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This report presents a study of the epoxidation of limonene employing methyltrioxorhenium (MTO) as catalyst. The influence of base ligands, namely t-butylpyridine, 4,4′-dimethyl-2,2′-bipyridine and pyrazole on the catalytic activity was investigated. The choice of the oxidant (H2O2 in water or H2O2 stabilized by urea) was also examined. The effect of the solvent has been studied in order to determine optimal conditions for the epoxidation of (+)-limonene. The best result was obtained when a molar ratio (+)-limonene:MTO:H2O2:t-butylpyridine of 100:0.5:10:150 was used at 25 °C in dichloromethane. 1,2-Limonene oxide was formed with 77% yield and 96% selectivity after 1 h with a TOF of ca. 900 h−1.

The epoxidation of α-pinene employing methyltrioxorhenium as catalyst is examined. The influence of mono- and bidentate Lewis basic additives (e.g. tbutylpyridine, 4,4′-dimethyl-2,2′-bipyridine, and Schiff-bases) is investigated. Additionally the impact of the oxidant (H2O2 in water or urea–hydrogen peroxide (UHP)) on the catalytic performance is studied. The effect of the solvent is also examined in order to determine the optimal conditions for the epoxidation of α-pinene. The best and straightforwardly applicable result is obtained when a ratio α-pinene:MTO:tbutylpyridine:UHP of 200:1:40:600 is applied at 0 °C in nitromethane. In this case, α-pinene oxide is formed with 95% yield after 3 h with a turnover frequency (TOF) of 610 h−1.