Deep Eutectic Solvents (DES) can be formed between a variety of quaternary ammonium salts and carboxylic acids. The physical properties are significantly affected by the structure of the carboxylic acid but the phase behavior of the mixtures can be simply modeled by taking account of the mole fraction of carboxylic acid in the mixture. The physical properties such as viscosity, conductivity, and surface tension of these DES are similar to ambient temperature ionic liquids and insight into the cause of these properties is gained using hole-theory. It is shown that the conductivity and viscosity of these liquids is controlled by ion mobility and the availability of voids of suitable dimensions, and this is consistent with the fluidity of other ionic liquids and molten salts. The DES are also shown to be good solvents for metal oxides, which could have potential application for metal extraction.

Eutectic mixtures of urea and a range of quaternary ammonium salts are liquid at ambient temperatures and have interesting solvent properties.

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Ionic liquids, or room temperature molten salts, have attracted increasing interest over recent years, particularly in the area of green chemistry, due to their advantageous properties including negligible vapour pressure and wide liquid range. 1-3 Work has focussed on liquids formed from dialkylimidazolium halides which are readily prepared from 1-methylimidazole and a slight excess of the desired haloalkane. 4 Addition of a suitable molar ratio of aluminium chloride to these salts gives rise to ionic liquids containing complex metal anions which have been used in a number of applications such as electroplating, electrochemical devices and catalysts for organic synthesis. 1,[4][5][6] The main disadvantage of imidazolium-based liquids is their relatively high cost for bulk applications, whilst chloroaluminate ionic liquids have the additional problem of their low tolerance to moisture, necessitating the use of glove box and Schlenk techniques to prepare and investigate their properties. The former problem may be overcome by using cheaper ammonium salts whereas the latter may be solved by replacing aluminium with less reactive metals.Recently, Freeman and coworkers have characterised ionic liquids formed from FeCl 2 or FeCl 3 and 1-butyl-3-methylimidazolium chloride. 7 However, other examples of ionic liquids made from metal chlorides other than aluminium are less well characterised and are mainly cited in conference proceedings 8 or in the patent literature. 9,10 Here we report the synthesis and characterisation of new moisture-stable, Lewis-acidic ionic liquids made from metal chlorides and quaternary ammonium salts that are commercially available or simple to synthesise. These offer the potential to tailor the physical properties e.g. melting point, viscosity and conductivity, and to tune the Lewis acidity by choosing a different metal or indeed combinations of metals.To investigate the parameters necessary for a salt to be liquid at or near room temperature we have heated a range of ammonium salts with zinc chloride in a 1+2 molar ratio and the results are shown in Since choline chloride, [Me 3 NC 2 H 4 OH]Cl, gave the lowest freezing point we have characterised this system in more detail. Heating mixtures of choline chloride and zinc chloride in molar ratios between 1+1 and 1+3 gave rise to clear colourless liquids, with the freezing points varying between ca. 65 °C (1+1), 25 °C (1+2) and 45 °C (1+3). Unlike analogous aluminium systems, 4,11,12 ratios with a molar excess of choline chloride, i.e. basic melts, do not form ambient temperature liquids in these systems. This would imply that complex zinc anions, in which the charge can be delocalised, are necessary in the formation of these ionic liquids. Further characterisation of the 1:2 liquid is described below.A 1 H NMR spectrum of the neat ionic liquid was recorded and shows resonances at d 2.97, 3.34 and 3.94 assigned to the methyl groups, N-CH 2 protons, and the CH 2 OH protons, respectively, of the choline cation. All signals were broad and poorly reso...

The solubility of 17 commonly available metal oxides in the elemental mass series Ti through Zn have been determined in three ionic liquids based on choline chloride. The hydrogen bond donors used were urea, malonic acid, and ethylene glycol. The results obtained are compared with aqueous solutions of HCl and NaCl. Some correlation is observed between the solubility in the deep eutectic solvents and that in aqueous solutions but some significant exceptions offer an opportunity for novel solvato-metallurgical processes.