preparation | add 2, 5-difluoro-3-methylbenzaldehyde and hydroxylamine hydrochloride with a certain amount of substance to a three-mouth flask equipped with thermometer, condenser tube and electric stirring, heat and keep at 70~75 ℃, react for 30min, then slowly add 20 (mass fraction) sodium carbonate aqueous solution and stir, bubble generation (can be tested with lime water). When the reaction slows down, adjust the pH to 8~9, stop dropping sodium carbonate aqueous solution. Continue to stir, light red precipitate appears, let stand until light red gradually turns milky white. Filter out the precipitate, wash it with water for 2-3 times, and dry it to obtain milky white solid powder 2, 5-difluoro-3-methylbenzaldehyde oxime, which is weighed for later use. Add 2, 5-difluoro-3-methylbenzaldehyde oxime and acetic anhydride into a three-mouth bottle according to a certain amount ratio, heat to 110~120 ℃, react for 3h, the reaction liquid is light orange liquid, cool down, let stand, and white crystals appear. Suction filtration to obtain crystals, dissolve with alcohol, hot filtration to remove insoluble matter, filtrate is extracted and separated with water to obtain clean colorless needle-like crystals, dry at low temperature to obtain 2, 5-difluoro-3-methylbenzonitrile. |