Abstract
A new method of the oxidation of natural limonene, obtained from waste orange peels, using relatively inexpensive MoO2-containing activated carbon catalysts is presented. The contents of molybdenum in the catalysts were equal to 0.68, 1.32, and 2.64 wt%, and these new materials were investigated using various instrumental methods (ICP-AES, XRD, SEM, and GC), as well as liquid nitrogen sorption. The oxidation of limonene was performed separately with H2O2 and t-butyl hydroperoxide (TBHP) as the oxidants under the following conditions: temperature of 70 °C, molar ratio of limonene/oxidant = 1:2, methanol concentration 95 wt%, catalyst content 2.45 wt%, and reaction times of 0.5–72 h. All catalysts were active in the oxidation of limonene. With H2O2 as the oxidant, carveol (selectivity of 42–65 mol%) and perillyl alcohol (selectivity of 10–30 mol%) were the main products of the limonene oxidation, and carvone and 1,2-epoxylimonene diol were by-products. For the oxidations with TBHP, the conversion of limonene was lower than with hydrogen peroxide. This new environmentally friendly method allows for the transformation of organic waste material into industrially important value-added products.
Highlights
Terpenes have been utilized as components of fragrances in perfumery and cosmetics and as food additives [1]
In this work we propose the mechanism of limonene oxidation to carveol and perillyl alcohol in the presence of MoO2 catalysts supported on the EuroPh activated carbon material
We presented a new method of perillyl alcohol and carveol production by the oxidation of limonene obtained from waste orange peels by H2O2 or t-butyl hydroperoxide (TBHP) in the presence of activated carbon catalysts containing molybdenum in the form of MoO2
Summary
Terpenes have been utilized as components of fragrances in perfumery and cosmetics and as food additives [1]. Terpenes have found therapeutic applications in medicine and have been reported to have significant antiinflammatory, antioxidant, antiviral, antimicrobial, anticancer and analgesic properties [2]. More than 25,000 terpenes have been identified, some of them are repelling agents and protect plants from insects and animals [3]. There has been an increasing interest in the utilization of many monoterpenes in medicine and in studies on their molecular and cellular effects [4]. This interest is mainly connected with their properties, such as: high antitumor activity, commercial availability, low cost, oral bioavailability, and low toxicity [5]
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