Supercritical carbon dioxide catalysis

The combination of ionic liquids with supercritical carbon dioxide is an attractive approach, as these solvents present complementary properties (volatility, polarity scale.). Compressed CO2 dissolves quite well in ionic liquid, but ionic liquids do not dissolve in CO2. It decreases the viscosity of ionic liquids, thus facilitating mass transfer during catalysis. The separation of the products in solvent-free form can be effective and the CO2 can be recycled by recompressing it back into the reactor. Continuous flow catalytic systems based on the combination of these two solvents have been reported [19]. This concept is developed in more detail in Section 5.4. 

The only ceramic membranes of which results are published, are tubular microporous silica membranes provided by ECN (Petten, The Netherlands).[10] The membrane consists of several support layers of a- and y-alumina, and the selective top layer at the outer wall of the tube is made of amorphous silica (Figure 4.10).[24] The pore size lies between 0.5 and 0.8 nm. The membranes were used in homogeneous catalysis in supercritical carbon dioxide (see paragraph 4.6.1). No details about solvent and temperature influences are given but it is expected that these are less important than in the case of polymeric membranes. 

P. G. Jessop, Y. Hsiao, T. Ikariya, R. Noyori, Homogeneous Catalysis in Supercritical Fluids Hydrogenation of Supercritical Carbon Dioxide to Formic Acid, Alkyl Formates, and Formamides ,J. Am Chem Soc 1996,118, 344-355. 

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. ... 

In laboratory-scale homogeneous catalysis applications, in the last decade further investigations have been carried out in which a less soluble organo-metallic catalyst system was utilized for metathesis reactions [46]. Under RCM-conditions, it was possible to convert substrates with functional groups that were problematic due to their potential to inactivate the rutheniiun catalyst here, the conversion in supercritical carbon dioxide avoids the protection of critical amino groups as an additional synthetic step. Consequently, it was possible to synthesize a number of carbo- and heterocyclic products with varying ring size (C4 to Cie). 

From an industrial point of view, homogeneous catalysis has significant advantages concerning selectivities and due to mild reaction conditions [47]. In fact, there is only a limited munber of processes established in industrial applications because of the disadvantageous separabihty of the catalyst from substrate and product. A possible and convenient solution for this limitation can be the application of supercritical carbon dioxide as part of a reaction system due to the following ... 

Leitner W (1999) In Knochel P (ed) Reactions in Supercritical Carbon Dioxide (scC02) in Modern Solvent Systems. Top Curr Chem 206 107 Morita DK, David SK (1998) Chem Commun, p 1397 Wegner A, Leitner W (1999) Chem Commun, p 1583 Sellin M, Cole-Hamilton DJ (2000) J Chem Soc, Dalton Trans, p 1681 Solinas M, Pfaltz A, Leitner W (2004) J Am Chem Soc 126 16124 Leitner W, Scurto AM (1998) Imobilization of Organometallic Catalysts using Supercritical Fluids. In Cornils B, Herrmann WA (eds) Aqueous Organometallic Catalysis. WUey, Weinheim, p 664... 

Evaluation of Supercritical Carbon Dioxide as a Tuneable Reaction Medium for Homogeneous Catalysis... 

Keywords Supercritical carbon dioxide Solubility measurement Homogeneous catalysis Multi-phase catalysis Hydroformylation... 

Peris E (2006) Routes to N-Heterocydic Carbene Complexes. 21 83-116 Fitter S, Dinjus E, lonescu C, Maniut C, Makarczyk P, Patcas F (2008) Evaluation of Supercritical Carbon Dioxide as a Tuneable Reaction Medium for Homogeneous Catalysis. 23 109-147... 

Liu, F., Abrams, M.B., Baker, R.T., and Tumas, W., Phase-separable catalysis using room temperature ionic liquids and supercritical carbon dioxide, Chem. Commun., 433-434,2001. 

Table 2.1. Homogeneous Catalysis in Liquid or Supercritical Carbon Dioxide... 

Michor, H. Marr, R. Gamse, T. Enzymatic Catalysis in Supercritical Carbon Dioxide Effect of Water Activity. High Pressure Chem. Eng. 1996a, 12, 115-120. 

Michor, H. Marr, R. Gamse, T. Schilling, T. Klingsbichel, E. Schwab, H. Enzymatic Catalysis in Supercritical Carbon Dioxide Comparison of Different Lipases and a Novel Esterase. Biotechnol. Lett. 1996b, 18, 79-84. Miller, D. A. Blanch, H. W. Prausnitz, J. M. Enzyme-Catalyzed Interesterification of Triglycerides in Supercritical Carbon Dioxide. Ind. Eng. Chem. Res. 1991, 30, 939-946. 

Leitner W (2002) Supercritical carbon dioxide as a green reaction medium for catalysis. Acc Chem Res 35(9) 746-756... 

Bhanage BM, Shirai M, Arai M et al (1999) Multiphase catalysis using water-soluble metal complexes in supercritical carbon dioxide. Chem Commun 14 1277-1278... 

Solinas M, Jiang J, Stelzer O et al (2005) A cartridge system for organometallic catalysis sequential catalysis and separation using supercritical carbon dioxide to switch phases. Angew Chem Int Ed 44(15)2291-2295... 

Chandler K, Culp CW, Lamb DR et al (1998) Phase-transfer catalysis in supercritical carbon dioxide kinetic and mechanistic investigations of cyanide displacement on benzyl chloride. Ind Eng Chem Res 37(8) 3252-3259... 

Kainz S, Koch D, LeitnerW etal (1997) Perfluoroalkyl-substituted arylphosphanes as ligands for homogenous catalysis in supercritical carbon dioxide. Angew Chem Int Ed 36(15) 1628-1630... 

Francio G, Wittmann K, Leitner W (2001) Highly efficient enantioselective catalysis in supercritical carbon dioxide using the perfluoroalkyl-substituted ligand (R, S)-3-H2F6-BINAPHOS. J Organomet Chem 621(1-2) 130-142... 

Komoto I, Kobayashi S (2004) Lewis acid catalysis in supercritical carbon dioxide. Use of poly(ethylene glycol) derivatives and perfluoroalkylbenzenes as surfactant molecules which enable efficient catalysis in scC02. J Org Chem 69(3) 680-688... 

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