Step B: Synthesis of 3-hydroxyisonicotinic acid: 3-aminoisonicotinic acid (108.86 g, 788.13 mmol) was dissolved in water (1740 mL), followed by slow addition of sulfuric acid (84.020 mL, 1576.3 mmol). The resulting yellow slurry was cooled to below 10°C and a solution of sodium nitrite (60.359 g, 874.83 mmol) in water (510 mL) was added dropwise while maintaining the temperature below 10°C. Subsequently, the reaction mixture was heated to 80°C, at which point a large amount of precipitate generation was observed. After the suspension was cooled to 65°C, glacial acetic acid (88 mL, continuous decantation) and concentrated ammonium hydroxide (190 mL) were added sequentially to adjust the final pH to about 4.5. The precipitate was collected by vacuum filtration and washed with cold water. The solid was dried in air for 16 h to give the final free flowing granular 3-hydroxyisonicotinic acid (99.37 g, 91% yield).
