Mangrove tree aerial root extract mediated green synthesis of Ag/FeO/rGO nanocomposite and its application as a catalyst for one pot synthesis of 7-phenyl-6H,7H-benzo[4,5]imidazo[2,1-b]chromeno[4,3-d][1,3]thiazin-6-one derivatives.

In this study, we report the green preparation of magnetically separable Ag/FeO/rGO nanocomposites using mangrove tree aerial root extract as a stabilising agent. The morphology, size, chemical composition, magnetic property and other characteristic parameters of synthesised Ag/FeO/rGO nanocomposite were determined by analytical techniques like Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results proved that mangrove tree aerial root extract has the ability to reduce Ag ions, graphene oxide (GO) to Ag nanoparticle and reduced graphene oxide (rGO), respectively. The prepared Ag/FeO/rGO nanocomposite was used successfully as a prompt catalyst for synthesis of 7-phenyl-6H,7H-benzo[4,5]imidazo[2,1-b]chromeno[4,3-d][1,3]thiazin-6-one derivatives by one-pot multi-component reaction of 4-hydroxycoumarin (10 mmol), 2-mercaptobenzimidazole (10 mmol) and different arylaldehyde (10 mmol) in the presence of ethanol (10 ml) as an eco-benign solvent at reflux condition. By utilising this protocol, we have constructed 7-phenyl-6H,7H-benzo[4,5]imidazo[2,1-b]chromeno[4,3-d][1,3]thiazin-6-one derivatives in good to excellent yield of 80-90%. This synthesis involves the formation of C-C, C-N and C-S bonds. The synthesised organic heterocyclic compounds were examined for the green matrix properties such as atom economy (AE), E-factor and product mass intensity (PMI). This green protocol is of big interest due to employing simple, non-toxic heterogeneous, separable, reusable Ag/FeO/rGO as an eco-safe heterogeneous catalyst and environmentally benign ethanol as a green solvent without the use of any harmful mineral acid and toxic transition metal catalyst.