Osmium tetroxide

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Osmium tetroxide
IUPAC name
Osmium tetroxide
Preferred IUPAC name
Osmium tetraoxide
Systematic IUPAC name
Other names
Osmium(VIII) oxide
Molar mass 254.23 g/mol
Appearance White volatile solid
Odor Acrid, chlorine-like
Density 4.9 g/cm3
Melting point 40.25 °C (104.45 °F; 313.40 K)
Boiling point 129.7 °C (265.5 °F; 402.8 K)
5.70 g/100 ml (10 °C)
6.23 g/100 ml (25 °C)
Solubility Very soluble in aq. ammonia, benzene, t-butanol, diethyl ether, ethanol, phosphoryl chloride, sulfuric acid
Solubility in carbon tetrachloride 375 g/100 ml
Vapor pressure 7 mmHg (20 °C)
-364.976 kJ/mol
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Osmium tetroxide (or osmium(VIII) oxide) is the chemical compound with the formula OsO4, the most important oxide of osmium metal, due to is variety of uses in organic chemistry.



OsO4 is a Lewis acid and a mild oxidant. It reacts with alkaline aqueous solution to give the perosmate anion OsO

Osmium tetraoxide is moderately soluble in water, with which it reacts reversibly to form osmic acid.

Osmium tetroxide, it is readily reduced by hydrogen in solution to osmium metal. Most organic materials will also reduce it.


Osmium tetroxide is a white to slight yellowish solid, volatile, with an acrid chlorine-like odor.


Osmium tetroxide is sold by chemical suppliers, but due to its toxicity it's not easy to acquire, and most companies might not sell to the public, especially due to its high toxicity.


OsO4 is formed slowly when osmium powder reacts with oxygen at ambient temperature.

Reaction of bulk solid requires heating to above 400 °C, and is also very slow.


  • Oxidize alkenes to the vicinal diols
  • Lemieux–Johnson oxidation
  • Compound collecting



OsO4 is highly poisonous, even at low exposure levels, and must be handled with appropriate precautions. In particular, inhalation at concentrations well below those at which a smell can be perceived can lead to pulmonary edema and subsequent death. Noticeable symptoms can take hours to appear after exposure.

OsO4 also stains the human cornea, which can lead to blindness if proper safety precautions are not observed. The permissible exposure limit for osmium(VIII) oxide (8 hour time-weighted average) is 200 µg/m3. Osmium(VIII) oxide can penetrate plastics and therefore is stored in glass under refrigeration.


Osmium tetroxide must be kept in ampoules, and kept in a fridge or freezer. This compound must only be handled in a well ventilated area, or in a glovebox.


Any reducing agent will convert it to the less harmful osmium metal. Since the metal is very expensive, it's best to recycle it.


  1. Nikol'skii, A. B.; Ryabov, A. N.; Zhurnal Neorganicheskoi Khimii; vol. 10; (1965); p. 1 - 5; Zhurnal Neorganicheskoi Khimii; vol. 10; (1965); p. 3 - 9

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