Carbon Monoxide

Title: Carbon Monoxide
CAS Registry Number: 630-08-0
Molecular Formula: CO
Molecular Weight: 28.01
Percent Composition: C 42.88%, O 57.12%
Literature References: Produced on an industrial scale by partial oxidation of hydrocarbon gases from natural gas or by the gasification of coal and coke. Conveniently prepd in the laboratory by heating calcium carbonate with Zn dust: Weinhouse, J. Am. Chem. Soc. 70, 442 (1948); by dehydration of formic acid with H2SO4: Gilliland, Blanchard, Inorg. Synth. 2, 81 (1946). Purification of carbon monoxide bought in steel cylinders: A. Klemenc, Die Behandlung und Reindarstellung von Gasen (Vienna, 1948) p 160; Glemser in Handbook of Preparative Inorganic Chemistry vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) p 646. Review: R. Pierantozzi in Kirk-Othmer Encyclopedia of Chemical Technology vol. 5 (Wiley-Interscience, New York, 4th ed., 1993) pp 97-122. Review of clinical toxicology: Stewart, Annu. Rev. Biochem. 15, 409-423 (1975); D. Gorman et al., Toxicology 187, 25-38 (2003); of industrial toxicology: Patty's Industrial Hygiene and Toxicology vol. 2F, G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, New York, 4th ed., 1994) pp 4523-4552.
Properties: Highly poisonous, odorless, colorless, tasteless gas. Very flammable, burns in air with a bright blue flame. Ignition pt in air: 700°. mp -205.0°. bp -191.5°. d4-195 (liq) 0.814. d (gas) 0.968 (air = 1.000). d40 at 760 mm: 1.250 g/liter. The top pressure is 1500 psi. Flammable limits in air: 12 to 75 vol %. Crit press 35 atm, crit temp -139°. Heat capacity at 20°: 6.95 cal/mole/°C. Heat value per m3: 3033 kcal. Heat of formation: -26.39 kcal/mol. Dec into carbon and carbon dioxide between 400 and 700°, at lower temp when in contact with catalytic surfaces. Above 800° the equilibrium reaction favors CO formation. Hopcalite, a mixture of the oxides of manganese and copper, catalyzes the decompn at room temp, as does Pd on silica gel. Sparingly sol in water: 3.3 ml/100 ml H2O at 0°; 2.3 ml/100 ml H2O at 20°; freely absorbed by a concd soln of cuprous chloride in HCl or in NH4OH. Appreciably sol in some organic solvents, such as ethyl acetate, CHCl3, acetic acid. The soly in methanol and ethanol is about 7 times as great as the soly in water.
Melting point: mp -205.0°
Boiling point: bp -191.5°
Density: d4-195 (liq) 0.814; d (gas) 0.968 (air = 1.000); d40 at 760 mm: 1.250 g/liter
CAUTION: Combines with the hemoglobin in the blood to form carboxyhemoglobin which disrupts oxygen transport and delivery throughout the body. Potential symptoms of overexposure by inhalation are headache, tachypnea, nausea, vomiting, lassitude, fatigue, dizziness, confusion, hallucinations; dimness of vision; irritability, impaired judgement; cyanosis; depression of S-T segment of electrocardiogram, angina, syncope; coma. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 2003) p 54; Clinical Toxicology of Commercial Products, R. E. Gosselin et al., Eds. (Williams & Wilkins, Baltimore, 5th ed., 1984) Section III, pp 94-101.
Use: As reducing agent in metallurgical operations especially in the Mond process for the recovery of nickel; in organic synthesis especially in the Fischer-Tropsch processes for petroleum-type products and in the oxo reaction; in the manuf of metal carbonyls.
Carbon Nitride Carbon Suboxide Carbon Tetrachloride Carbon Tetrafluoride Carbon Tetraiodide

Carbon monoxide
Wireframe model of carbon monoxide
Ball-and-stick model of carbon monoxide Spacefill model of carbon monoxide
CAS number 630-08-0 YesY
PubChem 281 YesY
ChemSpider 275 YesY
UNII 7U1EE4V452 YesY
EC number 211-128-3
UN number 1016
KEGG D09706 YesY
MeSH Carbon+monoxide
ChEBI CHEBI:17245 YesY
RTECS number FG3500000
Beilstein Reference 3587264
Gmelin Reference 421
Jmol-3D images Image 1
Molecular formula CO
Molar mass 28.010 g/mol
Appearance colorless gas
Odor odorless
Density 789 kg/m3, liquid
1.250 kg/m3 at 0 °C, 1 atm
1.145 kg/m3 at 25 °C, 1 atm
Melting point −205.02 °C; −337.04 °F; 68.13 K
Boiling point −191.5 °C; −312.7 °F; 81.6 K
Solubility in water 27.6 mg/1 L (25 °C)
Solubility soluble in chloroform, acetic acid, ethyl acetate, ethanol, ammonium hydroxide, benzene
kH 1.04 atm-m3/mol
Refractive index (nD) 1.0003364
Dipole moment 0.122 D
heat capacity C
29.1 J/K mol
Std molar
entropy So298
197.7 J·mol−1·K−1
Std enthalpy of
formation ΔfHo298
−110.5 kJ·mol−1
Std enthalpy of
combustion ΔcHo298
−283.4 kJ/mol
MSDS External MSDS
EU Index 006-001-00-2
EU classification Flammable F Very Toxic T+
R-phrases R61 R12 R26 R48/23
S-phrases S53 S45
NFPA 704
NFPA 704.svg
Flash point −191.0 °C; −311.8 °F; 82.1 K
Autoignition temperature 609 °C; 1,128 °F; 882 K
Explosive limits 12.5–74.2%
Related compounds
Related carbon oxides Carbon dioxide
Carbon suboxide
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Carbon monoxide (CO) is a colorless, odorless, and tasteless gas that is slightly less dense than air. It is toxic to humans and animals when encountered in higher concentrations, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions. In the atmosphere, it is spatially variable and short lived, having a role in the formation of ground-level ozone.

Carbon monoxide consists of one carbon atom and one oxygen atom, connected by a triple bond that consists of two covalent bonds as well as one dative covalent bond. It is the simplest oxocarbon, and isoelectronic with the cyanide ion and molecular nitrogen. In coordination complexes the carbon monoxide ligand is called carbonyl.

Carbon monoxide is produced from the partial oxidation of carbon-containing compounds; it forms when there is not enough oxygen to produce carbon dioxide (CO2), such as when operating a stove or an internal combustion engine in an enclosed space. In the presence of oxygen, including atmospheric concentrations, carbon monoxide burns with a blue flame, producing carbon dioxide.[1] Coal gas, which was widely used before the 1960s for domestic lighting, cooking, and heating, had carbon monoxide as a significant fuel constituent. Some processes in modern technology, such as iron smelting, still produce carbon monoxide as a byproduct.[2]

Worldwide, the largest source of carbon monoxide is natural in origin, due to photochemical reactions in the troposphere that generate about 5×1012 kilograms per year.[3] Other natural sources of CO include volcanoes, forest fires, and other forms of combustion.

In biology, carbon monoxide is naturally produced by the action of heme oxygenase 1 and 2 on the heme from hemoglobin breakdown. This process produces a certain amount of carboxyhemoglobin in normal persons, even if they do not breathe any carbon monoxide. Following the first report that carbon monoxide is a normal neurotransmitter in 1993,[4][5] as well as one of three gases that naturally modulate inflammatory responses in the body (the other two being nitric oxide and hydrogen sulfide), carbon monoxide has received a great deal of clinical attention as a biological regulator. In many tissues, all three gases are known to act as anti-inflammatories, vasodilators, and promoters of neovascular growth.[6] Clinical trials of small amounts of carbon monoxide as a drug are ongoing.[7]