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The liquid-phase hydrogenation of α-pinene on a Pd/C catalyst at 0–100°С and hydrogen pressures of 1–11 atm was studied. It was found that the order of reaction with respect to pinene increased with hydrogen pressure and did not depend on temperature, whereas the selectivity of cis-pinane formation decreased with temperature and increased with hydrogen pressure. A mechanism was proposed for the hydrogenation of α-pinene. According to this mechanism, the selectivity of cis-pinane formation depends on the following two factors: (a) a temperature-dependent equilibrium between adsorbed α-pinene species, which are cis- and trans-pinane precursors, and (b) competition between the hydrogenation and β-H-elimination of surface σ-pinanyl complexes. The ratio between the rates of these reactions depends on the concentration of surface hydride species, and this concentration depends on the pressure of hydrogen. |
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