An ionic liquid gel: a heterogeneous catalyst for Erlenmeyer–Plochl and Henry reactions

Abstract

An ionic liquid gel has been prepared by entrapping 1-butyl-3-methylimidazolium hydroxide ([Bmim]OH) in an aqueous agar gel. The ionic liquid gel has been characterized by Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and energy dispersive X-ray analysis (EDX). The ionic liquid gel has been successfully employed as a heterogeneous catalyst in the Erlenmeyer–Plochl reaction involving aldehydes, hippuric acid and acetic anhydride as well as in the Henry reaction between aldehydes and nitromethane in ethanol at room temperature. The heterogeneity of the ionic liquid gel has been confirmed by conducting hot filtration tests and leaching studies. Additionally, the ionic liquid gel could be easily recovered by simple filtration and reused five times without significant loss in catalytic activity.