The kinetics of reversible Diels–Alder reactions in the gas phase. Part II. Cyclopentadiene and ethylene

Abstract

The title reaction has been investigated in both directions in a static system. At temperatures in the range 521–570 K the addition of ethylene to cyclopentadiene (CPD) results in the formation solely of norbornene (NB) and the decomposition of the latter produces only ethylene and CPD. In a vessel of high surface : volume ratio, small quantities of nortricyclene are formed heterogenously. Kinetic studies support second and first orders for the addition and decomposition respectively. The mechanism C₂H₄+ CPD[graphic omitted]NB is almost certainly homogeneous and molecular in nature. Least means squares analysis of the data yields equations (i) and (ii). Equilibrium log(k₁/s^–1)=(14.26 ± 0.28)–(44.54 ± 0.72 kcal mol^–1)/RTln10 (i) log (k₁/l mol^–1s^–1)=(7.59 ± 0.63)–(23.67 ± 1.56 kcal mol^–1)/RTln10 (ii) studies suggest that, for the addition, these Arrhenius parameters may be slightly high. Higher temperature investigations on this system (at equilibrium) indicate that no significant homogeneous molecular isomerisation of NB occurs with an activation energy < ca. 54 kcal mol^–1.