Synthesis and applications of novel imidazole and benzimidazole based sulfonic acid group functionalized Bronsted acidic ionic liquid catalysts

In this study, a variety of imidazole/benzimidazole based sulfonic acid group functionalized Bronsted acidic ionic liquids (BAILs) were synthesized. Catalytic activities of BAILS were assessed using multicomponent coupling reactions. Catalytic activities of BAILs were high when compared with those of solid acid catalysts such as H-ZSM-5. H-BETA, and sulfonic acid functionalized SBA-15 catalysts. The Hammett acidity order determined from UV-visible spectroscopy of BAILS is consistent with their activity order observed in acid-catalyzed reactions. Theoretical studies demonstrate that the hydrogen bonding plays a key role in tuning the acidity of BAILs. Recycling experiments suggest that these novel BAILS can be reused without significant loss in catalytic activity. Novel BAILS offer several attractive features such as low cost, high catalytic activity, and recyclability. (C) 2011 Elsevier B.V. All rights reserved.