Amine-modified hierarchically structured zeolites as acid-base bi-functional catalysts for one-pot deacetalization-Knoevenagel cascade reaction

Hierarchically structured zeolites (HSZs) with crystalline microporous frameworks and penetrating mesoporosity have been developed and used as efficient solid acid catalysts in many chemical processes, especially when bulky molecules are involved. Herein, a new kind of HSZs-based acid-base bi-functional catalyst (HSZs-NH₂) was developed by a facile one-step organic amine modification method. As-synthesized materials were characterized by XRD, BET, FE-SEM, TEM, ICP and CHN elemental analysis. In the one-pot deacetalization-Knoevenagel cascade reaction between benzaldehyde dimethyl acetal and ethyl cyanoacetate, HSZs-NH₂ materials were highly active whereas amine-modified microporous ZSM-5 only showed a very limited activity. Among them, HSZs-NH₂(0.2) exhibited the best catalytic performance. Even over six cycles, the regenerated HSZs-NH₂(0.2) retained 100% conversion of benzaldehyde dimethyl acetal and 96% yield of the target product ethyl trans-α-cyanocinnamate. Furthermore, it is suggested that, depending on the modification amount of organic amine, there exist at least two kinds of amine species in the resultant HSZs-NH₂ catalysts, one (free amine) is base-catalytically active and the other (restricted one) is almost catalytically inactive.