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|Preferred IUPAC name
Carbonyl dichloride 
Carbon dichloride oxide
3D model ( JSmol)
CompTox Dashboard (EPA)
|COCl2, also CCl2O|
|Molar mass||98.92 g/mol|
|Odor||Suffocating, like musty hay|
|Density||4.248 g/L (15 °C, gas)
1.432 g/cm3 (0 °C, liquid)
|Melting point||−118 °C (−180 °F; 155 K)|
|Boiling point||8.3 °C (46.9 °F; 281.4 K)|
|Solubility||Soluble in benzene, toluene, acetic acid
Decomposes in alcohol and acid
|Vapor pressure||1.6 atm (20°C)|
|Safety data sheet||ICSC 0007|
|R-phrases (outdated)||R26 R34|
|S-phrases (outdated)||(S1/2) S9 S26 S36/37/39 S45|
|NFPA 704 (fire diamond)|
Threshold limit value (TLV)
|Lethal dose or concentration (LD, LC):|
LC 50 ( median concentration)
|500 ppm (human, 1 min)
340 ppm (rat, 30 min)
438 ppm (mouse, 30 min)
243 ppm (rabbit, 30 min)
316 ppm (guinea pig, 30 min)
1022 ppm (dog, 20 min)
145 ppm (monkey, 1 min)
LC Lo ( lowest published)
|3 ppm (human, 2.83 h)
30 ppm (human, 17 min)
50 ppm (mammal, 5 min)
88 ppm (human, 30 min)
46 ppm (cat, 15 min)
50 ppm (human, 5 min)
2.7 ppm (mammal, 30 min)
|NIOSH (US health exposure limits):|
|TWA 0.1 ppm (0.4 mg/m3)|
|TWA 0.1 ppm (0.4 mg/m3) C 0.2 ppm (0.8 mg/m3) [15-minute]|
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|Y (what is YN ?)|
Phosgene is the organic chemical compound with the formula COCl2. It is a colorless gas; in low concentrations, its odor resembles that of freshly cut hay or grass. Phosgene is a valued industrial building block, especially for the production of precursors of polyurethanes and polycarbonate plastics.
Structure and basic properties
Phosgene is a planar molecule as predicted by VSEPR theory. The C=O distance is 1.18 Å, the C−Cl distance is 1.74 Å and the Cl−C−Cl angle is 111.8°. It is one of the simplest acyl chlorides, being formally derived from carbonic acid.
- CO + Cl 2 → COCl 2 (Δ H rxn = −107.6 kJ/mol)
This reaction is exothermic and is typically performed between 50 and 150 °C. Above 200 °C, phosgene reverts to carbon monoxide and chlorine, Keq(300 K) = 0.05. World production of this compound was estimated to be 2.74 million tonnes in 1989.
Phosgene is fairly simple to produce, but as a scheduled chemical weapon is usually considered too dangerous to transport in bulk quantities. Instead, phosgene is usually produced and consumed within the same plant, as part of an 'on demand' process. This involves maintaining equivalent rates of production and consumption, which keeps the amount of phosgene in the system at any one time fairly low, reducing the risks in the event of an accident.
Upon ultraviolet (UV) radiation in the presence of oxygen simple organochlorides such as chloroform slowly convert into phosgene. Phosgene is also formed as a metabolite of chloroform, likely via the action of cytochrome P-450.
Phosgene was synthesized by the Cornish chemist John Davy (1790–1868) in 1812 by exposing a mixture of carbon monoxide and chlorine to sunlight. He named it "phosgene" in reference of the 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 dye manufacturing.
Reactions and uses
The reaction of an organic substrate with phosgene is called phosgenation.
Synthesis of carbonates.
Diols react with phosgene to give either linear or cyclic carbonates (R = H, alkyl, aryl):
- HOCR 2−X−CR 2OH + COCl 2 → 1⁄n [OCR 2−X−CR 2OC(O)−] n + 2 HCl
- One example is the reaction of phosgene with bisphenol A.  to form Polycarbonates.
Synthesis of isocyanates
Such reactions are, on laboratory scale, conducted in the presence of a base such as pyridine that absorbs the hydrogen chloride. On industrial scale, phosgene is used in excess to increase yield and avoid side reactions. The excessive Phosgene is separated during the work-up of resulting end products and recycled to the process, remaining amounts of phosgene being decomposed with water, using activated carbon as a catalyst.
In the research laboratory phosgene finds limited use in organic synthesis. A variety of substitutes have been developed, notably trichloromethyl chloroformate ("diphosgene"), a liquid at room temperature, and bis(trichloromethyl) carbonate ("triphosgene"), a crystalline substance. Aside from the above reactions that are widely practiced industrially, phosgene is also used to produce acyl chlorides and carbon dioxide from carboxylic acids:
- RCO 2H + COCl 2 → RC(O)Cl + HCl + CO 2
Such acid chlorides react with amines and alcohols to give, respectively, amides and esters, which are commonly used intermediates. Thionyl chloride is more commonly and more safely employed for this application. A specific application for phosgene is the production of chloroformic esters:
- ROH + COCl 2 → ROC(O)Cl + HCl
Phosgene is stored in bulks and metal cylinders. The outlet of cylinders is always standard, a tapered thread that is known as CGA 160
Phosgene is used in industry preferably for the production of "aromatic" Diisocyanates like Toluenediisocyanate (TDI) and Methlyenediphenyldiisocyanate (MDI ), precursors for production of polyurethanes, and for the production of polycarbonate (PC), which is used for the production of advanced plastics like compact disks or eye lenses. More than 90% of the worldwide produced phosgene is being produced for these uses in a dimension of more than 3 Mio tons per year, the biggest production units are located in United Arabic Republic, USA (Tx and La), Germany, China (Shanghai area), Japan and South Korea. The most important producers are DOW, Covestro (Bayer outsource), and BASF. Another use is for production of "aliphatic" diisocyanates like Hexamethylenediisocyanate (HDI) and Isophoronediisocyanate (IPDI), precursors for the production of advanced coatings. One more important use is the production of monoisocanates like Methylisocyanate, precursors for the production of herbicides.
- COCl 2 + H 2O → CO 2 + 2 HCl
Analogously, upon contact with ammonia, it converts to urea:
- COCl 2 + 4 NH 3 → CO(NH 2) 2 + 2 NH 4Cl
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. Although less toxic than many other chemical weapons such as sarin, phosgene is still regarded as a viable chemical warfare agent because of its simpler manufacturing requirements when compared to that of more technically advanced chemical weapons such as the first-generation nerve agent tabun.
Phosgene was first deployed as a chemical weapon by the French in 1915 in World War I. It was also used in a mixture with an equal volume of chlorine, with the chlorine helping to spread the denser phosgene. Phosgene was more potent than chlorine, though some symptoms took 24 hours or more to manifest.
Toxicology and Safety
Phosgene is an insidious poison as the odor may not be noticed and symptoms may be slow to appear.
The odor detection threshold for phosgene is 0.4 ppm, four times the threshold limit value. Its high toxicity arises from the action of the phosgene on the OH-, NH2- and SH- groups of the proteins in the pulmonary alveoli, the site of gas exchange, forming ester-, amide-, and thioester functional groups in accord with the reactions discussed above. They disrupt the blood–air barrier, causing a lung edema. The extent of damage in the alveoli depends not primarily on the concentration of phosgene in the inhaled air, but on the dose (amount of inhaled phosgene), approximately "concentration" × "durance of exposition". Therefore, persons who may be exposed to phosgene in case of accidental releases usually wear indicator badges closely to nose and mouth, indicating the inhaled dose. This allows an immediate adequate therapy. In case of low or moderate quantities of inhaled phosgene the exposed person would be observed and be subjected to precautionary therapy and then released after several hours. In case of doses of inhaled phosgene above 150 ppm x min a pulmonary edema often develops, which can detected by X-ray and regressive oxygen concentration in the blood. Several hours after exposition, in some cases 2 to 3 days, inhalation can eventually result in a fatality. The risk connected to a phosgene inhalation is based not so much on its toxicity (modern chemical weapons like sarin or tabun are more toxic by far) but on its typical effects: the affected person may not develop any symptoms for hours, until finally an edema would develop and then be treated medically, and therapy could be too late. All fatalities that occurred connected to accidental releases with the industrial handling of phosgene went this way. On the other hand, pulmonary edemas, once survived, use to heal out mid - and longterm without consequences, only for some days or weeks lung function might be limited.
- The first major incident happened in May 1928, eleven tons of phosgene escaped from a war surplus store in central Hamburg. Three hundred people were poisoned, of whom ten died.
- In the second half of 20th century several fatal phosgene-related incidents happened in Europe, Asia and the US, most of them investigated by authorities and the outcome having been made accessible to the public. Phosgene was initially blamed for the Bhopal disaster, but investigations clearly resulted in methyl isocyanate being responsible for the numerous intoxications and fatalities.
- The last major incidents happened on January 23, 2010 and in May 2016: An accidental release of phosgene gas at a DuPont facility in West Virginia killed one employee. The US Chemical Safety Board released a video detailing the accident. On May 26, phosgene was released in a BASF plant in South Korea, a contractor inhaled a lethal dose of phosgene.
- Bhopal disaster
- Carbonyl bromide
- Carbonyl fluoride
- Oxalyl chloride
- Merck Index, 11th Edition, 7310.
- Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 798. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
- NIOSH Pocket Guide to Chemical Hazards. "#0504". National Institute for Occupational Safety and Health (NIOSH).
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- CBRNE - Lung-Damaging Agents, Phosgene May 27, 2009
- Wolfgang Schneider; Werner Diller. "Phosgene". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_411.
- Nakata, M.; Kohata, K.; Fukuyama, T.; Kuchitsu, K. (1980). "Molecular Structure of Phosgene as Studied by Gas Electron Diffraction and Microwave Spectroscopy. The rz Structure and Isotope Effect". Journal of Molecular Spectroscopy. 83: 105–117. doi:10.1016/0022-2852(80)90314-8.
- Singh, Hanwant Bir (December 1976). "Phosgene in the ambient air". Nature. 264 (5585): 428–429. doi:10.1038/264428a0.
- Pohl, Lance R.; Bhooshan, B.; Whittaker, Noel F.; Krishna, Gopal (December 1977). "Phosgene: A metabolite of chloroform". Biochemical and Biophysical Research Communications. 79 (3): 684–691. doi:10.1016/0006-291X(77)91166-4.
- John Davy (1812). "On a gaseous compound of carbonic oxide and chlorine". Philosophical Transactions of the Royal Society of London. 102: 144–151. doi:10.1098/rstl.1812.0008. JSTOR 107310. Phosgene was named on p. 151: " ... it will be necessary to designate it by some simple name. I venture to propose that of phosgene, or phosgene gas; from φως, light, γινομαι, to produce, which signifies formed by light; ... "
- R. L. Shriner, W. H. Horne, and R. F. B. Cox (1943). "p-Nitrophenyl Isocyanate". Organic Syntheses.CS1 maint: multiple names: authors list (link); Collective Volume, 2, p. 453
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- Annex on Implementation and Verification ("Verification Annex") Archived 2006-05-15 at the Wayback Machine.
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- Davy's account of his discovery of phosgene
- International Chemical Safety Card 0007
- CDC - Phosgene - NIOSH Workplace Safety and Health Topic
- 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
- Use of Phosgene in WWII and in modern-day warfare
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