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carbon monoxide, chemical compound, CO, a colorless, odorless, tasteless, extremely poisonous gas that is less dense than air under ordinary conditions. 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. At high pressures and elevated temperatures it reacts with hydrogen in the presence of a catalyst to form methanol, and under similar conditions reacts with methanol to produce acetic acid. It is also used in the production of polycarbonate and polyurethane as well as detergents. As a reducing agent, removing oxygen from many compounds, it is used in the reduction of metals, e.g., iron (see blast furnace), from their ores.
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 oxygen) by decomposition of carbon dioxide at very high temperatures (above 2,000℃). It is present in the exhaust of internal-combustion engines (e.g., in automobiles) and is generated in coal stoves, furnaces, and gas appliances that do not get enough air (because of a faulty draft or for other reasons).
Carbon monoxide is an extremely poisonous gas. Breathing air that contains as little as 0.1% carbon monoxide by volume can be fatal; a concentration of about 1% can cause death within a few minutes. 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, expert medical attention. When carbon monoxide is inhaled, it reacts with hemoglobin, the red blood pigment that normally carries oxygen to all parts of the body. Because carbon monoxide is attracted to the hemoglobin about 210 times as strongly as is oxygen, it takes the place of oxygen in the blood, causing oxygen starvation throughout the body. Carbon monoxide detectors for homes are now readily available.
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, react 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 (see smog). Carbon monoxide is also a constituent of tobacco smoke.
carbon monoxideA molecule, CO, consisting of an atom of oxygen bound to a carbon atom. It is commonly found in giant molecular clouds, where there is one CO molecule to about 10 000 hydrogen molecules. Collisions with hydrogen and other molecules easily excite the CO molecules and cause them to emit characteristic radio waves at wavelengths that are integer submultiples of 2.6 mm. Carbon monoxide is thus used in radio astronomy as the best tracer of molecular gas over wide areas: the molecular hydrogen in the cool clouds has no emission at radio wavelengths. The CO emission lines are analyzed to determine the density, velocity, and temperature of the molecules in the clouds.
CO, carbon (II) oxide, a compound of carbon and oxygen; a colorless, odorless gas. Carbon monoxide was first isolated in 1776, when the French physician J.-M.-F. de Lassone obtained CO by heating charcoal with zinc oxide. The density of carbon monoxide is 0.00125 g/cm3 at a temperature of 0°C and a pressure of 0.1 meganewton per sq m (MN/m2), or 1 kilogram-force per sq cm (kgf/cm2). The compound has a melting point of -205°C, a boiling point of - 191.5°C, a critical temperature of -140°C, and a critical pressure of 3.46 MN/m2 (34.6 kgf/cm2). Although the carbon atom in carbon monoxide formally has a + 2 oxidation state, the high stability of the CO molecule (the dissociation energy being 1,036 kilojoules per mole, or 247 kilocalories per mole) and the short internuclear distance (1.128 angstroms) strongly suggest that the oxygen and carbon atoms have a supplementary donor-acceptor bond (:).
Carbon monoxide is an oxide that does not form salts and does not react under ordinary conditions with water, acids, or alkalies. It is characterized by its reducing properties and tendency to undergo addition reactions. Thus, in the presence of light and catalysts, carbon monoxide combines with chlorine; upon heating, it combines with oxygen to form carbon dioxide (CO2). With sulfur, it forms carbonyl sulfide (COS), and with certain metals it forms metal carbonyls, for example, Ni(CO)4 and Fe(CO)5. At elevated temperatures, carbon monoxide reduces metal oxides to the free metals (Fe, Pb, Ni, Cu) and reacts with hydrogen to yield, depending on the reaction conditions, methane, a mixture of higher alcohols, aldehydes, or ketones.
Carbon monoxide is present in the atmosphere in very small amounts. It is encountered in the form of small inclusions in layers of hard coal. The compound is always formed from the combustion of carbon and carbon compounds when there is insufficient air, and it is present in significant amounts in flue gases, automotive-vehicle exhaust gases (2–10 percent by volume), and tobacco smoke (0.5–1 percent). Thus, it is a source of atmospheric pollution. Measures have been taken in many countries to reduce the concentration of carbon monoxide in the atmosphere of industrial cities.
Carbon monoxide is produced industrially by the reaction of red-hot coal with either carbon dioxide: C + CO2 = 2CO or steam: C + H2O = CO + H2. The producer gas and water gas obtained in the process are used as gaseous fuels. Carbon monoxide is obtained in the laboratory by heating formic acid with sulfuric acid at 100°C: HCOOH = H2O + CO.
Carbon monoxide is used in the chemical industry for the synthesis of alcohols, hydrocarbons, aldehydes, and organic acids, as well as for the production of synthetic liquid fuel.
Carbon monoxide poisoning is possible both in the workplace and at home. It can arise from working near blast furnaces or open-hearth furnaces or in foundries, from procedures of engine testing, and from using flue gases for drying and heating. Poisoning from this compound occurs in the chemical industry and in garages; the use of firewood for heating can also cause poisoning. Upon entering the organism through the respiratory organs, carbon monoxide reacts with hemoglobin to form carboxyhemoglo-bin, which does not possess the ability to transfer oxygen to the tissues. In addition, the coefficient of oxygen utilization by the tissues decreases. Hypocapnia, inhibition of the dissociation of oxyhemoglobin, and enzymatic disorders of tissue respiration result. The iron in blood plasma plays a protective role, forming a compound with carbon monoxide that hinders the formation of carboxyhemoglobin and facilitates the removal of carbon monoxide from the tissues.
With acute carbon monoxide poisoning, there is headache, vertigo, nausea, vomiting, asthenia, dyspnea, and rapid pulse. There can also be a rapid loss of consciousness, as well as convulsions, coma (with subsequent motor excitation), disorders relating to circulation and respiration, and damage to the optic nerve. Toxemic pneumonia may develop within two or three days. First aid calls for removing the victim into the open air, massaging the chest, administering ammonium hydroxide vapors, and providing a hot beverage. Chronic poisoning is accompanied by headache, vertigo, and insomnia; there is emotional instability, and the victim’s ability to remember and focus attention is adversely affected. Organic damage to the central nervous system, vasospasms, and an increase in the erythrocyte count in the blood are also possible. Preventive measures include monitoring the condition of gas lines and the amount of local ventilation, removing exhaust gases containing carbon monoxide from work areas, aerating buildings, conforming to safety rules in work involving explosives, and using gas masks. Regular medical examinations are recommended for workers exposed to the danger of carbon monoxide poisoning. In the home, poisoning can be prevented through the proper use of gas burners and furnaces.
A. A. KASPAROV
REFERENCESRemy, H. Kurs neorganicheskoi khimii, vol. 1. Moscow, 1972. (Translated from German.)
Akhmetov, N. S. Neorganicheskaia khimiia, 2nd ed. Moscow, 1975.
Tiunov, L. A., and V. V. Kustov. Toksikologiia okisi ugleroda. Leningrad, 1969.