Fe3O4@C - SO3H Novel, green and recyclable acid catalysts for the synthesis of 2-amino-4H-chromene derivatives

A novel iron oxide nanoparticle (Fe3O4@C-SO3H) fabricated with carbon and sulfonic acid was prepared using the concept of green chemistry protocol. The usage of agro-waste extract for core-shell Fe3O4 preparation and its biochar powder as a carbon source for the fabrication of the catalyst was the dual benefit. This prepared catalyst was employed for the synthesis of 4H-chromene derivative via a three-component one-pot reaction of resorcinol, aryl aldehyde, and malononitrile in ethanol under microwave irradiation. The method was found to be nontoxic, inexpensive, faster, and simple work-up with greener solvent, and gave excellent product isolation with about 91 % yield in 4 min microwave irradiation in the presence of 25 mg catalyst. The catalyst could be recovered after the reaction by an external magnet and reused for up to four runs without any considerable loss in its catalytic activity. The prepared catalyst was characterized by FT-IR, and prominent bands were observed for surface functionalization. The XRD data revealed prominent peaks for the formation of Fe3O4@C-SO3H, and the results are comparable with the reported literature; the VSM data gives a clear idea about the magnetic nature of the catalyst and respective surface-modified core shells, the surface morphology, and the required elements present are confirmed by FE-SEM and EDX. TGA admits that the thermal stability of the catalyst is up to 600 degrees C under a nitrogen atmosphere. The 1 H- & 13 C-NMR and LC-MS analysis are explored for the analysis of the formation of final 2-amino-4H-chromene derivatives. Further antimicrobial activities of the selected compounds were performed, and the results are promising and comparable with the reference.