A comparative study on the catalytic activity of Fe3O4@SiO2-SO3H and Fe3O4@SiO2-NH2 nanoparticles for the synthesis of spiro [chromeno [2, 3-c] pyrazole-4, 3′-indoline]-diones under mild conditions

Sulfuric acid and (3-aminopropyl)-triethoxysilane were successfully attached to the core-shell structure of Fe3O4@SiO2 nanoparticles separately. The prepared nanoparticles were characterized by vibrating sample magnetometer, powder X-ray diffraction, scanning electronic microscopy, thermal gravimetric analysis, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. To compare the efficiency of the two prepared functionalized magnetic nanoparticles, they were employed as catalysts for the synthesis of spirooxindole containing chromene ring fragments in one-pot four-component reactions. Sulfuric acid-functionalized magnetic nanoparticles showed high catalytic activity in mild reaction conditions and short reaction times and excellent yields of products. The catalyst was easily separated using a magnet and reused for several cycles of reactions without any significant loss of catalytic activity.