Ethyl vinyl ether → 3-(Trifluoromethyl)pyrazole

To a solution of 4.4 moles hydrazine.hydrochloride in 2.2 L of methanol in a 3-necked flask, equipped with a mechanical stirrer, a reflux condenser and a dropping funnel an equimolar amount of ETFBO which had been manufactured by addition of trifluoroacetyl chloride to ethyl vinyl ether was added dropwise over about 4 hours under N2 atmosphere. The temperature of the reaction mixture was kept below 15° C. After 12 h of reflux, the reaction batch was filtered in a 2-L flask and concentrated under vacuum (an identical batch was made under the same conditions, yield of both crude products was ca. 95%). Subsequently, the combined crude product was purified by shortpass-vacuum distillation at 27 mbar. The yield was 1105 g, which corresponded to 92% of the theoretical yield.