Grafting of cinchonine onto rice husk nanosilica and its potential application in the synthesis of 2‐arylideneindan‐1,3‐diones and 2‐arylidene-5,5-dimethyl-1,3-cyclohexanedione

In this study, an eco-friendly and green procedure for Knoevenagel condensation reaction of aromatic aldehydes with indan-1,3-dione and dimedone was reported utilizing a rice husk silica‐anchored cinchonine nanocomposite as a heterogeneous catalyst in aqueous media. Without the need for an additional surfactant, rice husk was utilized as a raw material to create nanosilica. Through the grafting of 3-mercaptopropyl) trimethoxysilane, the rice husk nanosilica was modified. Next, azobisisobutylonitrile initiator was used to trigger the thiol-ene free radical interaction of the SH groups with the Cinchonine's alkene function. The morphology and structure of the nano SiO₂-S-cinchonine were characterized using fourier transform infrared spectra, field emission scanning electron microscope, and energy-dispersive X-ray spectroscopy. The catalytic activity of the nanocomposite was investigated in the synthesis of 2-arylideneindan-1,3-diones and 2-arylidene-5,5-dimethyl-1,3-cyclohexanedione through an aqueous medium at 80 °C by the Knoevenagel condensation reaction. The advantages of this method are simple methodology, high yields, easy work-up, and green solvent.