MIL-101(Cr), an Efficient Heterogeneous Catalyst for One Pot Synthesis of 2,4,5-tri Substituted Imidazoles under Solvent Free Conditions

Abstract

A chromium-containing metal-organic framework (MOF), MIL-101 (Chromium(III) benzene-1,4-dicarboxylate), was used to catalyze the one pot, three component synthesis of some 2,4,5-trisubstituted imidazoles under solvent-free conditions. The advantages of using this heterogeneous catalyst include short reaction time, high yields, easy and quick isolation of catalyst and products, low amount of catalyst needed, and that the addition of solvent, salt, and additives are not needed. This catalyst is highly efficient and can be recovered at least 5 times with a slight loss of efficiency. The structure of the metal-organic frameworks (MOF) was confirmed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (HNMR) were performed to confirm some of the synthesized products. Experimental data indicated that the optimum amount of catalyst was 5 mg for benzil (1 mmol), 4-chlorobenzaldehyde (1 mmol), and ammonium acetate (2.5 mmol), and the synthetic route to the various imidazoles is performed in 10 min by 95% yield, an acceptable result rivalling those of other catalysts.

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“…The XRD pattern of Cr-MOF is shown in Figure d and Figure S1. The five characteristics peaks at angles 5.27°, 8.57°, 9.18°, 10.46°, and 16.69° match with the literature, which confirmed the successful synthesis of Cr-MOF. − These angles were indexed to the indices (5 1 1), (8 2 2), (7 5 3), (10 2 2), and (13 9 5), similar to the previously reported literature . The peaks observed at small angles characterize the mesoporous nature of MOF.…”