Bentonite with high loading of ionic liquid: A potent non-metallic catalyst for the synthesis of dihydropyrimidinones

Abstract

In attempt to devise an environmentally-benign metal-free catalyst, ionic liquid was supported on bentonite that is a natural clay. To enhance the loading of ionic liquid, bentonite was first functionalized with a dendritic moiety through successive reactions with 2,4,6-trichloro-1,3,5-triazine and 1,3-diaminopropane. Then, the terminal functionalities of dendron were adorned with ionic liquids via reaction with 1-methyl imidazole. The study of the catalytic activity of the resultant catalyst for promoting Biginelli reaction in aqueous media under mild reaction condition approved high activity of the designed composite, superior to that of bentonite. To investigate the role of ionic liquid content in the activity of the catalyst, two model catalysts were prepared through immobilization of ionic liquid on bentonite and bentonite decorated with dendron of lower generation. It was found that the presence of the dendritic moiety could increase grafting of ionic liquid on bentonite and consequently improve the catalytic activity of final catalyst. Notably, the catalyst was highly recyclable. Moreover, analysis of the recycled catalyst indicated the stability of the catalyst.