Kinetics and mechanisms of elimination of ethyl 3‐phenyl and ethyl 3‐methyl‐3‐phenyl glycidates in the gas phase

Abstract

AbstractThe gas‐phase elimination kinetics of the title compounds were examined in a static reaction system over the temperature range 350.2–399.7°C and the pressure range 16.5–107 Torr (1 Torr = 133.3 Pa). The reactions are homogeneous, unimolecular and follow a first‐order rate law. The rate coefficients are given by the following Arrhenius equations: for ethyl 3‐phenylglycidate, log [k1 (s−1)] = (12.15±0.46)−(190.1±5.8) kJ mol−1 (2.303 RT)−1, and for ethyl 3‐methyl‐3‐phenyl glycidate, log [k1 (s−1)] = (12.02±0.19)−(182.9±2.4) kJ mol−1 (2.303 RT)−1. The ethyl side of the ester is eliminated as ethylene through a concerted six‐membered cyclic transtion state, while the unstable intermediate glycidic acid rapidly decarboxylates to give the corresponding substituted aldehyde. The glycidic acid appears to lose CO2 gas by way of a five‐membered cyclic transition state type of mechanism. Copyright © 2004 John Wiley & Sons, Ltd.