Green, One-Pot, Solvent-Free Synthesis of 1,2,4,5-Tetrasubstituted Imidazoles Using a Brønsted Acidic Ionic Liquid as Novel and Reusable Catalyst

Abstract

3-Methyl-1-(4-sulfonic acid)butylimidazolium hydrogen sulfate [(CH₂)₄SO₃HMIM][HSO₄], a Brønsted acidic ionic liquid, has been used as an efficient, green, and reusable catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles using benzil, an aromatic aldehyde, and a primary amine in the presence of ammonium acetate under solvent-free conditions. The catalyst could be recycled and reused several times without noticeably decreasing the catalytic activity.

Keywords:

• Brønsted acidic ionic liquids
• multicomponent reactions
• one-pot synthesis
• solvent-free conditions
• tetrasubstituted imidazole

Notes

^a 2 mmol benzil, 2 mmol 4-methyl benzaldehyde, 2 mmol aniline, and 2 mmol ammonium acetate at 140 °C.

^b Isolated yields.

^a Isolated yields.

^a Isolated yields.

^a All the products were characterized by ¹H NMR and IR spectral data and comparision of their melting points with those of authentic samples.

^b Isolated yields.