Tungstate-H2O2 system is alternative to chlorine and organic peroxides
A promising hydrogen peroxide-based system formulated by a team of Japanese researchers converts a wide range of linear and cyclic olefins to epoxides with high selectivity and maximum H2O2 efficiency [Science, 300, 964 (2003)].
Cleaner oxidations using H2O2 have been an important target for industrial synthesis of epoxides, which are used as monomers and chiral intermediates. The use of H2O2 is an advance over more expensive organic peroxides and peracids or environmentally unfavored chlorine-based oxidations. Water is typically the sole by-product.
The researchers, led by chemistry professor Noritaka Mizuno of the University of Tokyo, screened silicotungstate catalysts for their ability to aid activation of H2O2 to form reactive oxygen species. The ammonium salt of the novel polyoxometallate cluster [-SiW10O34(H2O)2]4 provided the highest catalytic activity, they note. It allows conversion of olefins to the corresponding epoxides in acetonitrile at 32 °C with most yields above 90% and essentially 100% selectivity and 100% H2O2 utilization.
The homogeneous catalyst can be recovered by evaporating the solvent to dryness and washing with n-hexane. It can be used at least five times without loss of performance or degradation to other tungsten compounds.
The reaction system is a "major advance" in the use of H2O2 as an oxidant for synthesis of small-molecule epoxides, notes Terry Collins, a chemistry professor and director of the Institute for Green Oxidation Chemistry at Carnegie Mellon University. "This work fits into the pursuit of sustainability because it enables greater use of one of nature's most important oxidizing agents, hydrogen peroxide, allowing us to move further away in technology from oxidizing agents of our own design that lead to persistent pollutants."