In a 20 L autoclave, 7.5 g of anhydrous methanol and 1.66 Kg (10 mol) of 2-carboxyphenylboronic acid were added and stirring was initiated to mix the reactants. The temperature of the reaction kettle was slowly raised to 40 °C and maintained in the range of 40 to 55 °C. Subsequently, thionyl chloride (1.31 Kg, 11 mol) was slowly added dropwise to the reaction kettle, and after the dropwise addition was completed, the temperature was raised to reflux condition and the reaction was continued for 2-3 hours. The completion of the reaction was confirmed by thin layer chromatography (TLC, unfolding agent ratio of n-heptane: ethyl acetate = 2:1). Upon completion of the reaction, the reaction solution was cooled and subsequently subjected to reduced pressure distillation to remove the solvent. The residue was cooled to -10°C to 10°C and stirred at this temperature for 1 hour. Next, the drying process was stopped by filtration under reduced pressure at 80 °C until no impurities were confirmed to be present by hydrogen nuclear magnetic resonance (HNMR, observing the peak at 3.21 ppm with DMSO-d6 as solvent). Finally, the mixture was stirred at room temperature, filtered and dried at room temperature to give 1.74 Kg of the white solid product 2-(methoxycarbonyl)phenylboronic acid in 96.7% yield with 19.8% water and 140.5% Karl Fischer moisture.
