Gas Phase Thermolyses. Part 5. Thermally-Induced Rearrangement of Methyl Acetate in the Gas Phase

The pure unimolecular gas-phase thermolysis of 18O-labelled methyl acetate has been investigated by the flash vacuum thermolysis–field-ionization mass spectrometry method, in combination with collision-activation mass spectrometry in the temperature range 1 043–1 404 K. Minor amounts of keten, as a result of 1,2-elimination of methanol, were detected.

The predominant reaction is shown to be the intramolecular oxygen to oxygen methyl group migration. The isomerization is discussed in terms of vibrational excitation of specific in-plane bending modes observed for the methyl acetate molecule. The low-pressure rate constants for the isomerization at 1 253 and 1 404 K were calculated from the collision activation mass spectra.