Stereochemical features and kinetic model of the heterogeneous catalytic hydrogenation of 5-ethylidene-2-norbornene

Abstract

Specific features of the stereochemistry and kinetics of the liquid-phase hydrogenation of E/Z-5-ethylidene-2-norbornene (1) in the presence of the palladium catalyst Pd(0.25%)/γ-Al₂O₃ are considered. The process proceeds under mild conditions (25–75 °C, hydrogen pressure 1 atm) sequentially and stereoselectively without destruction of the carbocyclic framework. The molar ratio of E/Z- and endo/exo-isomers of the compounds at all reaction steps is unchanged and coincides with the stereoisomer ratio in the initial diene. The kinetic data indicate a distinct separation of the steps in time: the partial hydrogenation of the norbornene bond is first observed, and then the ethylidene bond is hydrogenated. The activation energies for each step are determined. The results of the detailed kinetic studies made it possible to propose a consistent mathematical model for the hydrogenation of compound 1.