Add 4.0 g of glyoxylic acid monohydrate (0.04 mol), 1.2 g of urea (0.02 mol), and 10 mL of 10% hydrochloric acid into the beaker. Stir evenly. After releasing the heat, pour it into a dropping funnel and set aside. Add 3.6 g (0.06 mol) of urea, 5.6 g (0.06 mol) of phenol, and 10% hydrochloric acid, and stir evenly in a three-necked flask. Heat to 90 ℃, slowly add the glyoxylic acid-urea mixture dropwise and control the dropping speed for about 4 hours. After the dropwise addition is completed, continue the heat preservation reaction for 2 hours to complete the reaction. Change the reaction device to a vacuum distillation device to recover excess phenol. After evaporating about 1/3 of the volume of the solution, cool to about 15°C to crystallize, filter, and use the filter cake. Wash with water 2 to 3 times until neutral and dry to obtain 5.8 g of white solid 5-(4-Hydroxyphenyl)-2,4-imidazolidinedione.
