Formation and functionalization of surface Diels-Alder adducts on ethenylene-bridged periodic mesoporous organosilica

The Diels-Alder cycloaddition of two common dienes (cyclopentadiene and anthracene) to the double carbon-carbon bonds of an ethenylene-bridged periodic mesoporous organosilica was studied and compared to that of benzocyclobutene. The resulting materials were characterized by several techniques such as X-ray and thermal analyses, DRIFT, (13)C and (29)Si MAS NMR and porosimetry. They showed that the mesopores were decorated with the Diels-Alder adducts with negligible structural degradation and with the concomitant reduction of the surface area and pore size. The formation of surface adducts was even successful with a relatively hindered diene such as anthracene. The surface Diels-Alder adducts were stable and susceptible to further functionalization. Thus, after being sulfonated, the resulting solids were used as acid catalysts in the esterification of acetic acid with ethanol, a process in which they proved to be very active. In fact, each acid site of these hybrid materials was up to three times more active than a similar site in Amberlyst-15, a commercial acid resin.