Ionic liquids economic issues

Another environmental issue is the use of organic solvents. The use of chlorinated hydrocarbons, for example, has been severely curtailed. In fact, so many of the solvents favored by organic chemists are now on the black list that the whole question of solvents requires rethinking. The best solvent is no solvent, and if a solvent (diluent) is needed, then water has a lot to recommend it. This provides a golden opportunity for biocatalysis, since the replacement of classic chemical methods in organic solvents by enzymatic procedures in water at ambient temperature and pressure can provide substantial environmental and economic benefits. Similarly, there is a marked trend toward the application of organometal-lic catalysis in aqueous biphasic systems and other nonconventional media, such as fluorous biphasic, supercritical carbon dioxide and ionic liquids. ... 

There is little doubt that intrepid entrepreneurs will continue to champion ideas for the application of ionic liquids. Without a doubt, further uses of these materials will be found and justified for commercial use. However, the perceived disadvantages, and particularly the toxicity issues, will temper enthusiasm until the data obtained provide reassurances that an ionic-liquid-based process satisfies all the economic, toxicological, safety, and (in the pharmaceutical industry) FDA regulatory criteria to justify implementation. 

As ionic liquids are stiU expensive in comparison with conventional molecular solvents, their efficient recycling is an important issue that addresses the economics of their use, especially in large-scale applications. The most studied examples are the 1,3-dialkylimidazolium-based ionic liquids where the ionic solvent is usually recycled through several cycles of the reaction. Numerous examples describe the immobilization of a transition metal catalyst in the ionic liquid phase of a biphasic system. A variety of palladium coupling reactions, such as the Heck [27], Suzuki... 

The final part will summarise the key issues from each of the two subsections and will also briefly discuss strategies and techniques for the sustainable reuse and recycling of ionic liquids in industrial processes, with the aim of reducing exposure as well as making sensible economical use of them... 

The all-decisive requirement for the fractionation by means of CPF consists of the availability of a suitable solvent enabling the realization of liquid-liquid equilibria. For some polymers, such solvents are unknown. In such cases, it is possible to evade this issue by transforming the polymer into a soluble derivative. This strategy has been applied to cellulose although several direct solvents for cellulose (e.g., N-methylmorpholine-N-oxide, ionic liquids, and dimethylacetamide (DMAc) plus liCl) exist, it is probably more economic to realize the fractionation through the derivatives. Two such products, hydroxylethyl cellulose and trimethylsilylcellulose, ° have been fractionated by means of CPF. For hydroxylethyl cellulose water was used as solvent and THF served as nonsolvent, while toluene and dimethyl sulfoxide were used in the case of trimethylsilylcellulose. 

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