Ionic liquids: solvent properties and organic reactivity

Ionic liquids are a fascinating class of novel solvents, which are attracting attention as possible 'green' alternative to volatile molecular organic solvents to be applied in catalytic and organic reactions and electrochemical and separation processes. Over 200 room temperature ionic liquids are known but for most of them physico-chemical data are incomplete or lacking. Furthermore, despite the incredible number of potential ionic liquids (evaluated as > 10(14)), generally only a few imidazolium-based salts are used in synthesis. Moreover, most of the data reported to date were focused on the effect that these new solvents have on chemical reaction products; only a few reports evidence the effect on reaction mechanisms or rate or equilibrium constants. In this review, the physico-chemical properties of the most used ionic liquids, that are relevant to synthesis, are discussed and a decided emphasis is placed on those properties that most clearly illuminate the ability of ionic liquids to affect the mechanistic aspects of some organic reactions. Copyright (c) 2004 John Wiley & Sons, Ltd.