Kinetics for etherification of ethyl 2-bromoisobutyrate via solid/liquid phase transfer catalysis

摘要

Phase transfer catalyzed reactions such as esterification, hydrolysis, and halide exchange were reported to conduct successfully in solid-liquid phase transfer catalysis (SLPTC). In the present work, the kinetics for synthesizing ether-esters from the etherification of ethyl 2-bromoisobutyrate under solid-liquid phase transfer conditions was investigated. The reaction was carried out in a stirred batch reactor with isothermal jacket, using potassium 4-benzyloxyphenoxide as the solid reactant. The potassium salt was prepared from deprotonation of 4-benzyloxyphenol with potassium hydroxide in aqueous solution. Using the solid/liquid system, the usual hydrolysis of ester compounds in alkali aqueous/organic phases cam be prevented under anhydrous conditions. High conversion of etherification of ethyl 2-bromoisobutyrate in organic solvent can be obtained. The experimental data were described by pseudo-first-order kinetics. Various quaternary 'onium salts were employed to compare their efficiencies for etherification. Effects of agitation speed, reaction temperature, organic solvent and small quantities of water addition were explored to find the optimal operating conditions. From the experimental results, the reaction rates are not influenced by the stirring speed when the agitation speed exceeds 350 rpm. The reaction rate increases with increasing the polarity of solvent. The temperature effects as well as the activation energy for various phase transfer catalysts were investigated. The activation energy for TBAB was calculated to be 15.2 Kcal/mole. Small quantities of water addition can also enhance the reactivity of catalyst. [References: 12]