https://www.chem.ccu.edu.tw/~joyce/referance/gump/IL/Chem.%20Rev.%201999,%2099,%202071.pdf

Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis

Ionic liquids are salts that are liquid at low temperature (<100 degrees C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.

Ionic Liquids-New "Solutions" for Transition Metal Catalysis.

Ionic liquids as electrolytes

Ionic liquids are defined today as liquids which solely consist of cations and anions and which by definition must have a melting point of 100 °C or below. Originating from electrochemistry in AlCl3 based liquids an enormous progress was made during the recent 10 years to synthesize ionic liquids that can be handled under ambient conditions, and today about 300 ionic liquids are already commercially available. Whereas the main interest is still focussed on organic and technical chemistry, various aspects of physical chemistry in ionic liquids are discussed now in literature. In this review article we give a short overview on physicochemical aspects of ionic liquids, such as physical properties of ionic liquids, nanoparticles, nanotubes, batteries, spectroscopy, thermodynamics and catalysis of/in ionic liquids. The focus is set on air and water stable ionic liquids as they will presumably dominate various fields of chemistry in future.

Air and water stable ionic liquids in physical chemistry

Ionic liquids are low melting point salts that represent an exciting new class of reaction solvents for catalysis. Being composed entirely of ions, they possess negligible vapour pressures, and the wide range of possible cations and anions means that other solvent properties may be easily controlled. There is currently great interest in the use of these materials as solvents for a wide range of applications, including catalysis. Many reactions show advantages when carried out in ionic liquids, either with regard to enhanced reaction rates, improved selectivity, or easier reuse of catalysts. This review is intended to bring the reader up to date on the developments involving ionic liquids in catalytic applications over the previous 18 months. Recent spectroscopic investigations into the solvent properties of ionic liquids with relevance to catalysis are discussed first, followed by a critical review of the major developments in transition metal, Lewis acid, and enzyme catalysed processes in these solvents. Particular emphasis is given to the combination of ionic liquids with supercritical fluids, Pd-based catalysts, and enzymes. Wherever possible, the results gained in ionic liquids are critically compared with those obtained using other catalytic systems.

Phillip D. Armitage

Papers

Molybdenum chloro complexes in room-temperature chloroaluminate ionic liquids: stabilization of hexachloromolybdate(2-) and hexachloromolybdate(3-)