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.