Green solvents, ionic liquids

A challenging goal in RE separation is to develop an effective process to enhance separation and minimize environmental pollution. But what is the satisfied dilute and extractant The desired dilute should be nonvolatile, nonflammable, and low toxicity, while high efficiency, high stability, low cost, and low acid and base consumption are required for the candidate extractant. In recent years, as a green solvent, ionic liquid gained extensive attention and showed tremendous potential to RE green separation. 

Abbott et al. [98-103] reported the synthesis and characterization of new moisture-stable, Lewis acidic ionic liquids made from metal chlorides and commercially available quaternary ammonium salts (see Chapter 2.3). They showed that mixtures of choline chloride (2-hydroxyethyltrimethylammonium chloride, [Me3NC2H40H]Cl and MCU (M=Zn, Sn) give conducting and viscous liquids at or around room temperature. These deep eutectic solvents/ionic liquids are easy to prepare, are water-and air-stable, and their low cost enables their use in large-scale applications. Furthermore, they reported [104] that a dark green, viscous liquid can be formed by mixing choline chloride with chromium(III) chloride hexahydrate and that the... 

Garcia, S. Lourenco, N.M.T. Lousa, D. Sequeira, A.F. Mimoso, P. Cabral, J.M.S. Afonso, C.A.M. Barreiros, S. A comparative study of biocatalysis in non-conventional solvents ionic liquids, supercritical fluids and organic media. Green Chem. 2004, 6 (9), 466-470. 

S. (2004) A comparative study of biocatalysis in non-conventional solvents ionic liquids, supercritical fluids and organic media. Green Chem., 6 (9), 466-470. 

The choice of reaction solvent is also of concern in the synthesis of new TSILs. Toluene and acetonitrile are the most widely used solvents, the choice in any given synthesis being dictated by the relative solubilities of the starting materials and products. The use of volatile organic solvents in the synthesis of ionic liquids is decidedly the least green aspect of their chemistry. Notably, recent developments in the area of the solventless synthesis of ionic liquids promise to improve this situation [10]. 

In cases in which product solubility in the ionic liquid and the product s boiling point are high, the extraction of the product from the ionic liquid with an additional organic solvent is frequently proposed. This approach often suffers from some catalyst losses (due to some mutual solubility) and causes additional steps in the workup. Moreover, the use of an additional, volatile extraction solvent may nullify the green solvent motivation to use ionic liquids as nonvolatile solvents. 

Ionic liquids have several important features that make them attractive for use as solvents, particularly in green chemistry ... 

Recently, room temperature ionic liquids (RT-ILs) have attracted much attention for their excellent properties, e.g., wide temperature range of liquid phase, ultra-low vapor pressure, chemical stability, potential as green solvents, and high heat capacities [64,65]. These properties make them good candidates for the use in many fields, such as thermal storage [66], electrochemical applications, homogeneous catalysis [67], dye sensitized solar cells [68], and lubricants [69,70]. 

S., Kula, M.R., and Kragl, U. (2003) Enzymatic Condensation Reactions in ionic liquids, in Ionic Liquids as Green Solvents, ACS Symposium Series, Vol. 856 (eds R.D. Rogers and... 

Room-temperature ionic liquids have received much attention as green designer solvents. We first demonstrated that ionic liquids acted as good medium for lipase-catalyzed production of polyesters. The polycondensation of diethyl adipate and 1,4-butanediol using lipase CA as catalyst efficiently proceeded in l-butyl-3-methylimidazolinium tetrafluoroborate or hexafluorophosphate under reduced pressure. The polymerization of diethyl sebacate and 1,4-butanediol in l-butyl-3-methylimidazolinium hexafluorophosphate took place even at room temperature in the presence of lipase BC. ... 

Earle, M.J. Seddon, K.R. (2002) Ionic Liquids Green Solvents for the Euture. Clean Solvents, 819, 10-25. 

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