Oxone in microemulsion for diastereoselective epoxidation of R-limonene to trans-limonene dioxide

Abstract

Some catalytic processes developed for the synthesis of epoxy resins, polycarbonates or even non-isocyanate polyurethanes from cis/trans-limonene dioxide exhibit low or complete absence of reactivity of cis-limonene dioxide (cis-LDO). This study focuses on the development of a process for exclusively producing trans-LDO. The technique involves uses a chiral ketone as a catalyst that reacts with oxone to form the corresponding chiral dioxirane which epoxidises R-limonene. The effect of various organic solvents and the importance of the surfactant (for micelle formation) were evaluated. It was found that when epoxidation is performed using a chiral ketone in presence of a microemulsion, high conversion and diastereoselectivity was reached. The chiral ketone catalyst tested in this way gave an LDO yield close to 100%, consisting almost exclusively of trans-LDO (97%). When acetone catalyst was employed instead of the chiral ketone, a mixture of cis and trans-LDO was obtained with a selectivity to trans diastereoisomers of only 39%. The diastereoselective epoxidation process developed is easy to reproduce and could be considered ready for industrial implementation.