(2) Etherification reaction: the above organic layer was mixed with 29 g of potassium carbonate and 33 g of bromopropane, heated to 80 °C under stirring conditions and reacted for more than 5 h. The reaction was monitored by HPLC until the intermediate was completely converted. Subsequently, (3) 340 g of water was added to the reaction system for washing, and the layers were left to separate. The organic layer was separated and concentrated under reduced pressure. After desolventization, the temperature was lowered slightly by adding 250 g of ethanol and 10 g of activated charcoal, and the temperature was raised to 60 °C. After stirring for 1 hour, the reaction mixture was filtered. The filtrate was placed in a rotating refrigerator for overnight crystallization, followed by diafiltration and vacuum drying to give 55.7 g of light yellow solid powder. The product yield was determined to be 95.4% (calculated based on 2-mercaptobenzoic acid), with a melting point of 99-103 °C and a purity of 99.1% by HPLC.
