Ionic liquids opportunities

Diels-Alder reactions in ionic liquids Opportunities for ionic liquids in recovery of biofuels... 

From our point of view, this is exactly what commercial ionic liquid production is about. Commercial producers try to make ionic liquids in the highest quality that can be achieved at reasonable cost. For some ionic liquids they can guarantee a purity greater than 99 %, for others perhaps only 95 %. If, however, customers are offered products with stated natures and amounts of impurities, they can then decide what kind of purity grade they need, given that they do have the opportunity to purify the commercial material further themselves. Since trace analysis of impurities in ionic liquids is still a field of ongoing fundamental research, we think that anybody who really needs (or believes that they need) a purity of greater than 99.99 % should synthesize or purify the ionic liquid themselves. Moreover, they may still need to develop the methods to specify this purity. 

As one would expect, in those cases in which the ionic liquid acts as a co-catalyst, the nature of the ionic liquid becomes very important for the reactivity of the transition metal complex. The opportunity to optimize the ionic medium used, by variation of the halide salt, the Lewis acid, and the ratio of the two components forming the ionic liquid, opens up enormous potential for optimization. However, the choice of these parameters may be restricted by some possible incompatibilities with the feedstock used. Undesired side reactions caused by the Lewis acidity of the ionic liquid or by strong interaction between the Lewis acidic ionic liquid and, for example, some oxygen functionalities in the substrate have to be considered. 

Of course, these concentration effects will be highly dependent on the nature of the substrate dissolved in the ionic liquid, as well as on the nature of the ionic liquid s cation and anion. Given the enormous opportunity to vary these last two, it becomes clear that a detailed understanding of the role of the ionic liquid in reaction mixtures is far from complete. Clearly, this limited understanding is currently restricting our opportunities to benefit from the full potential of an ionic liquid solvent in a given synthetic application. 

Many ionic liquids are stable at temperatures over 300 °C, providing the opportunity to carry out high-temperature reactions at low pressure. 

Recently, there has been considerable interest in developing molten salts that are less air and moisture sensitive. Melts such as l-methyl-3-butylimidazolium hexa-fluorophosphate [211], l-ethyl-3-methylimidazolium trifluoromethanesulfonate [212], and l-ethyl-3-methylimidazolium tetrafluoroborate [213] are reported to be hydro-phobic and stable under environmental conditions. In some cases, metal deposition from these electrolytes has been explored [214]. They possess a wide potential window and sufficient ionic conductivity to be considered for many electrochemical applications. Of course if one wishes to take advantage of their potential air stability, one loses the opportunity to work with the alkali and reactive metals. Further, since these ionic liquids are neutral and lack the adjustable Lewis acidity common to the chloroaluminates, the solubility of transition metal salts into these electrolytes may be limited. On a positive note, these electrolytes are significantly different from the chloroaluminates in that the supporting electrolyte is not intended to be electroactive. 

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. ... 

Riisager A, Fehrmann R, Wasserscheid P, van Hal R (2005) In Rogers RD, Seddon KR (eds) Ionic liquids IIIB fundamentals, progress, challenges, and opportunities - transformations and processes. ACS Symposium Series, vol. 902, 23 334... 

A unique opportunity was created for the carbonylation of alkylamines or aromatic amines with CO2 in CsOH-treated [BMIM]C1, as both reactants have sufficient solubility in the ionic liquid. The products are symmetric urea derivatives. Yields >90% were obtained from the carbonylation of alkylamines, but lower yields were obtained with aromatic amines. The products precipitated when water was added 193). 

Enantioselective hydrogenation in ionic liquids is worthy of attention because of the prospects for efficient reuse of metal complexes with expensive chiral ligands. The opportunities and challenges involved in the application of ionic liquids for chiral synthesis have been assessed recently 213). 

Domarfska, U., Marciniak, A., and Bogel-Lukasik, R., Phase equilibria (SLE, LLE) of N, N-dialkylimidazolium hexafluorophosphate or chloride, in Ionic Liquids lllA Fundamentals, Progress, Challenges, and Opportunities Properties and Structure, R.D. Rogers and K.R. Seddon (Eds), Washington, D.C., 2005 ACS, NY, 2003. 

R.D. and Seddon, K.R. (2005) Ionic Liquids IIIB Fundamentals, Challenges and Opportunities, ACS, Washington DC. 

Roberts, N. J., Lye, G. J. Application of room temperature ionic liquids in biocatalysis Opportunities and challenges. In Ionic Liquids Industrial Applications for Green Chemistry, Rogers, R. D., Sheldon, K. R. Eds., American Chemical Society Washington, D.C., 2002, Vol. ACS Symposium Series 818. 

What is dear from this introduction is that the journey into the area of metal deposition from ionic liquids has tantalizing benefits. It is also dear that we have only just begun to scratch the surface of this topic. Our models for the physical properties of these novel fluids are only in an early state of devdopment and considerably more work is required to understand issues such as mass transport, spedation and double layer structure. Nudeation and growth mechanisms in ionic liquids will be considerably more complex than in their aqueous counterparts but the potential to adjust mass transport, composition and spedation independently for numerous metal ions opens the opportunity to deposit new metals, alloys and composite materials which have hitherto been outside the grasp of electroplaters. 

Yang, Q. and Dionysiou, D. (2005) Room temperature ionic liquids as solvent media for the photolytic degradation of environmentally important organic contaminants. Ionic liquids I IB Fundamentals, Progress, Challenges and Opportunities Transformations and Processes. ACS Symp. Ser., 902,... 

Dyson, P. J. Geldbach, T. J. Moro, F. Taeschler, C. Zhao, D. In Ionic Liquids III Fundamentals, Progress, Challenges, and Opportunities, ACS Symposium Series 901,2005. 

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