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Ionic Liquids, Green Futures and a Thermochemical Database

Posted on 14. June, 2011.

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Ionic liquids offer manifold prospects as solvents for the extraction and processing of materials while avoiding or minimising the handling, inadvertent release and ultimate disposal of more common organic solvents.

The June issue of Science Progress considers the potential applications of ILs. Chris Rhodes discusses the many advantages of using ILs. Because of their negligible vapour pressure, high thermal stability, profound lack of flammability, and tailorable solubility for particular compounds, ILs have many ‘‘green’’ environmental applications.

Don Jenkins then describes efforts to develop a standard thermochemical database from which to guide the efforts of synthetic chemists in the preparation of tailored and novel ILs for particular applications. Such a focussed framework should obviate much wasted laboratory effort.

Progress in Science Current Commentary
Ionic Liquids and Green Futures

Christopher J. Rhodes

Ionic liquids (ILs) offer manifold prospects as solvents1 for the extraction and processing of materials while avoiding or minimising the handling, inadvertent release and ultimate disposal of more common organic solvents. As the name implies, ILs are frequently liquid at room temperature and consist entirely of ionic species, in contrast to more usual pure liquids like water and acetone, which contain electrically neutral molecules. An IL is a salt in which either or both of the ions are large, and the cation possesses a low degree of symmetry. These aspects tend to diminish the lattice energy of the crystalline state of the salt and therefore reduce the melting point.

There are in general two principal kinds of IL, those that are simple salts consisting of a single anion and a single cation and others known as binary ionic liquids which are salts involving an equilibrium. As an example, [C2H5NH3+] [NO3–] is a simple salt that exhibits simple melting behaviour, whereas the binary ionic liquid systems furnished by mixtures of aluminium(III) chloride and 1,3- dialkylimidazolium chlorides contain a number of different ionic species with melting points that vary according to the quantity of each component. In consequence of their negligible vapour pressure, high thermal stability, profound lack of flammability, and tailorable solubility for particular compounds, ILs have many ‘‘green’’/environmental applications and are attracting increasing attention in many fields, including organic chemistry, electrochemistry, catalysis, physical chemistry, engineering, fuel and environmental industries.

doi: 10.3184/003685011X13051285144048

Recent Initiatives in Experimental Thermodynamic Studies on Ionic Liquids - the Emergence of a Standard Thermochemical Database

Harry Donald Brooke Jenkins

One of the ultimate goals in the exciting on-going development and study of ionic liquids (ILs) must be the quest to establish ‘‘before synthesis’’ tools that could be used to predict and guide synthetic chemists towards ILs having ‘‘tuned’’ target properties. The tools needed in this exercise will come from many sources, not least from the acquisition of standard experimental thermodynamic data. The routine measurement of such data for new compounds had become very much a thing of the past in traditional chemistry. However with the surge of interest across the globe seen in these relatively new IL materials has come a recognition of the need to acquire experimental data and this review article seeks to assemble much of the emerging thermochemical data for ILs in one place. After all, there are very few data in current existing thermochemical databases that could offer much of a clue concerning the specific thermodynamic behaviour of ILs. We are charting new territory here.

Development of any new large scale commercial process is preceded these days by a full study of its thermodynamic feasibility, usually at the pilot stage, and thus such data as are reported here are of the utmost value in this respect. It has a secondary role too in enabling predictions of missing data to become feasible and hence in predicting synthetic outcomes ahead of practical experiment. This commentary tracks very recent trends and developments on the more quantitative and thermodynamic aspects of this exciting chemistry.

doi:10.3184/003685011X13051250311491