The Synthesis And Aqueous Catalytic Performances Of Fiber-Supported Organocatalysts

Recently,fiber material has become a new supporter for heterogeneous catalysis because of its unique structure and properties.Polyacrylonitrile fiber(PANF)is abundant with cyano groups,which makes it easy to immobilize many organic active functions through amination reaction.The polypropylene fiber(PPF)can be modified by free radical grafting due to the abundance of C-H bonds on the polypropylene chains.Based on these,a series of polyacrylonitrile fiber and polypropylene fiber supported organocatalysts were originally prepared and used to investigate their catalytic performances in several organic reactions in aqueous phase.A series of quaternary ammonium salt functionalized PANF were originally prepared by amination and quaternization,which subsequently determined by series of characterizations.The structure-activity relationship,reaction conditions,substrate expansion,application in flow chemistry and reusability of fiber catalysts were investigated by aqueous reduction reaction in details.The results show that catalysts made up of quaternary ammonium salts with larger cationic radii,longer alkyl chains and better lipophilicity can effectively promote the reduction to afford excellent yields.The optimized catalyst could be applied to efficiently reduce water insoluble aldehydes(yields: 93-99%),ketones(yields: 91-99%),aryl azides(yields: 68-98%),and benzyl halides(yields: 95-99%),and the reduction of 1-naphthaldehyde by the optimized catalyst was performed in continuous flow processing with excellent conversion(99%),which exhibits the potential industrial application of the fiber catalyst.Besides,the activity of the catalyst kept the same as the first use after the 15 th run,which displays outstanding recyclability and reusability of the fiber catalyst.Three types of PANF-supported chiral pyrrolidine have been designed and prepared by multistep reactions,which were subsequently evaluated by asymmetric Michael addition of ketones to nitrostyrenes in water.The reaction conditions,solvent effect,substrate expansion and reusability of catalyst have been systemically investigated.The investigation of structure-activity relationship shows that the reaction activity enhanced with the increasing of the hydrophilicity of fiber catalyst.Besides,the enantioselectivity(ee value)was closely related to the ionic microenvironment in the surface layers of fiber catalyst.Then the scope of nitroolefins was expanded and the reactions with different nitrostyrenes show high activities(83-96% yield),high diastereoselectivities(d.r.>92:8),and excellent enantioselectivities(83-99% ee value).Finally,the fiber catalyst was further applied to simple flow chemistry system.The results show that the fiber catalyst can effectively catalyze the asymmetric Michael addition and the ee value was up to 99% after 4th run,which exhibits its excellent catalytic performance and potential in industrial application.A series of organic acid-base bifunctionalized polypropylene fiber catalysts(FABCs)were originally developed using a synthetic strategy by successively grafting of acrylic acid and 4-vinylpyridine,which was used to catalyze a series of nucleophilic addition reactions.The catalytic performance of FABCs were evaluated by nitro-aldol and Knoevenagel reactions,which show that the reactions can be efficiently catalyzed by FABCs in a cooperative catalyzing model and their activities were closely related to the acid-base ratio.An optimized bifunctional catalyst can effectively catalyze a Gewald reaction(yields: 91-97%),a tandem Michael-Henry reaction(yields: 87-99%)and the synthesis of 2-amino-2-chromenes(yields: 91-97%)in water,which implied the widely application of this fiber catalyst.In addition,this optimized bifunctional fiber catalyst can be recycled for 10 times without obvious decrease in activity,which exhibits excellent recyclability and reusability.