Enantioselective aerobic oxidation of olefins by magnetite nanoparticles at room temperature: a chiral carboxylic acid strategy

Abstract

Asymmetric oxidations of organic compounds are limited in their synthetic scope and by practical factors, such as the use of complex catalyst synthesis. A simple and cheap nanostructured catalyst system comprising magnetite nanoparticles stabilized by L-(+)-tartaric acid (Fe₃O₄/tart-NPs) was successfully synthesized in diethylene glycol. The catalyst was characterized by FT-IR, TGA, ICP-AES, XRPD, SEM and dynamic light scattering (DLS). The catalytic activity of Fe₃O₄/tart-NPs dispersion in acetonitrile in the presence of isobutyraldehyde was studied in selective aerobic oxidation of olefins to form asymmetric epoxide, an important intermediate for the synthesis of biologically active compounds. In addition, the magnetically recoverable nanocatalyst Fe₃O₄/tart-NPs can be conveniently separated and recovered from the reaction system by applying an external magnetic field and reused for five cycles without the loss of activity after each cycle. These results demonstrate that the heterogeneous nanocatalysts possess potential applications for green and sustainable development. As synthesized nanoparticles of Fe₃O₄/tart-NPs are cheap and easy to synthesize asymmetric catalysts which were prepared without the involvement of difficult and cumbersome procedures for the synthesis of complicated asymmetric ligands. Possible reaction mechanisms were outlined.