Third-liquid phase-transfer catalyzed esterification of sodium benzoate with novel dual-site phase-transfer catalyst under ultrasonic irradiation

The green process for esterification of sodium benzoate and 2-phenoxyethyl bromide by ultrasound-assisted third-liquid phase-transfer catalysis (TLPTC) with novel dual-site phase-transfer catalyst 1,4-bis(trihexylammoniomethyl)benzene dibromide (BTHAMBB) was developed. BTHAMBB was synthesized by reacting p-xylylene dibromide with trihexylamine, and had specific feature to form third-liquid phase without extra inorganic salts. In this TLPTC system, the overall reaction rate with ultrasound irradiation was higher by 25% than that at silence condition. The product yield of esterification without catalyst at 60 °C and 300 rpm was only 2% in 4 h of reaction even under 28 kHz/300 W of ultrasonic irradiation, but was raised to 72.7% by using third-liquid phase, which contained above 97% of added BTHAMBB with highly concentrated catalytic intermediate (0.6–0.7 M), demonstrating the good catalytic efficiency of BTHAMBB for TLPTC.

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► A novel and active dual-site phase-transfer catalyst BTHAMBB was synthesized.
► The catalyst BTHAMBB can form the third-liquid phase without adding extra salts.
► Above 97% of catalyst was concentrated in a small volume of the third-liquid phase.
► The product yield 72.7% in 4 h of reaction was achieved with the third-liquid phase.
► The green esterification catalyzed by BTHAMBB under ultrasound was developed.