Surfactant containing Si-MCM-41: An efficient basic catalyst for the Knoevenagel condensation

Si-MCM-41 molecular sieves, which are largely used in a number of acid and redox catalyzed reactions, as reported by the literature, were used as basic catalyst for the Knoevenagel condensation. This reaction involves the condensation of carbonyl compounds with active methylene compounds to generate unsaturated products. The catalyst, which pores were occluded by the organic template, provided high activity in mild conditions, even under 10 °C. The high activity is due to the presence of siloxy anions, of high basicity, located in the pore cavity of the hexagonally ordered mesopores. Ion exchange procedures evidenced the presence of these high basic sites as a consequence of the high pH increase of the solution containing tetramethylammonium chloride, or the high H+ consumption, added to a the medium as HCl, to keep constant pH. O 1s XPS and 29Si CP/MAS NMR measurements confirmed the existence of only ≡SiO−CTA+ ionic pair, which is the basic site itself.