Carbon monoxide

Carbon monoxide

Name = Carbon monoxide
ImageFileL1 = Carbon monoxide 2D.svg
ImageSizeL1 = 100px
ImageNameL1 = Structure of the carbon monoxide molecule
ImageFileR1 = Carbon-monoxide-3D-vdW.png ImageSizeR1 = 120px
ImageNameR1 = Space-filling model of the carbon monoxide molecule
IUPACName = Carbon monoxide
OtherNames = Carbonic oxide
Section1 = Chembox Identifiers
CASNo = 630-08-0
ChemSpiderID = 275
RTECS = FG3500000

Section2 = Chembox Properties
Formula = CO
MolarMass = 28.0101 g/mol
Appearance = Colourless, odorless gas
Density = 0.789 g/cm³, liquid
1.250 g/L at 0°C, 1 atm.
1.145 g/L at 25°C, 1 atm.
(lighter than air)
Solubility = 0.0026 g/100 mL (20 °C)
MeltingPt = -205 °C (68 K)
BoilingPt = -192 °C (81 K)
Dipole = 0.112 D (3.74×10−31 C·m)

Section7 = Chembox Hazards
FlashPt = Flammable gas
EUClass = Highly flammable (F+)
Repr. Cat. 1
Toxic (T)
NFPA-H = 4
NFPA-F = 4
RPhrases = R12, R23, R33, R48, R61
SPhrases = S9, S16, S33, S45, S53

Section8 = Chembox Related
Function = oxides
OtherFunctn = carbon dioxide; carbon suboxide; dicarbon monoxide; carbon trioxide

Carbon monoxide, with the chemical formula CO, is a colorless, odorless, tasteless yet highly toxic gas. Its molecules consist of one carbon atom covalently bonded to one oxygen atom. There are two covalent bonds and a coordinate covalent bond between the oxygen and carbon atoms.

Carbon monoxide is produced from the partial combustion of carbon-containing compounds, notably in internal-combustion engines. Carbon monoxide forms in preference to the more usual carbon dioxide when there is a reduced availability of oxygen present during the combustion process. Carbon monoxide has significant fuel value, burning in air with a characteristic blue flame, producing carbon dioxide. Despite its serious toxicity, CO plays a highly useful role in modern technology, being a precursor to myriad products.


Carbon monoxide is so fundamentally important that many methods have been developed for its production. [Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 200. ISBN 0-12-352651-5.]

Producer gas is formed by combustion of carbon in oxygen at high temperatures when there is an excess of carbon. In an oven, air is passed through a bed of coke. The initially produced CO2 equilibrates with the remaining hot carbon to give CO. The reaction of O2 with carbon to give CO is described as the Boudouard equilibrium. Above 800 °C, CO is the predominant product::O2 + 2 C → 2 CO :ΔH = -221 kJ/molThe downside of this method is if done with air it leaves a mixture that is mostly nitrogen.

Synthesis gas or Water gas is produced via the endothermic reaction of steam and carbon::H2O + C → H2 + CO :ΔH = 131 kJ/mol

CO also is a byproduct of the reduction of metal oxide ores with carbon, shown in a simplified form as follows::MO + C → M + CO :ΔH = 131 kJ/molSince CO is a gas, the reduction process can be driven by heating, exploiting the positive (favorable) entropy of reaction. The Ellingham diagram shows that CO formation is favored over CO2 in high temperatures.

CO is the anhydride of formic acid. As such it is conveniently produced by the dehydration of formic acid, for example with sulfuric acid. Another laboratory preparation for carbon monoxide entails heating an intimate mixture of powdered zinc metal and calcium carbonate.:Zn + CaCO3ZnO + CaO + CO

Another laborotory method to generate CO is reacting sucrose and sodium hydroxide in a closed system.


The CO molecule possesses a bond length of 0.1128 nm.cite journal | author = O. R. Gilliam, C. M. Johnson and W. Gordy | title = Microwave Spectroscopy in the Region from Two to Three Millimeters | year = 1950 | journal = Physical Review | volume = 78 | issue = 2 | pages = 140 | doi = 10.1103/PhysRev.78.140] Formal charge and electronegativity difference cancel each other out. The result is a small dipole moment with its negative end on the carbon atom [cite book | author = W. Kutzelnigg | title = Einführung in die Theoretische Chemie | publisher = Wiley-VCH | isbn = 3-527-30609-9] . The reason for this, despite oxygen's greater electronegativity, is that the highest occupied molecular orbital has an energy much closer to that of carbon's p orbitals, meaning that greater electron density is found near the carbon. In addition, carbon's lower electronegativity creates a much more diffuse electron cloud, enhancing the dipole moment. This is also the reason that almost all chemistry involving carbon monoxide occurs through the carbon atom, and not the oxygen.

The molecule's bond length is consistent with a partial triple bond. The molecule has a small dipole moment and can be represented by threefact resonance structures:


Principal chemical reactions

Industrial uses

Carbon monoxide is a major industrial gas that has many applications in bulk chemicals manufacturing. [Elschenbroich, C.;Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) Wiley-VCH: Weinheim, 2006. ISBN 3-527-28165-7]

High volume aldehydes are produced by the hydroformylation reaction of alkenes, CO, and H2. In one of many applications of this technology, hydroformylation is coupled to the Shell Higher Olefin Process to give precursors to detergents.

Methanol is produced by the hydrogenation of CO. In a related reaction, the hydrogenation of CO is coupled to C-C bond formation, as in the Fischer-Tropsch process where CO is hydrogenated to liquid hydrocarbon fuels. This technology allows coal to be converted to petrol.

In the Monsanto process, carbon monoxide and methanol react in the presence of a homogeneous rhodium catalyst and HI to give acetic acid. This process is responsible for most of the industrial production of acetic acid.

Carbon monoxide is a principle component of syngas, which is often used for industrial power.Carbon monoxide(CO) is also used in industrial scale operations for purifying Nickel (Mond Process}.

Coordination chemistry

Most metals form coordination complexes containing covalently attached carbon monoxide. Only those in lower oxidation states will complex with carbon monoxide ligands. This is because there must be sufficient electron density to facilitate back donation from the metal dxz-orbital, to the π* molecular orbital from CO. The lone pair on the carbon atom in CO, also donates electron density to the dx²−y² on the metal to form a sigma bond. In nickel carbonyl, Ni(CO)4 forms by the direct combination of carbon monoxide and nickel metal at room temperature. For this reason, nickel in any tubing or part must not come into prolonged contact with carbon monoxide (corrosion). Nickel carbonyl decomposes readily back to Ni and CO upon contact with hot surfaces, and this method was once used for the industrial purification of nickel in the Mond process. [cite journal | author= Mond L, Langer K, Quincke F| title= Action of carbon monoxide on nickel| journal=Journal of the Chemical Society | year=1890| pages=749–753 | doi = 10.1039/CT8905700749| volume= 57]

In nickel carbonyl and other carbonyls, the electron pair on the carbon interacts with the metal; the carbon monoxide donates the electron pair to the metal. In these situations, carbon monoxide is called the carbonyl ligand. One of the most important metal carbonyls is iron pentacarbonyl, Fe(CO)5:

Many metal-CO complexes are prepared by decarbonylation of organic solvents, not from CO. For instance, iridium trichloride and triphenylphosphine react in boiling methoxyethanol or DMF) to afford IrCl(CO)(PPh3)2.

Organic and main group chemistry

In the presence of strong acids and water, carbon monoxide reacts with olefins to form carboxylic acids in a process known as the Koch-Haaf reaction. [OrgSynth | author = Koch, H.; Haaf, W. | title = 1-Adamantanecarboxylic Acid | year = 1973 | collvol = 5 | collvolpages = 20 | prep = cv5p0020] In the Gattermann-Koch reaction, arenes are converted to benzaldehyde derivatives in the presence of AlCl3 and HCl. [OrgSynth | title = "p"-Tolualdehyde | author = G. H. Coleman, David Craig | collvol = 2 | collvolpages = 583 | year = 1943 | prep = cv2p0583] Organolithium compounds, e.g. butyl lithium react with CO, but this reaction enjoys little use.

Although CO reacts with carbocations and carbanions, it is relatively unreactive toward organic compounds without the intervention of metal catalysts. [Chatani, N.; Murai, S. "Carbon Monoxide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi|10.1002/047084289]

With main group reagents, CO undergoes several noteworthy reactions. Chlorination of CO is the industrial route to the important compound phosgene. With borane CO forms an adduct, H3BCO, which is isoelectronic with the acylium cation [H3CCO] +. CO reacts with sodium to give products resulting from C-C coupling such as Na2C2O2 (sodium acetylenediolate), and potassium to give K2C2O2 (potassium acetylenediolate) and K2C6O6 (potassium rhodizonate).

Carbon monoxide in the atmosphere

Carbon monoxide, though thought of as a pollutant today, has always been present in the atmosphere, chiefly as a product of volcanic activity. It occurs dissolved in molten volcanic rock at high pressures in the earth's mantle. Carbon monoxide contents of volcanic gases vary from less than 0.01% to as much as 2% depending on the volcano. It also occurs naturally in bushfires. Because natural sources of carbon monoxide are so variable from year to year, it is extremely difficult to accurately measure natural emissions of the gas.

Carbon monoxide has an indirect radiative forcing effect by elevating concentrations of methane and tropospheric ozone through chemical reactions with other atmospheric constituents (e.g., the hydroxyl radical, OH.) that would otherwise destroy them. Through natural processes in the atmosphere, it is eventually oxidized to carbon dioxide. Carbon monoxide concentrations are both short-lived in the atmosphere and spatially variable.

Anthropogenic CO from automobile and industrial emissions may contribute to the greenhouse effect and global warming. In urban areas carbon monoxide, along with aldehydes, reacts photochemically to produce peroxy radicals. Peroxy radicals react with nitrogen oxide to increase the ratio of NO2 to NO, which reduces the quantity of NO that is available to react with ozone. Carbon monoxide is also a constituent of tobacco smoke.

Carbon monoxide in the cigarette

Over 4000 chemical compounds are created when a cigarette burns, many of which are toxic and/or carcinogenic. Carbon monoxide, nitrogen oxides, hydrogen cyanide and ammonia are all present in cigarette smoke. []

Role in physiology and food

Carbon monoxide is used in modified atmosphere packaging systems in the US, mainly with fresh meat products such as beef and pork. The CO combines with myoglobin to form carboxymyoglobin, a bright cherry red pigment. Carboxymyoglobin is more stable than the oxygenated form of myoglobin, oxymyoglobin, which can become oxidized to the brown pigment, metmyoglobin. This stable red colour can persist much longer than in normally packaged meat, giving the appearance of freshness.cite journal | author=Sorheim, S, Nissena, H, Nesbakken, T | title=The storage life of beef and pork packaged in an atmosphere with low carbon monoxide and high carbon dioxide | journal=Journal of Meat Science | year=1999 | pages=157–64 | volume=52 | issue=2 | doi = 10.1016/S0309-1740(98)00163-6] Typical levels of CO used are 0.4% to 0.5%.The technology was first given generally recognized as safe status by the FDA in 2002 for use as a secondary packaging system. In 2004 the FDA approved CO as primary packaging method, declaring that CO does not mask spoilage odour.cite journal | author=Eilert EJ | title=New packaging technologies for the 21st century | journal=Journal of Meat Science | year=2005 | pages=122–27 | volume=71 | issue=1 | doi = 10.1016/j.meatsci.2005.04.003] Despite this ruling, the technology remains controversial in the US for fears that it is deceptive and masks spoilage. [cite news | url = | title = Low-Oxygen Packaging with CO: A Study in Food Politics That Warrants Peer Review| accessdate = 2007-04-18]

One reaction in the body produces CO. Carbon monoxide is produced naturally as a breakdown of heme (which is one of hemoglobin moieties), a substrate for the enzyme heme oxygenase. The enzymatic reaction results in breakdown of heme to CO, biliverdin and Fe3+ radical. The endogenously produced CO may have important physiological roles in the body (eg as a neurotransmitter or a blood vessels relaxant). In addition CO regulates inflammatory reactions in a manner that prevents the development of several diseases such as atherosclerosis or severe malaria.

CO is a nutrient for methanogenic bacteria, [cite journal | author = R. K. Thauer | title = Biochemistry of methanogenesis: a tribute to Marjory Stephenson. 1998 Marjory Stephenson Prize Lecture | year = 1998 | journal = Microbiology | volume = 144 | issue = 9 | pages = 2377–2406 | url = | format = Free] a building block for acetylcoenzyme A. This theme is the subject for the emerging field of bioorganometallic chemistry. In bacteria, CO is produced via the reduction of carbon dioxide via the enzyme carbon monoxide dehydrogenase, an Fe-Ni-S-containing protein. [cite book | title = Bioorganometallics: Biomolecules, Labeling, Medicine | author = Jaouen, G., Ed. | publisher = Wiley-VCH | location = Weinheim | year = 2006 | isbn = 3-527-30990-X]

A haeme-based CO-sensor protein, CooA, is known. [cite journal | author = Roberts, G. P.; Youn, H.; Kerby, R. L. | title = CO-Sensing Mechanisms | journal = Microbiology and Molecular Biology Reviews | year = 2004 | volume = 68 | pages = 453–473 | doi = 10.1128/MMBR.68.3.453-473.2004 | pmid = 15353565] The scope of its biological role is still unclear, it is apparently part of a signaling pathway in bacteria and archaea, but its occurrence in mammals is not established.

CO is also currently being studied in several research laboratories throughout the world for its anti-inflammatory and cytoprotective properties that can be used therapeutically to prevent the development of a series of pathologic conditions such as ischemia reperfusion injury, transplant rejection, atherosclerosis, sepsis, severe malaria or autoimmunity. There are yet no clinical applications of CO in humans.


It was first described by the Spanish doctor Arnaldus de Villa Nova in the 11th century; but the creation of Carbon monoxide was first made by the French chemist de Lassone in 1776 by heating zinc oxide with coke. He mistakenly concluded that the gaseous product was hydrogen as it burned with a blue flame. The gas was identified as a compound containing carbon and oxygen by the English chemist William Cumberland Cruikshank in the year 1800.

The toxic properties of CO were first thoroughly investigated by the French physiologist Claude Bernard around 1846. He poisoned dogs with the gas, and noticed that their blood was more "rutilant" in all the vessels. 'Rutilant' is a French word, but also has an entry in English dictionaries, meaning ruddy, shimmering, or golden. However, it was translated at the time as crimson, scarlet, and now is famously known as 'cherry pink'.

During World War II, carbon monoxide was used to keep motor vehicles running in parts of the world where gasoline was scarce. External charcoal or wood burners were fitted, and the carbon monoxide produced by gasification was piped to the carburetor. The CO in this case is known as "wood gas". Carbon monoxide was also reportedly used on a small scale during the Holocaust at some Nazi extermination camps, and in the Action T4 "euthanasia" program.

ource concentrations

* 0.1 ppm - natural background atmosphere level (MOPITT)
* 0.5 to 5 ppm - average background level in homescite web
title = Basic Information : Carbon Monoxide
accessdate = 2007-12-01
* 5 to 15 ppm - levels near properly adjusted gas stoves in homes
* 100-200 ppm - Mexico City central area from autos etc.cite book
last = Singer
first = Siegfried Fred
title = The Changing Global Environment
pages = pp. 90
month = March
date = 1975
url =,M1
isbn = 9789027704023
* 5,000 ppm - chimney of a home wood fire cite web
last = Gosink
first = Tom
title = What Do Carbon Monoxide Levels Mean?
work = Alaska Science Forum
publisher = Geophysical Institute, University of Alaska Fairbanks
date = 1983-01-28
url =
format = HTML
accessdate = 2007-12-01
* 7,000 ppm - undiluted warm car exhaust - without catalytic converter
* 30,000 ppm - undiluted cigarette smoke


Carbon monoxide is a significantly toxic gas and has no odor or color. It is the most common type of fatal poisoning in many countries.cite journal | author=Omaye ST. | title=Metabolic modulation of carbon monoxide toxicity | journal=Toxicology | year=2002 | pages=139–50 | volume=180 | issue=2 | doi = 10.1016/S0300-483X(02)00387-6] Exposures can lead to significant toxicity of the central nervous system and heart. Following poisoning, long-term sequelae often occurs. Carbon monoxide can also have severe effects on the fetus of a pregnant woman. Symptoms of mild poisoning include headaches and dizziness at concentrations less than 100 ppm. Concentrations as low as 667 ppm can cause up to 50% of the body's haemoglobin to be converted to carboxy-haemoglobin (HbCO). Carboxy-haemoglobin is quite stable but this change is reversible. Carboxy-haemoglobin is ineffective for delivering oxygen, resulting in some body parts not receiving oxygen needed. As a result, exposures of this level can be life-threatening. In the United States, OSHA limits long-term workplace exposure levels to 50 ppm.

The mechanisms by which carbon monoxide produces toxic effects are not yet fully understood, but haemoglobin, myoglobin, and mitochondrial cytochrome oxidase are thought to be compromised. Treatment largely consists of administering 100% oxygen or hyperbaric oxygen therapy, although the optimum treatment remains controversial.cite journal | author=Buckley NA, Isbister GK, Stokes B, Juurlink DN. | title=Hyperbaric oxygen for carbon monoxide poisoning : a systematic review and critical analysis of the evidence | journal=Toxicol Rev | year=2005 | pages=75–92 | volume=24 | issue=2 | pmid = 16180928 | url= | format = Abstract | doi=10.2165/00139709-200524020-00002] Domestic carbon monoxide poisoning can be prevented by the use of household carbon monoxide detectors.

ee also

* Carbon monoxide (data page)
*Boudouard reaction
* Carbon monoxide poisoning
* Criteria air contaminants
* Undersea and Hyperbaric Medical Society Hyperbaric Treatment for CO Poisoning
* Rubicon Foundation research articles on CO Poisoning


External links

* [ International Chemical Safety Card 0023]
* [ National Pollutant Inventory - Carbon Monoxide]
* [ NIOSH Pocket Guide to Chemical Hazards]
* [ External MSDS data sheet]
* [ Carbon Monoxide Kills Awareness Campaign Site]
* [ Carbon Monoxide Purification Process]
* [ Carbon Monoxide Hazards with Backpacking Stoves]
* [ USFDA IMPORT BULLETIN 16B-95, May 1999]
* [ FDA Agency Response Letter GRAS Notice No. GRN 000083]
* [ Carbon Monoxide in Fresh Meat site]
* [ Carbon Monoxide Network & Forum]
* [ Microscale Gas Chemistry Experiments with Carbon Monoxide]
* Research on the therapeutic effects of CO [ (Gulbenkian Science Institute)]
* [ Instant insight] outlining the physiology of carbon monoxide from the Royal Society of Chemistry
* [] Article about Sen. Chris mandating CO detectors in new homes & hotels in Florida as of 2008.

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Look at other dictionaries:

  • carbon monoxide — n a colorless odorless very toxic gas CO that burns to carbon dioxide with a blue flame and is formed as a product of the incomplete combustion of carbon * * * a colourless almost odourless gas that is very poisonous. When breathed in it combines …   Medical dictionary

  • Carbon monoxide — Carbon Car bon (k[aum]r b[o^]n), n. [F. carbone, fr. L. carbo coal; cf. Skr. [,c]r[=a] to cook.] (Chem.) 1. An elementary substance, not metallic in its nature, which is present in all organic compounds. Atomic weight 11.97. Symbol C. it is… …   The Collaborative International Dictionary of English

  • carbon monoxide — UK US noun [U] ► ENVIRONMENT a poisonous gas formed when carbon is not burned completely, produced by vehicles and by heating equipment that is not working properly: »carbon monoxide poisoning/buildup/exposure → Compare CARBON DIOXIDE(Cf. ↑carbon …   Financial and business terms

  • carbon monoxide — 1873, so called because it consists of one carbon and one oxygen atom (as opposed to carbon dioxide, which has two of the latter) …   Etymology dictionary

  • carbon monoxide — ► NOUN ▪ a colourless, odourless toxic flammable gas formed by incomplete combustion of carbon …   English terms dictionary

  • carbon monoxide — n. a colorless, odorless, highly poisonous gas, CO, produced by the incomplete combustion of carbonaceous material: it burns with a pale blue flame …   English World dictionary

  • carbon monoxide — a colorless, odorless, poisonous gas, CO, that burns with a pale blue flame, produced when carbon burns with insufficient air: used chiefly in organic synthesis, metallurgy, and in the preparation of metal carbonyls, as nickel carbonyl. [1870 75] …   Universalium

  • carbon monoxide — noun an odorless very poisonous gas that is a product of incomplete combustion of carbon • Syn: ↑carbon monoxide gas, ↑CO • Hypernyms: ↑monoxide * * * ˌcarbon monˈoxide [carbon monoxide] [ˌkɑːbən mənˈɒksaɪd] …   Useful english dictionary

  • carbon monoxide — Carbonic Car*bon ic, a. [Cf. F. carbonique. See {Carbon}.] (Chem.) Of, pertaining to, or obtained from, carbon; as, carbonic oxide. [1913 Webster] {Carbonic acid} (Chem.), an acid {HO.CO.OH}, not existing separately, which, combined with positive …   The Collaborative International Dictionary of English

  • carbon monoxide — N UNCOUNT Carbon monoxide is a poisonous gas that is produced especially by the engines of vehicles. The limit for carbon monoxide is 4.5 per cent of the exhaust gas …   English dictionary

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