Phosgene

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Phosgene
Image:Phosgene.png Image:Phosgene-3D-vdW.png
General
Systematic name	Carbonyl chloride
Other names	Carbonic acid dichloride
Molecular formula	COCl₂
SMILES	O=C(Cl)Cl
Molar mass	98.9 g mol⁻¹
Appearance	colorless gas
CAS number	[75-44-5]
Properties
Density and phase	4.248 g dm⁻³, gas (15 °C)
Solubility in water	Reacts
Melting point	−118 °C (155 K)
Boiling point	8 °C (281 K)
Structure
Molecular shape	Planar
Dipole moment	? D
Hazards
MSDS	http://www.vngas.com/pdf/g67.pdf
EU classification	Very toxic (T+)
NFPA 704	Image:NFPA 704.svg 0 4 1
R-phrases	R26, R34
S-phrases	S1/2, S9, S26, S36/37/39, S45
Flash point	non-flammable
RTECS number	SY5600000
Related compounds
Other anions	Carbonyl fluoride
Other cations	Nitrosyl chloride
Related compounds	Carbonic acid Urea Carbon monoxide Chloroformic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Phosgene is the chemical compound with the formula COCl₂. It is also known as carbonyl chloride, or its military designation CG. This highly toxic gas gained infamy as a chemical weapon during World War I but it is also a valuable industrial chemical.

Phosgene gas has no color but may appear as a white or yellowish haze when released into air. In lower concentrations its odor resembles recently cut hay or green corn (maize) while at higher concentrations it may be strong and unpleasant. The odor may not be noticed by all people exposed.

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 member of a class of organic chemicals known as alkylating agents. These agents can react with both DNA and with enzymes (polymerases) that are responsible for replication of DNA in cells. As such, it is considered to be a carcinogen, even at low exposure levels.

1 Production
2 Uses
3 History
4 Safety
5 References
6 External links

[edit] Production

Around 2 million tons produced annually<ref name="cbwinfo">http://cbwinfo.com/Chemical/Pulmonary/CG.shtml</ref> for use in the manufacture of isocyanates, polyurethane and polycarbonates, pesticides, herbicides and dyes.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, i.e. the reactor must be 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.

Upon ultraviolet radiation in the presence of oxygen, chloroform is converted into significant amounts of phosgene via a radical reaction. Brown glass flasks for chloroform prevent this reaction.

Because of safety issues, phosgene is almost always produced and consumed within the same chemical plant. It is listed on schedule 3 of the Chemical Weapons Convention: all production sites manufacturing more than 30 tonnes per year must be declared to the OPCW.<ref>http://www.opcw.org/html/db/cwc/eng/cwc_annex_verification_part_VIII.html</ref> Although much less dangerous than nerve agents, phosgene is still regarded as a chemical warfare agent.

[edit] Uses

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.

In the laboratory, the use of the gaseous phosgene has been supplanted by diphosgene (Chloroformic acid ester), which is a liquid at room temperature, or triphosgene, a crystalline substance.

[edit] History

Further information: Use of poison gas in World War I

Phosgene was synthesized by the chemist John Davy (1790-1868) in 1812 using sunlight on a mixture of carbon monoxide and chlorine. He named it in reference to use of light to promote the reaction; from Greek, phos (light) and gene (born). It gradually became important in the chemical industry as the 19th century progressed, particularly in the manufacture of dyes.

Phosgene was stockpiled as part of military arsenals until well after World War II, the United States only disposing of its stockpiles in 1969. Even before then the importance of phosgene as a weapon had declined as the more lethal nerve agents entered stockpiles.

[edit] Safety

Phosgene is an insidious poison as symptoms may be slow to appear. Like many reactive chlorides, gas combines with water in the tissues of the respiratory tract to form carbon dioxide and hydrochloric acid.

[edit] References

[edit] External links

Link page to external chemical sources.

Image:WMD-chemical.svg This article forms part of the series <center>Chemical warfare
Blood agents:	Cyanogen chloride (CK) – Hydrogen cyanide (AC)
Blister agents:	Lewisite (L) – Sulfur mustard gas (HD, H, HT, HL, HQ) – Nitrogen mustard gas (HN1, HN2, HN3)
Nerve agents:	G-Agents: Tabun (GA) – Sarin (GB) – Soman (GD) – Cyclosarin (GF) – GV \| V-Agents: VE – VG – VM – VX
Pulmonary agents:	Chlorine – Chloropicrin (PS) – Phosgene (CG) – Diphosgene (DP)
Incapacitating agents:	Agent 15 (BZ) – KOLOKOL-1
Riot control agents:	Pepper spray (OC) – CS gas – CN gas (mace) – CR gas	v • d • e</div>