| Carbon monoxide |
| Image:Carbon monoxide.jpg |
| General |
| Systematic name |
carbon monoxide |
| Other names |
carbonic oxide
coal gas |
| Molecular formula |
CO |
| Molar mass |
28.01 g/mol |
| Appearance |
colourless, odourless gas |
| CAS number |
[630-08-0] |
| Properties |
| Density and phase |
8.0 kg/cm3, liquid
1.145 g/cm3, gas at 298 K,
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 |
| Main hazards |
highly toxic,flammable |
| NFPA 704 |
   |
| Flash point |
? °C |
| R/S statement |
R: 12, 23, 33, 48, 61
S: 9, 16, 33, 45, 53 |
| 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 ? |
? |
| Related compounds |
carbon
methane
carbon dioxide |
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
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Carbon monoxide, chemical formula CO, is a colourless, odourless, flammable and highly toxic gas. It is a major product of the incomplete combustion of carbon and carbon-containing compounds.
Sources
Carbon monoxide has many common sources. The exhaust of the internal combustion engine, when burning a carbon-based fuel (i.e. almost any fuel except pure hydrogen) contains carbon monoxide, especially when the temperature is too low to effect complete oxidation of the hydrocarbons in the fuel to water and CO2, because the time (i.e., the residence time) available in the combustion chamber is too short, or because there is insufficient oxygen present. Usually, it is more difficult to design and operate a combustor for very low CO than for very low unburned hydrocarbons. Carbon monoxide is also present in small but significant concentrations in cigarette smoke. In the home, CO gas forms when fuels like natural gas, oil or wood do not burn completely in appliances such as furnaces and stoves, water heaters, ranges and ovens. Thus, common sources of carbon monoxide include leaky heat exchangers in furnaces; improperly or blocked vents for gas appliances, fireplaces and stoves; idling vehicles in attached or underground garages; or large collections of idling vehicles. Carbon monoxide gases can percolate through concrete hours after vehicles have left a garage.
In the past a significant source of CO was Town gas, used for illumination and heating from the 19th century. Town gas was made by passing steam through red-hot coke; the resultant reaction between the water and carbon generated a mixture of hydrogen and carbon monoxide. Town gas has now been replaced by natural gas (methane). Wood gas, the result of the incomplete combustion of wood, also contains carbon monoxide as a major component.
Toxicity
- For details, see Carbon monoxide poisoning.
Carbon monoxide is very dangerous.
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.
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:
Note that the octet rule is violated for the carbon atom in the two structures on the right.
The metal nickel forms a volatile compound with carbon monoxide, known as nickel carbonyl. The carbonyl decomposes readily back to the metal and gas, and this was used as the basis for the industrial purification of nickel.
Many other metals may form carbonyl complexes containing covalently attached carbon monoxide, these can be made by a range of different methods for instance boiling ruthenium trichloride with triphenyl phosphine in methoxyethanol (or DMF) the complex [RuHCl(CO)(PPh3)3] can be obtained. Nickel carbonyl is special as it can be formed by the direct combination of carbon monoxide and nickel metal at room temperature.
As in nickel carbonyl and other carbonyls, the electron pair on the carbon bonded to the metal. In this case carbon monoxide is regarded as a the carbonyl ligand.
Carbon monoxide and methanol are reacted together using a homogenous rhodium catalyst to form acetic acid in the Monsanto process which is responsible for most of the industrial production of acetic acid.
The CAS registry number of carbon monoxide is 630-08-0.
Carbon monoxide in the atmosphere
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.
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