N‐propylbenzoguanamine sulfonic acid‐functionalized magnetic nanoparticles: A novel and magnetically retrievable catalyst for the synthesis of 1,4‐dihydropyridine derivatives

The catalytic activity of N ‐propylbenzoguanamine sulfonic acid stabilized on silica‐coated nano‐Fe 3 O 4 particles (Fe 3 O 4 /SiO 2 ‐ N ‐propyl‐benzoguanamine‐SO 3 H) were proven to be as a novel magnetic solid acid catalyst for the synthesis of 1,4‐dihydropyridine derivatives in a one‐pot pseudo‐four‐component condensation reaction of barbituric acid, aromatic aldehydes, and ammonium acetate or aniline with high yield and short reaction times. The structure and magnetic properties of the obtained nanoparticles were characterized via Fourier transform infrared spectroscopy (IR), field emission scanning electron microscopy (FE‐SEM), transmission electron microscope (TEM), energy dispersive X‐ray analysis (EDXA), X‐ray diffraction (XRD), thermogravimetry analysis (TGA), differential thermal analysis (DTA) and vibrating sample magnetometry (VSM), atomic absorption spectroscopy (AAS), and inductively coupled plasma–mass spectrometry (ICP‐MS). The results demonstrated that the average size of the synthesized magnetite nanoparticles is about 25 nm. In addition, the heterogeneous catalyst can be easily recovered magnetically and can be reused for further runs without significant loss of its catalytic activity.