Silica grafted polyethylenimine as heterogeneous catalyst for condensation reactions

Primary amine groups were attached to a silica surface by using α,ω-diamines derivatives and (3-glycidyloxypropyl)-trimethoxysilane activation. The same activation was used to graft polyethylenimine, which also contains secondary and tertiary amine groups. These silica aminated structures were tested as heterogeneous catalysts in nitroaldol condensation with nitromethane, the derivative with the polyethylenimine moiety being the more active catalyst. This catalyst also showed efficiency in the Knoevenagel condensation of benzaldehydes with ethyl cyanoacetate under very mild reaction conditions and showed much the same efficiency when used in consecutive reaction runs. A reaction mechanism with participation of the several amine groups of the catalysts is discussed.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (85 K)Download as PowerPoint slideHighlights► A heterenogeneous material with poliethylenimine grafted in a silica matrix (ASCPEI) can be easily synthesized. ► ASCPEI catalyzes nitroaldol condensations. ► ASCPEI is an efficient catalyst for Knoevenagel condensation reactions with ethyl cyanoacetate.