Ionic liquids, multiphase catalysis with

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

Liquid-liquid multiphasic catalysis with the catalyst present in the ionic liquid phase relies on the transfer of organic substrates into the ionic liquid or reactions must occur at the phase boundary. One important parameter for the development of kinetic models (which are crucial for up-scaling and proper economic evaluation) is the location of the reaction. Does the reaction take place in the bulk of the liquid, in the diffusion layer or immediately at the surface of the ionic liquid droplets ... 

Multiphasic Catalysis with Ionic Liquids in Combination with Compressed CO2 5.4... 

MULTIPHASIC CATALYSIS WITH IONIC LIQUIDS - ENGINEERING ASPECTS... 

The use of ionic liquids has been successfully studied in many transition metal-catalyzed hydrogenation reactions, ranging from simple alkene hydrogenation to asymmetric examples. To date, almost all applications have included procedures of multiphase catalysis with the transition-metal complex being immobilized in the ionic liquid by its ionic nature or by means of an ionic (or highly polar) ligand. 

Olivier-Bourbigou H, Forestiere A (2003) Ionic liquids in multiphasic reactions. In Wasserscheid P,Welton T (eds) Ionic liquids in synthesis. Wiley-VCH,Weinheim,p 258 Wasserscheid P (2003) Multiphasic catalysis with ionic liquids in combination with compressed COj. In Wasserscheid P, Welton T (eds) Ionic liquids in synthesis. Wiley-VCH,Weinheim,p 281 Keim W (2003) Green Chem 5 105... 

Notably, the use of liquid polymers in multiphase catalysis with SCCO2 is not restricted to transition metal catalysts. Biocatalysts can also be used in this environment, as demonstrated by the yeast-catalyzed reduction of a (i-ketoester that gave excellent (99%) enantioselectivity in PMPS-710 and the ionic liquid [P(Me)(Bu)3][ Bu)3][03SCgH4pMe] [Eq. (8)]. The product was isolated by extraction with water or SCCO2, respectively [54]. 

Wasserscheid, P. and Kuhlmann, S., Multiphasic Catalysis Using Ionic Liquids in Combination with Conpressed CO2 , in Ionic Liquids in Synthesis, 2nd Ed., Eds. P. Wasserscheid and T. Welton, Mley-VCH, Weinheim (2008), pp. 558-569. 

One of the key factors controlling the reaction rate in multiphasic processes (for reactions talcing place in the bulk catalyst phase) is the reactant solubility in the catalyst phase. Thanks to their tunable solubility characteristics, the use of ionic liquids as catalyst solvents can be a solution to the extension of aqueous two-phase catalysis to organic substrates presenting a lack of solubility in water, and also to moisture-sensitive reactants and catalysts. With the different examples presented below, we show how ionic liquids can have advantageous effects on reaction rate and on the selectivity of homogeneous catalyzed reactions. 

As described in the introductory chapter, biphasic catalysis has been around for a long time, but despite a few notable successes such as the Shell Higher Olefin Process (SHOP) and the Rhone-Poulenc-Ruhrchemie hydroformylation process, very few biphasic processes have made it into the industrial arena. The limitations of the solvents used so far in biphasic (or multiphasic) catalysis appear to be overcome by ionic liquids, and even if the perfect ionic liquid is not yet available, then there seems to be almost no limit to the number of new ionic liquids that can be made. It has been estimated that up to 1018 different ionic liquids may exist[1 2] and with such a vast number to choose from it is essential that understanding increases in order to allow accurate predictions of their properties and functions, opening up the possibility of designer solvents. 

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