The general procedure for the synthesis of 4,6-dichloro-1H-pyrimidin-2-one from 2,4,6-trichloropyrimidine was carried out as follows: an aqueous 3.8 M sodium hydroxide solution (10 mL, 38.7 mmol) was slowly added to a vigorously stirred solution of 2,4,6-trichloropyrimidine (4.74 g, 25.8 mmol) in tetrahydrofuran (THF, 80 mL). The reaction progression was monitored by liquid chromatography-mass spectrometry (LC-MS) and the product peak (m/z 165, retention time 4.08 min) and residual 2,4,6-trichloropyrimidine (retention time 5.28 min) were observed. After 48 hours of reaction, the reaction mixture was concentrated under reduced pressure and filtered, retaining the filtrate. The resulting precipitate was dissolved in hot water (120 mL) and the pH of the solution was subsequently adjusted to 2 with 3.6 M hydrochloric acid and cooled at 0 °C. The precipitate was collected by filtration, washed with water and dried under reduced pressure to give the first batch of 4,6-dichloro-1H-pyrimidin-2-one (1.17 g, 27% yield) as a white solid. The retained filtrate was concentrated to near dryness and the above purification steps were repeated to afford the second batch of 4,6-dichloro-1H-pyrimidin-2-one (2.03 g, 48% yield) as a white solid. The total yield of the two batches of product was 3.2 g with an overall yield of 75%.
