Phosphorous acid functionalized polyacrylonitrile fibers with a polarity tunable surface micro-environment for one-pot C–C and C–N bond formation reactions

Abstract

The preparation and application of fiber catalysts have attracted much attention. However, research on the effect of the micro-environment of fiber catalysts on the catalytic activities though of special importance is limited. In this work, a novel strategy for the synthesis of phosphoric acid-functionalized polyacrylonitrile fibers with a polarity tunable surface micro-environment by hydrophobic groups for one-pot C–C and C–N bond formation reactions is reported. The special hydrophobic surface micro-environment of the fiber catalysts is proven to promote the catalytic activities impressively in cyclocondensation of β-ketoesters with 2-aminobenzamides, the Knoevenagel condensation as well as the multi-component Biginelli reactions in green solvents. Both the surface synergy of the catalytic sites and hydrophobic auxiliary groups (benzyl or n-butyl) in the surface of fiber catalysts and interface acceleration in reaction medium play an important role in the highly efficient promotion of catalytic activity. Thereby a surface synergistic mechanism is proposed to explain the micro-environment effect. In addition, the fiber catalysts could be simply separated from the reaction system using tweezers and directly used in the next cycle without further treatment. Importantly, even after 10 reaction cycles in water or ethanol, there is no significant loss in their catalytic activity. The results indicate that the phosphoric acid functionalized fibers show green and sustainable potential for industrial production.