Comparative catalytic performance of bare and functionalized iron oxide nanoparticles (APTES, chitosan, SiO 2 ) in the Hantzsch synthesis of diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate

Iron oxide nanoparticles (IONPs) were synthesized via the coprecipitation method and functionalized with APTES, chitosan, and SiO2 to improve their stability and catalytic performance. The bare IONPs exhibited a crystallite size of 12 nm and a high saturation magnetization. Functionalization reduced the Ms values for all nanoparticles. Thermogravimetric analysis (TGA) confirmed the presence of different coating agents. Transmission electron microscopy (TEM) micrographs revealed an average particle size under 20 nm. The catalytic activity of all nanoparticles was evaluated in the Hantzsch synthesis of a model 1,4-dihydropyridine (DHP). Naked IONPs reduced the reaction time from 1 h to 15 min and increased the product yield by around 20% compared to the uncatalyzed reaction. IONPs@APTES participated in the reaction via their amino groups, resulting in the incorporation of the catalyst into the DHP structure, as confirmed by Fourier-transform infrared (FT-IR) analysis. These results demonstrate that bare IONPs are more effective catalysts for short-time Hantzsch reactions.