General procedure for the synthesis of dimethyl 4-hydroxyphthalate from methanol and 4-hydroxyphthalic acid:
1. thionyl chloride (20 mL) was slowly added to a methanol (100 mL) solution of 4-hydroxyphthalic acid (20 g, 110 mmol).
2. The reaction mixture was stirred at 0 °C, then warmed to 80 °C and held for 4 hours.
3. Upon completion of the reaction, the volatiles were removed by distillation under reduced pressure to give dimethyl 4-hydroxyphthalate (C1-2) as a white solid (23 g, yield: 99%), which could be used in the next step without further purification. 4.
4. The structure of the product was confirmed by 1H NMR (CDCl3, 400 MHz) and mass spectrometry (ESI): 1H NMR δ 7.77 (d, J = 8.8 Hz, 1H), 7.03 (d, J = 2 Hz, 1H), 6.95 (dd, J = 8.4 and 2.0 Hz, 1H), 3.93 (s, 3H), 3.88 (s, 3H); MS ( ESI) m/z 211 ([M+H]+).
