Facile pathway for synthesis of two efficient catalysts for preparation of 2-aminothiophenes and tetrahydrobenzo[b]pyrans

Abstract

We report here a new magnetically recyclable catalyst consisting of iron-substituted Keggin-type heteropolyacid (HPA) grafted on modified Fe3O4 nanoparticles. The synthesized hybrid nanomaterial exhibited the excellent catalytic efficiency in condensation reaction for the preparation of tetrahydrobenzo[b]pyrans under solvent-free conditions as well as in the synthesis of 2-aminothiophenes via Gewald reaction. It must be noted that, HPA supported magnetite nanoparticles catalyzed the preparation of tetrahydrobenzo[b]pyrans, whereas for Gewald reaction amine-functionalized magnetite nanoparticles acted as a catalyst. Different characterization techniques such as Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) were used to characterize the hybrid nanomaterial. The reusability of catalyst was affirmed by using in consecutive runs for five times. Performance of prepared catalyst was compared with the various previously reported catalysts; the newly synthesized catalysts found to be most efficient with regard to reaction time, yield and ease of catalyst separation.