Organic-inorganic hybrid catalysts for acid- and base-catalyzed reactions

Stable heterogeneous catalysts with adjustable base strength have been prep ared by grafting organic amine bases into the the pores of the inorganic me soporous material, MCM-41, and to a porous styrene-divinylbenzene resin. Th e activities of these catalysts are compared for the formation of the monog lyceride from lauric acid and glycidol, and the Knoevenagel condensation of heptaldehyde with benzaldehyde to form alpha-n-amylcinnamaldehyde (jasmina ldehyde). Also included in the comparison are catalysts prepared by incorpo rating K2O, BaO and K2O/La2O3 into MCM-41. The resin-based catalyst suffers from poor thermal and mechanical stability. The organic-inorganic hybrid m aterial containing the strong hindered amine base, TBD (1,5,7-triazabicyclo [4,4,0]dec-5-ene), performs well for the monoglyceride reaction at 110 degr ees C, and the catalyst can be re-used for at least 11 cycles with little l oss of activity. However, it deactivates if it is used in the coupling reac tion with aldehydes. This is obviously caused by loss of the base at the hi gher reaction temperature of 170 degrees C, and by poisoning of the strong basic sites with benzoic acid which is formed by oxidation or through the C annizzaro disproportionation of benzaldehyde. The more weakly basic catalys ts based on MCM-41 with K2O/La2O3 can be used at a higher reaction temperat ure to compensate for their lower intrinsic activity, and their activity ca n be restored by calcination. (C) 2000 Elsevier Science B.V. All rights res erved.