Kinetics of the thermal unimolecular reactions of cyclopropane and cyclobutane behind reflected shock waves

Abstract

The kinetics of the thermal reactions of cyclopropane and cyclobutane behind reflected shock waves have been studied in a single-pulse chemical shock tube. Comparisons of methods for obtaining reflected-shock temperatures and for estimating the extent of unimolecular fall-off are presented.

In the temperature range 950–1653 K, the predominant reaction of cyclopropane is the unimolecular isomerization to propene. Fully-corrected first-order rate constants are in good agreement with extrapolated low-temperature literature data up to ca. 1130 K, but at higher temperatures, previously reported curvature in the Arrhenius plot is confirmed.

Between 891 and 1400 K, cyclobutane decomposes unimolecularly giving ethylene as the only observable product. Fully-corrected first-order rate constants for this reaction are also in agreement with extrapolated low-temperature literature data up to ca. 1080 K but pronounced curvature in the Arrhenius plot is evident above this temperature. Possible explanations for these anomalies above ca. 1100 K are discussed.