General procedure for the synthesis of 6-chloro-5-nitronicotinic acid from 2-chloro-3-nitro-5-methylpyridine: Sodium dichromate (2.5 g) was slowly added to a mixture of 2-chloro-3-nitro-5-methylpyridine (1.0 g, 6.5 mmol) and concentrated sulfuric acid (27 mL). The reaction mixture was stirred at room temperature for 15 hours and then slowly poured into crushed ice to quench the reaction. The mixture was extracted with ethyl acetate (EtOAc). The organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to give 6-chloro-5-nitronicotinic acid (product) as a green solid (1.0 g, 85% yield).1H NMR (300 MHz, DMSO-d6) δ: 13.32 (s, 1H, carboxylate proton), 8.64 (d, J = 2.4Hz, 1H, pyridine ring proton), 8.37 ( d, J = 2.4Hz, 1H, pyridine ring proton).
