GENERAL STEPS: 500 g (15.6 mol) of methanol was added to a 1000 ml three-necked flask. Under stirring conditions, 73.9 g (0.53 mol) of ethyl glycinate hydrochloride was added and the temperature was slowly raised to 50-55°C until the ethyl glycinate hydrochloride was completely dissolved. Subsequently, 67.5 g (0.27 mol) of copper sulfate pentahydrate was added to this solution and stirring was continued until complete dissolution and stirring was maintained at 50-55°C for 0.5 hr. Next, triethylamine was added dropwise to the reaction system and the pH was adjusted to 8.5-9.0. Then, 92 g (0.5 mol) of p-methylsulfonylbenzaldehyde was added, and the reaction temperature was maintained at 50-55 °C and the pH was maintained between 8.5-9.0 by adding triethylamine. During the reaction, the progress of the reaction was monitored by HPLC, and the reaction was judged to be complete when the percentage of peak area of p-methylsulfonylbenzaldehyde was less than 2%. At the end of the reaction, methanol was recovered by decompression distillation, and the temperature inside the reaction flask was controlled to be no more than 50 °C during the distillation process. After the recovery of methanol, 600 g of water was added to the reaction flask, and after sufficient stirring, 146.7 g of ethyl 3-(p-toluenesulfonylphenyl)serinate was obtained by centrifugation, with a moisture content of 10.0%, a purity of 97.2% and a yield of 92%.
