Synthesis Of Polyacrylonitrile Fiber Supported-Prolinamides And Study On Their Catalytic Performances

The immobilization of homogeneous catalyst can achieve easy separation and recovery,and enable multiple reuses,which conforms to the trend of green chemistry and sustainable development.Polyacrylonitrile fiber(PANF)is a kind of cheap and easily available textile material with high mechanical strength,good thermal-stability,acid-base resistance and organic solvent tolerance.The fiber has cyano and ester groups,which can be readily converted to various catalytic active groups by chemical transformation,thus being considered as a desired catalyst support with a good application prospect.In this paper,various prolinamide small molecules were introduced to polyacrylonitrile fiber by covalent bonding to obtain a series of fiber-immobilized heterogeneous catalysts.The structure,composition and surface morphology of fiber catalysts were characterized by different techniques and their catalytic performances were then researched systematically.A series of prolinamide small molecules were synthesized from L-proline methyl ester hydrochloride through aminolysis reaction of ester,and were subsequently immobilized onto PANF for the preparation of novel prolinamide functionalized fiber catalysts with different linkers.Prolinamide fiber PAN_PA-2F with suitable linker length and hydrophobic property showed excellent catalytic performances in Knoevenagel and Knoevenagel-Michael multicomponent reactions.The reactions proceeded smoothly in water and diverse?,?-unsaturated nitrile and2-amino-4H-chromene derivatives were obtained.The high catalytic activity of PAN_PA-2F was attributed to the favorable hydrophobic microenvironment formed in the surface layer of fiber.Fiber catalyst could be conveniently and quickly recovered from reaction system by filtration,and was reused for 10 and 8 runs,respectively,without significant decrease of yields.Above reactions were also accomplished well in scale-up experiments.The catalyst was further applied in a continuous-flow process for the catalysis of Knoevenagel reaction and the yield remained above 95%after 50 h,which showed the potential application of fiber catalyst in the chemical industry.A variety of amine functionalized fiber catalysts were prepared and their wettability was tuned by the introduction of hydrophilic hydroxyl group.Prolinamide fiber PAN_EF-PLA with hydrophilic character could efficiently promote aldol reaction of p-nitrobenzaldehyde with acetone in water to give addition product(yield:89%,selectivity:98%)under mild conditions and its activity proved to be higher than those of mono-functionalized fiber,hydrophobic-modified fiber,physically mixed fibers and even better than its small molecule catalyst.It was also found that PAN_EF-PLA exhibited superior activity and selectivity in comparison to conventional silica-supported acid-base bifunctional catalysts.Fiber catalyst has high stability in aqueous catalytic reaction and could be reused for 7 runs.This investigation illustrates a simple approach to promote aldol reaction through the introduction of auxiliary group with the aim of constructing favorable reaction environment around the catalytic sites of fiber.Three fiber-supported metal catalysts were successfully prepared through the covalent immobilization of prolinamide unit onto PANF and consequent chelation of different copper(?)salts in aqueous solution.Among these,fiber immobilized cupric chloride was an efficient catalyst in Chan-Lam coupling of arylboronic acids with imidazole and diverse N-arylimidazole derivates were obtained.The catalytic system was further applied to synthesize N-arylsulfonamide derivates.Fiber catalyst could be reused for 5 runs and high catalytic activity was also maintained in gram-scale experiment.