Under nitrogen protection, 20.0 g of 5-hydroxy-1H-imidazole-4-carboxamide hydrochloride dihydrate prepared according to the method of Reference Example 2 was dissolved in 240 mL of a 0.45 mol/L hydrochloric acid solution, and heated to 50°C to dissolve it completely. Maintaining the reaction temperature at 50 °C, 40 mL of an aqueous solution containing 14.3 g of sodium formate was added slowly and dropwise over 35 minutes. Upon completion of the reaction, the reaction mixture was cooled to an internal temperature of 5 °C and stirring was continued for 90 minutes. The resulting crystals were collected by filtration, and the crystals were washed sequentially using a mixture comprising 20 mL of acetone and 40 mL of water and 60 mL of acetone, resulting in 12.6 g of 5-hydroxy-1H-imidazole-4-carboxamide-3/4 hydrate, the product being a pale yellow crystal. The water content of the product was 8.6% (determined by Karl Fischer method). Infrared spectra (ATR method) showed characteristic absorption peaks located at 1655, 1619, 1584, 1551 cm1. Powder X-ray diffraction pattern and infrared absorption spectra (ATR method) are demonstrated in Fig. 8, Table 3 and Fig. 9, respectively.
