Kinetics for benzoylation of sodium phenoxide by liquid–liquid phase-transfer catalysis

The kinetics for phase-transfer catalyzed benzoylation of sodium phenoxide (PhONa) to synthesize phenyl benzoate in a liquid–liquid system and the behaviors of the catalytic intermediate were investigated. Using tetra-n-butylammonium bromide (TBAB) as the catalyst with the molar ratio to PhONa equal to 0.1, the product yield was above 98% within 1 h of reaction at 10 °C and 150 rpm. The benzoylation was observed strongly dependent on the agitation speed, and mainly occurred in the aqueous/organic interfacial region when non-polar organic solvent was used. The catalytic intermediate, tetra-n-butylammonium phenoxide (PhOQ), produced from PhONa with TBAB in the aqueous phase was not observed in the organic phase during the reaction using heptane as the solvent; while in dichlorobenzene, its amount was about 20–30% of the initial usage of catalyst. The concentrations of PhOQ for different agitation speeds are near constant after 20 min of duration; thus the pseudo-first-order kinetics can be successfully applied to describe the reaction system. Extra additions of NaOH also affected the overall reaction rate significantly due to the extraction of PhOQ into the organic phase was influeznced by hydroxide anion. The concentration of PhOQ decreased with increasing amount of NaOH at a usage of greater than 0.025 mol. The catalytic intermediate plays an important role in liquid–liquid phase-transfer catalyzed benzoylation.