Regularities of the heterogeneous catalytic hydrogenation of 5-vinyl-2-norbornene

The liquid-phase hydrogenation of 5-ethenylbicyclo[2.2.1]hept-2-ene (5-vinyl-2-norbornene, VNE) in the presence of the palladium catalyst Pd/γ-Al2O3 (PC-25) in an n-heptane medium at 76 °C was studied. The hydrogenation proceeds via a complicated mechanism through (exo/endo)-2-vinylnorbornanes and (Z/E)-2-ethylidenenorbornanes to form (exo/endo)-2-ethylnorbornanes. The reaction products were identified, the main reaction routes were determined, and the material balance was studied. The isomerization of (exo/endo)-2-vinylnorbornanes to (Z/E)-2-ethylidenenorbornanes with the conversion close to 100% was found for the reaction in a hydrogen atmosphere. The molar ratios of the stereoisomers of the substrate and of the intermediate and final hydrogenation products are retained at all steps of the process. The parallel-sequential mechanism was proposed for the process. The zero kinetic time order with respect to VNE was established in a wide range of its initial concentrations.