Non-chloroaluminate Lewis-acid-catalyzed reactions

Friedel-Crafts Acylation. Acylation reactions have been carried out in acidic chloroaluminate(III) ionic liquids (125,126). The regioselectivities and reaction rates are comparable to the best known for the traditional acylations. However, the consumption of the ionic liquid as a catalyst was high, as in the industrial process that is carried out with AICI3. 

The ionic liquids made of ferric chloride and tin chloride displayed good properties as alternative catalysts in the acylation reactions (127). For the acylation of mesitylene with acetylchloride and for the acylation of anisole with acetylanhydride, the best results were obtained with a ferric chloride-containing ionic liquid. The conversions were much higher, and the selectivity obtained was in the same range relative to those observed with the Al- and Sn-chloride-containing ionic liquids. 

In-situ IR-spectroscopic characterization of the Friedel-Crafts acylation of benzene in ionic liquids derived from AICI3 and FeCl3 showed that the mechanism of the reaction in ionic liquids was the same as that in 1,2-dichloroethane (128). The immobilization of ferric chloride-containing ionic liquid onto solid supports (e.g., silica and carbon) however failed to catalyze the acylation reaction, because leaching was a serious problem. When the reaction was carried out with gas-phase reactants, catalyst deactivation was observed. 

Diels-Alder Reactions. The Diels-Alder reaction is one of the reactions that has been most thoroughly investigated with ionic liquids (1). Adding a Lewis acidic catalyst such as Sc(OTf)3 to ionic liquids improves endo selectivity (129). Ionic liquid co-solvent was found to activate the Lewis-acidic Sc(OTf)3 catalyst in 

Unusually high diastereoselectivity and enantioselectivity in Diels-Alder reactions were achieved in ionic liquids at room temperature (131). The selectivity rivals that of the reaction in conventional solvents, for which a low temperature (e.g., — 78°C) is needed. Furthermore, the rate of the reaction is much higher in the ionic liquids than in the conventional solvents, because the reaction is carried out at room temperature in ionic liquids. 

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