Friedel-Crafts Acylation of Aromatic Compounds in Ionic Liquids

This article first reviews the application of ionic liquids in Friedel-Crafts acylation reactions. Ionic liquids can be used as catalyst solvents, the active component on solid carriers, or just as the solvent. One advantage of using ionic liquids in acylation reactions is the enhanced reaction rates, conversion, and selectivity. The acylation mechanisms of aromatic compounds in ionic liquids are also reviewed and analyzed. The acetylium cation [RCO]+ was confirmed to be the key intermediate in the acetylation reactions, and the replacement of a traditional solvent with the ionic liquid did not alter the acylation mechanism. With good consideration, we propose two rational acylation mechanisms for the Friedel-Crafts acylation of aromatics in the Lewis acidic ionic liquid and in the Lewis acid-ionic liquid system. Although the reaction rates, the conversion, and the selectivity for the acylation in ionic liquids are high, the separation of aryl ketone products from ionic liquids and the recycle of the ionic liquids are still a problem.