CATALYSIS The ongoing pressure for the chemical industry to reduce the amounts of organic solvents (VOCs) has led to the development of novel reaction media. While alternative approaches such as heteregenous catalysis and aqueous reaction media exist they may not represent generic solutions to these problems.
The use of neoteric solvents such as supercritical CO2 [1], aqueous biphasic systems [2] and ionic liquids [3-5] has been shown to be one of the most promising areas of research. The performances of these systems have of course to be superior in terms of activity selectivity and reclyability in order to be applied industrially. The rhodium-catalyzed hydroformylation of 1-octene in ECOENGTM 418 (1-butyl-3-methyl-imidazolium octylsulfate) for example [6] has significantly higher TOF numbers than in conventional processes.
Ionic Liquids have also been investigated in Heck reactions and related C-C couplings [9-11] and show several advantages like significantly increased turnover frequencies, easier product recovery and recyclability of the ionic catalyst layer. Biphasic catalysis in ionic liquids is an ideal approach to overcome problems such as separating the dissolved catalyst from the products and by-products of the reaction [12]. A very interesting recent development is the use of ionic liquid/compressed CO2 in transition metal catalysis as sc CO2 is surprisingly soluble in some ionic liquids but the reverse is not the case [13]. In addition to the examples mentioned above a lot of other catalytic reactions have been successfully run in ionic liquids demonstrating the broad versatility and numerous advantages of this new and powerful methodology. It can be expected that within the next two years we will see an industrial application of ionic liquids in the field of transition metal catalysis. Solvent Innovation offers a synthesis and catalysis kit with specially selected ionic liquids. For more information about catalytic reactions performed in ionic liquids please contact info@solvent-innovation.com [1] P. G. Jessop, W. Leitner (eds.) ?Chemical Synthesis Using Supercritical Fluids" Wiley-VCH, Weinheim, 1999 . [2] B. Cornils, Org. Process Res. Dev. 1998 , 2 , 121. [3] P. Wasserscheid, T. Welton (eds.) ? Ionic Liquids in Synthesis" , Wiley-VCH, Weinheim 2003. [4] P. Wasserscheid, W. Keim, Angew. Chem. Int Ed. 2000 , 39 , 3772. [5] J. Dupont et al., Chem. Rev. , 2002 , 102, 3667. [6] P. Wasserscheid et al. Green Chemistry , 2002 , 2, 404. [7] J. Dupont et al. Tetrahedron Asymmetry 2001 , 12(13) , 1825 [8] P. Wasserscheid et al. Chem.-Ing.-Technik 2001 , 73 , 715. [9] W. A. Herrmann et al., J. Organomet Chem. 2003 , 229. [10] T. Welton et al., Organometallics 2003 , 5351. [11] K. R. Sed don et al., Org. Lett. 1999 , 1 , 997. [12] H. Olivier-Bourbigou, A. Forestiere in Ionic Liquids in Synthesis , Wiley-VCH, Weinheim 2003 , 258-279. [13] P. Wasserscheid in Ionic Liquids in Synthesis , Wiley-VCH, Weinheim 2003 , 281-288.
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Generally the ionic liquid can be regarded as an "innocent" solvent (weakly coordinating anions such as [PF6] and [BF4] ), as a ligand, as a co-catalyst or the catalyst itself. In this context ionic liquids have been applied in numerous different catalytic reactions. Hydrogenation reactions [7-8] are particularly promising as the diffusion of hydrogen into ionic liquids is relatively fast and biphasic procedures are often possible. The use of ionic liquids in oxidation reactions also offers several advantages due to their non-volatile and non-flammable nature.