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Gas phase kinetics of pyrolysis of 1‐methyl‐1‐cyclopropene
Author(s) -
Hopf Henning,
Wachholz Gerhard,
Walsh Robin
Publication year - 1985
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19851180914
Subject(s) - chemistry , torr , arrhenius equation , isomerization , kinetics , reaction rate constant , pyrolysis , atmospheric temperature range , gas phase , homogeneous , polymer chemistry , decomposition , organic chemistry , thermodynamics , activation energy , catalysis , physics , quantum mechanics
The title study has been carried out in the temperature range 210 – 250°C. The isomerisation products are 2‐butyne (91 – 94%), 1,3‐butadiene (5 – 8%), and 1,2‐butadiene (1 – 2%). No other products were detected and material recovery was complete within experimental error (±5%). The reaction obeyed first‐order kinetics, with the products formed by parallel pathways, and appeared to be both unimolecular and homogeneous although some surface sensitivity was detected in packed vessels. Studies of pressure dependence showed characteristic rate constant „fall‐off” below 20 Torr (SF 6 ) and 100 Torr (N 2 ). Within at least 2% of the high pressure limit, the following Arrhenius equation for overall decomposition was found:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log ({\rm k/s}^{{\rm - 1}}) = (12.91 \pm 0.15) - (160 \pm 1.5{\rm kJ\, mol}^{{\rm - 1}})/RT\ln 10 $$\end{document} Arrhenius equations were similarly found for the individual pathways. The figures are discussed in the light of Transition State Theory and represent a significant improvement over a previous study. It is argued that all products arise via 1,2‐H shifts in a diradical‐like intermediate and the propensities for different H shifts are discussed. A 1‐methyl substituent, rather surprisingly, deactivates cyclopropene in its isomerisation reactions.