1. Synthesis of 6-nitro-5-hydroxynicotinic acid (B2): 5-hydroxynicotinic acid (B1) (7.0 g, 50 mmol) was dissolved in concentrated H2SO4 and 9 mL of 90% fuming HNO3 (9 mL) was added slowly. The reaction mixture was transferred to a sealed tube and the reaction was stirred at 55-60°C for 4 days. Upon completion of the reaction, the mixture was slowly poured into ice water and the pH was adjusted with 50% NaOH solution to 3. Subsequently, the aqueous phase was saturated by the addition of MgSO4 and extracted with isopropanol (4 x 45 mL). The organic phases were combined and concentrated under reduced pressure to remove the isopropanol to give 5.93 g (64% yield) of B2 as a yellow solid. The mass spectrum (APCI) showed (M + H)+ of 185. 1H-NMR (DMSO-d6) δ 8.01 (d, 1H, Ar-H), 8.41 (d, 1H, Ar-H).
