synthesis of 5-Fluoro-2-nitrophenylacetic acid: To a mixture of 23.2g of 3-fluorophenylacetic acid and 100ml. of conc. sulfuric acid is added dropwise 6.5ml. of conc. nitric acid while maintaining the tempera ture below 40°C. The mixture is stirred at ambient temperature for 24 hours and then poured onto one kilogram of ice. The resulting precipitate is recovered by filtering, washed with water and dried in vacuo to obtain crude 5-fluoro-2-nitrophenylacetic acid, m.p. 137-142°C.
The general procedure for the synthesis of 5-fluoro-2-nitrophenylacetic acid using 3-fluorophenylacetic acid as starting material was as follows: 3-fluorophenylacetic acid (5 g, 36.7 mmol) was dissolved in 30 mL of chloroform, followed by the addition of ammonium nitrate (3.12 g, 38.9 mmol). The reaction mixture was cooled to 0 °C and trifluoroacetic anhydride (16.02 mL, 113 mmol) was added slowly and dropwise at this temperature. The reaction was stirred continuously at 0 °C for 3 hours. Upon completion of the reaction, water was slowly added to quench the reaction. The chloroform layer was separated, washed with water and subsequently dried and concentrated with anhydrous sodium sulfate. By crystallization from the crude product in ethyl acetate and grinding with acetonitrile, 5.25 g of the target product 5-fluoro-2-nitrophenylacetic acid was obtained as a brown solid in 87% yield. Mass spectrometry (APCI) analysis resulted in 199 [M-H]+.
[1] Journal of Organic Chemistry, 1995, vol. 60, # 20, p. 6389 - 6396
[2] Bioorganic and Medicinal Chemistry Letters, 2005, vol. 15, # 20, p. 4560 - 4563
[3] Patent: US2004/67960, 2004, A1. Location in patent: Page/Page column 19
[4] Patent: US4160032, 1979, A
