The invention relates to the technical field of synthesis of compounds, in particular to a synthesis method of 2, 4-dihydroxy-5-cyanopyrimidine, which specifically comprises the following steps: S1, mixing N-cyano acetyl urethane and N, N-
dimethylformamide dimethyl acetal according to a
mass ratio of 1: (0.8-1) in a
solvent at the temperature of 10-30 DEG C, and adding the mixture into a reaction kettle to obtain a primary
mixed solution; s2, stirring the primary
mixed solution, heating to 60-70 DEG C, keeping the temperature, and reacting for 2-4 hours until the raw materials are completely converted, so as to obtain a secondary
mixed solution; s3, reducing the temperature of the mixed solution obtained in the step S2 to 0-10 DEG C, dropwise adding stronger
ammonia water within 1-2 hours, heating to 60-70 DEG C, and keeping the temperature for 1-2 hours; and S4, cooling the solution obtained in the step S3 to 0-10 DEG C again, dropwise adding concentrated
hydrochloric acid, adjusting the pH value to 1-2, keeping the temperature for 1-2 hours, filtering, washing and
drying to finally obtain the 2, 4-dihydroxy-5-cyanopyrimidine. According to the method, the yield is increased to 92-95%, the purity is stabilized at 99.5% or above, the usage amount of an
organic solvent and waste
discharge are reduced, and the method conforms to the
green chemistry concept.