Direct synthesis of acid–base bifunctional mesoporous MCM-41 silica and its catalytic reactivity in Deacetalization–Knoevenagel reactions

A series of acid–base bifunctional mesoporous MCM-41 silica materials with a p6mm symmetry have been synthesized through a simple co-condensation approach of tetraethylorthosilicate (TEOS), 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-tertbutyloxycarbonyl(aminopropyl)trimethoxysilane (3TBS) with supramolecular templates of cetyltrimethylammonium bromide (CTAB). Syntheses were followed by oxidation to form surface sulfonic acid groups and the thermal treatment to recover the amino groups. These new materials were characterized by X-ray diffraction (XRD), transmission electron micrographs (TEM), N2 adsorption–desorption, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), 29Si magic-angle spinning (MAS) NMR and 13C magic-angle spinning (MAS) NMR. The catalytic activities of the mono and bifunctional mesoporous hybrid materials were evaluated in one-pot sequential synthesis of benzylidene ethyl cyanoacetate from ethyl cyanoacetate with benzaldehyde dimethylacetal. Among all the catalysts evaluated, the bifunctional samples containing amine and sulfonic acid groups displayed excellent catalytic activity. The most efficient catalyst almost gave ∼100% conversion of benzaldehyde dimethylacetal within 30 min.