Synthesis And Characterization Of N-(Ortho-Substituted Phenyl) Maleimides

N-substituted phenyl maleimides are one kind of thermal improvers which are developed recently.When copolymerized with common vinyl monomers,the resulting copolymers contain five-member planar rings in the chain can hinder the rotation of the imides residues around the backbone chain of the macromolecules,resulting in a greater structural stiffness and a higher thermal stability.In this study we synthesized a series of N-(o-substituted phenyl) maleimides.Two synthetic methods were adopted according to different aniline o-substituted groups:acetic anhydride method and azeotropic method.N-(2-Methylphenyl maleimide,N-(2-Chlorophenyl) maleimide were prepared from maleic anhydride and the correspongding aniline using acetic anhydride as dehydrator,triethylamine and metallic salt as catalyst, hydroquinone as polymerization retarder.Through orthogonal experiments, the optimal synthesis process of N-(2-Methylphenyl maleimide is as follows:when 2-Toluidine is 0.05mol,the mol rate of maleic anhydride is 1.1;triethylamine and acetic anhydride are 2mL and 12mL respectively; the reaction temperature is 55°C;the reaction time is 2H;the yield of crude product is 80.8%,and the purity is 95.3%.After recrystallization,the finally yield is 68.6%,and the purity is 99.3%.The optimal synthesis process of N-(2-Chlorophenyl) maleimide is as follows:when 2-Chloroaniline is 0.05mol,the mol rate of maleic anhydride is 1.1; triethylamine and acetic anhydride are 2mL and 9mL respectively;the reaction temperature is 50℃;the reaction time is 1.5H;the yield of crude product is 84.1%,and the purity is 93.1%.After recrystallization,the finally yield is 71.4%,and the purity is 98.3%.N-(2-Ethylphenyl) maleimide,N-(2-Nitrophenyl) maleimide and N-(2-Hydroxyphenyl) maleimide were prepared from maleic anhydride and the correspongding aniline using Toluene and DMF as mixed solvent, p-Toluenesulfonic acid as catalyst.Through orthogonal experiments,the optimal synthesis process of N-(2-Ethylphenyl) maleimide is as follows: when 2-Ethylaniline is 0.05mol,the mol rate of maleic anhydride is 1.1; p-Toluenesulfonic acid is 0.6g;the reaction temperature is 135℃;the reaction time is 3.5H;the yield of crude product is 78.2%,and the purity is 97.4%.After recrystallization,the finally yield is 69.5%,and the purity is 99.6%.The optimal synthesis process of N-(2-Nitrophenyl) maleimide is as follows:when 2-Nitroaniline is 0.05mol,the mol rate of maleic anhydride is 1.1;p-Toluenesulfonic acid is 0.6g;the reaction temperature is 130℃; the reaction time is 3H;the yield of crude product is 40.6%,and the purity is 96.5%.After recrystallization,the finally yield is 35.7%,and the purity is 98.6%.The optimal synthesis process of N-(2-Hydroxyphenyl) maleimide is as follows:when 2-Aminophenol is 0.05mol,the mol rate of maleic anhydride is 1.1;p-Toluenesulfonic acid is 0.7g;the reaction temperature is 145℃;the reaction time is 4.5H;the yield of crude product is 52.3%,and the purity is 96.2%.After recrystallization,the finally yield is 30.2%,and the purity is 99.2%.Through optimal conditions,the synthesis process was improved and developed.The yields of each product were reached or surpassed the yields of the concerned documents,the qualities of the product was met the requirement.The structures were confirmed by melting point/IR/¹H-NMR/¹³C-NMR.This synthesis process of N-(o-substituted phenyl) maleimides has the value of being industrialized.