General procedure for the synthesis of 2,5-diamino-4,6-dihydroxypyrimidine hydrochloride from 2,5-diamino-4,6-dichloropyrimidine hydrochloride: 2,5-diamino-4,6-dihydroxypyrimidine hydrochloride (0.14 mol, 25 g) was placed in a dry reactor, and dry 1,2,3-trichloropropane (51.96 mL) was added and stirred. Subsequently, tetramethylammonium chloride (0.29 mol, 31.25 g) and phosphorous trichloride (0.54-0.81 mol, 83.28-124.9 g, 50.6-75.9 mL) were added sequentially. The reaction mixture was heated to reflux (about 115°C) and maintained for 24 hours. Upon completion of the reaction, it was cooled to below 50°C and ice water (24.44 mol, 440.44 g) was added slowly, keeping the temperature below 55°C. The pH was adjusted to 6.5-7.0 with 50% sodium hydroxide solution (3.12 mol, 124.92 g, 163.3 mL), keeping the temperature below 55°C, and stirring was continued for 30 minutes. Subsequently, the reaction mixture was stirred at 50-60°C and tetrahydrofuran (3.7 mol, 267.0 g, 300 mL) was added. Insoluble material was removed by diatomaceous earth filtration and the filter cake was washed with ethyl acetate (20.5 mol, 1806.58 g, 2002.86 mL). The organic phases (tetrahydrofuran and ethyl acetate) were combined, washed three times with water (5.57 mol, 100.32 g, 100.32 L), dried with sodium bicarbonate and filtered. Ethyl acetate was removed by vacuum distillation, hexane (0.77 mol, 66.14 g, 100.36 mL) was added to the residue, cooled to below 10°C, filtered, and the resulting solid was dried in vacuo at 50°C to afford the title product, 2,5-diamino-4,6-dichloropyrimidine (0.09 mol, 15.71 g), as a slightly brownish solid in about 65% yield .
