Silica functionalized sulphonic acid coated with ionic liquid: an efficient and recyclable heterogeneous catalyst for the one-pot synthesis of 1,4-dihydropyridines under solvent-free conditions†
Silica-supported sulphonic acid catalysts were prepared and coated with ionic liquid, and their catalytic activities were evaluated for the one-pot synthesis of 1,4-dihydropyridines. Different catalysts with an ionic liquid layer (SCILLs) have been prepared with a view to determine the most active catalyst. Silica sulphonic acid coated with [BMIM][PF6] was found to be the most active catalyst and can be recycled for several runs without the loss of significant activity. It was characterized using SEM, TEM, TGA and FTIR.