production method | the preparation method is to add cyanoacetic acid and ethyl urea in the reaction kettle, after stirring at 40~50 ℃ for 0.5H, acetic anhydride was added dropwise, the reaction temperature was gradually increased, and the reaction temperature was controlled to not exceed 80 ℃. After stirring at 70~80 ℃ for 2H, distillation was performed under reduced pressure, after the acetic acid and unreacted acetic anhydride are distilled off, water is added, and the remaining acetic acid is distilled off under reduced pressure, and the temperature is raised to above 90 ° C, the reaction solution was made into a homogeneous solution, which was put into a crystallization kettle while hot, stirred and cooled to 0-5 ° C., allowed to crystallize, and filtered to obtain a finished product. |