Synthesis
Example 5: Synthesis of (E)-3-(2,4-difluorophenyl)acrylic acid
1. 77.5 g of 2,3-difluoroaniline was slowly added dropwise to a mixture consisting of 124 mL of concentrated hydrochloric acid, sulfuric acid and 472 mL of water at 0 °C.
2. maintaining the reaction temperature at 0 °C, a solution of 48.3 g of sodium nitrite dissolved in 90 mL of water was slowly added dropwise.
3. After the dropwise addition was completed, the reaction mixture was continued to be stirred at 0°C for 30 minutes.
4. sulfamic acid was added to quench the excess nitrite.
5. In a separate vessel, 0.34 g of palladium(II) acetate was added to 54.8 g of acrylic acid and the mixture was heated to 47°C.
6. the diazonium salt solution prepared in step 4 was slowly added dropwise over a period of 2 hours at 47 °C, controlling the reaction temperature to not exceed 49 °C. the reaction was carried out at the same time.
7. after completion of the dropwise addition, the reaction mixture was continued to be stirred at the same temperature for 2 hours.
8. After completion of the reaction, the mixture was cooled to room temperature and the solid product was collected by filtration.
9. The solid product was washed with water and dried. 10.
10. 105.1 g of (E)-3-(2,4-difluorophenyl)acrylic acid was obtained in 95% yield of the theoretical value, with a melting point of 204-205 °C. The reaction was carried out at the same temperature.
