[CH2:1]([O:3][C:4]1[N:9]=[C:8]([F:10])[CH:7]=[C:6]([NH:11][NH2:12])[N:5]=1)[CH3:2].[C:13](=S)=[S:14].[O-]CC.[Na+].Cl>C(O)C.O>[CH2:1]([O:3][C:4]1[N:5]2[C:13](=[S:14])[NH:12][N:11]=[C:6]2[CH:7]=[C:8]([F:10])[N:9]=1)[CH3:2]A 1.74 g (10 mmol) sample of 2-ethoxy-4-fluoro-6-hydrazinopyrimidine was dissolved in 20 mL of absolute ethanol and 2.84 g (37 mmol) of carbon disulfide and 3.20 g (10 mmol) of 21 percent by weight sodium ethoxide were added. The mixture was heated at reflux with stirring for 3 hours and then was cooled by adding 20 mL of ice water. The mixture was then acidified to a pH of about 2 by adding 2 mL of 6.25N hydrochloric acid diluted to 8 mL with water. The yellow precipitate that formed was recovered by filtration, washed with water, and dried to obtain 0.85 g (40 percent of theory) of 5-ethoxy-7-fluoro-1,2,4-triazolo[4,3-c]pyrimidine-3(2H)-thione. The proton and carbon NMR spectra of this material were consistent with its assigned structure.
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