Carbon monoxide
Encyclopedia : C : CA : CAR : Carbon monoxide
| Carbon monoxide | |
|---|---|
 
| |
| General | |
| Systematic name | Carbon monoxide |
| Other names | Carbonic oxide, Coal gas |
| Molecular formula | CO |
| Molar mass | 28.01 g/mol |
| Appearance | Colorless, odorless gas |
| CAS number | [630-08-0] |
| Properties | |
| Density and phase | 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 in water | 0.0026 g/100 ml (20°C) |
| in ethanol in methanol | Soluble |
| Melting point | -205°C (68 K) |
| Boiling point | -192°C (81 K) |
| Structure | |
| Molecular shape | Linear |
| Dipole moment | 0.112 D (3.74×10−31 C·m) |
| Hazards | |
| MSDS | External MSDS |
| EU classification | Highly flammable (F+) Repr. Cat. 1 Toxic (T) |
| NFPA 704 | |
| R-phrases | R12, R23, R33, R48, R61 |
| S-phrases | S9, S16, S33, S45, S53 |
| Flash point | Flammable gas |
| RTECS number | FG3500000 |
| Supplementary data page | |
| Structure & properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related oxides | carbon dioxide carbon suboxide dicarbon monoxide |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) [Chemical infoboxInfobox disclaimer and references] | |
Carbon monoxide, chemical formula CO, is a colorless, odorless, tasteless, and highly toxic gas. It is a major product of the incomplete combustion of carbon and carbon-containing compounds. Under ordinary conditions, it is less dense than air. During fires, it accumulates on the ground, so that if poisoning causes loss of consciousness, the amount of carbon monoxide inhaled increases and so fatality is radically increased. It is very slightly soluble in water and burns in air with a characteristic blue flame, producing carbon dioxide; it is a component of producer gas and water gas, which are widely used artificial fuels. It is a reducing agent, removing oxygen from many compounds and is used in the reduction of metals, e.g., iron , from their ores. At high pressures and elevated temperatures it reacts with hydrogen in the presence of a catalyst to form methanol. Carbon monoxide is formed by combustion of carbon in oxygen at high temperatures when there is an excess of carbon. It is also formed with a byproduct oxygen by decomposition of carbon dioxide at very high temperatures (above 2,000 °C), as the Ellingham diagram shows it is more stable oxide than CO2 in high temperatures. It is present in the exhaust of internal-combustion engines, such as those found in automobiles; and is generated in coal stoves, furnaces, and gas appliances functioning in low-oxygen environments (often due to insufficient ventilation.)
Polluting effect
Carbon monoxide from automobile and industrial emissions is a dangerous pollutant that 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.Toxicity
Carbon monoxide is dangerous and life-threatening to humans and other forms of air-breathing life, as inhaling even relatively small amounts of it can lead to hypoxic injury, neurological damage, and possibly death. A concentration of as little as 0.04% (400 parts per million) carbon monoxide in the air can be fatal. The gas is especially dangerous because it is not easily detected by human senses. Early symptoms of carbon monoxide poisoning include drowsiness and headache, followed by unconsciousness, respiratory failure, and death. First aid for a victim of carbon monoxide poisoning requires access to fresh air; administration of artificial respiration and, if available, oxygen; and, as soon as possible, medical attention.
When carbon monoxide is inhaled, it takes the place of oxygen in hemoglobin, the red blood pigment that normally carries oxygen to all parts of the body. Because carbon monoxide binds to hemoglobin several hundred times more strongly than oxygen, its effects are cumulative and long-lasting, causing oxygen starvation throughout the body. Prolonged exposure to fresh air (or pure oxygen) is required for the CO-tainted hemoglobin (carboxyhemoglobin) to clear.
The effects of carbon monoxide in parts per million are listed below:
- 35 ppm (0.0035%) Headache and dizziness within six to eight hours of constant exposure
- 100 ppm (0.01%) Slight headache in two to three hours
- 200 ppm (0.02%) Slight headache within two to three hours
- 400 ppm (0.04%) Frontal headache within one to two hours
- 800 ppm (0.08%) Dizziness, nausea, and convulsions within 45 minutes. Insensible within two hours.
- 1,600 ppm (0.16%) Headache, dizziness, and nausea within 20 minutes. Death in less than two hours.
- 3,200 ppm (0.32%) Headache, dizziness and nausea in five to ten minutes. Death within 30 minutes.
- 6,400 ppm (0.64%) Headache and dizziness in one to two minutes. Death in less than 20 minutes.
- 12,800 ppm (1.28%) Death in less than three minutes.
Carbon monoxide detectors for homes are now readily available and are increasingly being required by municipal building codes.
Physiological role
Carbon monoxide is produced naturally by the body. The breakdown-product of hemoglobin, heme, is a substrate for the enzyme heme oxygenase which produces CO and biliverdin. This is the only reaction in the body which produces CO.The biliverdin is converted to bilirubin by biliverdin reductase in macrophages of the reticuloendothelial system. The lipid soluble unconjugated bilirubin is transported in the blood bound to albumin, taken up by the hepatocytes, conjugated with glucuronic acid and transported into the bile canaliculi for excretion from the body.
The endogenously produced CO may have important physiological roles in the body (eg as a neurotransmitter).
History
Carbon monoxide was first prepared by the French chemist de Lassone in 1776 by heating zinc oxide with coke but thought it to be hydrogen by mistake as it burned with a blue flame. It was identified as a compound containing carbon and oxygen by the English chemist William 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 Two, 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 "producer gas". Carbon monoxide was also used as an extermination method during the Holocaust at some Nazi extermination camps.
Chemistry
The structure of the CO molecule is best described using molecular orbital theory. The length of the bond (0.111 nm) indicates that it has a partial triple bond character. The molecule has a small dipole moment and is often represented by three resonance structures:
Nitrogen is isoelectronic to carbon monoxide, which means it has the same electron configuration. This leads to some similarities in physical and chemical behavior.
Many other metals may form complexes containing covalently attached carbon monoxide, although many are not made directly from CO. For instance, boiling ruthenium trichloride with triphenyl phosphine in methoxyethanol (or DMF) gives [RuHCl(CO)(PPh3)3]. Nickel carbonyl is special as it form by the direct combination of carbon monoxide and nickel metal at room temperature. For this reason, pure nickel tubing and parts 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. [DOI]
As in nickel carbonyl and other carbonyls, the electron pair on the carbon interacts - or in lab jargon - is donated to the metal. In this case carbon monoxide is regarded as a carbonyl ligand.
Carbon monoxide is a major industrial gas that has many applications in bulk chemicals manufacturing, including the production of methanol by hydrogenation and aldehydes by the hydroformylation reaction. It is also used in the industrial production of phosgene.
Carbon monoxide and methanol react in the presence of a homogeneous rhodium catalyst and HI to give acetic acid in the Monsanto process, which is responsible for most of the industrial production of acetic acid.
In the presence of strong acids and water, carbon monoxide reacts with olefins to form carboxylic acids in another important process known as the Koch-Haaf reaction.
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. Carbon monoxide is created when carbon-containing fuels are burned incompletely. 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.
See also
Reference
External links
- [International Chemical Safety Card 0023]
- [National Pollutant Inventory - Carbon Monoxide]
- [NIOSH Pocket Guide to Chemical Hazards]
- [CID 281] from PubChem
- [United States Environmental Protection Agency Carbon Monoxide page]
- [External MSDS data sheet]
- [Carbon Monoxide Kills Campaign Site]
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
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