Chitosan and functionalized graphene oxide nanocomposite as a novel and highly efficient catalyst for production of bis-coumarins under solvent-free conditions

Chitosan and functionalized graphene oxide nanocomposite was used as efficient, sustainable, and recyclable catalyst in the production of bis-coumarins using 4-hydroxycoumarin and aromatic aldehydes under solvent-free conditions. Chitosan was first functionalized using chloroacetyl chloride. Afterward, graphene oxide was modified by aliphatic amine and then with dithioglycolic acid, giving rise to thiol (SH)-functionalized graphene oxide after reduction. The nanocomposite was prepared from the reaction of 2-chloroacetyl-functionalized chitosan and thiol-modified graphene oxide, followed by oxidization of thiols to SO3H groups using hydrogen peroxide. The nanocomposite (catalyst) was characterized using field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, differential thermogravimetry, FT-IR, and MAP analysis. The nanocomposite showed superior properties over previously reported ones, including nontoxicity, environmental compatibility, solvent-free condition, simple work-up, no by-products, thermal stability, and recoverability.