Pyrolysis of Styrene. Kinetics and Mechanism of the Equilibrium Styrene Benzene + Acetylene

Article abstract of DOI:10.1021/j100203a052

The thermal unimolecular decomposition of styrene into benzene and acetylene, C6H5CH=CH2 -> C6H6 + HCCH (1), was investigated in a low pressure (ca. 10 mTorr) flow reactor by on-line mass spectrometry between 1180 and 1350 K.Measured rates can be calculated, via RRKM extrapolation, from the expression log (K₁, s^-1) = 14.38 - 17076/T, which was derived by detailed balance from high-pressure (ca. 50 Torr) low-temperature (878-973 K) kinetic data for the reverse reaction.This value of E₁ = 77.9 kcal/mol allows for the generation of vinylidene, H2C=C:; the carbene isomer of acetylene, as a primary product of the title reaction.A non-radical process involving the rate-determining extrusion of H2C=C: from a <4.1.0>-7-methylene cyclohepta-2,4-diene intermediate in equilibrium with styrene is consistent with kinetic and thermochemical considerations.