Development of a selective, solvent-free epoxidation of limonene using hydrogen peroxide and a tungsten-based catalyst

The development of a limonene epoxidation process using environment-friendly H2O2, with high H2O2 conversion (approximate to 95%) and selectivity to the epoxide (100%), is reported in this paper. Parametric studies of temperature, oxidant, solvent, acid concentration and sodium sulphate amounts were performed with the focus on establishing a rapid and highly selective process. Approximately 95% conversion of H2O2 at 100% selectivity to limonene-1,2-epoxide was achieved in 15 minutes with a single-step addition of oxidant. The operating conditions included a 323 K temperature in a solvent-free environment, with a limonene/H2O2/catalyst molar ratio of 4:1:0.005, using a tungsten-based polyoxometalates. To prevent the hydrolysis of the epoxide, the reaction mixture was saturated with sodium sulphate. An acid concentration of lower than 0.04 M was used and found to have significant effect on the selectivity. Kinetic studies were performed to allow modelling of the reaction scheme. The activation energy was determined to be approximate to 36 kJ mol(-1).