反应详情

温度

-78 °C

Under N2, fuming nitric acid (4.7 mL, 112.0 mmol) was added slowly over 10 min to acetic anhydride (16.6 mL, 175.6 mmol) cooled in a dry ice/acetone bath to −78° C. 5-methyl-2-thiophene carboxylic acid (5.0 g, 35.2 mmol) was added in 1 g portions over 10 min to the solution. The reaction was kept at −20° C. for 1 h before quenching over ice. The yellow solid was filtered off and washed with water (200 mL). The crude product was recrystallized from 95% EtOH to give 5-methyl-4-nitro-2-thiophene carboxylic acid as a pale yellow solid (4.6 g, 70%). 1H NMR (400 MHz, CD3OD) δ (ppm) 8.13 (s, 1H) 2.82 (s, 3H).

1. custombefore quenching over ice
2. filtrationThe yellow solid was filtered off
3. washwashed with water (200 mL)
4. customThe crude product was recrystallized from 95% EtOH