3-(Trifluoromethyl)pyrazole

59938-06-6

20154-03-4

Example 2 Preparation of 3-(trifluoromethyl)-1H-pyrazole: In a three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a dropping funnel, a solution of 4.4 moles of hydrazine hydrochloride dissolved in 2.2 L of methanol was added. Under nitrogen protection, an equimolar amount of (E)-1-ethoxy-3-trifluoromethyl-1,3-butadiene (ETFBO) was slowly added through the dropping funnel in a titration process for about 4 hours while the temperature of the reaction mixture was controlled to remain below 15 °C. After completion of the dropwise addition, the reaction mixture was refluxed for 12 hours. At the end of the reaction, the reaction solution was filtered and transferred to a 2L flask and concentrated under vacuum (another batch of reaction prepared in parallel under the same conditions, the total yield of the two batches of crude product was about 95%). After combining the two batches of crude product, purification was carried out by short-range vacuum distillation (27 mbar), resulting in 1105 g of pure product in 92% yield of the theoretical value.