Cooperatively Catalyzed Henry Reaction through Directed Metal-Chitosan Interactions

The main focus of the present work is on identifying the critical parameters involved in inducing acid-base cooperative catalytic interaction in hybrid metal-polymer materials. To makes these hybrid materials Ti or Sn acid sites are grafted to the hydroxy groups of chitosan (CS). The cooperative catalytic interactions between the Ti/Sn and the primary amine sites on CS are tested for the nitro-aldol condensation of nitromethane with 4-nitro-benzaldehyde. The observed results show that the synthesis conditions have a pronounce effect on the 3D arrangement of the hybrid materials, which in turn affect the reaction activity and selectivity. The catalysts are characterized using N₂-pysisorption, XRD, FTIR, XPS and HRTEM in conjunctions with reaction kinetic analysis. Using the combined results, a reaction mechanism is proposed, which emphasizes the effect of proximity and orientation of the Lewis acid (Ti or Sn) and base (NH₂) active sites on cooperative catalysis in the Henry reaction.