Synthesis of pyrroles catalyzed by MIL-53(Al) via Paal-Knorr reaction under mild condition

Abstract

Metal-organic framework MIL-53(Al) was synthesized by a solvothermal method using aluminium nitrate as the aluminium source and 1,4- benzenedicarboxylic acid (H2BDC) as the organic ligand. The structure of MIL-53(Al) was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The catalytic activity and recyclability of MIL-53(Al) catalyst were evaluated based on the Paal-Knorr reaction between aniline and acetonylacetone. The reaction conditions were optimized and the results showed that the MIL-53(Al) catalyst exhibited good catalytic activity and recyclability based on the PaalKnorr reaction. With the molar ratio of MIL-53(Al) catalyst of 10 mol %, the molar ratio of aniline and acetonylacetone of 1:1.2, and without solvents, the conversion of aniline could reach 100 % and the selectivity of 2,5-dimethyl-1-phenyl-1H-pyrrole has high yield (95-100 %) after 2 hours by ultrasound activation. The MIL-53(Al) catalyst can be reused five times without significant degradation in the catalytic activity.