Synthesis of Quinoline Derivatives via the Friedländer Annulation Using a Sulfonic Acid Functionalized Liquid Acid as Dual Solvent-Catalyst

Abstract

4-Imidazol-1-yl-butane-1-sulfonic acid (ImBu-SO₃H) has been synthesized and completely characterized by FT-IR, one-dimensional NMR spectroscopy (¹H, ¹³C). The “plausible” alternative structures of ImBu-SO₃H were discussed by NMR. The title liquid acid showed interesting dual solvent-catalytic property, which was studied experimentally in the synthesis of quinoline derivatives via the Friedländer annulation and provided good yield within short reaction time. ImBu-SO₃H was successfully recycled by water extraction, instead of organic solvent extraction, with an average recovered yield of 82% for five subsequent runs. The recycled liquid acid showed almost no loss of the catalytic activity even after five consecutive runs.

Keywords:

• Brönsted acid
• dual solvent-catalyst
• Friedländer annulation
• quinoline
• sulfonic acid-functionalized liquid

Acknowledgments

The authors are grateful to staff members in the Analytical and Testing Center of Professor Reza Research Institute and Malaya for partial support.

Additional information

Funding

This work was supported by a High Impact Research Grant (No. RP025A/B/C-14AET) for Scientific Research from University of Malaya, Malaysia.