A reflux reaction was carried out for 2 hours using 5-methoxy-2-thio-2,3-dihydropyrimidin-4(1H)-one (21.5 g, 0.137 mol) as starting material, mixed with chloroacetic acid (21.5 g, 0.227 mol) in water (585 mL). Subsequently, concentrated hydrochloric acid (85 mL) was added to the reaction system and the reflux reaction was continued for 16 hours. Upon completion of the reaction, the reaction mixture was cooled to room temperature and the solid product was precipitated. The solid was collected by filtration, washed with water and dried to afford 5-methoxy-2,4-dihydroxypyrimidine (18.2 g, 94% yield). Mass spectrometry analysis showed (M + H)+ = 143.
