Synthesis
General procedure for the synthesis of 3,5-bis(trifluoromethyl)benzeneboronic acid from trimethyl borate, 3,5-bis(trifluoromethyl)bromobenzene, and electrophoretic-grade water: in a three-necked, dry, round-bottomed flask equipped with a rod-shaped magnetic stirrer, a 500-ml dropping funnel, condenser tube, and nitrogen introduction tube, 9.30 g of magnesium flakes were added under nitrogen protection and 220 ml of tetrahydrofuran (THF), which had been distillate-purified, were added ). The temperature of the reaction system was maintained in the range of 0 to 5°C by means of an ice bath. At this temperature, 44.0 mL of 3,5-bis(trifluoromethyl)bromobenzene was slowly added through a dropping funnel and the addition process was controlled to be completed within 1 hour. After the addition was completed, the reaction was slowly warmed to room temperature and continued for 16 hours to obtain a dark brown viscous solution. Subsequently, the reaction solution was cooled to -70°C in a dry ice/acetone bath and 28.97 mL of trimethyl borate was slowly added dropwise through a dropping funnel. After completion of the dropwise addition, the reaction solution was allowed to warm naturally to room temperature and the reaction was continued for 12 hours to obtain a brown viscous solution. Under cooling in an ice bath, 144.5 ml of 37 wt% aqueous hydrochloric acid solution was mixed with 63.3 ml of distilled water and slowly added to the reaction solution over a period of 1 hour, after which the reaction was continued for 24 hours. Upon completion of the reaction, the red organic layer was separated using a partition funnel. The organic layer was concentrated under reduced pressure to remove the solvent and the solid residue obtained was purified by recrystallization in distilled water. The resulting white crystals were collected, washed with petroleum ether and dried at room temperature for 24 hours to afford the target product 3,5-bis(trifluoromethyl)benzeneboronic acid (6FBB) (19.44 g, yield: 85%).
