Gas-phase Unimolecular Pyrolyses of cis- and trans-'l,'i- Dimethyloxetan

Abstract

The gas phase pyrolyses of both cis and trans isomers of 2,3-dimethyloxetan have been studied at temperatures from 415–483°C and at initial pressures from 2 to 32 Torr. Both isomers undergo two modes of decomposition producing either propene and acetaldehyde or but-2-ene (cis and trans) and formaldehyde. The cis—trans isomerisation of the starting material is relatively unimportant. The reactions all appear to be unimolecular processes in their first-order regions and the following rate expressions were obtained: cis isomer→C3H6+ CH3CHO : logl0(kl/S–l)=(15.70 ± 0.22)–(63 216 ± 621) K/4.576T, cis isomer→C4H8+ CH2O : logl0(k2/S–l)=(15.24 ± 0.25)–(62 493 ± 715) K/4.576T, trans isomer→C3H6+ CH3CHO : loglO(k3/S–1)=(15.91 ± 0.25)–(64 652 ± 664) K/4.576T, trans isomer→C4H8+ CH2O : 1og10(k4/S–1)=(15.49 ± 0.26)–(63 676 ± 745) K/4.576T. Possible mechanisms involving 1 + biradical intermediates are discussed.