General procedure for the synthesis of 2-hydroxy-5-nitropyrimidine from 2-hydroxypyrimidine hydrochloride: 2-hydroxypyrimidine hydrochloride (25.92 g, 0.20 mol) was added in batches to concentrated sulfuric acid (200 mL), and stirred until completely dissolved. Subsequently, potassium nitrate (39.1 g, 0.40 mol) was added to the reaction system and the mixture was stirred and reacted at 95°C for 3 days. Upon completion of the reaction, the reaction mixture was slowly poured into ether (3 L) under vigorous stirring, by repeated decantation and ether displacement until a solid was precipitated. The solid product was collected by filtration, washed with ether and then the solid was dissolved in ethanol. Solid sodium bicarbonate was added to the ethanol solution and the insoluble material was removed by filtration. The filtrate was concentrated under reduced pressure to afford the target product 2-hydroxy-5-nitropyrimidine (10.72 g, 39% yield). The product was characterized by 1H NMR (CDCl3): δ 12.00-10.00 (1H, broad single peak), 9.15 (2H, single peak).
