Oxidation of Alkenes in Supercritical Carbon Dioxide Catalyzed by Molybdenum Hexacarbonyl

In supercritical CO2, olefin oxidation to epoxides or diols using a Mo(CO)6 catalyst precursor and using t-BuOOH as oxidant proceeds in nearly quantitative yields. The highest yields and fastest rates of diol and epoxide formation were observed with cis-alkenes, while trans-alkenes were considerably less reactive. Phenyl-substituted olefins show a tendency to cleave to their corresponding aldehyde. The use of 70 wt % aqueous solutions of tert-butyl hydroperoxide yield the trans-diol, while anhydrous decane solutions of t-BuOOH give the epoxide. Clearly Mo(CO)6 proved to be the most effective oxygen transfer catalyst for these reactions. Several other oxygen transfer catalysts were tested but proved to be less effective under these conditions. An autoclave equipped with quartz windows allowed for the qualitative determination of a homogeneous reaction environment in the supercritical fluid.