The general procedure for the synthesis of 6-aminopyridine-3-sulfonic acid from 2-aminopyridine was as follows: (i) 2-aminopyridine (80 g, 0.85 mol) was added to fuming sulfuric acid (320 g) in batches over 30 minutes. Subsequently, the resulting reaction mixture was heated and reacted at 140°C for 4 hours. After completion of the reaction, it was cooled to room temperature, the reaction was slowly poured into ice (200 g) and stirring was continued for 2 hours under ice/salt bath conditions. The resulting suspension was separated by filtration and the solids were washed sequentially with ice water (200 mL) and cold industrial methylated alcohol (IMS, 200 mL). Finally, the pyridine-2-amino-5-sulfonic acid solid product (111.3 g) was obtained by filtration drying. lRMS (Thermospray) analysis result: m/z 175 (M + 1)+.
[1] Patent: US6440982, 2002, B1
[2] Patent: US6251904, 2001, B1
[3] Zhurnal Russkago Fiziko-Khimicheskago Obshchestva, 1920, vol. 50, p. 495
[4] Chem. Zentralbl., 1923, vol. 94, # III, p. 1021
[5] Bulletin de la Societe Chimique de France, 1939, vol. <5> 6, p. 736,738
