Novel SO ₃H-functionalized ionic liquids based on benzimidazolium cation: Efficient and recyclable catalysts for one-pot synthesis of biscoumarin derivatives

In this article, a new group of SO ₃H-functionalized ionic liquids based on benzimidazolium cation was synthesized and used as environmentally benign catalysts for the one-pot synthesis of biscoumarin derivatives. The ionic liquids showed high catalytic activities and reusabilities with good to excellent yields of the desired products. H ₀ (Hammett function) values and the minimum-energy geometries of SO ₃H-functionalized ionic liquids were determined and the results revealed that the acidities and catalytic activities of ionic liquids in the synthesis of biscoumarin derivatives were related to their structures. Graphical Abstract: The simple, more efficient way for synthesis of biscoumarin derivatives has been developed. This new method abandon the traditional hazardous organic liquid and is carried out by using a one-pot reaction of 4-hydroxycoumarin with aromatic aldehydes in the presence of novel SO ₃H-functionalized ionic liquids based on benzimidazolium cation as catalysts. The ionic liquids showed high catalytic activities and reusabilities with good to excellent yields of the desired products. H ₀ (Hammett function) values and the minimum-energy geometries of SO ₃H- functionalized ionic liquids were determined and the results revealed that the acidities and catalytic activities of ionic liquids in the synthesis of biscoumarin derivatives were influenced by their structures.[Figure not available: see fulltext.]