[NH2:1][C:2]1[N:7]([CH2:8][CH3:9])[C:6](=[O:10])[NH:5][C:4](=[O:11])[CH:3]=1.[N:12]([O-])=[O:13].[Na+]>C(O)(=O)C.O>[NH2:1][C:2]1[N:7]([CH2:8][CH3:9])[C:6](=[O:10])[NH:5][C:4](=[O:11])[C:3]=1[N:12]=[O:13]To a solution of 6-amino-1-ethyl-1,3-dihydropyrimidine-2,4-dione (5.0 g, 32.3 mmol) in a mixture of 50% acetic acid/water (50 ml) at 70° C. was added sodium nitrite (4.45 g, 64.5 mmol) in portions over a period of 30 minutes. The mixture was stirred at 70° C. for a further 30 minutes. The reaction mixture was cooled, and the precipitate filtered off, and washed with water, then methanol, to provide 6-amino-1-ethyl-5-nitroso-1,3-dihydropyrimidine-2,4-dione, a compound of formula (14).
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