Synthesis, characterization, and properties of imidazole dicationic ionic liquids and their application in esterification

Three kinds of imidazole based dicationic [C2(Mim)2], [C3(Mim)2], [C4(Mim)2] with traditional counter anion HSO4- ionic liquids (ILs) were synthesized. Key physicochemical properties, such as thermal stability, solubility in common solvents, acidic property and corrosion of ILs for Austenitic stainless steel 316 were determined. Esterification of alcohols by carboxylic acids has been carried out at room temperature in a group of imidazole dicationic ionic liquid. The catalytic performance was found to be much better than that of conventional non-cation functionalized ionic liquids and the corrosion was five times weaker than sulfuric acid. The esters were easily recovered due to immiscibility with the ionic liquid and reported imidazole dicationic ionic liquids were a promising catalyst for esterification reaction.

• Three kinds of imidazole based dicationic ionic liquids were synthesized efficiently.
• Key physicochemical properties of dicationic ionic liquids were determined.
• Dicationic ILs as catalyst, esterification has been carried out at room temperature.
• Catalytic activity of three kinds of dicationic ILs with C2, C3, C4 differed little.
• The IL catalysts can be easily recovered without any other chemical residued.