SnCl4-functionalized nano-Fe3O4 encapsulated-silica particles as a novel heterogeneous solid acid for the synthesis of 1,4-dihydropyridine derivatives

A novel type of green heterogeneous solid acid was prepared by the immobilization of SnCl4 on the surface of Fe3O4@SiO2 (Fe3O4@SiO2-SnCl4) and characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) analysis, N-2 adsorption-desorption (BET) study and transmission electron microscopy (TEM). The activity of this solid acid was investigated via the synthesis of 1,4-dihydropyridine derivatives using a three or four component coupling reaction between an aldehyde, 1,3-dicarbonyl compound, and ammonium acetate under ultrasonic irradiation, which yielded excellent results with easy work-up in a short time. 1,4-dihydropyridine derivatives were characterized by FT-IR and (HNMR)-H-1 spectroscopy.