Synthesis
The general procedure for the synthesis of 1-methyl-3-phenyl-1H-pyrazole-5-carboxylic acid from methyl 1-methyl-3-phenyl-1H-pyrazole-5-carboxylate was as follows: 1-methyl-3-phenyl-1H-pyrazole-5-carboxylic acid methyl ester (1.00 g, 6.23 mmol) was dissolved in a mixed solvent of ethanol (10 mL) and water (10 mL), and then lithium hydroxide mono hydrate (0.582 g, 13.87 mmol). The reaction mixture was stirred at 50 °C until the reaction was complete as monitored by high performance liquid chromatography (HPLC). After completion of the reaction, the mixture was concentrated to dryness and the residue was dissolved in water and extracted with dichloromethane (DCM). The aqueous phase was acidified with 1N hydrochloric acid to pH < 3. The precipitated solid was collected by filtration and dried under high vacuum to afford 1-methyl-3-phenyl-1H-pyrazole-5-carboxylic acid (0.887 g, 95% yield) as a white solid. The mass spectrum (APCI positive ion mode) showed m/z 203 (100%) ([M+H]+).
References
[1] Patent: WO2008/11131, 2008, A2. Location in patent: Page/Page column 260
[2] Chemische Berichte, 1933, vol. 66, p. 1690,1692
[3] Patent: EP1176140, 2002, A1. Location in patent: Page 49 - 50
