Why Ionic Liquids in Mutiphasic Catalysis

Notwithstanding their very low vapor pressure, their good thermal stability (for thermal decomposition temperatures of several ionic liquids see Refs. [11,12]) and their wide operating range, the key property of ionic liquids is the potential to tune their physical and chemical properties by varying the nature of the anions and cations. An illustration of their versatility is given by their exceptional solubility characteristics, which make them good candidates for multiphasic reactions (see Section 3.3). Their miscibility with water, for example, depends not only on the hydrophobicity of the cation, but also on the nature of the anion and on the temperature. 

N -Dialkylimidazolium cations are of particular interest because they generally give low melting salts, are more thermally stable than their tetraalkylammonium 

Catalyst phase Product phase Advantages Limitations 

Water (-fco-solvent) Organic liquid Easy product separation and catalyst recycling Lower cost of chemical processes Lack of toxicity of water Low reaction rate for water poorly miscible substrates Mass transfer limits rate of reaction Treatment of spent water 

Polar solvent Organic liquid Solvent effect Use of volatile organic solvent Co-miscibility of the two phases 

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