids (DSILs). Specifically, the (water + [EMIM][SCN]x[MeSO3](1-x)) system is examined here: vapor-liquid and solid-liquid equilibria, volumetric and viscosity behaviors were experimentally determined at three DSIL compositions (x approx. 0.75, 0.5, and 0.25 or 0.20) and several water contents xw. Water activity was measured at seven temperatures from (288.15 to 318.15) K and for xw from 0.3 to 1, freezing temperature for xw from 0.8 to 1, density and dynamic viscosity at two temperatures (298.15 and 323.15 K) and for xw from 0 to 0.9. The acquired data were treated as those for the ternary system (water + [EMIM][SCN] + [EMIM][MeSO3]) and modeled coherently together with its binary subsystems. The ternary water activity data were successfully correlated by the extended NRTL model, adopting for the aqueous parent IL binaries the parameters we evaluated previously, and fitting just those remaining for the (IL + IL) pair. The established model was shown to predict perfectly the measured SLE data. This model further provides an otherwise hardly procurable insight into the energetics of the DSIL. As inferred from the model, the ([EMIM][SCN] + [EMIM][MeSO3]) binary system exhibits quite large positive deviations from ideality, its excess Gibbs energy stemming from the very endothermic mixing of the two ILs which is only partially compensated by the positive excess entropy. The (IL + IL) mixture exhibits a positive, but very small excess volume, only slightly increasing as temperature increases, while its viscosity is much greatly affected by both temperature and the DSIL composition. The viscosity deviation from the linear mixing rule is for the DSIL negative and large but obeying quite accurately the linear mixing rule of logarithmic viscosity. For the aqueous mixtures of both parent ILs, the logarithmic viscosity deviation is high and greatly composition asymmetric. Coherent and sufficiently accurate representation of the volumetric and viscosity data for the ternary system and all its binary subsystems was achieved by Padé approximants with temperature-dependent parameters amended with a ternary term. Compared to the neat [EMIM][MeSO3], [EMIM][SCN]x[MeSO3](1-x) with smaller contents of [EMIM][SCN] (x < 0.2) and water (xw < 0.2) shows higher water affinity, while having considerably lower viscosity. Thus, the use of this DSIL as a water absorption medium for desiccation and cooling applications was found to be very beneficial.

Quantitative Control Factors of Double Salt Ionic Liquids Catalysis in the Coupling Reaction of Epoxied and Methanol

Quantitative Control Factors of Double Salt Ionic Liquids Catalysis in the Coupling Reaction of Epoxied and Methanol

Synthetic auxin-based double salt ionic liquids as herbicides with improved physicochemical properties and biological activity

Over the past decade, numerous advantages of double salt ionic liquids have been discovered, including beneficial physicochemical properties and a synergistic increase in biological activity resulting from competitive interaction among three or more ions based on their chemical structures. Therefore, we applied the approach mentioned above in our study by designing new ionic liquids consisting of amphiphilic choline-like cations and two or three anions derived from synthetic auxins. The influence of combining three anions with herbicidal activity in one compound on its physical, chemical and biological properties is discussed here for the first time. Double salts were obtained according to a fast, reliable and sustainable synthesis method, which made it possible to obtain pure ionic liquids, reaching 99–100% efficiency. Comparison of NMR spectra of products containing one or more anions has revealed that the introduction of additional ions has a clear impact on the chemical environment of atoms, which may explain the observed changes in double salt properties. The effects of the addition of the 2nd and 3rd anions on basic physicochemical parameters (including density, refractive index, viscosity, phase transitions, solubility and surface activity) were studied. Biological experiments have confirmed that the herbicidal activity of the obtained ionic liquids with three herbicide anions is higher than that of commercial preparations and most tested ionic liquids with only one biologically active anion, which confirms numerous advantages of the “double salt ionic liquid” approach.

Insights into Non‐Ideal Behavior of Double Salt Ionic Liquids with Common Cation: Volumetric Behaviour, Molecular Dynamics Simulations and NMR Experiments

AbstractThe designer concept of ionic liquid (ILs) allows combination of different types of cation with anion to manipulate desire sets of physico‐chemical properties. The additional degree of freedom to improve these properties is addition of second IL, i. e. mixture of two pure ILs, known as “Double Salt Ionic Liquids (DSILs)”. Depending on variation in physico chemical properties, DSILs could be ideal or non‐ideal solution. The present study was explores non‐ideal behaviour of three novel combination of imidazolium based DSILs using physico‐chemical properties. The proposed DSILs are homogeneous mixtures of two pure ILs with common cation and two different anions: ethylsulfate and bis(trifluoromethylsulfonyl)imide / trifluoromethanesulfonate / thiocyanate. The densities, ρ and speeds of sound, u for proposed DSILs were determined at different temperatures. The excess molar volumes VmE and excess molar isentropic compressibilities KS,mE were calculated and discussed in view of chemical structures of pure ILs, nature of anions and type of interaction between ions. The VmE were found to be positive for all cases, whereas positive or negative KS,mE were observed for studied DSILs. The behaviour of DSILs was explained by molecular dynamics simulations in terms of interaction energies and hydrogen bonds between components of DSILs as well as 1H NMR results. The results indicate random distribution of anions around imidazolium cation and structural changes during formulation of DSILs.

Ultraslow Relaxation in Aprotic Double Salt Ionic Liquids.

A mixture of two pure ionic liquids (ILs) or double salt ILs (DSILs) can push the limits of ILs in terms of unraveling their unique physicochemical properties and potential in clean technology. While the correlated ion dynamics and heterogeneity in the bulk of pure ILs have been reported, such a phenomenon at longer timescales in DSILs has never been elucidated. Here, a combination of temperature-dependent polarized dynamic light scattering and rheological measurements has been employed to reveal the presence of structural and ultraslow relaxation in three DSILs, each containing a 1-ethyl-3-methylimidazolium cation and two different anions. The slow relaxation caused by Brownian diffusion of cluster-like arrangements occurs at a timescale of a few to several hundred milliseconds; both the relaxation processes, nevertheless, are Arrhenius in nature. Notably, slow relaxation in the DSILs is much different compared to that in the pure ILs. The decay of intensity correlation functions (ICFs) and average hydrodynamic correlation length of the clusters and their response to temperature markedly vary with the nature of the two anions present in the DSILs. Stretched exponential analyses of the ICFs disclose the cluster-to-cluster transfer of ionic species as well as percolation dynamics among clusters. The identity of anions also governs whether the DSILs follow or violate the Stokes-Einstein relationship or not.

Rational design of double salt ionic liquids as extraction solvents: Separation of thiophene/n‐octane as example

AbstractAlthough double salt ionic liquids (DSILs) offer significant advantages over classical two‐ion ionic liquids as separation solvents, relevant studies are still scarce and a systematic DSIL selection method is thus highly desirable. In this contribution, a rational method for designing DSILs as extraction solvents is proposed and exemplified by the thiophene/n‐octane separation. The effects of additional degrees of freedom for DSIL design (i.e., double cations and/or anions and the ion ratio) on the thermodynamic properties are first analyzed by COSMO‐RS. Then, a multilevel DSIL design method combining the prediction of infinite dilution thermodynamic properties, the estimation of physical properties, the evaluation of phase equilibrium behavior, and the experimental validation is proposed. By applying this method, [C2MIm][OAc] x[NO3]1‐x (x = [0, 1]) and [C2MIm][OAc] x[SCN]1‐x (x = [0.70, 1]) are identified as promising DSIL solvents for the thiophene/n‐octane separation. Correspondingly, the liquid–liquid equilibria of {DSILs + thiophene + n‐octane} with the designed DSILs are experimentally studied.

Double Salt Ionic Liquids for Lignin Hydrolysis: One Cation for Catalyst and Solvent Anions

Hydrolysis of lignin, the only direct renewable source of aromatics, is a promising strategy to obtain industrially important aromatic compounds owing to the nature of the bonds that dominate the lignin structure. In this study, we developed an imidazolium cation-based double salt ionic liquid (DSIL) for lignin hydrolysis with hydrogen sulfate as catalyst and diethyl phosphate as reaction media, and investigated the hydrolytic cleavage as a function of different reaction conditions and recyclability of catalytic system. Under mild conditions, value-added aromatics such as 2-methoxy phenol, 2,6-dimethoxy phenol, vanillin, and 4-hydroxy-3,5-dimethoxy benzaldehyde were obtained. Although yields are currently low, this study revealed that 1-ethyl-3-methylimidazolium hydrogen sulfate is an effective catalyst for lignin hydrolysis and the DSIL strategy could be promising for biomass utilization.

Double Salt Ionic Liquids for Lignin Hydrolysis: One Cation for Catalyst and Solvent Anions

Humanity has always relied on Nature for survival, but today we take oil as a feedstock and use it to produce chemicals to suit any purpose, from fuels and medicines to plastics. By reducing our reliance on Nature, we have forgotten our respect of Nature in the process. The world is now covered in oil in the form of non-biodegradable synthetic plastics which mar our landscapes and threaten our oceans. By 2050 there is predicted to be more plastic in the ocean than fish. At the same time, plastics represent a $654 billion market worldwide and are ubiquitous in modern life. Simply eliminating synthetic plastic use with no viable alternatives would be almost impossible and catastrophic from both a social and economic point of view. Chemists make new chemicals and that has led to the development of a chemical industry that knows how to sell these chemicals. The more chemicals we make, the more the industry seeks new and better markets to sell them into. New, more sustainable technologies have been forced into the business of ‘replacements’ and must follow the same commercialization pathways as the old technologies they are trying to replace. The unsustainable practices, however, have often had decades or more head start and thus the economics to replace them are often insurmountable without government or policy intervention. The technologies to directly replace synthetic plastics with renewable biopolymers from plants and animals are there, but the consistencies of supply and economies of scale to make them competitive are not. With a plethora of abundant natural and renewable resources (in terms of both quantity and diversity), from water purification - to cosmetics - to medical applications, the quality of human life can greatly benefit (and improve at the same time) from new, innovative technologies using building blocks obtained directly from plants and animals. With this mission in mind, we are exploring the entire range of the “biorefinery concept,” from dissolution, and conversion of plant and animal resources into value added chemicals and extraction of essential oils or vital chemicals, to isolation of pure biopolymers and production of new biomaterials from them. Because we can directly dissolve Nature’s raw materials, we can shape them, functionalize them, blend them, and use other non-chemistry means to produce advanced functional materials. These new, innovative materials represent new market opportunities which we will develop and promote.

Mixed metal double salt ionic liquids comprised of [HN222]2[ZnCl4] and AlCl3 provide tunable Lewis acid catalysts related to the ionic environment.

Two solids of differing Lewis acidities, triethylammonium tetrachlorozincate ([HN222]2[ZnCl4]) and AlCl3, have been combined across 0.1 to 0.9 mole fractions (with respect to [HN222]2[ZnCl4]), and homogeneous solid double salts or mixed metal [HN222]2x[(1 - x)AlCl3 + xZnCl4] double salt ionic liquids (DSILs) were obtained at x = 0.33, 0.4, and 0.5 with varying Lewis acidities. The characterization of the prepared DSILs (melting point, color, homogeneity, 1H, 13C, and 27Al nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), single crystal X-ray diffraction (SCXRD), and matrix-assisted laser-desorption ionization time-of-flight (MALDI-TOF) mass spectrometry) suggests that [HN222]2[ZnCl4] transfers Cl- from [ZnCl4]2- to the stronger Lewis acid AlCl3, forming intermediate acidic DSILs with [AlCl4]- and [Al2Cl7]- anions and mixed anionic Zn species. Qualitative Lewis acidity measurements using acetonitrile as an IR-active probe showed that the acidity of the DSILs decreased as the amount of [ZnCl4]2- increased. In a Beckman rearrangement reaction of acetophenone oxime, significant catalytic activity was observed for the DSIL at x = 0.33, where the activity of the DSIL was found to be even higher than [HN222][Al2Cl7], AlCl3, [HN222]2[ZnCl4], or ZnCl2 despite its lower Lewis acidity, apparently due to the synergistic effect of AlCl3 and [ZnCl4]2- as Cl- donors for the formation of catalytically active species. The findings illustrate a DSIL-based approach for modifying the catalytic activity of a known complex without changing its inner coordination sphere.

Application of COSMO-RS for pre-screening ionic liquids as thermodynamic gas hydrate inhibitor

Gas hydrate forms in oil and gas pipelines under low temperature and high pressure which result in flow assurance issues. To solve this, ionic liquids are introduced to act as dual inhibitors. Currently, the main method of studying the performances of ionic liquids is by conducting sometimes laborious experiments. Trial and error method as well as selection through literature are often employed in choosing the appropriate ionic liquids for gas hydrate inhibition. These methods are costly and probabilistic. In this work, Conductor-Like Screening Model for Real Solvents (COSMO-RS) software is used to pre-screen ionic liquids based on the fundamental property of the ionic liquid-hydrate system. The main energy that affects ionic liquid inhibition ability was found to be the hydrogen bonding energy (EHB). Results showed that increasing anion EHB improves inhibition ability while increasing cation EHB decreases the inhibition ability. Studies on the hydrogen bonding energies for double salt ionic liquids showed that the combination of chloride [Cl−] and hydrogen sulphate [HSO4] as the anion has high hydrogen bonding energy. The introduction of the hydroxyl group [OH−] in the cation increased the hydrogen bonding energy between anion and water. The proposed ionic liquids for experimental tests are [EMIM][Cl][HSO4], [OH-EMIM] [Cl] and [OH-EMIM][HSO4].

Noncovalent interactions underlying binary mixtures of amino acid based ionic liquids: insights from theory

Mixtures of ionic liquids formed by blending a common 1-methyl-3-butylimidazolium [Bmim] cation with the dicarboxylic amino acid anions viz., aspartic acid [Asp], asparagine [Asn], glutamic acid [Glu], and glutamine [Gln], have been investigated by employing dispersion corrected density functional theory. Binary mixtures of [Bmim]2[Asp][Asn] and [Bmim]2[Glu][Gln] ionic liquids emerge with distinct structural patterns. Competition between the constituting anions towards cationic binding sites in acidic and basic (polar) amino acid binary mixtures engenders diverse noncovalent interactions, viz., C-HO hydrogen bonding, π-π stacking, and lpπ and CHπ interactions, which impart local liquid structure to these systems governing the structural and physicochemical properties of such double salt ionic liquids (DSILs). The DSIL conformers reveal distinct structural features arising from the middle, normal and front arrangements of anions combined with parallel, antiparallel, rotated or displaced orientations of the cations. The inclusion of dispersion corrections through the D3 method affects their binding energies significantly bringing forth alteration in their energy rank order. Molecular insights accompanying the ion aggregates provide directives for the use of DSILs with improved performance in tribological applications.

Double salt ionic liquids based on 1-ethyl-3-methylimidazolium acetate and hydroxyl-functionalized ammonium acetates: strong effects of weak interactions.

The properties of double salt ionic liquids based on solutions of cholinium acetate ([Ch][OAc]), ethanolammonium acetate ([NH3(CH2)2OH][OAc]), hydroxylammonium acetate ([NH3OH][OAc]), ethylammonium acetate ([NH3CH2CH3][OAc]), and tetramethylammonium acetate ([N(CH3)4][OAc]) in 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) were investigated by NMR spectroscopy and X-ray crystallography. Through mixture preparation, the solubility of [N(CH3)4][OAc] is the lowest, and [Ch][OAc] shows a 3-fold lower solubility than the other hydroxylated ammonium acetate-based salts in [C2mim][OAc] at room temperature. NMR and X-ray crystallographic studies of the pure salts suggest that the molecular-level mechanisms governing such miscibility differences are related to the weaker interactions between the -NH3 groups and [OAc]-, even though three of these salts possess the same strong 1 : 1 hydrogen bonds between the cation -OH group and the [OAc]- ion. The formation of polyionic clusters between the anion and those cations with unsatisfied hydrogen bond donors seems to be a new tool by which the solubility of these salts in [C2mim][OAc] can be controlled.

Double Salt Ionic Liquids Containing the Trihexyl(tetradecyl)phosphonium Cation: The Ability to Tune the Solubility of Aromatics, Ethers, and Lipophilic Compounds

Ionic liquids (ILs) certainly have some interesting properties and this has led to tremendous growth in interest, knowledge, and applications of these materials in a diverse array of science and technology. However, the field is still dominated by study of the simplest binary salts and an over reliance on ‘magic’ solvent properties which currently limits their creative use for new technologies. Lately, the scientific community has been attracted towards “IL/IL mixtures” prepared by mixing two or more ILs, and (as was the case with the early studies of the binary salts), a focus on specific physicochemical properties. Interestingly, crystalline salts dissolved in ILs are seen as a different class of liquids (e.g., high ionicity ILs). We have found that the physical, chemical, and biological (i.e., the materials) properties of IL/IL mixtures (or Double Salt Ionic Liquids, DSILs, as we like to call them) seem to be mainly controlled by the intrinsic ion interactions which are influenced by the exact ion composition. Perhaps, a new way of thinking about these multi-ion fluids is needed in order to direct research toward an understanding of the complex and varied types of interionic forces possible in a liquid. We have proposed the DSIL concept to help guide our work towards obtaining this deeper understanding. In this nomenclature, any homogeneous liquid containing three or more ions (no matter how they are prepared) are described as DSILs and are defined by the specific ion combinations present. In this presentation, these concepts will be illustrated by discussion of the chemical, physical, and biological properties of several DSIL systems chosen to explore different interactions between the ions (i.e., Coulombic, hydrogen bonding, dispersion, etc.). While we will present physical properties as a function of composition, we will focus more on chemical properties illustrated by the solubilities of pharmaceuticals and on biological properties illustrated by changes in membrane transport, both as a function of ion composition. Spectroscopic studies will be presented to provide insight into specific ion-ion interactions. For example, the solubility of active pharmaceutical ingredients with different acidity and lipophilicity are finely tunable by varying the ratio of the ions (Figure 1). Such studies support the concept that each DSIL is a unique ionic fluid that is able to provide tunable property sets derived from the ions present and that these properties can be controlled by choosing the nature and the abundance of the ions. Figure 1

Double Salt Ionic Liquids Containing the Trihexyl(tetradecyl)phosphonium Cation: The Ability to Tune the Solubility of Aromatics, Ethers, and Lipophilic Compounds

The chemical and physical properties of an ionic liquid (IL) can be tuned with the addition of a second IL, forming a Double Salt Ionic Liquid (DSIL). Here, the solubilities of lipophilic solutes with long alkyl chains (e.g., heptane, methyl palmitate) were tuned in the DSIL [C4mim]x[P66614](1-x)[NTf2] ([C4mim]+ = 1-butyl-3-methylimidazolium, [P66614]+ = trihexyl(tetradecyl)phosphonium, [NTf2]- = bis(trifluoromethylsulfonyl)imide) by increasing the [P66614]+ concentration. Additionally, density and viscosity of the DSILs were also modified with the [P66614]+ concentration. The solubility of solvents totally miscible with [P66614][NTf2], such as benzene and toluene, could only be tuned in the DSILs when [P66614]+/[NTf2]- ≤ 0.33, since at higher ratios these solutes were totally miscible with the DSILs. The interactions between the ions account for the different solvent behaviors in the DSILs. Using 1H NMR, 19F NMR, and FT-IR spectroscopy, a preferential interaction was observed between the [NTf2]- anion with [C4mim]+ compared to that with [P66614]+. Also, interactions between [C4mim]+ and [P66614]+ through alkyl chain aggregations were demonstrated.