Osmium tetroxide is an oxide of osmium (OsO4). Osmium tetroxide is the most important and most easily prepared compound of osmium. It has a number of specific applications in organic chemistry and in biochemistry. It is also a useful source of osmium compounds. It is remarkable in that it is one of the few volatile oxides of a heavy metal and that although the osmium is octavalent (of all elements only osmium and ruthenium reach as high an oxidation state) it is a reasonably controllable oxidising agent. It is from this latter property that most of its applications derive. Being an expensive chemical, available commercially only in small amounts, it is still considered a serious toxic compound for small-scale terrorist devices. On 6 April 2004, news agencies reported that the British police foiled a plot by members of El-Qaeda to prepare and detonate a bomb containing OsO4 in London[1].
The compound was discovered in 1803 by Smithson Tennant (1761-1815), and in the same year he isolated metallic osmium from it[2]. Fusion with alkali of the black residue remaining after treatment of native platinum with aqua regia followed by extraction and acidification of the melt gave. Industrially, OsO4, is made from crude platinum concentrates by oxidative acid distillation and is then separated from ruthenium tetroxide. In the laboratory it is best made by direct oxidation of osmium metal[3] or by the acid distillation with chlorate of almost any osmium compound
Osmium tetroxide is a non-combustible, colorless to pale yellow solid that has a disagreeable chlorine-like odor[4]. It slowly develops when powdered osmium metal is exposed to air. OsO4 is fairly soluble in water and in several organic solvents, but reacts as an oxidant with many of them. The substance is used in organic syntheses, mainly to oxidize unsaturated carbon-carbon bonds to dihydroxy compounds (glycols). Its most common usage is as a staining agent and a “fixant” in transmission electron microscopy. This chemical sublimes at room temperature, having a remarkable vapor pressure of about 7 mmHg at 20ºC (more typical for a liquid compound than for a solid), as compared to 17 mmHg for water, 2 mmHg for the nerve agent sarin, or 0.07 mmHg for the blistering agent sulfur mustard under the same conditions. It is highly poisonous, even at very low concentrations, and must be handled according to the appropriate precautions. Hours may pass between exposure and the appearance of noticeable symptoms. In almost all of its chemical reactions, a number of which are summarized in the diagram, OsO4, is reduced to compounds containing lower oxidation states. With ammonia, however, the tetrahedral osmiamate ion[OsO3, N]is formed, which is isoelectronic with OsO4.
It is used mainly for the cis-hydroxylation of olefinic double bonds to give glycols, for which purpose it is the smoothest and most efficient general reagent known. It tends to react faster with strained olefins, particularly in the presence of pyridine[6]. Aromatic hydrocarbons are hydroxylated only at the most reactive aromatic site (e.g. phenanthrene at the 9,10 position[7]). The reagent may be used either alone in an inert solvent, the resulting osmate (VI) ester being decomposed by bisulphite or hydrogen sulphide[5, 6], or, more commonly and economically, in the presence of an additional oxidant such as chlorate, hydrogen peroxide or periodate. These regenerate the OsO4, which is therefore functioning as a catalyst. Examples of simple hydroxylations with OsO4, are the production of glycerol from ally1 alcohol and of ethylene glycol from ethylene. The compound has been used in the synthesis of such species as cortisone, progesterone, and of reserpine-type alkaloids, and also in the degradative investigation of natural products such as columbin[5]. The glycol cleavage properties of periodate may be used together with the oxidising properties of OsO4, to convert olefins to aldehydes (e.g. trans-stilbene to benzaldehyde, cyclohexene to adipaldehyde), to ketones or to epoxides[8, 9].
Osmium tetroxide is also a reagent that is used in the dihydroxylation process in the synthesis of 3-[1-(2,4-Dichlorophenyl)-2-(1H-imidazol-1-yl) ethoxy]-1,2-propanediol (D436535). 3-[1-(2,4-Dichlorophenyl)-2-(1H-imidazol-1-yl) ethoxy]-1,2-propanediol is involved in biological studies as microsomal cytochrome P 450 isoenzymes from Penicillium italicum interaction with sterol demethylation inhibitor fungicides.
In biochemistry field, the compound is extensively used (normally in 2 percent aqueous solution, often called “osmic acid”) for cell and tissue studies, its unique fixation and staining properties having been recognised and used since 1861. It is used for both visible and electron microscopy of biological materials, but now the latter application is probably the more important. The purpose of fixation is to “freeze” cells without destruction or disruption of their organization or structure; staining is necessary for the resolution of cellular structure by increasing the apparent density of some parts of the tissue only. OsO4, is unique in that it both fixes and stains biological material. For the electron microscopist its most important functions are the preservation of sub-cellular ultrastructure and its ability to fix and stain membranes. For staining purposes it is often used with polar species such as uranyl or lead ions. The normal method used is to pre-treat the tissue with aldehydes, then to treat it by immersion in a dilute aqueous solution of OsO4, (or the tissue is exposed to OsO4, vapor) followed by washing, additional staining if required, dehydration with alcohol, embedding in resin and cutting into thin sections suitable for microscopy.
Like some other heavy metal tetra-oxo species, osmium tetroxide in electrolytes has the property of passifying iron electrodes[10].
Toxicity and health effect
OsO4 has an odor threshold of 0.0019 parts/million. Its lethal concentration time (LCt50) is considered to be 1316 mg/min/m3, similar to that for sulfur mustard[11]. Humans may tolerate a maximal concentration of 0.1 ppm in air for 1.5 hours or 0.0001 ppm for 6 hours without harmful effects[12]. McLaughlin and co-authors[13] reported that workers exposed to 0.01–0.53 ppm (0.1–0.6 mg/m3) suffered from lacrimation, conjunctivitis, vision disturbances, headaches and cough.
OsO4 can be compared to chemical warfare agents in terms of toxicity. Exposure to even low doses can be lethal. In addition, both OsO4 and chemical warfare agents share similar physiological effects. The first appearance of a physiological effect, also known as the threshold effect, is observed at a lower concentration for osmium tetroxide vapor than for chemical warfare agents such as phosgene, sulfur mustard or even the nerve agent sarin. The LCt50 of OsO4 is comparable to that of sulfur mustard, but since sulfur mustard has a much lower vapor pressure OsO4 can pose a greater inhalational threat. Under the same environmental conditions there will be much more OsO4 vapor in a closed space than sulfur mustard vapor[1].
Osmium tetroxide is a rapid, indiscriminative oxidizer that does not distinguish between organic tissue and inorganic materials. An inhalational toxicity study with rabbits proved futile, because of the rapid reduction of OsO4 by the skin, hair, mucous membranes, etc., as well as by the chamber walls[14]. Inhalation, ingestion, contact with skin and with mucous membranes may all result in severe consequences. Due to its high vapor pressure, most exposures are to vapor. These can cause severe chemical burns to the eyes, skin and respiratory tract[15]. Very short-term contact with the vapor may cause lacrimation, accompanied by cough, headaches and dizziness. OsO4 may cause irreversible blindness by turning the cornea black. Symptoms may not be noticeable until several hours after the exposure, which may be an appealing feature for terrorists. Affected people may not realize immediately the extent of its toxic effects. Another severe delayed effect following inhalational exposure is acute lung injury, which may be followed by non-cardiogenic pulmonary edema[1]. Direct contact with osmium tetroxide solution will turn the skin black (severe chemical burns due to strong oxidizing properties). Painful burns or contact dermatitis may result, depending on the concentration. OsO4 is not considered a carcinogen[1]. Death is mainly the result of complications due to the exposure.
Neutralization of the chemical on surfaces can be conveniently achieved by covering it with unsaturated oil (vegetable oil)[1]. Osmium tetroxide does not have a medical antidote; therefore the treatment is supportive and symptomatic, depending on the route of exposure. Initial treatment should focus on preventing further exposure. Victims should be removed from the contaminated area, undressed, and decontaminated by running water as soon as possible.
Spectrum method
In general, the 1960-90s saw a big growth in spectral and optical methods for determining osmium. One of the first methods was X-ray fluorescence, with a lot of benefits such as accuracy, non-destructiveness, and the ability to detect osmium without chemical extraction from biological samples. Also, this method is independent of the chemical state of osmium atoms.
It was observed that the reaction of OsO4 with thiourea in acid medium gave a red combination of[Os(thio)6]Cl3[16]. The results were not affected by systematic errors. The convenient, sensitive, reproducible, and accurate method for the spectrophotometric determination of osmium has been developed.
Electrochemical methods
A rapid potentiometric method was proposed by Zaky et al.[17]. The method is based on the addition of arsenite to Os(VIII) to reduce it to the metallic state. The excess of arsenite was oxidized by iodine dissolved in acetic acid. The liberated iodide was then potentiometrically titrated against mercury (II) using silver amalgam as the indicator electrode. Some binary and ternary mixtures were completely analyzed. Amin and Saleh described a simple, rapid, and accurate potentiometric method for the determination of Os (VIII) in the concentration range 0.4-4.0 mg•ml-1[18]. Hydrazine hydrochloride was added to Os (VIII) to reduce it to Os (IV). The excess of hydrazine hydrochloride was oxidized by iodine dissolved in acetic acid.
- Baker M, Kosal ME. Osmium Tetroxide – a New Chemical Terrorism Weapon? http://CNS miis edu/pubs/week/040413 htm 2004
- D. McDonald, Platinum Metals Rev., 1961, 5, 146; Smithson Tennant, Phil. Trans., 1804, 94, 411
- G. Brauer, Handbook of Preparative Chemistry, Academic Press, New York, 1965, p. 1603
- Material Safety Data Sheet (MSDS). Osmium tetroxide. http://www proscitech com au/catalogue/msds/c010 pdf 2007.
- L. F. Fieser and M. Fieser, Reagents for Organic Synthesis, Wiley, New York, 1967, PP 475,759
- R. Criegee, B. Marchand and H. Wannowius,Ann., 1942, 550, 99
- G. M. Badger, Qzturt. Rev., 1951,5,160
- R. J. Collin, W. P. Griffith, F. Phillips and A. C. Skapski, Biochim. Biophys. Acra, 1973, 320, 745; J. Chem. Soc., Dalton Trans., 1974, I094
- R. Pappo, D. S. Allen, R. U. Lemieux and W. S. Johnson, J. Org. Chem., 1956,z1,478
- G. H. Cartledge, Corrosion, 1967,18,316t
- CBWInfo.com. Improvised Chemical Agent: Osmium Tetroxide. http://cbwinfo com/Chemical/HistandMisc/oso4 shtml 2004.
- Grant WM. Toxicology of the Eye. 2nd edn. Springfield, IL: Charles C. Thomas, 1974:769.
- McLaughlin AIG, Milton R, Perry KMA. Toxic manifestations of osmium tetroxide. Br J Ind Med 1946;3:183–6.
- Osmium Tetroxide. MSDS Division of Occupational Health and Safety. http://dohs ors od nih gov/pdf/Osmium%20Tetroxide%20REVISED pdf 2007.
- National Academy of Sciences. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals.Washington, DC: National Academies Press, 1995:364.
- BRATULESCU G., GANESCU I., GANESCU A. Thiocyanatochrome complexes in analytical chemistry. Determination of osmium(III). J. Serb. Chem. Soc. 70, (8-9), 1113, 2005.
- ZAKY M., KILLA H.M., ISSA Y.M. Some observations on the application of arsenite reduction to the potentiometric determination of osmium(VIII) and to the analysis of mixtures. Microchem. J. 44, (1), 54, 1991.
- AMIN A.S., SALEH H.M. Utilization of hydrazine hydrochloride in the potentiometric determination of osmium(VIII): Analysis of binary and ternary mixtures. Sci. Pharm. 69, (2), 367, 2001.
Osmium is a blue－white metal. It is found in
platinum ores and in the naturally occurring alloy osmiridium.
Osmium when heated in air or when the finely
divided form is exposed to air at room temperature, oxidizes
to form the tetroxide (OsO4), osmic acid. Osmium
tetraoxide is a colorless, crystalline solid or pale-yellow
mass. Unpleasant, acrid, chlorine-like odor. A liquid above
41°C.
solid with an unpleasant odour
Osmium tetroxide is a strong oxidant. Numerous organic
substances reduce it to black osmium dioxide (OsO2) or to
osmium metal.
Pale, yellow crystalline solid; chlorine-like acrid odor; monoclinic crystals having terahedral structure; density 5.1 g/cm3; melts at 40.6°C; vaporizes at 129.7°C; sublimation begins below its boiling point; vapor pressure 11 torr at 27°C; critical temperature 405°C; critical pressure 170 atm; moderately soluble in water, 7.24 g/100mL at 25°C; soluble in most organic solvents.
Osmium tetroxide is used in histopathological laboratories
to stain the adipose tissue and as a stabilizing agent in
scanning electron microscopy. In the chemical
industry, it is used as a catalyst in the organic synthesis,
particularly as the oxidizing agent in olefin-to-glycol conversion
(546, 567). In the past, osmium tetroxide in the form
of aqueous solution was used in forensic medicine to examine
fingerprints. Osmium tetroxide is also used in
medicine to treat rheumatoid arthritis.
Osmium (VIII) tetraoxide (Os8+ + 4O2-→ OsO4) is a yellow crystal and probably the most
important compound used as an oxidizing agent, as a biological stain in microscopy, and to
detect fingerprints.
Oxidizing agent, particularly for converting olefins to glycols. Catalyzes chlorate, peroxide, periodate, and other oxidations: P. N. Rylander, Organic Syntheses with Noble Metal Catalysts (Academic Press, New York, 1973) pp 121-144. As fixing and staining agent for cell and tissue studies.
ChEBI: An osmium coordination entity consisting of four oxygen atoms bound to a central osmium atom via covalent double bonds.
Osmium tetroxide is obtained as an intermediate during recovery of osmium metal from osmiridium or other noble metal minerals (See Osmium). In general, oxidation of an aqueous solution of an osmium salt or complex, such as sodium osmate with nitric acid, yields the volatile tetroxide which may be distilled out from the solution. In the laboratory, the compound can be prepared by oxidation of the osmium tetrachloride, OsCl4, or other halide solutions with sodium hypochlorite followed by distillation.
Osmium tetroxide may also be produced by heating finely divided osmium metal in a stream of oxygen or air at 300 to 400°C.
Osmium tetroxide is obtained by heating, at 300–400°C,
finely divided osmium metal in the stream of air or oxygen
(546). Commercially, it is received during osmium
smelting and platinum annealing. Osmium tetroxide
may also be produced by oxidizing osmium with aqua regia
or nitric acid. It is often formed at room temperature
from osmium metal powder.
A colorless or yellow solid with a pungent odor of chlorine. Melting point about 104°F. Boiling point 266°F (begins to sublime below melting point). Density 4.9 g / cm3. Soluble in alcohol. Toxic by inhalation and a strong irritant to the eyes and mucous membranes.
Osmium tetraoxide is incompatible with hydrochloric acid andeasily oxidized organic materials. Contact with other materials may cause fire. . Reacted explosively with1-methylimidazole [J. Chem. Soc., Dalton Trans., 1979, 1084].
Osmium tetroxide is poisonous by all routes of exposure. The vapor is an eye irritant and can produce tears and damage. The vapor also can cause upper respiratory tract irritation.
LD50 oral (mouse): 162 mg/kg
LCLO inhalation (mouse): 40 ppm (104 mg/m 3)/4 hr.
The acute toxicity of osmium tetroxide is high, and it is a severe irritant of the eyes and
respiratory tract. Exposure to osmium tetroxide vapor can damage the cornea of the eye.
Irritation is generally the initial symptom of exposure to low concentrations of osmium tetroxide
vapor, and lacrimation, a gritty feeling in the eyes, and the appearance of rings around lights may
also be noted. In most cases, recovery occurs in a few days. Concentrations of vapor that do not
cause immediate irritation can have an insidious cumulative effect; symptoms may not be noted
until several hours after exposure. Contact of the eyes with concentrated solutions of this
substance can cause severe damage and possible blindness. Inhalation can cause headache,
coughing, dizziness, lung damage, and difficult breathing and may be fatal. Contact of the vapor
with skin can cause dermatitis, and direct contact with the solid can lead to severe irritation and
burns. Exposure to osmium tetroxide via inhalation, skin contact, or ingestion can lead to
systemic toxic effects involving liver and kidney damage. Osmium tetroxide is regarded as a
substance with poor warning properties.
Chronic exposure to osmium tetroxide can result in an accumulation of osmium compounds in
the liver and kidney and damage to these organs. Osmium tetroxide has been reported to cause
reproductive toxicity in animals; this substance has not been shown to be carcinogenic or to show
reproductive or developmental toxicity in humans.
TOXIC; inhalation, ingestion or skin contact with material may cause severe injury or death. Contact with molten substance may cause severe burns to skin and eyes. Avoid any skin contact. Effects of contact or inhalation may be delayed. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause pollution.
Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated.
Flammability and Explosibility
Noncombustible
Poison by ingestion, inhalation, and intraperitoneal routes. Human systemic effects by inhalation: lachrymation and other eye effects and structural or functional changes in trachea or bronch. Experimental reproductive effects. Mutation data reported. Explodes on contact with 1 -methylimidazole. Catalytic decomposition of hydrogen peroxide can be hazardous. See also OSMIUM
Osmium may be alloyed with platinum
metals, iron, cobalt, and nickel; and it forms compounds
withtin and zinc. The alloy with iridium is used in
the manufacture of fountain pen points, engraving tool;
record player needles; electrical contacts; compass needles;
fine machine bearings; and parts for watch and
lock mechanisms. The metal is a catalyst in the synthesis
of ammonia; and in the dehydrogenation of organic compounds. It is also used as a stain for histological
examination of tissues. Osmium tetroxide is used as an
oxidizing agent, catalyst, and as a fixative for tissues in
electron microscopy. Other osmium compounds find use
in photography. Osmium no longer is used in incandescent
lights or in fingerprinting.
In
particular, all work with osmium tetroxide should be conducted in a fume hood to
prevent exposure by inhalation, and splash goggles and impermeable gloves should
be worn at all times to prevent eye and skin contact. Osmium tetroxide as solid or
solutions should be stored in tightly sealed containers, and these should be placed in
secondary containers.
It is VERY TOXIC and should be manipulated in a very efficient fume cupboard. It attacks the eyes severely (use also face protection) and is a good oxidising agent. It is volatile and has a high vapour pressure (11mm) at room temperature. It sublimes and volatilises well below its boiling point. It is soluble in *C6H6, H2O (7.24% at 25o), CCl4 (375% at 25o), EtOH and Et2O. It is estimated by dissolving a sample in a glass-stoppered flask containing 25mL of a solution of KI (previously saturated with CO2) and acidified with 0.35M HCl. After gentle shaking in the dark for 30minutes, the solution is diluted to 200mL with distilled H2O saturated with CO2 and titrated with standard thiosulfate using starch as indicator. This method is not as good as the gravimetric method. Hydrazine hydrochloride (0.1 to 0.3g) is dissolved in 3M HCl (10mL) in a glass-stoppered bottle. After warming to 55-65o, a weighed sample of OsO4 solution is introduced, and the mixture is digested on a water bath for 1hour. The mixture is transferred to a weighed glazed crucible and evaporated to dryness on a hot plate. A stream of H2 is started through the crucible, and the crucible is heated over a burner for 20-30minutes. The stream of H2 is continued until the crucible in cooled to room temperature, and then the H2 is displaced by CO2 in order to avoid rapid combustion of H2. Finally the crucible is weighed. [Grube in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol II pp 1603 1965, Anderson & Yost J Am Chem Soc 60 1822 1938.] § Available commercially on a polymer support.
Osmium tetroxide is a strong oxidizer.
Reacts with combustibles and reducing materials. Reacts
with hydrochloric acid to form toxic chlorine gas. Forms
unstable compounds with alkalis.
Consult with environmental
regulatory agencies for guidance on acceptable disposal
practices. Generators of waste containing this contaminant
(≥100 kg/mo) must conform with EPA regulations
governing storage, transportation, treatment, and waste
disposal.
