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Very low‐pressure pyrolysis (VLPP) of pentynes. I. Kinetics of the retro‐ene decomposition of pent‐1‐yne
Author(s) -
King Keith D.
Publication year - 1981
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.550130304
Subject(s) - chemistry , rrkm theory , thermal decomposition , fission , ene reaction , reaction rate constant , decomposition , pyrolysis , kinetics , allene , atmospheric temperature range , ethylene , shock tube , yield (engineering) , computational chemistry , kinetic energy , thermodynamics , organic chemistry , shock wave , nuclear physics , catalysis , physics , quantum mechanics , neutron
The thermal unimolecular decomposition of pent‐1‐yne has been investigated over the temperature range of 923–1154 K using the technique of very low‐pressure pyrolysis (VLPP). Under the experimental conditions the reaction proceeds predominantly via a molecular retro‐ene pathway to yield allene and ethylene. There was some evidence for the occurrence of the higher energy C 3 C 4 bond fission pathway at the high end of the temperature range. Interpretation of the data with the aid of RRKM theory and taking into account a decrease in gas‐wall collision efficiency with temperature yields the following high‐pressure rate constant expression for the retro‐ene pathway:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{ - 1}) = (12.8 \pm 0.4) - (57.0 \pm 2.0)/\theta $$\end{document}at 1100 K where θ = 2.303 RT kcal/mol and the A factor was assigned from the results of shock‐tube studies of similar molecules. These rate parameters are independent of the inclusion of the bond fission pathway in the RRKM calculations. The results are compared with previous data on the retro‐ene decomposition of alkynes.