Water → 3-Chloro-4-nitrobenzoic acid

2-Chloro-4-methyl-1-nitro-benzene (1.2 g, 6.99 mmol) in a mixture of water and pyridine (2/1, 30 mL) was heated at 90° C. then potassium permanganate (5.2 g, 32.9 mmol) was added in 4 portions at intervals of 1.5 hours. The reaction mixture was heated at 90° C. for 8 hours and then more potassium permanganate (2 g) was added and the resulting mixture was stirred at 90° C. overnight. More potassium permanganate (2 g) was added and the resulting mixture was stirred at 90° C. for 1 hour, the solid was filtered off on a CELITE™ pad. Water (50 mL) was added to the filtrate; the resulting mixture was acidified until pH<2 and was extracted 3 times with ethyl acetate. The combined organic extracts were washed with water and brine, dried over anhydrous sodium sulfate, filtered and evaporated under reduced pressure to give 1.19 g (84% yield) of 3-chloro-4-nitro-benzoic acid as a light yellow solid without further purifications