Cooperative Catalysis by Boronic Acid-Amine Bifunctionalized Polyacrylonitrile Fibers in Henry Reaction
Haotian Zhang, Haonan Zhang, Huimin Du, Jian Xiao, Minli Tao, Ning Ma, Wenqin Zhang
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 (PAN EA F) via amide bond formation to fabricate boronic acid-amine bifunctional PANFs as recyclable heterogeneous catalysts by using the amino N atoms of PAN EA F as anchoring points. The so-obtained fiber catalysts PAN EA–BA1 F and PAN EA–BA2 F 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. PAN EA–BA2 F exhibited a higher substrate selectivity than PAN EA–BA1 F, 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 PAN EA–BA1 F-catalyzed condensation was explained.