Epoxidation of α-pinene catalyzed by methyltrioxorhenium(VII): Influence of additives, oxidants and solvents

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.

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► Methyltrioxorhenium catalyzes the epoxidation of α-pinene.
► The reaction is hampered by diol formation.
► Product formation highly depends on the reaction conditions.
► Optimization of reaction parameters yields 95% α-pinene oxide in 3 h.