Steric factors in the gas phase elimination kinetics of ethyl N ‐benzyl‐ N ‐cyclopropylcarbamate and ethyl diphenylcarbamate

The elimination kinetics of ethyl N ‐benzyl‐ N ‐cyclopropylcarbamate and ethyl diphenylcarbamate were investigated over the temperature range of 349.9–440.0°C and the pressure range of 31–106 Torr. These reactions have been found to be homogeneous, unimolecular, and obey a first‐order rate law. The products are ethylene, carbon monoxide, and the corresponding secondary amine. The rate coefficient is expressed by the following Arrhenius equations: For ethyl N ‐benzyl‐ N ‐cyclopropylcarbamate log k 1 (s −1 ) = (12.94 ± 0.09) − (198.5 ± 0.9) kJ mol −1 (2.303RT) −1For ethyl diphenylcarbamate log k 1 (s −1 ) = (12.91 ± 0.18) − (208.2 ± 2.4) kJ mol −1 (2.303RT) −1The presence of phenyl and bulky groups at the nitrogen atom of the ethylcarbamate showed a decrease in the rate of elimination. Steric factor may be operating during the process of decomposition of these substrates. These reactions appear to undergo a semipolar six‐membered cyclic transition type of mechanism.© 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 67–71, 2002