Preparation of 4-methylthiobenzoic acid:

In a 10mL round-bottom flask, 0.77g of 4-methylthiobenzyl alcohol and 2g of diethylene glycol dimethyl ether were added sequentially. The resulting mixture was reacted in an ultrasonic reactor under open-air ultrasonic radiation at 40kHz/30W/70℃ for 30 minutes. The diethylene glycol dimethyl ether was removed under reduced pressure, and recrystallization yielded 0.79g of 4-methylthiobenzoic acid, with a yield of 95%.
An environmentally friendly method for synthesizing the benzoic acid compounds directly from 4-methylthiobenzyl alcohol as the starting material, using inexpensive, green, and safe air as the oxidant and inexpensive diethylene glycol dimethyl ether as the accelerator under solvent-free conditions.