Nanocrystalline FeOClx grafted MCM-41 as active mesoporous catalyst for the solvent-free multi-condensation reaction

Abstract

Thermal condensation reaction between the surface silanol groups of MCM-41 and FeCl₃ led to the formation of nanocrystalline iron oxychloride (FeOCl) grafted MCM-41 and its role as an active Lewis acid site for the solvent-free multi-condensation reaction has been demonstrated. TGA/TGA-FTIR-GC-MS analysis of the FeCl₃/MCM-41 material showed the release of HCl molecules as a result of the condensation reaction and the formation of FeOCl_x species on the surface of MCM-41. Solid state Si²⁹ NMR and HT-XRD analysis of these materials clearly showed the grafting of FeOCl_x species on the surface of MCM-41 and nanocrystalline FeOCl_x formation during the thermal condensation reaction. HRTEM mapping and EDX mapping further confirm the nanocrystalline iron oxychloride species formation and its uniform distribution on the surface of MCM-41. It was further demonstrated that these materials were found to be highly active towards solvent-free one pot multi condensation reaction between napthols, amides and aldehydes to produce pharmaceutically active alkylnapthols. The role of calcination temperature was demonstrated to be a key factor in the formation and distribution of FeOCl_x species, therefore the catalytic activity of these materials vary as a function of calcination temperature. XPS analysis of these materials confirmed the presence of FeOCl_x species and its role as an active acid site for the multi-condensation reaction was proposed.