Environmentally benign catalyst: Synthesis, characterization, and properties of pyridinium dicationic molten salts (ionic liquids) and use of application in esterification

A series of pyridinium based dicationic [C6(Mpy)2], [C10(Epy)2], [C10(Bpy)2] with traditional counter anions such as Br−, BF4−, PF6− and Tf2N− molten salts (ionic liquids (ILs)) were synthesized. Most of them can be classified as ionic liquids (mp < 100 °C). Key physicochemical properties, such as melting point, thermal stability and solubility in common solvents were determined. The synthesized dicationic salt 1,1′-hexane-1,6-diylbis (3-methylpyridinium) dibromide tested for the esterification of carboxylic acid derivatives with a variety of alkyl halides in the presence of triethylamine. The esterification was carried out under mild reaction conditions and without any additional organic solvent. The results showed that carboxylic acids were successfully converted into esters with good yields and high selectivity. The produced esters were easily recovered due to immiscibility with the ionic liquid as green reaction medium. The ionic liquid was recycled and reused. Thus, reported dicationic ionic liquid was a promising catalyst for esterification reaction.

A series of pyridinium based dicationic [C6(Mpy)2], [C10(Epy)2], [C10(Bpy)2] with traditional counter anions such as Br−, BF4−, PF6− and Tf2N molten salts (ionic liquids) were synthesized. 1,1(-hexane-1,6-diylbis (3-methylpyridinium) dibromide [C6(Mpy)2] (Br)2 used as catalyst for the simple, facile and environmentally benign method for the conversion of carboxylic acids to their corresponding ester.Figure optionsDownload as PowerPoint slideHighlights
► A set of pyridinium based dicationic ionic liquids were synthesized.
► Dicationic IL [C6(Mpy)2] (Br)2 used as catalyst for the esterification of carboxylic acids.
► Reaction carried out under mild reaction conditions and without any additional organic solvent.
► Good yields and high selectivity.
► The dicationic IL recycled and reused.