Novel ionic liquid [2-Eim] HSO4 as a dual catalytic-solvent system for preparation of hexahydroquinolines under green conditions

Abstract

A novel Brønsted acidic ionic liquid 2-ethylimidazolium hydrogen sulfate, [2-Eim] HSO₄, was synthesized. Its structure was investigated using FT-IR, ¹H NMR, ¹³C NMR, UV, TGA and DTA spectroscopy. This ionic liquid was utilized as a highly efficient and homogeneous catalyst for the promotion of hexahydroquinolines via one-pot multi-component condensation of aromatic aldehydes, dimedone, ethyl acetoacetate, and ammonium acetate at room temperature and neat conditions. Also, optimization of the reaction conditions was investigated using the response surface method (Central Composite Design (CCD)). This new method consistently has the advantages of excellent yields and short reaction times. Furthermore, the catalyst could be reused and recovered at least four times without appreciable loss of activity.