Kinetics of the thermal gas phase reactions of cis- and trans-2,3-epoxybutane

Abstract

The kinetics of the gas-phase decomposition of cis- and trans-2,3-epoxybutane have been studied over the temperature range 668–740 K. cis–trans Isomerization occurs at much slower rates than structural isomerization to butan-2-one, but-3-en-2-ol, ethyl vinyl ether and isobutyraldehyde. Isobutyraldehyde and ethyl vinyl ether are formed almost exclusively from cis-2,3-epoxybutane. The above reactions are homogeneous, first-order, non-radical processes and account for considerably more than 80% of the observed decomposition. The following reaction rates were obtained for the decomposition of cis-2,3-epoxybutane: k(trans-2,3-epoxybutane)= 10^{14·59 ∓ 0·53} exp (–61830 ∓ 1680/1·987T) s^–1, k(butan-2-one)= 10^{13·60 ∓ 0·21} exp (–56320 ∓ 660/1·987T) s^–1, k(but-3-en-2-ol)= 10^{12·18 ∓ 0·94} exp (–53990 ∓ 2990/1·987T) s^–1, k(ethyl vinyl ether)= 10^{12·94 ∓ 0·96} exp (–55230 ∓ 3040/1·987T) s^–1, k(isobutyraldehyde)= 10^{12·99 ∓ 0·62} exp (–55970 ∓ 1970/1·987T) s^–1 Reaction rates from trans-2,3-epoxybutane were: k(cis-2,3-epoxybutane)= 10^{14·67 ∓ 0·49} exp (–63010 ∓ 1590/1·987T) s^–1, k(butan-2-one)= 10^{14·24 ∓ 0·65} exp (–59290 ∓ 2120/1·987T) s^–1, k(but-3-en-2-ol)= 10^{12·73 ∓ 0·81} exp (–55650 ∓ 2600/1·987T) s^–1, k(ethyl vinyl ether)= 10^{14·23 ∓ 0·75} exp (–62780 ∓ 2440/1·987T) s^–1

A mechanism for formation of products is proposed.

RRKM Calculations for the unimolecular fall-off and chemical activation effects in the pyrolysis of 1,2-epoxyethane and 2,3-epoxybutane are attempted in order to decide on the cause of the observed decrease in isomerization rates and increase in fragmentation rates at pressures below 20 Torr.