Catalytic Isomerization of α-Pinene Epoxide Over a Natural Zeolite

Abstract

Isomerization of α-pinene epoxide was carried out over a Colombian natural zeolite as potential geocatalyst with heulandite, chabazite and clipnotilolite as main crystallographic phases; the heulandite was identified as the active phase. Over synthetic zeolites, isomerization of α-pinene epoxide depended on Si/Al ratio, unit cell and the kind of structure. The best solvent was toluene and not isomerization activity was observed in presence of solvents with carboxyl groups. Complete α-pinene epoxide conversion and 45% selectivity to campholenic aldehyde were obtained at 70 °C, with fencholenic aldehyde, carveol, and p-cymene as main by-products. Decrease of activity of natural zeolite was associated with loss of acid sites. A reaction mechanism based on experimental and computational data was proposed including adsorption of α-pinene epoxide on Fe or Al sites of the natural zeolite; a reaction rate constant of 4.02 × 10–4 mol g−1 min−1 was estimated from a pseudo homogeneous kinetic model.