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Heterogeneous catalysis is an important branch of sustainable chemistry. In this work, a series of polyacrylonitrile fiber (PANF) fiber catalysts (PANF-E, PANF-EDs, and PANF-D) with different catalytic micro-environments are developed and characterized by elemental analysis, Fourier-transfer infrared spectroscopy, x-ray diffraction, thermogravimetric/differential scanning calorimetry analysis, scanning electron microscopy, and mechanical strength measurements to demonstrate the successful immobilization of the different amines as well as evaluate the physical strength and thermal stability of the fiber catalysts at different stages. The catalytic activities of the fiber catalysts are tested by one-pot three-component Knoevenagel-Michael reaction to the synthesis of substituted 2-amino-4H-chromenes in which the influences of surface polarities, kinds and proportions of functional groups on the fiber catalysts activities were investigated. Among the prepared catalysts, the PANF-D with higher density of tertiary amino group and hydrophilic micro-environment exhibited the best catalytic activity to efficiently catalyze the three-component reaction in water with excellent substrate suitability (92-98%). In addition, the catalyst can be easily separated from the catalytic system and conveniently reused at least ten times. Moreover, the PANF-D performs well in scaled-up experiment in a simple fixed-bed reactor with a yield of 97% which allows it to have great potential for further cleaner industrial applications. [ABSTRACT FROM AUTHOR]

This work has been developed to study the effect of fiber catalyst surface polarity on catalyst performance. Taking 4-dimethyl amine pyridine (DMAP) derivative functionalized polyacrylonitrile fiber catalyst (PANDMAPF) as the template catalyst, its surface property was adjusted through the introduction of phenyl and hydroxyl groups on PANDMAPF. Elemental analysis (EA), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and mechanical strength test are used to characterize and demonstrate the successful synthesis of different fiber catalysts. The catalytic performance of different fiber catalysts was tested by the reaction of one-pot three-component synthesis 2-amino-2-chromenes. The results showed that reducing the surface polarity of the catalyst could not only improve the activity of the catalyst, but also make the three-component reaction which could only be carried out in high polar solvents (water and methanol), but also proceed effectively in lower polar solvents (such as ethanol and n-butanol). Therefore, the activity and selectivity of the catalyst can be effectively regulated by introducing different polar auxiliary functional groups on the surface of the fiber catalyst, which provides a theoretical basis for the design and synthesis of high activity and selectivity fiber catalyst. [ABSTRACT FROM AUTHOR]

Abstract: The l-lysine functionalized polyacrylonitrile fiber (PANLF) was prepared by grafting the l-lysine into a commercially available polyacrylonitrile fiber and showed highly catalytic activity for Knoevenagel condensation reaction. With low temperature (45 °C) and short reaction time (1 h), the fiber catalyst was well applicable to Knoevenagel condensation of a wide range of aldehydes and the yields could reach up to 99%. Interestingly, only in water could the reaction take place smoothly (with a yield of 88%) and a polar micro-environment promoted reaction process had been proposed to explain this phenomenon. Besides, the fiber catalyst has advantages of easy preparation, high functional degree, strong mechanical strength and thermal stability, etc. And it can be reused at least 5 times without further treatment and performed well in scaled-up experiment (amplified 50 times) and flow chemistry experiment (no loss of catalytic activity after 48 h), which indicates its potential application in industry application.Graphical Abstract: [ABSTRACT FROM AUTHOR]