The general procedure for synthesizing 2,3-difluorophenylhydrazine hydrochloride from 2,3-difluoroaniline was as follows: to an aqueous solution (100 mL) of sodium nitrite (27.8 g), a concentrated hydrochloric acid solution (620 mL) of 2,3-difluoroaniline (40 g) was added slowly and dropwise at -20° C. The reaction mixture was stirred for 1 hour. The reaction mixture was kept stirred at -20°C for 1 hour. Subsequently, a concentrated hydrochloric acid (200 mL) solution of tin(II) chloride (117 g) was added slowly and dropwise at the same temperature, and then the reaction mixture was warmed up to 0 °C and stirring was continued for 2 hours. Upon completion of the reaction, the resulting solid product was collected by filtration, washed sequentially with water and hexane, and finally concentrated and dried under reduced pressure to afford the target compound 2,3-difluorophenylhydrazine hydrochloride as a white solid (32.6 g, 73% yield). The structure of the product was confirmed by 1H-NMR (DMSO-d6), δ: 6.96-7.19 (3H, m), 8.70 (1H, brs), 10.66 (3H, brs).
