Osmium tetroxide

Osmium tetroxide

Names
IUPAC name Osmium tetroxide
Preferred IUPAC name Osmium tetraoxide
Systematic IUPAC name Tetraoxoosmium
Other names Osmium(VIII) oxide
Properties
Chemical formula	OsO4
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)
Solubility in water	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)
Thermochemistry
Std enthalpy of formation (ΔfHo298)	-364.976 kJ/mol
Hazards
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.

Properties

Chemical

OsO₄ is a Lewis acid and a mild oxidant. It reacts with alkaline aqueous solution to give the perosmate anion OsO
4(OH)2−
2.

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.

Physical

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

Availability

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.

Preparation

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

Reaction of bulk solid requires heating to above 400 °C

Projects

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

Handling

Safety

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.

Storage

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.

Disposal

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

References

Relevant Sciencemadness threads

• Why is osmium tetroxide volatile?
• Osmium tetroxide
• Osmium tetroxide decomposition