|Preferred IUPAC name
Carbon dichloride oxide
3D model (JSmol)
CompTox Dashboard (EPA)
|COCl2, also CCl2O|
|Odor||Suffocating, like musty hay|
|Density||4.248g/L (15 °C, gas)|
1.432g/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||1.6atm (20°C)|
|Safety data sheet|||
|GHS Signal word||Danger|
|H280, H330, H314|
|P260, P280, P303+361+353+315, P304+340+315, P305+351+338+315, P403, P405|
|NFPA 704 (fire diamond)|
Threshold limit value (TLV)
|Lethal dose or concentration (LD, LC):|
LC50 (median concentration)
|500ppm (human, 1min)|
340ppm (rat, 30min)
438ppm (mouse, 30min)
243ppm (rabbit, 30min)
316ppm (guinea pig, 30min)
1022ppm (dog, 20min)
145ppm (monkey, 1min)
LCLo (lowest published)
|3ppm (human, 2.83h)|
30ppm (human, 17min)
50ppm (mammal, 5min)
88ppm (human, 30min)
46ppm (cat, 15min)
50ppm (human, 5min)
2.7ppm (mammal, 30min)
|NIOSH (US health exposure limits):|
|TWA 0.1ppm (0.4mg/m3)|
|TWA 0.1ppm (0.4mg/m3) C 0.2ppm (0.8mg/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).
|what is ?)(|
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.
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.
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" from Greek (phos, light) and (genna?, to give birth) in reference of the use of light to promote the reaction. It gradually became important in the chemical industry as the 19th century progressed, particularly in dye manufacturing.
The reaction of an organic substrate with phosgene is called phosgenation.
Diols react with phosgene to give either linear or cyclic carbonates (R = H, alkyl, aryl):
On an industrial scale, phosgene is used in excess to increase yield and avoid side reactions. The phosgene excess is separated during the work-up of resulting end products and recycled into the process, with any remaining phosgene decomposed in water using activated carbon as the catalyst.
In the research laboratory, due to safety concerns phosgene nowadays 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 previous reactions that are widely practiced industrially, phosgene is also used to produce acyl chlorides and carbon dioxide from carboxylic acids:
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 such as benzyl chloroformate:
In the synthesis of choroformates phosgene is used in excess to prevent formation of the corresponding carbonate ester.
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 for the production of aromatic di-isocyanates like toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI), which are precursors for production of polyurethanes and some polycarbonates. More than 90% of the worldwide produced phosgene is used in these processes, with the biggest production units located in the United States (Texas and Louisiana), Germany, Shanghai, Japan, and South Korea. The most important producers are Dow Chemical, Covestro, and BASF. Phosgene is used in the production of aliphatic diisocyanates such as hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI), which are precursors for the production of advanced coatings. Phosgene is also used to produce monoisocanates, used as pesticide precursors (e.g. methylisocyanate.)
Analogously, upon contact with ammonia, it converts to urea:
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.
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 pulmonary alveoli (the site of gas exchange), respectively forming ester, amide and thioester functional groups in accord with the reactions discussed above. This results in disruption of the blood-air barrier, eventually causing pulmonary edema. The extent of damage in the alveoli does not primarily depend on phosgene concentration in the inhaled air, with the dose (amount of inhaled phosgene) being the critical factor. Dose can be approximately calculated as "concentration" × "duration of exposure". Therefore, persons in workplaces where there exists risk of accidental phosgene release usually wear indicator badges close to the nose and mouth. Such badges indicate the approximate inhaled dose, which allows for immediate treatment if the monitored dose rises above safe limits. 
In case of low or moderate quantities of inhaled phosgene, the exposed person is to be monitored and subjected to precautionary therapy, then released after several hours. For higher doses of inhaled phosgene (above 150 ppm × min) a pulmonary edema often develops which can detected by X-ray imaging and regressive blood oxygen concentration. Inhalation of such high doses can eventually result in fatality within hours up to 2-3 days of the exposure.
The risk connected to a phosgene inhalation is based not so much on its toxicity (which is much lower in comparison to modern chemical weapons like sarin or tabun) but rather on its typical effects: the affected person may not develop any symptoms for hours until an edema appears, at which point it could be too late for medical treatment to assist. All fatalities as a result of accidental releases from the industrial handling of phosgene occurred in this fashion. On the other hand, pulmonary edemas treated in a timely manner usually heal in the mid- and longterm, without major consequences once some days or weeks after exposure have passed. Nonetheless, the detrimental health effects on pulmonary function from untreated, chronic low-level exposure to phosgene should not be ignored; although not exposed to concentrations high enough to immediately cause an edema, many synthetic chemists (e.g. Leonidas Zervas) working with the compound were reported to experience chronic respiratory health issues and eventual respiratory failure from continuous low-level exposure.
If accidental release of phosgene occurs in an industrial or laboratory setting, it can be mitigated with ammonia gas; in the case of liquid spills (e.g. of diphosgene or phosgene solutions) an absorbent and sodium carbonate can be applied.