Selective synthesis of high-added value chemicals from α-pinene epoxide and limonene epoxide isomerization over mesostructured catalysts: Effect of the metal loading and solvent

Isomerization of α-pinene epoxide was performed over several Fe or Cu supported on MCM-41 and SBA-15 catalysts. The effect of the metal loading and polarity of the solvent on substrate conversion and selectivity was analyzed. It was found that materials containing Fe are more active but less selective to campholenic aldehyde and trans-carveol than materials with Cu, difference that was related with the size of the metal oxide particles and strength/type of the acid sites. An increasing of the solvent polarity decreases formation of campholenic aldehyde, the most desirable compound from α-pinene epoxide. Also, it was showed that trans-carveol is an intermediate in the production of p-cymene. Selectivity to campholenic aldehyde up to 82% can be achieved over Cu/MCM-41 as heterogeneous catalyst at soft reaction conditions (70 °C, 2.5 h, 25 mg, 750 rpm, toluene as solvent). From limonene epoxide isomerization over Fe/SBA-15, dihydrocarvone and limonene-1,2-diol production depended on the type of solvent. An increasing of polarity of the solvent, appears to increase selectivity to dihydrocarvone while limonene-1,2-diol is favored with solvents of lower polarity (mainly cyclohexane and hexane). Reuse of Fe materials were also tested for both monoterpene epoxides showing that Fe supported on MCM-41 and SBA-15 can be used several times (up to 5 times) without any loss of catalytic activity for the synthesis of campholenic aldehyde from α-pinene epoxide and dihydrocarvone (and limonene-1,2-diol) from limonene epoxide.