Journal of Molecular Catalysis A: Chemical 252 (2006) 186–193 The chemical reactivity of some terpenes investigated by alumina catalyzed epoxidation with hydrogen peroxide and by DFT calculations Juliana M. de S. e Silva, F´ abio S. Vinhado, Dalmo Mandelli 1 , Ulf Schuchardt ∗ , Roberto Rinaldi ∗∗ Instituto de Qu´ ımica, Universidade Estadual de Campinas, P.O. Box 6154, 13083-970 Campinas-SP, Brazil Received 23 December 2005; received in revised form 7 February 2006; accepted 8 February 2006 Available online 31 March 2006 Abstract The selectivity of the alumina catalyzed epoxidation of (S)-limonene, citronelal, citral, citronelol and (1S)-()-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)-()-pinene (chemo-selectivity). Nonetheless, we were not able to achieve a stereo-selective epoxidation of the terpenes using alumina and hydrogen peroxide. © 2006 Elsevier B.V. All rights reserved. Keywords: Epoxidation; Terpenes; DFT calculation; Alumina; Hydrogen peroxide 1. Introduction Terpenes are natural and sustainable feedstocks for the fine chemical industry, as they can be used as intermediates and ingredients for flavours, fragrances and pharmaceuticals [1]. The epoxidation of terpenes is an attractive chemical transforma- tion as these epoxides are versatile building blocks [1]. Several reviews are available in the recent literature concerning more environmental friendly ways to do epoxidations [2–4]. How- ever, even nowadays the most useful way to obtain epoxides is the reaction between a peracid and the desired olefin, which cannot be considered an environmental friendly process due to the formation of stoichiometric amounts of the corresponding acid [2]. ∗ Corresponding author. Tel.: +55 19 37883071; fax: +55 19 37883023. ∗∗ Corresponding author. E-mail addresses: ulf@iqm.unicamp.br (U. Schuchardt), rinaldi@iqm.unicamp.br (R. Rinaldi). 1 Permanent address: Pontif´ ıcia Universidade Cat´ olica de Campinas, Facul- dade de Qu´ ımica, 13020-904 Campinas-SP, Brazil. The use of terpenes as starting materials for fine chemical synthesis requires selective methodologies of epoxidation since terpenes contain alkene functional groups with different degrees of substitution and, in addition, they have other functionali- ties which can be oxidized and/or effect the chemistry of the carbon–carbon double bonds [5,6]. Aluminas have been used by organic chemists as cat- alysts or as supports for reagents and catalysts to obtain fine chemicals [7,8]. We have shown that alumina itself is already active for the epoxidation of nucleophilic alkenes with anhydrous hydrogen peroxide, obtaining selectivities in the 70–90% range [9]. The epoxidation activity of alumina has already been reported [10], however, the reactions showed low epoxide yields and used a large excess of alumina and oxidant. In this report, we describe the site-, chemo- and stereo- selectivity of the alumina catalyzed epoxidation of some ter- penes ((S)-limonene, citronelal, citral, citronelol and (1S)-()- pinene) with hydrogen peroxide and perform density functional calculations in order to achieve a better understanding of the different selectivities observed. 1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2006.02.042