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The photochemistry of methyl cyclobutyl ketone. Part 2. Temperature dependence and the acetyl radical decomposition
Author(s) -
Baldwin Philip J.,
CanosaMas Carlos E.,
Frey H. Monty,
Walsh Robin
Publication year - 1987
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.550191105
Subject(s) - chemistry , arrhenius equation , radical , methyl radical , photochemistry , photodissociation , decomposition , ketone , atmospheric temperature range , reaction mechanism , yield (engineering) , kinetic energy , thermodynamics , activation energy , organic chemistry , physics , quantum mechanics , catalysis
Following earlier room‐temperature studies, gaseous mixtures of methyl cyclobutyl ketone (MCK) diluted in argon have been photolyzed at temperatures up to 205°C. Experiments have been carried out at a variety of pressures (up to ca. 2 atm) at wavelengths of 313 nm (steady state conditions) and 308 nm (pulsed photolysis). The results are consistent with a mechanism dominated by radical‐radical reactions involving acetyl, methyl, and cyclobutyl radicals. Acetyl radical processes predominate at lower temperatures while methyl radical reactions are more important at high temperatures. The results are interpreted via kinetic modelling of a mechanism in which a key role is played by the acetyl radical decomposition reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ ({\rm M} +)\,{\rm CH}_{\rm 3} {\rm CO}\mathop {\longrightarrow}\limits^{\rm 3} {\rm CH}_{\rm 3} + {\rm CO\, (+ M)} $$\end{document}Values for k 3 have been obtained and its temperature and pressure dependence are fitted by RRKM theory and a weak‐collisional activation model to yield\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(}k_3 ^\infty /{\rm s}^{ - 1}) = 13.3 - 17.5{\rm\, kcal\, mol}^{{\rm - 1}} /RT\ln 10 $$\end{document}This high‐pressure limiting Arrhenius equation is consistent with other studies in the same temperature range, but is difficult to reconcile with higher temperature investigations.