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Kinetics and thermochemistry of the gas phase reaction of methyl ethyl ketone with iodine. II. The heat of formation and unimolecular decomposition of 2‐iodo‐3‐butanone
Author(s) -
Solly Richard K.,
Golden David M.,
Benson Sidney W.
Publication year - 1970
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.550020505
Subject(s) - chemistry , hydrogen iodide , ketone , reaction rate constant , iodide , butanone , methyl vinyl ketone , equilibrium constant , isopropyl , methyl iodide , arrhenius equation , chemical kinetics , transition state , activation energy , kinetics , iodine , medicinal chemistry , organic chemistry , catalysis , physics , quantum mechanics , solvent
Equilibrium constants for the reaction CH 3 COCH 2 CH 3 + I 2 ⇌ CH 3 COCHICH 3 + HI have been computed to fit the kinetics of the reaction of iodine atoms with methyl ethyl ketone. From a calculated value of S 298 0 (CH 3 COCHICH 3 ) = 93.9 ± 1.0 gibbs/mole and the experimental equilibrium constants, Δ H f 0 (CH 3 COCHICH 3 ) is found to be −38.2 ± 0.6 kcal/mole. The Δ(Δ H f 298 0 ) value on substitution of a hydrogen atom by an iodine atom in the title compound is compared with that for isopropyl iodide. The relative instability of 2‐iodo‐3‐butanone (3.4 kcal/mole) is presented as further evidence for intramolecular coulombic interaction between partial charges in polar molecules. The unimolecular decomposition of 2‐iodo‐3‐butanone to methyl vinyl ketone and hydrogen iodide was also measured in the same system. This reaction is relatively slow compared to the formation of the above equilibrium. Rate constants for the reaction over the temperature range 281°–355°C fit the Arrhenius equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(}{{k_{\rm 3} } \mathord{\left/ {\vphantom {{k_{\rm 3} } {{\rm sec}^{ - 1} }}} \right. \kern-\nulldelimiterspace} {{\rm sec}^{ - 1} }}{\rm )} = {\rm 13}{\rm .4} - {{(41.9 \pm 0.5)} \mathord{\left/ {\vphantom {{(41.9 \pm 0.5)} \theta }} \right. \kern-\nulldelimiterspace} \theta } $$\end{document}where θ = 2.303 RT kcal/mole. The stability of both the ground and transition states is discussed in comparing this activation energy with that reported for the unimolecular elimination of hydrogen iodide from other secondary iodides. The kinetics of the reaction of hydrogen iodide with methyl vinyl ketone were also measured. The addition of HI to the double bond is not rate controlling, but it may be shown that the rate of formation of 1‐iodo‐3‐butanone is more rapid than that for 2‐iodo‐3‐butanone. Both four‐ and six‐center transition complexes and iodine atom‐catalyzed addition are discussed in analyzing the relative rates.