Catalytic activity of aminopropyl xerogels in the selective synthesis of (E)-nitrostyrenes from nitroalkanes and aromatic aldehydes

Various aminopropyl-functionalized silicas (APS) were prepared by the sol-gel technique using different tetraethyl orthosilicate/ aminopropyltriethoxysilane (TEOS/ATS) ratios and tested as base catalysts for the nitroaldol reaction. The solids were fully characterized. It was proved that the amount of organic component strongly influences the composition and textural properties of the hybrid organic-inorganic materials. In particular, when ATS was increased to more than 40%, pore volume collapse was observed and a significant decrease in interaction with benzaldehyde reagent was revealed by FT-IR. Catalytic activity in the nitroaldol reaction was correlated with chemical composition and textural properties, suggesting that the catalyst efficiency depends on accessibility to the catalytic sites. In all cases, (E)-nitrostyrene was selectively obtained.