Phosgene

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**Properties**
General

Name	Phosgene
Chemical formula	C O Cl₂
Appearance	Colourless gas
Physical
Formula weight	98.9 amu
Melting point	155 K (-118 °C)
Boiling point	281 K (8 °C)
Density	1.43 ×10³ kg/m³ (liquid)
Solubility	slowly decomposes in water
Thermochemistry
Δ_fH⁰_gas	-219.1 kJ/mol
Δ_fH⁰_liquid	? kJ/mol
Δ_fH⁰_solid	? kJ/mol
S⁰_{gas, 1 bar}	283.5 J/mol·K
S⁰_{liquid, 1 bar}	? J/mol·K
S⁰_solid	? J/mol·K
Safety
Ingestion	Nausea and vomiting may result.
Inhalation	Highly toxic, causes coughing, burning sensation in chest, severe exposure can result in bloody sputum, fatal destruction of lung tissue.
Skin	Irritant, may cause severe burns, especially on moist skin.
Eyes	May result in severe burns.
More info	Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals/7/6917.html)
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

Phosgene (also known as carbonyl chloride, C O Cl₂) is a highly toxic gas or refrigerated liquid that was used as a chemical weapon in World War I. It has no color, but is detectable in air by its odor, which resembles moldy hay. It is a manufactured chemical, but small amounts occur naturally from the breakdown of chlorinated compounds. Phosgene can also result from the combustion of chlorine-containing organic compounds.

Phosgene is a particularly insidious poison, as phosgene exposure often has no initial symptoms. Symptoms usually appear within 24 hours, but can take up to 72 hours to manifest. The gas combines with water in the tissues of the respiratory tract to form carbon dioxide and hydrochloric acid. The acid then dissolves the membranes in the lungs. Fluid fills the lungs, and death results from a combination of blood loss, shock, and respiratory failure. Unlike nerve agents, phosgene must be inhaled to cause harm and cannot be absorbed through the skin.

Production and use

Industrially, phosgene is produced by passing purified carbon monoxide and chlorine gas through a bed of highly porous carbon, which acts as a catalyst. The chemical equation for their reaction is

CO + Cl₂ → COCl₂

The reaction is exothermic, so the reactor must be continually cooled to carry away the heat it produces. Typically, the reaction is carried out between 50°C and 150°C. Above 200°C, phosgene decomposes back into carbon monoxide and chlorine.

Because of the safety issues with storing and transporting it, phosgene is almost always produced and consumed within the same chemical plant. Phosgene is used chiefly in the production of polymers including polyurethanes, polycarbonates, and polyureas. It is also used to produce isocyanates and acid chlorides as intermediates in the dye, pesticide, and pharmaceutical industries. It is possible to use phosgene to isolate certain metals including aluminium and uranium from their ores, but these methods are not widely used.

History

Phosgene was synthesized by the chemist John Davy (1790-1868) in 1812. It was first used as a weapon at in 1915 when the Germans added small quantities of it to chlorine to increase the latter's "efficiency". Soon after, use of pure phosgene was begun. Phosgene was responsible for most of the about 100,000 gas-caused deaths during World War I.

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