Immobilized SbCl3@Chitosan as a green heterogeneous catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles

In this work, an efficient, green and retrievable heterogeneous chitosan-supported antimony trichloride catalyst (SbCl3@Chitosan) was synthesized by dispersing antimony trichloride on amine functionalized chitosan modified with methyl salicylate and characterized by using Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Powder X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and ICP-AES analysis. FTIR indicated the various functionalities present in the catalyst such as 3299–3367 cm−1 (N–H and O–H), 2924 and 2874 cm−1 (C–H), 1424 cm−1 (CH2), 1376 cm−1 (CH3), 1151 cm−1 (C–O–C), 1059 and 1020 cm−1 (C–O of chitosan), 1559 cm−1 (C–N), 1653 cm−1 (C = O stretching of amide), 1302 and 1376 cm−1 (Sb–Cl). TGA showed that the catalyst was stable upto 200 °C thereby determining its thermal stability. The characteristic peaks appeared in the powder XRD of the catalyst confirmed the crystal face of antimony. The surface morphology of the catalyst revealed through SEM images exhibited a uniform distribution, and the majority of particles displayed a near-spherical morphology. ICP-AES analysis data revealed the overall content of antimony present in the synthesized catalyst. The catalytic activity of the catalyst was evaluated for the synthesis of 1,2,4,5-tetrasubstituted imidazoles under green reaction conditions. The present method for the synthesis of tetrasubstituted imidazoles has broader significance due to synthesis of various imidazole derivatives in high to excellent yields (83–95%) with short reaction times and high purity under solvent-free conditions with a simple work-up procedure. Moreover, the aforementioned catalyst (SbCl3@Chitosan) could be easily separated from the reaction mixture and reused for five runs without any decline in its catalytic activity.