During the past decade, ionic-liquid-based Aqueous Biphasic Systems (ABS) have been the focus of a significant amount of research. Based on a compilation and analysis of the data hitherto reported, this critical review provides a judicious assessment of the available literature on the subject. We evaluate the quality of the data and establish the main drawbacks found in the literature. We discuss the main issues which govern the phase behaviour of ionic-liquid-based ABS, and we highlight future challenges to the field. In particular, the effect of the ionic liquid structure and the various types of salting-out agents (inorganic or organic salts, amino acids and carbohydrates) on the phase equilibria of ABS is discussed, as well as the influence of secondary parameters such as temperature and pH. More recent approaches using ionic liquids as additives or as replacements for common salts in polymer-based ABS are also presented and discussed to emphasize the expanding number of aqueous two-phase systems that can actually be obtained. Finally, we address two of the main applications of ionic liquid-based ABS: extraction of biomolecules and other added-value compounds, and their use as alternative approaches for removing and recovering ionic liquids from aqueous media.

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Recently, many studies concerning the environmental impact of ionic liquids (ILs) have shown that despite their unique properties and clear advantages in an ever wide range of applications and processes, ILs are not intrinsically green. In a search for biodegradable and low toxicity, a new type of ILs has been developed, the deep eutectic solvents (DESs). In this context, the aim of this work is to provide accurate densities, viscosities, and refractive indices for DESs prepared using cholinium chloride as the hydrogen bond acceptor and several carboxylic acids (levulinic, glutaric, malonic, oxalic, and glycolic) as the hydrogen bond donors. The impact of two different synthetic methodologies, heating and grinding, in the thermophysical properties of the prepared DESs was assessed. The obtained DESs were analyzed using NMR spectroscopy, FTIR, and electrospray ionization mass spectrometry in order to check their structures and purities. Thermophysical properties, densities, viscosities, and refractive indices were rationalized in terms of the chemical structure of the prepared DESs. The effect of the presence of water in the thermophysical properties of the compounds was also evaluated. Finally, comparisons between the DESs and the corresponding ILs are presented.

The ionic nature of ionic liquids (ILs) results in a unique combination of intrinsic properties that produces increasing interest in the research of these fluids as environmentally friendly "neoteric" solvents. One of the main research fields is their exploitation as solvents for liquid-liquid extractions, but although ILs cannot vaporize leading to air pollution, they present non-negligible miscibility with water that may be the cause of some environmental aquatic risks. It is thus important to know the mutual solubilities between ILs and water before their industrial applications. In this work, the mutual solubilities of hydrophobic yet hygroscopic imidazolium-, pyridinium-, pyrrolidinium-, and piperidinium-based ILs in combination with the anions bis-(trifluoromethylsulfonyl)imide, hexafluorophosphate, and tricyanomethane with water were measured between 288.15 and 318.15 K. The effect of the ILs structural combinations, as well as the influence of several factors, namely cation side alkyl chain length, the number of cation substitutions, the cation family, and the anion identity in these mutual solubilities are analyzed and discussed. The hydrophobicity of the anions increases in the order [C(CN) 3 ] < [PF 6 ] < [Tf 2 N] while the hydrophobicity of the cations increases from [C n mim] < [C n mpy] e [C n mpyr] < [C n mpip] and with the alkyl chain length increase. From experimental measurements of the temperature dependence of ionic liquid solubilities in water, the thermodynamic molar functions of solution, such as Gibbs energy, enthalpy, and entropy at infinite dilution were determined, showing that the solubility of these ILs in water is entropically driven and that the anion solvation at the IL-rich phase controls their solubilities in water. The COSMO-RS, a predictive method based on unimolecular quantum chemistry calculations, was also evaluated for the description of the water-IL binary systems studied, where it showed to be capable of providing an acceptable qualitative agreement with the experimental data.

Controversy behind the postulation that ionic liquids (ILs) are entirely green materials emerged a few years ago. This statement is not always valid, and properties such as toxicity and chemical/thermal stability of ILs should be fully characterized to evaluate their potential use as green solvents. Therefore, in this work, the thermal and chemical decompositions of hexafluorophosphate- and tetrafluoroborate-based ILs in aqueous solutions were evaluated. The experimental conditions employed allowed the study of the possible decomposition of both anions, the effect of the cation side alkyl chain length, the influence of the pH of the aqueous solutions, as well as the temperature influence. Three experimental techniques were employed to fully characterize those anions' stability, electrospray mass spectrometry, nuclear magnetic resonance spectroscopy, and pH measurements of the equilibrium aqueous solutions. The results noticeably indicate that it is suitable to use aqueous solutions of hexafluorophosphate-based ILs at moderate temperatures while acidic conditions promote the anion hydrolysis, even at low temperatures. On the other hand, the tetrafluoroborate-based ILs are not water-stable compounds since they hydrolyze under all of the conditions tested and the hydrolysis extent is markedly dependent on the temperature.

Experimental density measurements are reported, and the derived thermodynamic properties, such as the isothermal compressibility, the isobaric expansivity, and the thermal pressure coefficient are presented as Supporting Information for several imidazolium-based ionic liquids (ILs), namely, 1-ethyl-3-methyl-imidazolium bis-(trifluoromethylsulfonyl)imide [C 2 mim][NTf 2 ], 1-heptyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [C 7 mim][NTf 2 ], 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [C 8 mim][NTf 2 ], 1-ethyl-3-methylimidazolium tetrafluoroborate [C 2 mim][BF 4 ], and 1-butyl-3-methyl-imidazolium tricyanomethane [C 4 mim][C(CN) 3 ] in the pressure (0.10 < p/MPa < 30.00) and temperature (293.15 < T/K < 393.15) domains. These ILs were chosen to provide an understanding of the influence of the cation alkyl chain length and the anion influence on the properties under study. Experimental densities are correlated with the Tait equation with an average absolute deviation (AAD) less than 0.04 %. Experimental densities are in good agreement with the densities obtained by some recent predictive methods proposed in the literature.

Inspired by one of the major problems in the pharmaceutical industry, we advantageously used the formation of eutectic mixtures to synthesize new solvents. The aim of this work is to identify low viscosity, cheap, biodegradable and hydrophobic eutectic solvents from natural resources. Consequently, novel eutectic mixtures based on DL-menthol and naturally occurring acids, namely pyruvic acid, acetic acid, L-lactic acid, and lauric acid, were synthesized and are here reported for the first time. The obtained DLmenthol-based eutectic mixtures were analyzed using NMR and FTIR spectroscopy in order to check their structures and purities and to confirm the interaction of the two compounds leading to the eutectic formation. Important solvent thermophysical properties, such as density and viscosity, of the prepared eutectic solvents with different water contents (dried and watersaturated) were measured. Finally, taking advantage of their hydrophobic character, namely the formation of two phases with water at room temperature, four different biomolecules, caffeine, tryptophan, isophthalic acid, and vanillin, were extracted and the extraction efficiencies of the prepared eutectic solvents compared.

This work addresses the experimental measurements of the pressure (0.10 < p/MPa < 10.0) and temperature (293.15 < T/K < 393.15) dependence of the density and derived thermodynamic properties, such as the isothermal compressibility, the isobaric expansivity, the thermal pressure coefficient, and the pressure dependence of the heat capacity of several imidazolium-based ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate, [ . These ILs were chosen to provide an understanding of the influence of the cation alkyl chain length, the number of cation substitutions, and the anion influence on the properties under study. The influence of water content in the density was also studied for the most hydrophobic IL used, [omim]- [PF 6 ]. A simple ideal-volume model was employed for the prediction of the imidazolium molar volumes at ambient conditions, which proved to agree well with the experimental results.