Kinetics for phenolysis of ethyl 2-bromoisobutyrate via phase-transfer catalysis in a solid-liquid system

The kinetics of phase-transfer catalyzed etherification of sodium phenoxide with ethyl 2-bromoisobutyrate to produce ethyl 2-phenoxyisobutyrate in a s olid-liquid system has been investigated. Being catalyzed by the quaternary 'onium salts, the reaction was carried out in a stirred batch reactor to e xplore the effects of various operating variables. At a temperature of 80 d egrees C and a molar ratio of tetra-n-butylammonium bromide to sodium pheno xide equal to 0.372, 94% conversion was obtained after 4h, and no other sid e products were observed. A kinetic model of pseudo-first-order reaction ac companied by catalyst deactivation was proposed to describe the overall rea ction. A deactivation function was employed to evaluate the kinetic paramet ers. The decay of catalytic activity was mainly caused by the deposition of the salts produced on the surface of solid particles. The results show tha t the initial reaction rate was not influenced by the agitation rate when e xceeding 350 rpm, but the deactivation rate increased with increasing stirr ing speed and the amount of catalyst used. The intrinsic organic reaction w as conducted by the phase-transfer catalytic intermediate. The order of rea ctivity for different phase-transfer catalysts was determined as tetra-n-bu tylphosphonium bromide > tetra-lr-butylammonium bromide > tetra-n-butylammo nium iodide approximate to tetra-n-butylammonium hydrogen sulfate approxima te to Aliquat 336. The apparent activation energy for tetra-n-butylammonium bromide was estimated as 51.4 kJ mol(-1). This work provides an improved m ethod for synthesizing phenolic substances in solid-liquid phases and preve nting unfavorable side reactions. (C) 2000 Society of Chemical Industry.