1H-Pyrazole-3-carboxylicacid,4-chloro-(9CI)

Synthesis

A mixture of 4-chloro-3-methylpyrazole hydrochloride (20 mmol, 3.06 g; see step (a)) with potassium permanganate (50 mmol, 11.4 g) in 500 mL of water was stirred thoroughly. The mixture was first stirred at room temperature for 3 days, then warmed up to 70 °C and continued stirring for 5 hours. After completion of the reaction, the mixture was filtered and the filtrate was concentrated. To the concentrate was added 1 M aqueous hydrochloric acid (50 mL) followed by extraction with ethyl acetate (5 x 50 mL). The organic phases were combined, washed with saturated aqueous sodium chloride, dried over anhydrous sodium sulfate and concentrated to give 640 mg (22% yield) of the target product 4-chloro-1H-pyrazole-5-carboxylic acid as a white solid.1H NMR (DMSO-d6, 400 MHz) δ 13.47 (br s, 2H), 7.92 (br s, 1H).

References

[1] Patent: WO2007/45868, 2007, A1. Location in patent: Page/Page column 49
[2] Patent: WO2007/51981, 2007, A1. Location in patent: Page/Page column 52