Osmium tetroxide

Osmium tetroxide, also called osmium(VIII) oxide or (non-systematically) osmic acid, is a chemical compound made of osmium and oxygen. It has the chemical formula OsO
4. It is a Lewis acid, oxidising agent, and biological stain.

Oxidiser

A simplified mechanism for the oxidation of alkenes by OsO
4.

Osmium tetroxide is a useful oxidising agent in a name reaction called the Upjohn dihydroxylation. It reacts with alkenes to become cyclic osmate diesters. Water breaks apart the osmate, leaving a hydrated osmium(VI) compound and a diol. The diagram above shows osmium(VI) dioxide dihydroxide, but the actual chemistry of osmium(VI) in water is much more complicated.

Usually, a cooxidant like NMMO is used to regenerate osmium tetroxide, allowing it to act as a catalyst.

Osmium Tetroxide Media

• Krebs B., Hasse K.D. (1976). "Refinements of the Crystal Structures of KTcO4, KReO4 and OsO4. The Bond Lengths in Tetrahedral Oxo-Anions and Oxides of d0 Transition Metals". Acta Crystallographica B 32: 1334–1337. DOI:10.1107/S056774087600530X.

• Idealized depiction of the cis-dihydroxylation of alkenes.

• Lemieux–Johnson oxidation.svg

  Lemieux–Johnson oxidation

• CSD CIF KEWMEE.png

  Structure of OsO3(N-t-Bu) (multiple bonds are not drawn explicitly), illustrating the type of osmium(VIII)-oxo-imide that adds alkenes en route to the amino alcohol.

• Resin-Embedded Transmission Electron Microscope Sample.jpg

  A sample of cells fixed/stained with osmium tetroxide (black) embedded in epoxy resin (amber). The cells are black as a result of the effects of osmium tetroxide.

• Label for ampoules of OsO4.jpg

  Label for package of 10 ampoules containing 100 mg of OsO4 per ampoule