In contrast to a recently expressed, and widely cited, view that “Ionic liquids are starting to leave academic labs and find their way into a wide variety of industrial applications”, we demonstrate in this critical review that there have been parallel and collaborative exchanges between academic research and industrial developments since the materials were first reported in 1914 (148 references)

Applications of ionic liquids in the chemical industry

http://pubs.acs.org/doi/pdfplus/10.1021/cr300162p

Deep Eutectic Solvents (DESs) and Their Applications

Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.

Deep eutectic solvents: syntheses, properties and applications

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.

Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids

https://scholarlypublications.universiteitleiden.nl/access/item%3A3193534/view

Natural deep eutectic solvents as new potential media for green technology.

Novel solvent properties of choline chloride/urea mixtures

Preparation of novel, moisture-stable, Lewis-acidic ionic liquids containing quaternary ammonium salts with functional side chains

The solubility of a range of metal oxides in a eutectic mixture of urea/choline chloride is quantified, and it is shown that the dissolved metals can be reclaimed from a mixed metal oxide matrix using electrodeposition.

Selective extraction of metals from mixed oxide matrixes using choline-based ionic liquids.

The synthesis of ionic liquids based upon functionalized quaternary ammonium salts and metal salts of zinc, tin, or iron is demonstrated. The freezing point of these ionic liquids was studied as a function of the quaternary ammonium cation. The complex anions were identified and quantified using mass spectrometry and potentiometry. It is shown that the primary zinc anion is Zn2Cl5- with Zn3Cl7- becoming more abundant in more Lewis basic solutions. Similar results were observed for ionic liquids containing SnCl2. The surface tension was also measured and was used to explain the high viscosity of the ionic liquids in terms of the large ion:hole size ratio and the small probability of finding a hole of suitable dimensions adjacent to a given ion to permit movement. The phase behavior of a variety of quaternary ammonium halides/ZnCl2 mixtures is characterized and it is shown that the depression of freezing point is related to the increase in size of the component ions.

Raymond K. Rasheed

Papers

Novel solvent properties of choline chloride/urea mixtures

Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids

Preparation of novel, moisture-stable, Lewis-acidic ionic liquids containing quaternary ammonium salts with functional side chains

Selective extraction of metals from mixed oxide matrixes using choline-based ionic liquids.

Ionic liquids based upon metal halide/substituted quaternary ammonium salt mixtures.