Methyltrioxorhenium-catalyzed oxygen transfer reactions in ambient temperature ionic liquids

Increasingly, chemists in both academia and industry are faced with the enormous task of developing environmentally benign reagents and methods for effecting chemical transformations. The most promising areas of research towards these aims include the use of non-volatile, recyclable media, transition metal catalysts, and reagents that create non-toxic byproducts. This work combines all of the above ideas into a new catalytic system for the oxidation of unsaturated hydrocarbons to epoxides.; Improved methods and procedures were developed for synthesizing air- and moisture-stable, ambient temperature ionic liquids. Emphasis was placed on synthesizing colorless, imidazole-free, and halide-free ionic liquids that could be used to measure reaction kinetics reproducibly.; The catalyst methyltrioxorhenium (MTO) was used with aqueous hydrogen peroxide and urea hydrogen peroxide (UHP) to epoxidize olefins in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim]BF₄). Most of the olefins used in this study were epoxidized with at least 95% conversion. When UHP was used as the oxidant, the olefins were converted with high selectivity to the epoxide; none of the ring-opened diol product was observed. The products and any leftover reactants were removed from the ionic liquid solution by simple extraction with diethyl ether.; The kinetics of the reaction of MTO with hydrogen peroxide were monitored by ultraviolet-visible (UV-vis) spectrophotometry. The formation of the monoperoxorhenium complex was too fast to measure by conventional UV-vis. The formation of the diperoxorhenium complex has a rate constant of 0.20 M−1s −1 in 90% solutions of water-miscible ionic liquids. The rate constant for the formation of the diperoxorhenium complex was found to depend linearly on the concentration of water in the solution.; The reactions of both peroxorhenium complexes with olefinic substrates in water-miscible ionic liquids were studied spectrophotometrically using non-steady-state kinetics. The diperoxorhenium complex was found to be more reactive than the monoperoxorhenium complex in ionic liquids. Ionic liquids were shown to behave very similar to 1:1 mixtures of water/acetonitrile with respect to rates of olefin epoxidation using the MTO catalyst. The rate constants for olefin epoxidation using the MTO catalyst in ionic liquids were found to be much faster than the rate constants for the same reactions in acetonitrile.