Ionic liquid as catalyst

The acidic and catalytic properties of chloroaluminate(iii) ionic liquids are frequently said to arise from the species AI2CI7 which is generated according to Equation (5.1). 

It has been shown, however, that such catalysts may contain protons, either by design or because of the difficulty in removing all traces of moisture, and these protons have been shown to be superacidic with Hammett acidities up to —18. These protons will also play some role in the catalytic activity of these ionic liquids in practical situations. Ionic liquids in which superacidic protons have deliberately been generated by addition of small amounts of water, HCl or H2SO4 have been used to catalytically crack polyethene under relatively mild conditions. The main products are mixed C3-C5 alkanes, which would be a useful feedstock from waste polyethene recycling. In contrast to other cracking procedures no aromatics or alkenes are produced, although small amounts of polycyclic compounds are obtained. 

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BMIMJCI/SnCb ionic liquid as catalyst layer. 

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. 

Catalytic Hydrogenation using Ionic Liquids as Catalyst Phase... 

Organochloroaluminate ionic liquids as catalysts, 42 495-496 Organochromium catalysis attachment to support, 33 92-93 kinetics of polymerization, 33 93 support effects, 33 94-95 termination mechanism, 33 93-94 Organochromium catalysts, 33 58, 92-95... 

Ionic liquids as catalysts, solvents and conversion agents 154... 

Scheme 5.2-13 Biphasic, Pt-catalyzed hydroformylation of 1-octene with a slightly acidic [BMIMJCI/SnClj ionic liquid as catalyst layer.

Explore the use of ionic liquids as catalysts for aromatic alkylation reactions ... 

Seddon and co-workers described the Friedel-Crafts acylation reaction of benzene with ace-tylchloride using acidic chloroferrate ionic liquids as catalysts [38], In contrast to the same reaction in presence of acidic chloroaluminate systems the ketone product could be separated from the ionic liquid by solvent extraction, provided that the molar ratio of FeCl3 is in the range 0.51-0.55 in the applied ionic liquid catalyst (Scheme 1). 

Recently, our group described in collaboration with Tkatchenko et al. the Pd-catalyzed dimerisation of methylacrylate(MA) using a tetrafluoroborate ionic liquid as catalyst solvent (Scheme 6) [54]. 

Scheme 6. Pd-catalyzed dimerisation of methylacrylate using a tetrafluoroborate ionic liquid as catalyst solvent.

Fig. 4.58 Ruthenium salts in ionic liquids as catalysts for oxidation of alcohols.

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