Carbon monoxide

Names
IUPAC name Carbon monoxide
Other names Carbonic oxide gas Carbon protoxide Oxide of carbon Protoxide of carbon Carbonous oxide Carbonous acid gas Carbon(II) oxide Breath of carbon Oxygenated carbon Carbate Carbonyl Water gas Hydrocarbon gas Fuel gas Rauchgas Carbonic inflammable air Heavy inflammable air White damp Fire Damp Powder Gas Illuminating gas Dowson gas Mond gas Power gas Producer gas Blast furnace gas Coal gas Phlogiston Car gas
Identifiers
CAS Number	630-08-0 Y
3D model (JSmol)	Interactive image
Beilstein Reference	3587264
ChEBI	CHEBI:17245 Y
ChEMBL	ChEMBL1231840
ChemSpider	275 Y
ECHA InfoCard	100.010.118
EC Number	211-128-3
Gmelin Reference	421
KEGG	D09706 Y
MeSH	Carbon+monoxide
PubChem CID	281
RTECS number	FG3500000
UNII	7U1EE4V452 Y
UN number	1016
CompTox Dashboard (EPA)	DTXSID5027273
InChI InChI=1S/CO/c1-2 Y Key: UGFAIRIUMAVXCW-UHFFFAOYSA-N Y InChI=1/CO/c1-2 Key: UGFAIRIUMAVXCW-UHFFFAOYAT
SMILES #
Properties
Chemical formula	CO
Molar mass	28.010 g·mol−1
Appearance	Colorless
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/L (25 °C)
Solubility	soluble in chloroform, acetic acid, ethyl acetate, ethanol, ammonium hydroxide, benzene
Henry's law constant (kH)	1.04 atm·m3/mol
Magnetic susceptibility (χ)	−9.8·10−6 cm3/mol
Refractive index (nD)	1.0003364
Dipole moment	0.122 D
Thermochemistry
Heat capacity (C)	29.1 J/(K·mol)
Std molar entropy (S⦵298)	197.7 J/(K·mol)
Std enthalpy of formation (ΔfH⦵298)	−110.5 kJ/mol
Std enthalpy of combustion (ΔcH⦵298)	−283.0 kJ/mol
Pharmacology
ATC code	V04CX08 (WHO)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Poisonous by inhalation[1]
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H220, H331, H360, H372, H420
Precautionary statements	P201, P202, P210, P251, P260, P261, P264, P270, P281, P304+P340, P308+P313, P311, P314, P321, P377, P381, P403, P403+P233, P405, P501
NFPA 704 (fire diamond)	[3] 3 4 0
Flash point	−191 °C (−311.8 °F; 82.1 K)
Autoignition temperature	609 °C (1,128 °F; 882 K)
Explosive limits	12.5–74.2%
Lethal dose or concentration (LD, LC):
LC50 (median concentration)	8636 ppm (rat, 15 min) 5207 ppm (rat, 30 min) 1784 ppm (rat, 4 h) 2414 ppm (mouse, 4 h) 5647 ppm (guinea pig, 4 h)[2]
LCLo (lowest published)	4000 ppm (human, 30 min) 5000 ppm (human, 5 min)[2]
NIOSH (US health exposure limits):[1]
PEL (Permissible)	TWA 50 ppm (55 mg/m3)
REL (Recommended)	TWA 35 ppm (40 mg/m3) C 200 ppm (229 mg/m3)
IDLH (Immediate danger)	1200 ppm
Safety data sheet (SDS)	ICSC 0023
Related compounds
Other anions	Carbon monosulfide
Other cations	Silicon monoxide Germanium monoxide Tin(II) oxide Lead(II) oxide
Related carbon oxides	Carbon dioxide Carbon suboxide Oxocarbons
Supplementary data page
Carbon monoxide (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is YN ?) Infobox references

Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simplest carbon oxide. In coordination complexes, the carbon monoxide ligand is called carbonyl. It is a key ingredient in many processes in industrial chemistry.^[5]

The most common source of carbon monoxide is the partial combustion of carbon-containing compounds. Numerous environmental and biological sources generate carbon monoxide. In industry, carbon monoxide is important in the production of many compounds, including drugs, fragrances, and fuels.^[6] Upon emission into the atmosphere, carbon monoxide affects several processes that contribute to climate change.^[7]

Carbon monoxide has important biological roles across phylogenetic kingdoms. It is produced by many organisms, including humans. In mammalian physiology, carbon monoxide is a classical example of hormesis where low concentrations serve as an endogenous neurotransmitter (gasotransmitter) and high concentrations are toxic resulting in carbon monoxide poisoning. It is isoelectronic with both cyanide anion CN⁻ and molecular nitrogen N₂.

History

Prehistory

Humans have maintained a complex relationship with carbon monoxide since first learning to control fire circa 800,000 BC. Early humans probably discovered the toxicity of carbon monoxide poisoning upon introducing fire into their dwellings. The early development of metallurgy and smelting technologies emerging circa 6,000 BC through the Bronze Age likewise plagued humankind from carbon monoxide exposure. Apart from the toxicity of carbon monoxide, indigenous Native Americans may have experienced the neuroactive properties of carbon monoxide through shamanistic fireside rituals.^[8]

Ancient history

Early civilizations developed mythological tales to explain the origin of fire, such as Prometheus from Greek mythology who shared fire with humans. Aristotle (384–322 BC) first recorded that burning coals produced toxic fumes. Greek physician Galen (129–199 AD) speculated that there was a change in the composition of the air that caused harm when inhaled, and many others of the era developed a basis of knowledge about carbon monoxide in the context of coal fume toxicity. Cleopatra may have died from carbon monoxide poisoning.^[8]

Pre-industrial revolution

Georg Ernst Stahl mentioned carbonarii halitus in 1697 in reference to toxic vapors thought to be carbon monoxide. Friedrich Hoffmann conducted the first modern scientific investigation into carbon monoxide poisoning from coal in 1716. Herman Boerhaave conducted the first scientific experiments on the effect of carbon monoxide (coal fumes) on animals in the 1730s.^[8]

Joseph Priestley is considered to have first synthesized carbon monoxide in 1772. Carl Wilhelm Scheele similarly isolated carbon monoxide from charcoal in 1773 and thought it could be the carbonic entity making fumes toxic. Torbern Bergman isolated carbon monoxide from oxalic acid in 1775. Later in 1776, the French chemist de Lassone [fr] produced CO by heating zinc oxide with coke, but mistakenly concluded that the gaseous product was hydrogen, as it burned with a blue flame. In the presence of oxygen, including atmospheric concentrations, carbon monoxide burns with a blue flame, producing carbon dioxide. Antoine Lavoisier conducted similar inconclusive experiments to Lassone in 1777. The gas was identified as a compound containing carbon and oxygen by William Cruickshank in 1800.^[8][9]

Thomas Beddoes and James Watt recognized carbon monoxide (as hydrocarbonate) to brighten venous blood in 1793. Watt suggested coal fumes could act as an antidote to the oxygen in blood, and Beddoes and Watt likewise suggested hydrocarbonate has a greater affinity for animal fiber than oxygen in 1796. In 1854, Adrien Chenot similarly suggested carbon monoxide to remove the oxygen from blood and then be oxidized by the body to carbon dioxide.^[8] The mechanism for carbon monoxide poisoning is widely credited to Claude Bernard whose memoirs beginning in 1846 and published in 1857 phrased, "prevents arterials blood from becoming venous". Felix Hoppe-Seyler independently published similar conclusions in the following year.^[8]

Advent of industrial chemistry

Carbon monoxide gained recognition as an essential reagent in the 1900s.^[5] Three industrial processes illustrate its evolution in industry. In the Fischer–Tropsch process, coal and related carbon-rich feedstocks are converted into liquid fuels via the intermediacy of CO. Originally developed as part of the German war effort to compensate for their lack of domestic petroleum, this technology continues today. Also in Germany, a mixture of CO and hydrogen was found to combine with olefins to give aldehydes. This process, called hydroformylation, is used to produce many large scale chemicals such as surfactants as well as specialty compounds that are popular fragrances and drugs. For example, CO is used in the production of vitamin A.^[10] In a third major process, attributed to researchers at Monsanto, CO combines with methanol to give acetic acid. Most acetic acid is produced by the Cativa process. Hydroformylation and the acetic acid syntheses are two of myriad carbonylation processes.

Physical and chemical properties

Carbon monoxide is the simplest oxocarbon and is isoelectronic with other triply-bonded diatomic species possessing 10 valence electrons, including the cyanide anion, the nitrosonium cation, boron monofluoride and molecular nitrogen. It has a molar mass of 28.0, which, according to the ideal gas law, makes it slightly less dense than air, whose average molar mass is 28.8.

The carbon and oxygen are connected by a triple bond that consists of a net two pi bonds and one sigma bond. The bond length between the carbon atom and the oxygen atom is 112.8 pm.^[11][12] This bond length is consistent with a triple bond, as in molecular nitrogen (N₂), which has a similar bond length (109.76 pm) and nearly the same molecular mass. Carbon–oxygen double bonds are significantly longer, 120.8 pm in formaldehyde, for example.^[13] The boiling point (82 K) and melting point (68 K) are very similar to those of N₂ (77 K and 63 K, respectively). The bond-dissociation energy of 1072 kJ/mol is stronger than that of N₂ (942 kJ/mol) and represents the strongest chemical bond known.^[14]

The ground electronic state of carbon monoxide is a singlet state^[15] since there are no unpaired electrons.