Synthesis
The general procedure for the synthesis of pyrazole-3-carboxylic acid from 3-methylpyrazole was as follows: an aqueous solution of potassium permanganate (KMnO4, 40.9 g, 0.26 mol) was slowly added to a stirring solution of 3-methyl-1H-pyrazole (9.8 mL, 0.12 mol) dissolved in 0.5 L of water. The reaction mixture was heated to reflux and maintained for 5 hours. After completion of the reaction, the black suspension was cooled and filtered. The filtrate was concentrated to a smaller volume and acidified with 3 N hydrochloric acid (HCl). Subsequently, the precipitated white solid product was collected and washed with ethyl ether (Et2O) to give the final pyrazole-3-carboxylic acid in 100% yield.
References
[1] Journal of the American Chemical Society, 2000, vol. 122, # 44, p. 10810 - 10820
[2] Patent: WO2004/80999, 2004, A1. Location in patent: Page 43
[3] Russian Journal of Physical Chemistry, 1992, vol. 66, # 4, p. 463 - 465
[4] Zhurnal Fizicheskoi Khimii, 1992, vol. 66, # 4, p. 871 - 874
[5] Organic Mass Spectrometry, 1982, vol. 17, # 7, p. 299 - 303
