Kinetics of the thermal gas-phase decomposition of 2-(1-methylethoxy)propene and of 2,3-dimethyl-2,3-epoxybutane

Abstract

In the temperature range 554–610 K 2-(1-methylethoxy)propene undergoes a homogeneous, unimolecular elimination reaction to give propene and propanone as the only products and with rate constants (k_d) given by the equation k_d/S^–1= 10^{11.98 ± 0.46} exp (–168.1 ± 5.1 kJ mol^–1/RT). A polar transition state for the reaction is supported. The decomposition of 2,3-dimethyl-2,3-epoxybutane has been reinvestigated over the temperature range 642–733 K. 3,3-dimethylbutan-2-one (k_k), 2,3-dimethylbut-1-en-3-ol (k_a), and propene + propanone (k_p) are the major reaction products and are formed as the consequence of homogeneous, unimolecular processes with rate constants given by the equations k_k/S^–1= 10^{13.57 ± 0.46} exp (–233.4 ± 6.2 kJ mol^–1/RT)k_a/S^–1= 10^{11.81 ± 0.94} exp (–209.8 ± 12.5 kJ mol^–1/RT)k_p/S^–1= 10^{13.55 ± 0.34} exp (–235.0 ± 4.5 kJ mol^–1/RT). A silanised glass surface is shown to be effective in eliminating surface reactions in the decomposition of oxirans. Data on all alkyl oxiran studies are summarised and conclusions are drawn regarding the transition states for the reactions. In contrast to previous conclusions support is given to the involvement of polar transition states.