Preparation Of Nylon Supported Organobase Catalysts And Their Application In Knoevenagel Reaction

The Knoevenagel reaction is one of the typical reactions for the synthesis of carbon-carbon double bond products in organic synthesis.The resultingα,β-unsaturated compounds and their intermediates are widely used in the preparation of fine chemicals,pharmaceutical intermediates,perfume spices and functional compounds.Traditional catalytic systems generally use homogeneous organic bases,inorganic bases and Lewis acids as catalysts,which have disadvantages such as non-recyclable catalysts,high costs and difficult separation of products,meanwhile the waste generated in the separation causes additional environmental pollution.However,by immobilizing the homogeneous catalysts onto carrier materials,heterogeneous catalytic systems provide effective ways to achieve the catalyst recycling and simplify the separation operation,which is in line with the concept of green chemistry and the need for sustainable development.Therefore,the design and development of novel heterogeneous catalysts is of great importance.Nylon named polyamide,has many excellent properties,such as easy preparation,solvent corrosion resistance,toughness,abrasion resistance and so on.Surface modification of nylon fiber can be easily achieved through functional group conversion or radical grafting strategy.These characteristics give nylon fiber the potential to be used as catalyst carrier.In this paper,commercially available nylon fiber was selected as supporting material for the preparation of heterogeneous base catalysts and used in the Knoevenagel reaction.The details are showed as follows.(1)Nylon fabric catalyst(nylon 6-NH)was prepared by using borane to reduce the amide bonds to secondary amine groups.The base content of the fiber catalyst could reach0.66 mmol/g which was determined by acid-base titration.Benzaldehyde and methyl cyanoacetate were chosen as model substrates.The effects of catalyst dosage,solvent screening,reaction time and temperature were explored.The product could be obtained in97%yield after reacting in cyclohexane for 2 h at 80 ℃.In addition,the substrate scope and the recyclability of the catalytic system were investigated.The catalyst is suitable for a series of substrates and can be repeatedly for 10 times without obvious loss of activity.(2)Nylon fabric catalyst(nylon 6-AA-ter)was prepared by UV-induced grafting of acrylic acid on the surface of nylon fiber,followed by the introduction of tertiary amine groups via amide condensation.The base content of the fiber catalyst could reach 2 mmol/g which was determined by acid-base titration.Benzaldehyde and methyl cyanoacetate were chosen as model substrates.The effects of catalyst dosage,solvent screening,reaction time and temperature were explored.The product could be obtained in 99%yield after reacting in water for 3 h at room temperature.The catalyst could be reused for more than five times and showed excellent catalytic activity in the scale-up synthesis of coumarin,demonstrating its potential for industrial production applications.