5-Chloro-1H-pyrazole-3-carboxylic acid

15953-45-4

881668-70-8

General procedure for the synthesis of 5-chloro-pyrazole-3-carboxylic acid: a solution of potassium permanganate (3.5 g, 22 mmol) in water (120 mL) was added to a solution of 5-chloro-3-methylpyrazole (1.0 g, 8.8 mmol; see Intermediate (III) above) in water (50 mL) and tertiary butyl alcohol (1 mL) in batches over a period of 5 hours at 70 °C. The reaction mixture was stirred at 70 °C overnight and subsequently filtered through diatomaceous earth (Celite). The colorless filtrate was concentrated and acidified with 2 M aqueous hydrochloric acid. After filtration, 5-chloro-pyrazole-3-carboxylic acid was obtained as a white powder, which could be used directly without further purification (yield: 913 mg, 80%).1H-NMR (DMSO-d6) data: δ 6.80 (s, 1H), δ 4.40 (br s, 1H).