Synthesis
General procedure for the synthesis of 2-fluorophenylhydrazine from o-fluoroaniline: 500 g of o-fluoroaniline and 1500 mL of 37% concentrated hydrochloric acid were added to a 10 L three-necked flask and cooled to 2 °C using an ice-salt bath. 857 g of 35% aqueous sodium nitrite solution was added slowly and dropwise under stirring, and the reaction temperature was controlled to be maintained at 0 to 5 °C for 1.5 hours. Subsequently, 730 mL of 37% concentrated hydrochloric acid, 730 mL of water, and 480 g of zinc powder were added to the reaction solution, and the reaction temperature was maintained at 18 °C until the reaction was complete and the reaction solution turned off-white. Then, 30% sodium hydroxide solution was slowly added to adjust the pH of the reaction solution to 10.5, and this process took about 2 hours, and then crystals were precipitated, and 295 g of 2-fluorophenylhydrazine crude product was obtained by filtration. Purification step: 295 g of 2-fluorophenylhydrazine crude was dissolved in 5900 mL of water, heated to 60 ℃ to make it completely dissolved, and added appropriate amount of activated carbon to decolorize for 20 minutes, and then thermo-filtered to obtain a colorless filtrate. The filtrate was allowed to stand for 5 hours and then continued to stand for 2 hours, and the precipitated crystal precipitate was collected by filtration to finally obtain 238g of purified 2-fluorophenylhydrazine.
References
[1] Journal of Medicinal Chemistry, 1991, vol. 34, # 9, p. 2892 - 2898
[2] Chemistry - An Asian Journal, 2015, vol. 10, # 8, p. 1618 - 1621
[3] Molecules, 2016, vol. 21, # 11,
[4] Patent: CN106518723, 2017, A. Location in patent: Paragraph 0037-0046
[5] Patent: CN106518714, 2017, A. Location in patent: Paragraph 0017 - 0023
