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.

中文翻译：

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具有极性可调表面微环境的磷酸官能化聚丙烯腈纤维，用于一锅式C–C和C–N键形成反应

纤维催化剂的制备和应用引起了人们的广泛关注。然而，尽管特别重要，但是关于纤维催化剂的微环境对催化活性的影响的研究是有限的。在这项工作中，报道了一种通过疏水基团合成极性可调的表面微环境的磷酸官能化聚丙烯腈纤维的新策略，用于一锅式C–C和C–N键形成反应。事实证明，纤维催化剂的特殊疏水表面微环境可显着提高β-酮酸酯与2-氨基苯甲酰胺的环缩合，Knoevenagel缩合以及在绿色溶剂中的多组分Biginelli反应的催化活性。催化位点的表面协同作用和疏水性辅助基团（苄基或纤维催化剂表面的正丁基）和反应介质中的界面加速在高效提高催化活性方面起着重要作用。因此，提出了一种表面协同机理来解释微环境效应。另外，可以使用镊子将纤维催化剂简单地从反应体系中分离出来，并直接用于下一循环而无需进一步处理。重要的是，即使在水或乙醇中进行10个反应循环后，其催化活性也不会显着降低。结果表明，磷酸功能化纤维显示出绿色和可持续的工业生产潜力。