Title: Ionic Liquids
Literature References: Liquids composed entirely of ions; molten salts with melting points below 100°. Commonly consist of organic cations and inorganic anions. The cations most frequently used to generate ionic liquids are alkyl derivatives of imidazolium, pyridinium, ammonium and phosphonium. Early development: S. Sugden, H. Wilkins, J. Chem. Soc. 1929, 1291. Environmental risk assessment: B. Jastorff et al., Green Chem. 5, 136 (2003). Comprehensive description: R. D. Rogers, K. R. Seddon, Eds., ACS Symp. Ser. 818, 1-474 (2002). Review of prepn, properties and uses in synthesis and catalysis: T. Welton, Chem. Rev. 99, 2071-2083 (1999); P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 39, 3772-3789 (2000); of applications in organic synthesis: H. Zhao, S. V. Malhotra, Aldrichim. Acta35, 75-83 (2002); of use as reaction media for catalytic reactions: R. Sheldon, Chem. Commun. 2001, 2399-2407; for biocatalytic transformations: F. van Rantwijk et al., Trends Biotechnol. 21, 131-138 (2003); of commercial uses: J. H. Davis, Jr., P. A. Fox, Chem. Commun. 2003, 1209-1212.
Properties: Many are colorless, some are pale yellow to orange in color. No measurable vapor pressure. Thermally stable; many have liquid ranges of more than 300°. Dissolve a wide range of organic and inorganic compounds; soly of gases is generally good. Immisc with many organic solvents, forming biphasic systems.
Use: Highly polar, noncoordinating solvents with a broad range of green chemistry applications in organic synthesis and catalysis. |