Composite of cross-linked chitosan beads and a cyclodextrin nanosponge: A metal-free catalyst for promoting ultrasonic-assisted chemical transformations in aqueous media

Abstract

A novel carbohydrate-based catalytic composite was prepared through covalent decoration of cross-linked chitosan beads with a cyclodextrin nanosponge. In this regard, chitosan beads were fabricated and cross-linked with glutaraldehyde. Subsequently, they were reacted with an amino-functionalized cyclodextrin nanosponge. The resultant composite was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and elemental mapping analysis. Then the performance of the metal-free catalyst for promoting ultrasonic-assisted synthesis of dihydropyrimidinones and octahydroquinazolinones in aqueous media was appraised. It was found that the composite was highly efficient and recyclable. Moreover, the activity of the composite was superior to that of its individual components. It is assumed that incorporation of the cyclodextrin nanosponge, which has high capability for the formation of an inclusion complex in the structure of the composite, allows the catalyst to act as a molecular nanoreactor and promotes the reactions efficiently in aqueous media.