Sodium metal (30 mmol) was added to methanol (10 mL) and after complete dissolution, thiourea (10 mmol) and ethyl acetoacetate (10 mmol) were added sequentially. The reaction mixture was heated to reflux for 7 hours. After completion of the reaction, methanol was removed by distillation under reduced pressure and the residue was dissolved in an appropriate amount of water and the pH was adjusted to neutral with acetic acid. The precipitate was collected by filtration to give the pale yellow crystalline product methylthiouracil (1.26 g, 90% yield). The product was characterized as follows: melting point 275-277°C; 1H NMR (δ, ppm): 2.09 (s, 3H, 6-CH3), 5.52 (s, 1H, CH-pyrimidine), 11.98 [b.s, 2H, (NH)2]; 13C NMR (δ, ppm): 17.88, 103.38, 151.91, 160.32, 175.83. 175.83. Elemental analysis results (C5H6N2OS) calculated values: C, 42.24; H, 4.25; N, 19.70; S, 22.55; measured values: C, 42.24; H, 4.25; N, 19.70; S, 22.55.
