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

The 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 [ k 1 (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 [ k 1 (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 CO 2 gas by way of a five‐membered cyclic transition state type of mechanism. Copyright © 2004 John Wiley & Sons, Ltd.