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(fŏs`jēn), colorless poison gaspoison gas,
any of various gases sometimes used in warfare or riot control because of their poisonous or corrosive nature. These gases may be roughly grouped according to the portal of entry into the body and their physiological effects.
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, first used during World War I by the Germans (1915). When dispersed in air, the gas has the odor of new-mowed hay. The gas is highly toxic; when inhaled it reacts with water in the lungs to form hydrochloric acid and carbon monoxide. Because the upper respiratory tract is little affected, warning signs of exposure are slight, and symptoms may fail to appear for from 2 to 24 hours after exposure. However, the release of hydrochloric acid in the lungs causes pulmonary edema and may also cause bronchial pneumonia and lung abscesses; in severe cases death may result within 36 hours. Phosgene is now used in chemical synthesis. It may be prepared by the reaction of carbon monoxide with chlorine in the presence of a catalyst or by the oxidation of chloroform or carbon tetrachloride. Phosgene has the formula COCl2.



(also carbonyl chloride, carbon oxychloride, chloroformyl chloride), COCl2, a colorless gas with an odor of moldy hay. Phosgene has a boiling point of 8.2°C and a melting point of – 118°C. The density of gaseous phosgene is 3.5 times that of air. Phosgene is sparingly soluble in water and freely soluble in organic solvents.

Gaseous phosgene is slowly hydrolyzed by moisture in the air; in water, hydrolysis is fairly rapid. The gas reacts with alcohols (ROH) to form chlorocarbonates (C1COOR) and carbonates (ROCOOR) and with salts of carboxylic acids to form anhydrides of the acids; it reacts with metal oxides to form halides of the metals (for example, A1C13), with ammonia to form mainly urea and NH4C1, and with amines to form arylated (alkylated) ureas CO(NHR’)2 and isocyanates. The formation of diphenylurea (R’ = C6H5), which is insoluble in water, is used in qualitative and quantitative determinations of phosgene. Phosgene reacts with dialkylanilines to form derivatives of the diphenylmethane and triphenylmethane series. The reactions described above are among the many phosgene reactions used in the commercial production of solvents, dyes, pharmaceuticals, and polycarbonates.

Phosgene is prepared by the interaction of CO and Cl2 over activated carbon.

Phosgene is highly toxic, affecting the lower reaches of the respiratory tract. It disturbs gas exchange, interferes with the oxygen supply, increases the viscosity and coagulability of the blood, and impedes circulation. Mild and moderately severe cases of acute poisoning take the form of toxic bronchitis; serious cases are accompanied by neural and psychic disorders (affective disorders, hallucinations, deafness, and, sometimes, motor excitation) and, typically, pulmonary edema. Repeated acute poisoning can result in asthenia, chronic bronchitis, pneumonia, pleurisy, and, eventually, bronchiectasis, pulmonary abscess, and gangrene of the lungs. First aid includes the administration of oxygen for an extended period, intravenous injection of solutions of calcium chloride and glucose, and washing of the mucosa with a 2-percent solution of sodium bicarbonate. Safety measures include the hermetic sealing of equipment, the use of gas masks and protective clothing, and the ventilation of work areas.

During World War I, phosgene was used as a choking war gas. Concentrations of the order of 0.005 mg/liter are dangerous, and concentrations of 0.1–0.3 mg/liter cause death within 15 min. Phosgene poisoning manifests itself only after a delay of 2–12 hours. Gas masks are used for protection.



(organic chemistry)
COCl2 A highly toxic, colorless gas that condenses at 0°C to a fuming liquid; used as a war gas and in manufacture of organic compounds.


a colourless easily liquefied poisonous gas, carbonyl chloride, with an odour resembling that of new-mown hay: used in chemical warfare as a lethal choking agent and in the manufacture of pesticides, dyes, and polyurethane resins. Formula: COCl2
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