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Die NO‐katalysierte Isomerisierung von 3‐Methylen‐1,5,5‐trimethyl‐cyclohexen zu 1,3,5,5‐Tetramethyl‐1,3‐cyclohexadien in der Gas‐Phase. Thermodynamische Daten aus Gleichgewichtsmessungen
Author(s) -
Egger Kurt W.,
Jola M.
Publication year - 1969
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19690520211
Subject(s) - chemistry , enthalpy , methylene , equilibrium constant , yield (engineering) , standard enthalpy of formation , gas phase , additive function , thermodynamics , medicinal chemistry , physics , mathematical analysis , mathematics
The composition of equilibrated gaseous mixtures of 3‐methylene‐1,5,5‐trimethylcyclohexene (MTC) and 1,3,5,5‐tetramethyl‐1,3‐cyclohexadiene (TECD) have been measured for temperatures ranging between 302 and 410°C. Nitrogen oxide was used as catalyst. Equilibrium was approached from either side. The least squares regression analysis of the observed temperature dependence of the equilibrium constants K 1.2 = k 1 / k 2 = (TECD) eq. /(MTC) eq. yields (with standard errors)\documentclass{article}\pagestyle{empty}\begin{document}$$ \log K_{1.2} = (0.35 \pm 0.2) - (0.5 \pm 0.3)/4.58 \times 10^{- 3} T(^ \circ {\rm K)}{\rm .} $$\end{document}This results in Δ H 1.2 (300°K) = 0.4 ± 0.3 kcal/mole and Δ S 1.2 (300°K) = 1.4 ± 0.8 cal/°‐mole. The fact that the reaction is practically thermoneutral implies that the secondary, «biallylic» CH bond in MTC is equally strong as the primary «biallylic» CH bond of the 1‐methyl group in TECD. The observed enthalpy and entropy differences between the two isomers are in agreement with prediction based on the concept of additivity of thermodynamic increment properties (ref. [5]). The results of this work also yield a value of 23.7 cal/°‐mole for the entropy contribution characteristic of the 1,3‐cyclohexadiene ring structure. When combined with the A RRHENIUS parameters, reported earlier [1] for k 1 , the results of this work yield for the back reaction log k 2 (1/mole‐s) = 8.25–30.2/4.58 × 10 −3 T (°K).