Phosgene
From Wikipedia, the free encyclopedia
| Phosgene | |
|---|---|
  |
|
| General | |
| Systematic name | Carbonyl chloride |
| Other names | Carbonic acid dichloride CG |
| 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 | 1.17 D |
| Hazards | |
| MSDS | http://www.vngas.com/pdf/g67.pdf |
| EU classification | Very toxic (T+) |
| NFPA 704 |
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 is also a valuable industrial reagent and building block.
Phosgene gas has no color but may appear as a white or yellowish haze when released into air, due to refraction of light. In low 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. However, it is not considered to be a carcinogen. MSDS for the hazards of phosgene include:
"Highly toxic. Severe poison. Inhalation may be fatal. Odour does not give sufficient warning of lethal concentrations. Symptoms may be delayed up to 24 hours. Concentrations below 1 ppm may be harmful. Severe eye and skin irritant. Corrosive - may cause burns. Decomposes to further toxic compounds in the presence of water."
Contents |
[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).[1] It gradually became important in the chemical industry as the 19th century progressed, particularly in dye manufacturing.
Phosgene was stockpiled as part of military arsenals until well after World War II in the form of aerial bombs and mortar rounds[2], the United States 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] Production
Around 2 million tons are produced annually[3] 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, therefore the reactor must be cooled to carry away the heat it produces. Typically, the reaction is carried out between 50 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 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.[4] Although much less dangerous than nerve agents, phosgene is still regarded as a viable 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.[5] 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 gaseous phosgene has been supplanted by diphosgene (Chloroformic acid ester), a liquid at room temperature, or triphosgene, a crystalline substance. Despite being an efficient method of synthesizing acyl chloride from carboxylic acids, laboratory safety issues led to the use of its less toxic successor thionyl chloride.
[edit] Safety
Phosgene is an insidious poison as symptoms may be slow to appear.[6] Like many reactive chlorides, gas combines with water in the tissues of the respiratory tract to form hydrochloric acid.
Phosgene is stable when stored in a steel container, providing that the phosgene remains dry[7].
[edit] References
- ^ John Davy (1812). "On a Gaseous Compound of Carbonic Oxide and Chlorine". Philosophical Transactions of the Royal Society of London 102: 144-151.
- ^ FM 3-8 Chemical Reference handbook; US Army; 1967
- ^ http://cbwinfo.com/Chemical/Pulmonary/CG.shtml
- ^ http://www.opcw.org/html/db/cwc/eng/cwc_annex_verification_part_VIII.html
- ^ Hamley, P. "Phosgene" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley, New York, DOI: 10.1002/047084289X.rp149.
- ^ Borak J., Diller W. F. (2001). "Phosgene exposure: mechanisms of injury and treatment strategies". J Occup Environ Med 43 (2): 110-9. PMID 11227628.
- ^ FM 3-8 Chemical Reference handbook; US Army; 1967
[edit] External links
- Davy's account of his discovery of phosgene
- International Chemical Safety Card 0007
- NIOSH Pocket Guide to Chemical Hazards
- U.S. CDC Emergency Preparedness & Response
- U.S. EPA Acute Exposure Guideline Levels
- Regime For Schedule 3 Chemicals And Facilities Related To Such Chemicals, OPCW website
- CBWInfo website
- History of chemical warfare during World War I
- Use of Phosgene in WWII and in modern-day warfare (Refer to Section 4.C of the article)
 |
||
|---|---|---|
| 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 | Novichok agents | |
| 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 | |
