Functionalized mesoporous materials as efficient organocatalysts for the syntheses of xanthenes

Abstract

Highly efficient and recyclable heterogeneous organocatalysts containing acidic functional groups such as CO2H and SO3H have been synthesized by post-synthesis modification of 2D-hexagonal mesoporous silica materials SBA-15 and MCM-41, respectively. The CO2H functionalized material is obtained via Schiff-base condensation of 3-aminopropyl grafted SBA-15 with 4-formylbenzoic acid, whereas SO3H functionalized material is prepared via partial oxidation of 3-mercaptopropyl grafted MCM-41 with dilute aqueous H2O2. These functionalized mesoporous materials have been thoroughly characterized by powder X-ray diffraction (PXRD), nitrogen adsorption/desorption studies, transmission electron microscopy (TEM) and UV visible diffuse reflectance spectroscopy. Both these materials have highly ordered 2D-hexagonal mesoporous structures with high surface areas and well-defined pore sizes. These acid functionalized materials have been used as heterogeneous catalysts for the condensation of aromatic aldehydes with 2-napthol under mild conditions in the presence or absence of a solvent affording high yields of the value added xanthenes.