Cooperative Catalysis by Boronic Acid-Amine Bifunctionalized Polyacrylonitrile Fibers in Henry Reaction

Abstract

The acid–base pairing and fabrication method was herein employed to construct acid–base bifunctional heterogeneous catalysts. The boronic acid group was introduced into primary amine-functionalized polyacrylonitrile fiber (PANEAF) via amide bond formation to fabricate boronic acid-amine bifunctional PANFs as recyclable heterogeneous catalysts by using the amino N atoms of PANEAF as anchoring points. The so-obtained fiber catalysts PANEA–BA1F and PANEA–BA2F containing boronic acid groups attached on benzene and pyridine rings, respectively, were employed in the Henry reactions of aryl aldehydes with nitromethane. Catalytic investigations showed that their performance had great correlation with the change of boronic acid. PANEA–BA2F exhibited a higher substrate selectivity than PANEA–BA1F, and only the benzaldehydes with hydroxy, dimethylamino, and amide groups were reactive, which showed preliminary substrate specificity like enzyme catalysis. The in situ investigation with cyclododecane as solvent by Raman and Fourier transform infrared spectroscopy (FT-IR) analysis was conducted to clarify the catalytic difference. Moreover, the uncommon reverse reactivity order of benzaldehydes in PANEA–BA1F-catalyzed condensation was explained.