Nano-FeO encapsulated-silica supported boron trifluoride as a novel heterogeneous solid acid for solvent-free synthesis of arylazo-1-naphthol derivatives

Nano-Fe 3 O 4 encapsulated-silica supported boron trifluoride (Fe 3 O 4 @SiO 2 -BF 3 ) as a new type of green heterogeneous solid acid was prepared by the immobilization of BF 3 ·Et 2 O on the surface of Fe 3 O 4 @SiO 2 core-shell nanoparticles and characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), field emission-scanning electron microscope (FE-SEM), energy dispersive X-ray (EDS), and transmission electron microscope (TEM). Then, this super solid acid was used as an acidic reagent for the synthesis of aryl diazonium salts as a starting reactant, followed by its diazo coupling with 1-naphthol in a basic solvent-free medium at room temperature. The main advantages of this clean method were high yields, short reaction times, the possibility of performing it at room temperature, and no need of corrosive and toxic liquid acids and solvents. In addition, the long-term stability of aryl diazonium salts supported on Fe 3 O 4 @SiO 2 -BF 3 magnetic nanoparticles (MNPs) at room temperature was one of the most important results of this procedure. Fe 3 O 4 @SiO 2 -BF 3 nanoparticles were prepared as a novel solid acid and effectively applied for the solvent-free synthesis of arylazo-1-naphthols at room temperature.