Comparison of the efficiency of two imidazole-based dicationic ionic liquids as the catalysts in the synthesis of pyran derivatives and Knoevenagel condensations

摘要

In the present work, 3,3 '-(butane-1,4-diyl)bis(1-methyl-1H-imidazol-3-ium) dichloride ([C-4(MIm)(2)]center dot 2Cl) and 3,3(')-(butane-1,4-diyl)bis(1-methyl-1H-imidazol-3-ium) hydrogen sulfate ([C-4(MIm)(2)]center dot 2HSO(4)) were prepared via adequate, solvent-free methods and characterized using FT-IR, H-1 NMR, C-13 NMR, and potentiometric titration techniques. These reagents were investigated in the synthesis of 5-arylidene (thio)barbituric acids, 2-arylidene malononitriles, 4H-pyrans, and pyrano[2,3-d] pyrimidineones, and their catalytic activities were compared in the promotion of these reactions. Based on the obtained results, we found that [C-4(MIm)(2)]center dot 2Cl showed more catalytic efficiency where a basic or weak acidic media is needed. In contrast, [C-4(MIm)(2)]center dot 2HSO(4) is a powerful catalyst in reactions needing acidic catalysts to enhance the reaction rate. Using these reagents, the products were formed under mild and eco-friendly conditions in excellent yields during short reaction times without needing column chromatography for work-up.