carbon monoxide

a colorless, odorless, poisonous gas, CO, that burns with a pale-blue flame, produced when carbon burns with insufficient air: used chiefly in organic synthesis, metallurgy, and in the preparation of metal carbonyls, as nickel carbonyl.

[1870-75]

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Inorganic compound, a highly toxic, colourless, odourless, flammable gas, chemical formula CO. It is produced when carbon (including coal and coke) or carbon-containing fuel (including petroleum hydrocarbons; e.g., gasoline, fuel oil) does not burn completely to carbon dioxide, because of insufficient oxygen.

CO is present in the exhaust gases of internal combustion engines and furnaces. It is toxic because it binds to hemoglobin in blood much more strongly than does oxygen and thus interferes with transport of oxygen from lungs to tissues (see hypoxia; respiration). Symptoms of CO poisoning range from headache, nausea, and syncope to coma, weak pulse, respiratory failure, and death. CO is used industrially as a fuel and in synthesis of numerous organic compounds, including methanol, ethylene, and aldehydes.

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▪ chemical compound

      (CO), a highly toxic, colourless, odourless, flammable gas produced industrially for use in the manufacture of numerous organic and inorganic chemical products; it is also present in the exhaust gases of internal-combustion engines and furnaces as a result of incomplete conversion of carbon or carbon-containing fuels to carbon dioxide.

      Carbon monoxide's toxicity is a consequence of its absorption by red blood cells in preference to oxygen, thus interfering with the transport of oxygen from the lungs to the tissues, in which it is required. Indication of carbon monoxide poisoning include headache, weakness, dizziness, nausea, fainting, and, in severe cases, coma, weak pulse, and respiratory failure. Treatment must be prompt and includes respiratory assistance and the administration of oxygen, often with 5 percent carbon dioxide and sometimes under high pressure.

      For use in manufacturing processes, carbon monoxide is made by passing air through a bed of incandescent coke or coal, or by the reaction of natural gas with oxygen at high temperatures in the presence of a catalyst. The carbon monoxide resulting from these processes generally is contaminated with other substances, such as nitrogen or carbon dioxide, which may be removed if they are undesirable in the intended application.

      Carbon monoxide condenses to the liquid at -192° C (-314° F) and it freezes at -199° C (-326° F). It is only slightly soluble in water, and its physical properties closely resemble those of nitrogen.

      Carbon monoxide reacts with water vapour at high temperatures, forming carbon dioxide and hydrogen; this process has been used as a source of hydrogen for combination with nitrogen in the synthesis of ammonia. With caustic alkalies, carbon monoxide forms alkali formates, which can be converted into either formic acid or alkali oxalates for the production of oxalic acid. With certain metals, carbon monoxide forms compounds called carbonyls, many of which are volatile; this reaction has been used in the purification of nickel. Carbon monoxide and hydrogen are the starting materials in the manufacture of methanol and also are used in the preparation of aldehydes and alcohols from olefins and in making mixtures of liquid hydrocarbons suitable for use as fuels. Gas mixtures containing varying ratios of carbon monoxide and molecular hydrogen are called synthesis gas.

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