The chemical compound osmium tetroxide (OsO₄), also known as osmium tetraoxide, osmium(VIII) oxide, or osmic acid, is an oxide of the element osmium. IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... A substance is soluble in a fluid if it dissolves in that fluid. ... Water has the chemical formula H2O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. ... The melting point of a solid is the temperature at which it changes state from solid to liquid. ... The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid. ... In chemistry and biochemistry, acid dissociation constant, the acidity constant, or the acid-ionization constant (Ka) is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. ... A material safety data sheet or MSDS is a form containing data regarding the properties of a particular substance. ... Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances (as amended) is the main source of European Union law concerning chemical safety. ... R-phrases are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations. ... S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. ... The refractive index of a material is the factor by which the phase velocity of electromagnetic radiation is slowed relative to vacuum. ... The dielectric constant εr (represented as or K in some cases) is defined as the ratio: where εs is the static permittivity of the material in question, and ε0 is the vacuum permittivity. ... Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ... IR spectrum of a thin film of liquid ethanol. ... Nuclear Magnetic Resonance Spectroscopy most commonly known as NMR Spectroscopy is the name given to the technique which exploits the magnetic properties of nuclei. ... It has been suggested that Mass spectrum be merged into this article or section. ... // An ion is an atom or group of atoms with a net electric charge. ... // An ion is an atom or group of atoms with a net electric charge. ... Ruthenium tetroxide is RuO4. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... A chemical compound is a chemical substance formed from two or more elements, with a fixed ratio determining the composition. ... An oxide is a chemical compound of oxygen with other chemical elements. ... General Name, Symbol, Number osmium, Os, 76 Chemical series transition metals Group, Period, Block 8, 6, d Appearance silvery, blue cast Atomic mass 190. ...

Physical properties

Pure osmium tetroxide is colorless, but it is usually contaminated by a small amount of yellow-brown osmium dioxide (OsO₂), giving it a yellowish hue. OsO₄ is soluble in carbon tetrachloride (CCl₄) and moderately soluble in water. It is very volatile as it sublimes at room temperature. It has a characteristic odor similar to ozone. In fact, the element name osmium is derived from osme, Greek for odor.^[1] R-phrases , , , , S-phrases , , , , , Flash point non flammable RTECS number FG4900000 Supplementary data page Structure and properties n, εr, etc. ... Sublimation of an element or substance is a conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. ... Room temperature, in laboratory reports, is taken to be roughly 21–23 degrees Celsius (69-73 degrees Fahrenheit), or 294–296 kelvins. ... For other uses, see Ozone (disambiguation). ... A chemical element, often called simply element, is a chemical substance that cannot be divided or changed into other chemical substances by any ordinary chemical technique. ...

Structure

The osmium of OsO₄ has an oxidation number of 8, the highest possible oxidation state for a transition element. The osmium has a total electron count of 16 - 8 from its valence shell and 2 donated by each of the oxygens - and is a d⁰ metal. OsO₄ is tetrahedral, similar to permanganate (MnO₄^-), with which it is isoelectronic. General Name, Symbol, Number osmium, Os, 76 Chemical series transition metals Group, Period, Block 8, 6, d Appearance silvery, blue cast Atomic mass 190. ... The oxidation state or oxidation number is defined as the sum of negative and positive charges in an atom, which indirectly indicates the number of electrons it has accepted or donated. ... In chemistry, the oxidation state is a measure of the degree of oxidation of an atom in a chemical compound. ... The valence shell is the outermost shell of an atom, which contains the electrons most likely to account for the nature of any reactions involving the atom and of the bonding interactions it has with other atoms. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... The permanganate ion is MnO4-. A permanganate is a compound that contains this group. ... Two or more molecular entities (atoms, molecules, ions) are described as isoelectronic if they have the same number of valence electrons and the same structure (number and connectivity of atoms), but may differ in the elements involved. ...

Image File history File links Oso4. ...

Synthesis

OsO₄ is formed slowly when osmium powder reacts with O₂ at 298 K. Reaction of bulk solid requires heating to 670 K.^[2]

Os + 2 O₂ → OsO₄

Reactions

Oxofluorides

Osmium forms several oxofluorides, all of which are very sensitive to moisture. Red cis-OsO₂F₄ forms at 77 K as follows:

OsO₄ + HF + KrF₂ → cis-OsO₂F₄

OsO₄ also reacts with F₂ to form yellow OsOF₂:

2 OsO₄ + 2 F₂ → 2 OsO₃F₂ + O₂

OsO₄ reacts with one equivalent of [Me₄N]F at 298 K and 2 equivalents at 253 K:

OsO₄ + [Me₄N]F → [Me₄N][OsO₄F]

OsO₄ + 2 [Me₄N]F → [Me₄N]₂[cis-OsO₄F₂]^[3]

Oxidation of alkenes

OsO₄ will react with alkenes to deliver two hydroxyl groups on the same side of the alkene (syn-dihydroxylation) forming a dialcohol: Image File history File links Oso4rxn. ...

The following is the mechanism of the above reaction: Image File history File links Download high resolution version (909x275, 11 KB) Licensing I, the creator of this work, hereby release it into the public domain. ...

Since OsO₄ is highly toxic, a catalytic procedure has been developed where substoichiometric amounts of OsO₄ are used with another oxidizing agent such as H₂O₂, which reoxidizes the OsO₃ to OsO₄. Generic graph showing the effect of a catalyst in an hypotetical exothermic chemical reaction. ... Flash point Non-flammable. ...

Miscellaneous reactions

OsO₄ may be dissolved in aqueous alkalis such as NaOH:

OsO₄ + 2 NaOH → Na₂[cis-OsO₄(OH)₂] + O₂

OsO₄ reacts with NH₃ and KOH: Flash point 11°C R/S statement R: ? S: , , , , RTECS number BO0875000 Supplementary data page Structure and properties n, εr, etc. ...

OsO₄ + NH₃ + KOH → K[Os(N)O₃] + 2 H₂O

The [Os(N)O₃]^- anion is isoelectronic and isostructural with OsO₄.

OsO₄ + 4 (Me₃)NH^tBu → Os(N^tBu)₄ + 4 (Me₃)OH

OsO₄ will react in methanol with CO at 400 K and up to 200 bar of pressure to produce Os₃(CO)₁₂: CO can stand for: Carbon monoxide (molecular formula) Central Office (telecommunications and telephony) Chesapeake and Ohio Railroad (AAR reporting mark CO) Colombia (ISO 3166-1 digram and NATO country code) Colorado ( U.S. state postal symbol) Commanding Officer (military) Conscientious Objector (military) Continental Airlines (IATA airline code) Collaborative Browsing Co...

3 OsO₄ + 24 CO → Os₃(CO)₁₂ + 12 CO₂^[4]

Uses

Organic synthesis

In organic synthesis OsO₄ is widely used to oxidise alkenes to the dialcohols, adding two hydroxyl groups at the same side (syn addition). See reaction and mechanism above. One catalytic reaction with osmium tetroxide is the Sharpless bishydroxylation named after Nobelist K. Barry Sharpless. In the presence of chiral ligands, OsO₄ will catalyze the cis-dihydroxylation of pro-chiral alkenes to give chiral 1,2-diols. An alkene in organic chemistry is an unsaturated hydrocarbon containing at least one carbon to carbon double bond. ... Hydroxyl group The term hydroxyl group is used to describe the functional group -OH when it is a substituent in an organic compound. ... Ethylene undergoing syn and anti addition In organic chemistry, syn addition is the addition of two substituents to the same side (or face) of a double bond or triple bond, resulting in a decrease in bond order but an increase in number of substituents. ... Sharpless bishydroxylation or asymmetric dihydroxylation (AD) is a chemical reaction of an alkene with osmium tetroxide to form a diol (dialcohol). ... Karl Barry Sharpless (born April 28, 1941) is an American chemist renowned for his work on organometallic chemistry. ...

Biological staining

OsO₄ is a widely used staining agent used in transmission electron microscopy (TEM) to provide contrast to the image. As a lipid stain, it is also useful in scanning electron microscopy as an alternative to sputter coating. It embeds a heavy metal directly into cell membranes, creating a high secondary electron emission without the need for coating the membrane with a layer of metal, which can obscure details of the cell membrane. Osmium tetroxide is also used as a stain for lipids in optical microscopy. ... Transmission electron microscopy (TEM) is an imaging technique whereby a beam of electrons is focused onto a specimen causing an enlarged version to appear on a fluorescent screen or layer of photographic film (see electron microscope), or can be detected by a CCD camera. ... Figure 1: Structure of a Lipid. ... Low temperature SEM magnification series for a snow crystal. ... Sputter coating in microscopy is a process of covering a specimen with a very thin layer of heavy metal, generally a gold/palladium (Au/Pd) mixture. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ...

Osmium ore refining

OsO₄ is an intermediate in osmium ore refining. Osmium residues are reacted with Na₂O₂ forming [OsO₄(OH)₂]^2- anions, which, when reacted with chlorine (Cl₂) gas and heated, form OsO₄. The oxide is dissolved in alcoholic NaOH forming [OsO₂(OH)₄]^2- anions, which, when reacted with NH₄Cl, forms OsO₂Cl₂(NH₃)₄. This is ignited under hydrogen (H₂) gas leaving behind pure osmium (Os).^[5] General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... Sodium hydroxide (NaOH), also known as caustic soda or lye in North America, is a caustic metallic base used in industry (mostly as a strong chemical base) in the manufacture of paper, textiles, and detergents. ... Ammonium chloride or Sal Ammoniac (chemically ammonium chloride (NH4Cl); also nushadir salt, zalmiak, sal armagnac, sal armoniac, and salt armoniack) is, in its pure form, a clear white water-soluble crystalline salt with a biting taste. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...

Safety considerations

OsO₄ is highly poisonous, even at very 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. Pulmonary edema is swelling and/or fluid accumulation in the lungs. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ...

On the 6th April 2004 the American news organisation ABC News reported that British intelligence sources believed they had foiled a plot to detonate a bomb involving OsO₄ due to its poisonous properties.

External links

• International Chemical Safety Card 0528
• NIOSH Pocket Guide to Chemical Hazards
• European Chemicals Bureau
• BBC report on bomb plot
• BBC What is Osmium tetroxide article
• Osmium Tetroxide: Molecule of the Month
• Chemical Reactions

References

• Cotton, S. A. "Chemistry of Precious Metals," Chapman and Hall (London): 1997. ISBN 0751404136.
• Berrisford, D. J.; Bolm, C.; Sharpless, K. B., "Ligand Accelerated Catalysis", Angewandte Chemie, International Edition English, 1995, volume 34, pp. 1059-1070.