A Continuous-Flow Microreactor for Knoevenagel Condensation of Ethyl Cyanoacetate with Benzaldehyde: The Effect of Grafted Amino Groups on Catalytic Activity

Ethyl alpha-cyanocinnamate was synthesized in the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate in flow monolithic microreactor of 0.63 cm(3) volume. The catalytically active core was made of silica monolith modified with various amine group precursors. Structural properties of the support, surface density of NHx groups, and catalytic activity were investigated. It was found that the poly- or di-amine groups attached to the silica surface appeared to be more effective than the aminopropyl groups. Microreactors grafted with diamine functional groups, accompanied by hydrophobic methyl groups, showed the highest activity and stability. It was proved that the decisive role on the activity of catalysts was exerted by the presence of primary amines in diamine chain. The reaction conditions were optimized and it was found that almost full substrate conversion could be achieved in 6 min at 50 degrees C in the microreactor with low concentration of diamine groups equal to 0.33 mmol g(-1).

Automated summary

In this study, ethyl alpha-cyanocinnamate was synthesized using benzaldehyde and ethyl cyanoacetate in a flow monolithic microreactor. The effects of different amine group precursors on the catalysts' structural properties, surface density of NHx groups, and catalytic activity were investigated. It was found that microreactors modified with diamine functional groups showed the highest activity and stability, with primary amines playing a crucial role in determining the catalysts' activity. The reaction conditions were optimized, and almost complete substrate conversion was achieved within 6 minutes at 50 degrees Celsius with a low concentration of diamine groups (0.33 mmol g(-1)).