Kinetics of the diels–alder addition of ethene to cyclohexa‐1,3‐diene and its reverse reaction in the gas phase

The addition of ethene to cyclohexa‐1,3‐diene has been studied between 466 and 591 K at pressures ranging from 27 to 119 torr for ethene and 10 to 74 torr for cyclohexa‐1,3‐diene. The reaction is of the “Diels–Alder” type and leads to the formation of bicyclo[2.2.2]oct‐2‐ene. It is homogeneous and first order with respect to each reagent. The rate constant (in l./mol sec) is given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_a = - (25,970 \pm 50)/4.576{\rm T + }(6.66 \pm 0.02) $$\end{document}The retron‐Diels–Alder pyrolysis of bicyclo[2.2.2]oct‐2‐ene has also been studied. In the ranges of 548–632 K and 4–21 torr the reaction is first order, and its rate constant (in sec −1 ) is given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_p = - (57,300 \pm 100)/4.576{\rm T + }(15.12 \pm 0.04) $$\end{document}The reaction mechanism is discussed. The heat of formation and the entropy of bicyclo[2.2.2]oct‐2‐ene are estimated.