Sodium hydroxide (97%, 15.7 g, 381 mmol) was added to 500 mL of water and the suspension was stirred for 10 min at room temperature. 6-Methyl-2-thioxasulfinyl-1,2,3,4-tetrahydropyrimidin-4-one (98%, 53.5 g, 369 mmol) was added and the mixture was stirred until completely dissolved for 10 minutes. Iodomethane (28.99 mL, 461 mmol) was slowly added dropwise and the reaction mixture continued to be stirred for 4 hours at room temperature. After completion of the reaction, a colorless solid was obtained by filtration, washed with ice-cold water (2 x 100 mL) and dried under vacuum at 60 °C to give 6-methyl-4-hydroxy-2-methylthiopyrimidine (57 g, 98% yield) as a colorless solid. The product was analyzed by LC-MS: m/z = 156.9 [M + H]+; retention time (RT) = 0.61 min.
