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Ionic liquids - an overview

Posted on 21. October, 2011.

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As well as exhibiting catalytic activity for many chemical reactions, ionic liquids are used as replacements for conventional toxic solvents. They can be used to prevent chemical pollution. In Science Progress 94(3), Professor Harry Jenkins highlights the main characteristics of ionic liquids, presenting them in a form readily assimilated by newcomers to this area of research. An extensive glossary is featured as well as a chronological list which charts the major areas of development.

A virtually unprecedented exponential burst of activity resulted following the publication, in 1998, of an article by Michael Freeman (Freemantle, M. Chemical & Engineering News, 1998, March 30, 32), which speculated on the role and contribution that ionic liquids (ILs) might make in the future on the development of clean technology. Up until that time only a handful of researchers were routinely engaged in the study of ILs but frenzied activity followed that continues until the present day. Scientists from all disciplines related to Chemistry have now embarked on studies, including theoreticians who are immersed in the aim of improving the “designer role“ so that they can tailor ILs to deliver specified properties. This article, whilst not in any sense attempting to be exhaustive, highlights the main features that characterise ILs, presenting these in a form readily assimilated by newcomers to this area of research. An extensive glossary is featured in this article as well as a chronological list which charts the major areas of development. A number of sections briefly describes the role of ILs as solvents, hypergolic fuels, their use in some electrochemical devices such as solar cells and lithium batteries and their use in polymerisation reactions, followed by a concise summary of some of the other roles that they are capable of playing. The role of empirical, volume-based thermodynamics procedures, as well as large scale computational studies on ILs is also highlighted. These developments which are described are remarkable in that they have been achieved in less than a decade and a half, although knowledge of these materials has existed for much longer.

In summary, these IL materials can offer advantages across all major science areas including materials science, electrochemistry, organic, inorganic, bio and materials chemistry. They are often readily reclaimable following their use in solvation or catalytic processes. They also present us with a novel opportunity to study chemistry within a liquid medium at temperatures below 100 oC. To date, less than 1600 ILs have been characterised, it has been estimated that at least 1019 seem possible. They remain thermally stable at temperatures higher than more conventional covalent solvents as well as possessing a wider range of solubility than do ordinary solvents and are often much more miscible, offering examples of both hydrophobic and hydrophyllic solvents. In this sense, they offer us new types of media in which to carry out reactions.

doi: 10.3184/003685011X13138407794135

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