Immobilized proton sponge on inorganic carriers

1,8-bis(dimethylaminonaphthalene) (DMAN), a proton sponge, was grafted onto amorphous and pure-silica MCM-41. The results show that DMAN supported on MCM-41 is an excellent base catalyst for the Knoevenagel condensation between benzaldehyde and different active methylene compounds as well as for the Claisen-Schmidt condensation of benzaldehyde and 2'-hydroxyacetophenone to chalcones and flavanones. The influence of the solvent and the polarity of the support on the activity of the catalysts was studied. It was found that the activity of the supported catalyst is directly related to the polarity of the inorganic support. Moreover, the support can also preactivate the reagents by interaction of the carbonyl groups with the weakly acidic silanol groups of the MCM-41. This preactivation step enables DMAN, anchored onto MCM-41, to abstract protons with a higher pK(a) than that of the DMAN. Finally, the study of the deactivation and recycling of the DMAN anchored onto MCM-41 catalysts showed that it is a stable material with respect to deactivation and leaching and results in comparable rates in successive batch reactions. (C) 2002 Elsevier Science (USA).