Catalysis in ionic liquids

Ionic liquids, salts with melting points less than about 100 degrees C, present a wide range of properties for applications as catalysts, and there has been a spate of research recently concerned with catalytic applications of low-temperature ionic liquids. These typically consist of an organic cationic component with one or multiple heteroatoms, such as N, P. or S, and an inorganic or organic anion. The inertness of many ionic liquids toward most known catalysts makes them superior to water as solvents for catalysts, and from an environmental point of view. their low vapor pressures make them attractive as replacements for organic solvents. Other unique properties of ionic liquids, including the high thermal stability, broad ranges of temperatures over which they are liquids, the tunablity of their acidities, and their excellent retention of polar or charged catalysts make them appealing media for a broad range of catalytic applications. Reusable catalyst-ionic liquid systems make possible facile catalyst-product separation, providing economic incentives for the development of such systems for new processes and as replacements for the existing ones.