Carbon+Monoxide

Carbon monoxide (CO), also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It can be 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 however, it is short lived and spatially variable, since it combines with oxygen to form carbon dioxide and 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 (CO 2 ), such as when operating a stove or an internal combustion engine in an enclosed space. In the presence of oxygen, carbon monoxide burns with a blue flame, producing carbon dioxide. Coal gas, which was widely used before the 1960s for domestic lighting, cooking, and heating, had carbon monoxide as a significant constituent. Some processes in modern technology, such as iron smelting, still produce carbon monoxide as a byproduct.

Worldwide, the largest source of carbon monoxide is natural in origin, due to photochemical reactions in the troposphere that generate about 5 x 10 12 kilograms per year. 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, 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. Clinical trials of small amounts of carbon monoxide as a drug are on-going. ====

==="Carbon and oxygen together have a total of 10 [|valence electrons] in carbon monoxide. To satisfy the [|octet rule] for the carbon, the two atoms form a [|triple bond], with six shared electrons in three bonding molecular orbitals, rather than the usual double bond found in organic carbonyl compounds."===

===**Carbon monoxide is produced from partial oxidation of carbon containing compounds. It forms when there is not enough oxygen to produce Carbon dioxide (CO2). Carbon monoxide is one Carbon atom and 1 Oxygen atom connected by a triple bond that consists of 2 covalent bonds. Natural sources of CO are volcanoes, forest fires and other forms of combustion.**===

Industrial production
A major industrial source of CO is producer gas, a mixture containing mostly carbon monoxide and nitrogen, formed by combustion of carbon in air at high temperature 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/mol) Another source is " water gas ", a mixture of hydrogen and carbon monoxide produced via the endothermic reaction of steam and carbon: H2O + C → H2 + CO (ΔH = +131 kJ/mol) Other similar " synthesis gases " can be obtained from natural gas and other fuels. Carbon monoxide is also a byproduct of the reduction of metal oxide ores with carbon, shown in a simplified form as follows: MO + C → M + CO Since 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.

Laboratory preparation
Carbon monoxide is conveniently produced in the laboratory by the dehydration of formic acid, for example with sulfuric acid. Another method is heating an intimate mixture of powdered zinc metal and calcium carbonate, which releases CO and leaves behind zinc oxide and calcium oxide : Zn + CaCO3 → ZnO + CaO + CO

Coordination chemistry Most metals form coordination complexes containing covalently attached carbon monoxide. Only metals 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. This electron donation is also exhibited with the cis effect, or the the labilization of CO ligands in the cis position. 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 is used for the industrial purification of nickel in the Mond process.

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 2-methoxyethanol or DMF ) to afford IrCl(CO)(PPh 3 ) 2 . Metal carbonyls in coordination chemistry are usually studied using infrared spectroscopy.

Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is colourless, odorless, and tasteless, but highly toxic. It combines with [|hemoglobin] to produce carboxyhemoglobin, which is ineffective for delivering oxygen to bodily tissues. Concentrations as low as 667 ppm may cause up to 50% of the body's hemoglobin to convert to carboxyhemoglobin. A level of 50% carboxyhemoglobin may result in seizure, coma, and fatality. In the United States, the OSHA limits long-term workplace exposure levels above 50 ppm. Within short time scales, carbon monoxide absorption is cumulative, since the half-life is about 5 h in fresh air (see [|main article] ). The most common symptoms of carbon monoxide poisoning may resemble other types of poisonings and infections, including symptoms such as headache, nausea , [|vomiting] , [|dizziness] , [|fatigue] , and a feeling of weakness. Affected families often believe they are victims of food poisoning. Infants may be irritable and feed poorly. Neurological signs include confusion, disorientation, visual disturbance, [|syncope] and seizures. Some descriptions of carbon monoxide poisoning include retinal hemorrhages, and an abnormal cherry-red blood hue. In most clinical diagnoses these signs are seldom noticed. [|[22]] One difficulty with the usefulness of this the effect is that carbon monoxide merely corrects what would otherwise be an unhealthy appearance, since the chief effect of removing deoxygenated hemoglobin is to make an asphyxiated person appear more normal, or a dead person appear more life-like, similar to the effect of red colorants in embalming fluid. The "false" or unphysiologic red-coloring effect in anoxic CO-poisoned tissue is related to the meat-coloring commercial use of carbon monoxide, discussed below. Carbon monoxide binds to other molecules such as [|myoglobin] and [|mitochondrial] [|cytochrome oxidase]. Exposures to carbon monoxide may cause significant damage to the [|heart] and [|central nervous system], especially to the [|globus pallidus] ,often with long-term [|sequelae]. Carbon monoxide may have severe adverse effects on the [|fetus] of a pregnant woman. Carbon monoxide is known as a "silent killer." The carbon monoxide goes into the blood stream and displaces oxygen necessary for vital organs. It can eventually cause permanent brain damage and death.