Carbon Monoxide [CO]

Carbon monoxide (CO) is one of the two important oxides of carbon.

Preparation. Carbon monoxide can be made by reacting carbon with a limited supply of oxygen: 2C + O₂ → 2CO. On an industrial scale, it is produced by reacting carbon with air; the resulting gas, still containing the nitrogen from the air, is called producer gas: 2C + O₂/N₂(air) → 2CO + N₂. This producer gas is passed through a copper(I) chloride solution under pressure, forming the complex CuCl(CO).2H₂O, from which pure carbon monoxide can be released again at reduced pressure. In the laboratory, pure CO is made by warming methanoic (formic) acid with concentrated sulphuric acid, which acts as a dehydrating agent: HCOOH + H₂SO₄ → CO + H₂SO₄.H₂O.

Properties. Carbon monoxide is a colourless, odourless and highly poisonous gas, only slightly soluble in water. It burns in air with a blue flame to give carbon dioxide: 2CO + O₂ → 2CO₂. Treated with chlorine in the presence of light or charcoal, it gives the poisonous gas carbonyl chloride (phosgene), used in the synthesis of isocyanates: CO + Cl₂ → COCl₂. It is a strong reducing agent, capable of reducing metal oxides to the free metal, e.g. 3CO + Fe₂O₃ → 2Fe + 3CO₂. Under high pressure and temperature, a mixture of CO and H₂ -- synthesis gas or syn gas -- gives methanol: CO + 2H₂ → CH₃OH; in the oxo process, CO and H₂ are reacted with ethene to give propanal: CO + C₂H₄ + H₂ → CH₃CH₂CHO. In the Fischer-Tropsch synthesis, carbon monoxide reacts with hydrogen at a pressure below 50 atm, using metal catalysts at 500-700 K, to give saturated and unsaturated hydrocarbons: nCO + (2n+1)H₂ → CₙH₍₂ₙ₊₂₎ + nH₂O and nCO + 2nH₂ → CₙH₂ₙ + nH₂O. Carbon monoxide also forms numerous metal carbonyl complexes with transition metals, in which the metal is in the zero oxidation state (e.g. nickel tetracarbonyl [Ni(CO)₄], iron pentacarbonyl [Fe(CO)₅], chromium hexacarbonyl [Cr(CO)₆]), obtained simply by heating the metal in an atmosphere of CO. …