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

The acid-base pairing and fabrication method washereinemployed to construct acid-base bifunctional heterogeneouscatalysts. The boronic acid group was introduced into primary amine-functionalizedpolyacrylonitrile fiber (PAN(EA)F) via amide bond formationto fabricate boronic acid-amine bifunctional PANFs as recyclable heterogeneouscatalysts by using the amino N atoms of PAN(EA)F as anchoringpoints. The so-obtained fiber catalysts PAN(EA-BA1)F and PAN(EA-BA2)F containing boronic acid groupsattached on benzene and pyridine rings, respectively, were employedin the Henry reactions of aryl aldehydes with nitromethane. Catalyticinvestigations showed that their performance had great correlationwith the change of boronic acid. PAN(EA-BA2)F exhibiteda higher substrate selectivity than PAN(EA-BA1)F,and only the benzaldehydes with hydroxy, dimethylamino, and amidegroups were reactive, which showed preliminary substrate specificitylike enzyme catalysis. The in situ investigation with cyclododecaneas 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 PAN(EA-BA1)F-catalyzed condensation was explained.