Synthesis of spirooxindole derivatives catalyzed by GN/SO3H nanocomposite as a heterogeneous solid acid

In this study, we synthesized a GN/SO3H solid acid nanocomposite by immobilization of chlorosulfonic acid onto the surface of g-C3N4 . The nanocomposite was characterized by different techniques (transmission electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, atomic absorption spectroscopy, X-ray diffraction, and energy dispersive X-ray spectrometer). The GN/SO3H nanocomposite was then applied to the synthesis of spirooxindole derivatives via multicomponent reaction of isatins, 1,3-dicarbonyl compounds, and malononitrile at reflux conditions in an ethanol/water solvent (1:1). The heterogeneous nanocomposite showed high catalytic activity in one-pot; the multi-component reaction of malononitrile, isatins, and 1,3-dicarbonyl compounds under reflux conditions and the corresponding spirooxindole derivatives were synthesized in good to excellent yields (70-95%). We found that the nanocomposite can be easily recovered and reused for several times with a minimal decrease of its catalytic performance.