The chemical reactivity of some terpenes investigated by alumina catalyzed epoxidation with hydrogen peroxide and by DFT calculations

The selectivity of the alumina catalyzed epoxidation of (S)-limonene, citronelal, citral, citronelol and (1S)-(α)-pinene with aqueous 70 wt% and anhydrous 24 wt% hydrogen peroxide is described. DFT molecular orbital calculations were used aiming at a better understanding of the reactivity of these terpenes. The more nucleophilic carbon–carbon double bond, which has a higher molecular orbital energy, is preferentially epoxidized (site-selectivity). Furthermore, a preference for epoxidation in competition with other possible reactions is observed for citronelal, citral, citronelol and (1S)-(α)-pinene (chemo-selectivity). Nonetheless, we were not able to achieve a stereo-selective epoxidation of the terpenes using alumina and hydrogen peroxide