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 solid–liquid system has been investigated. Being catalyzed by the quaternary ‘onium salts, the reaction was carried out in a stirred batch reactor to explore the effects of various operating variables. At a temperature of 80 °C and a molar ratio of tetra-n-butylammonium bromide to sodium phenoxide equal to 0.372, 94% conversion was obtained after 4 h, and no other side products were observed. A kinetic model of pseudo-first-order reaction accompanied by catalyst deactivation was proposed to describe the overall reaction. A deactivation function was employed to evaluate the kinetic parameters. The decay of catalytic activity was mainly caused by the deposition of the salts produced on the surface of solid particles. The results show that the initial reaction rate was not influenced by the agitation rate when exceeding 350 rpm, but the deactivation rate increased with increasing stirring speed and the amount of catalyst used. The intrinsic organic reaction was conducted by the phase-transfer catalytic intermediate. The order of reactivity for different phase-transfer catalysts was determined as tetra-n-butylphosphonium bromide > tetra-n-butylammonium bromide > tetra-n-butylammonium iodide ≈ tetra-n-butylammonium hydrogen sulfate ≈ Aliquat 336. The apparent activation energy for tetra-n-butylammonium bromide was estimated as 51.4 kJ mol−1. This work provides an improved method for synthesizing phenolic substances in solid–liquid phases and preventing unfavorable side reactions. © 2000 Society of Chemical Industry