Catalytic Oxidation Processes for the Upgrading of Terpenes: State-of-the-Art and Future Trends

Abstract

Terpenic olefins constitute a relevant platform of renewable molecules, which could be used as key intermediates for the perfumery, flavoring, and pharmaceutical industries. The upgrading of these cheap and available agro-resources through catalytic oxidation processes remains of great interest, leading to the formation of either epoxides via the oxidation of the olefinic bond or α,β-unsaturated ketones by the Csp3-H functionalization at the α-position of the double bond. This critical review summarizes some of the most relevant homogeneous or heterogeneous catalysts designed for the oxidation of some abundant terpenic olefins in the last decade (2008–2018).

Photo-epoxidation of (α, β)-pinene with molecular O2 catalyzed by a dioxo-molybdenum (VI)-based Metal–Organic Framework

“…For a better understanding, it is well recognized that one of the main factors that governs the reactivity of monoterpenes is the level of substitution of the olefinic double bonds, as well as the type of carbon skeleton and the accessibility of its vinyl and allylic hydrogens. In this case, the presence of an additional substituent on α-pinene increases the electrophilic oxygen addition rate to the double bond (higher electron density) compared to the disubstituted double bond of β-pinene [4,9,52,53] (See Fig. 4).…”

“…Terpenes are a large and distinct class of natural hydrocarbons, usually obtained by steam distillation, extraction or enfleurage from some plants and flowers, such as lemon, orange and rosemary [1][2][3]. Currently, the oxy-functionalization of terpenes is one of the most important pathways for the valuation of natural renewable materials [4][5][6]. Among the huge diversity of terpenoids, pinene received considerable interest because it is the main component of turpentine, which is obtained from pine resin or as a secondary product of the pulp and paper industry.…”

Vanadium-doped phosphomolybdic acids as catalysts for geraniol oxidation with hydrogen peroxide

“…7,8 Nonetheless, hydrogen peroxide always requires a metal catalyst to be activated. 9,10 Several transition metal catalysts have been used in oxidations of terpene alcohols with hydrogen peroxide: niobium, 11 tungsten, 12 titanium, 13 and mixed metal oxides 14,15 are only some examples. Nonetheless, there is a class of compounds known as heteropolyacids (i.e., HPAs) that have received considerable attention.…”

Vanadium-doped sodium phosphomolybdate salts as catalysts in the terpene alcohols oxidation with hydrogen peroxide

“…3,4 The oxidation of terpenic alcohol is a synthetic route of interest, leading to the formation of valuable compounds such epoxides, through epoxidation of the olenic double bond, or carbonylic compounds, aer the oxidation of hydroxyl groups. 5,6 However, most of the oxidative processes that are industrially used still consume hazardous metal stoichiometric oxidants, which should be disposed of into the environment aer use.…”