5-Chloro-1-methyl-3-(trifluoromethyl)-1H-pyrazole-4-carboxylic acid

128455-62-9

128455-63-0

Example 5: 10 g of 5-chloro-1-methyl-3-(trifluoromethyl)-1H-pyrazole-4-carboxaldehyde was added to 50 mL of an aqueous solution containing 5 g of sodium hydroxide (2 equivalents). Under vigorous stirring, 34.4 g of 35% hydrogen peroxide solution was slowly added in 8 drops over a temperature range of 40°C to 50°C, taking 1.5 hours. After the dropwise addition was completed, the reaction mixture was continued to be stirred for 30 minutes and subsequently cooled to 15°C. The pH of the reaction solution was adjusted to 1 with concentrated hydrochloric acid and the solid product was precipitated. The crystals were collected by filtration and washed well with water, after which the crystals were dissolved in ether. The ether solution was dried over anhydrous magnesium sulfate and decolorized by activated carbon, and then the ether was removed by distillation under reduced pressure to give 8.6 g of 5-chloro-1-methyl-3-(trifluoromethyl)pyrrole-4-carboxylic acid in 80.0% yield and 197.5-199.5 °C melting point.