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Very low‐pressure pyrolysis (VLPP) of hex‐1‐ene. Kinetics of the retro‐ene decomposition of a mono‐olefin
Author(s) -
King Keith D.
Publication year - 1979
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550111005
Subject(s) - chemistry , ene reaction , rrkm theory , thermochemistry , arrhenius equation , thermal decomposition , decomposition , reaction rate constant , isomerization , kinetics , fission , radical , shock tube , computational chemistry , thermodynamics , organic chemistry , activation energy , catalysis , shock wave , nuclear physics , physics , quantum mechanics , neutron
The thermal unimolecular decomposition of hex‐1‐ene has been investigated over the temperature range of 915–1153 K using the technique of very low‐pressure pyrolysis (VLPP). The reaction proceeds via the competitive pathways of C 3 −C 4 fission and retro‐ene elimination, with the latter dominant at low temperatures and the former at high temperatures. This behavior results in an isokinetic temperature of 1035 K under VLPP conditions (both reactions in the unimolecular falloff regime). RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high‐pressure Arrhenius parameters given by log k 1 (sec −1 ) = (12.6 ± 0.2) ‐(57.7 ± 1.5)/θ for retro‐ene reaction, and log k 2 (sec −1 ) = (15.9 ± 0.2) ‐ (70.8 ± 1.0)/θ for C‐C fission, where θ = 2.303 RT kcal/mol. The A factors were assigned from the results of a recent shock‐tube study of the decomposition in the high‐pressure regime, and the activation energies were found by matching the RRKM calculations to the VLPP data. The parameters for C‐C fission are consistent with the known thermochemistry of n ‐propyl and allyl radicals. A clear measure of the importance of the molecular pathway in the decomposition of a mono‐olefin has been obtained.