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

In this study, a variety of imidazole/benzimidazole based sulfonic acid group functionalized Brönsted acidic ionic liquids (BAILs) were synthesized. Catalytic activities of BAILs were assessed using multi-component 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.

Imidazole and benzimidazole based sulfonic acid group functionalized Brönsted acidic ionic liquids (BAIL-1 to BAIL-7) were found to be novel acid catalysts in multi-component coupling reactions.Figure optionsDownload high-quality image (146 K)Download as PowerPoint slideHighlights
► Several imidazole/benzimidazole based Brönsted acidic ionic liquids were developed.
► Hydrogen bonding plays a key role in tuning the acidity of ionic liquids.
► Ionic liquids exhibited high activity compared to several solid acid catalysts.
► Ionic liquids can be recycled without significant loss in catalytic activity.