View source for Phosgene

{{Short description|Toxic gaseous compound (COCl2)}}
{{redirect|COCl2|the compound {{chem2|CoCl2}}|Cobalt(II) chloride}}
{{distinguish|phosphine|phosphene|oxalyl chloride|phosgene oxime}}
{{Chembox
| Watchedfields  = changed
| verifiedrevid  = 444050518
| Reference      = <ref>''[[Merck Index]]'', 11th Edition, '''7310'''.</ref>
| Name           = Phosgene
| ImageFile1_Ref = {{chemboximage|correct|??}}
| ImageFile      = Anhydrous_Liquid_Phosgene.png
| ImageCaption   = Liquified phosgene
| ImageFile1     = Phosgene-dimensions-2D.svg
| ImageFileL1    = 
| ImageClass1    = skin-invert-image
| ImageName1     = Full structural formula with dimensions
| ImageFile2     = Phosgene-3D-vdW.png
| ImageClass2    = bg-transparent
| ImageName2     = Space-filling model
| PIN            = Carbonyl dichloride<ref name=iupac2013>{{cite book |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book) |publisher=[[Royal Society of Chemistry]] |location=Cambridge |date=2014 |page=798 |isbn=978-0-85404-182-4 |doi=10.1039/9781849733069-FP001}}</ref>
| OtherNames     = {{ubl|Carbon dichloride oxide|Carbon oxychloride|Carbonyl chloride|CG|Chloroformyl chloride|Collongite|Dichloroformaldehyde|Dichloromethanal|Dichloromethanone}}
| Section1       = {{Chembox Identifiers
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 29365
| SMILES = ClC(Cl)=O
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 6131
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 117K140075
| InChI = 1/CCl2O/c2-1(3)4
| InChIKey = YGYAWVDWMABLBF-UHFFFAOYAH
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/CCl2O/c2-1(3)4
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = YGYAWVDWMABLBF-UHFFFAOYSA-N
| CASNo = 75-44-5
| CASNo_Ref = {{cascite|correct|CAS}}
| RTECS = SY5600000
| EINECS = 200-870-3
| UNNumber = 1076
| PubChem = 6371
}}
| Section2       = {{Chembox Properties
| Formula = {{chem2|COCl2}}
| C=1|O=1|Cl=2
| Appearance = Colorless gas
| Odor = Suffocating, like musty hay or grass<ref name=PGCH/>
| Density = 4.248{{nbsp}}g/L (15&nbsp;°C, gas)<br>1.432{{nbsp}}g/cm<sup>3</sup> (0&nbsp;°C, liquid)
| Solubility = Insoluble, hydrolyzes to [[Hydrogen chloride|hydrogen chloride]] and [[Carbon dioxide|carbon dioxide]].<ref>{{cite web |url=http://www.inchem.org/documents/icsc/icsc/eics0007.htm |title=PHOSGENE (cylinder) |work=Inchem (Chemical Safety Information from Intergovernmental Organizations) |publisher=International Programme on Chemical Safety and the European Commission}}</ref>
| SolubleOther = Soluble in [[benzene]], [[toluene]], [[acetic acid]]<br>Decomposes in [[alcohol (chemistry)|alcohol]] and [[acid]]
| MeltingPtC = −118
| BoilingPtC = 8.3
| VaporPressure = 1.6{{nbsp}}atm (20°C)<ref name=PGCH/>
| MagSus = −48·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
| Section3       = {{Chembox Structure
| MolShape = [[Trigonal planar]]
| Dipole = 1.17{{nbsp}}[[Debye|D]]
}}
| Section7       = {{Chembox Hazards
| ExternalSDS = [https://produkte.airliquide.de/gasekatalog/sdb/099-DE-DE-Phosgen.pdf]
| GHSPictograms = {{GHS05}}{{GHS06}}<ref name="GESTIS">{{GESTIS|ZVG=1340 |CAS=75-44-5 |Name=Phosgene |Date=16 March 2021 }}</ref>
| GHSSignalWord = '''Danger'''
| HPhrases = {{H-phrases|330|314}}<ref name=GESTIS/>
| PPhrases = {{P-phrases|260|280|303+361+353+315|304+340+315|305+351+338+315|403|405}}<ref name=GESTIS/>
| NFPA-H = 4
| NFPA-F = 0
| NFPA-R = 1
| FlashPt = [[Non-flammable]]
| TLV = 0.1{{nbsp}}[[Parts-per notation|ppm]] (1 ppm = 4 [[Milligram|mg]]/m<sup>3</sup>)
| PEL = TWA 0.1{{nbsp}}ppm (0.4{{nbsp}}mg/m<sup>3</sup>)<ref name=PGCH>{{PGCH|0504}}</ref>
| IDLH = 2{{nbsp}}ppm<ref name=PGCH/><br>1 ppm = 4 mg/m<sup>3</sup>
| REL = TWA 0.1{{nbsp}}ppm (0.4{{nbsp}}mg/m<sup>3</sup>) C 0.2{{nbsp}}ppm (0.8{{nbsp}}mg/m<sup>3</sup>) [15-minute]<ref name=PGCH/>
| LC50 = {{ubl|500{{nbsp}}ppm (human, 1{{nbsp}}min)|340{{nbsp}}ppm (rat, 30{{nbsp}}min)|438{{nbsp}}ppm (mouse, 30{{nbsp}}min)|243{{nbsp}}ppm (rabbit, 30{{nbsp}}min)|316{{nbsp}}ppm (guinea pig, 30{{nbsp}}min)|1022{{nbsp}}ppm (dog, 20{{nbsp}}min)|145{{nbsp}}ppm (monkey, 1{{nbsp}}min)|1{{nbsp}}ppm is 4{{nbsp}}mg/m<sup>3</sup>}}<ref name=IDLH>{{IDLH|75445|Phosgene}}</ref>
| LCLo = {{ubl|3{{nbsp}}ppm (human, 2.83{{nbsp}}h)|30{{nbsp}}ppm (human, 17{{nbsp}}min)|50{{nbsp}}ppm (mammal, 5{{nbsp}}min)|88{{nbsp}}ppm (human, 30{{nbsp}}min)|46{{nbsp}}ppm (cat, 15{{nbsp}}min)|50{{nbsp}}ppm (human, 5{{nbsp}}min)|2.7{{nbsp}}ppm (mammal, 30{{nbsp}}min)|1{{nbsp}}ppm is 4{{nbsp}}mg/m<sup>3</sup>}}<ref name=IDLH/>
}}
| Section8       = {{Chembox Related
| OtherCompounds = {{ubl|[[Thiophosgene]]|[[Formaldehyde]]|[[Carbonic acid]]|[[Urea]]|[[Carbon monoxide]]|[[Chloroformic acid]]|[[Phosgene oxime]]}}
}}
}}

'''Phosgene''' is an [[organic chemical compound]] with the [[chemical formula|formula]] {{chem2|COCl2}}. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass.<ref>[http://emedicine.medscape.com/article/832454-overview CBRNE - Lung-Damaging Agents, Phosgene] May 27, 2009</ref> It can be thought of chemically as the double [[acyl chloride]] analog of [[carbonic acid]], or structurally as [[formaldehyde]] with the hydrogen atoms replaced by chlorine atoms. In 2013, about 75–80 % of global phosgene was consumed for [[isocyanate]]s, 18% for [[polycarbonate]]s and about 5% for other [[fine chemicals]].<ref>{{Cite book |title=Best Available Techniques (BAT) reference document for the production of large volume organic chemicals |date=2017 |publisher= EU Publications Office |isbn=978-92-79-76589-6 |editor-last=Falcke |editor-first=Heino |location=Luxembourg |pages=443 |editor-last2=Holbrook |editor-first2=Simon |editor-last3=Clenahan |editor-first3=Iain |editor-last4=López Carretero |editor-first4=Alfredo |editor-last5=Sanalan |editor-first5=Teoman |editor-last6=Brinkmann |editor-first6=Thomas |editor-last7=Roth |editor-first7=Joze |editor-last8=Zerger |editor-first8=Benoit |editor-last9=Roudier |editor-first9=Serge}}</ref>

Phosgene is extremely poisonous and was used as a [[chemical weapon]] during [[World War I]], where it was [[Chemical weapons in World War I|responsible for 85,000 deaths]]. It is a highly potent pulmonary irritant and quickly filled enemy trenches due to it being a heavy gas.

It is classified as a [[List of Schedule 3 substances (CWC)|Schedule 3 substance]] under the [[Chemical Weapons Convention]]. In addition to its industrial production, small amounts occur from the breakdown and the [[combustion]] of [[Organochloride|organochlorine compounds]], such as [[chloroform]].<ref name=Ullmann>{{Ullmann |author1= Wolfgang Schneider |author2= Werner Diller |title= Phosgene |doi= 10.1002/14356007.a19_411}}</ref>

==Structure and basic properties==
Phosgene is a planar molecule as predicted by [[VSEPR theory]]. The C=O distance is 1.18&nbsp;[[angstrom (unit)|Å]], the C−Cl distance is 1.74&nbsp;Å and the Cl−C−Cl angle is 111.8°.<ref>{{cite journal |author1=Nakata, M. |author2=Kohata, K. |author3=Fukuyama, T. |author4=Kuchitsu, K. |title= Molecular Structure of Phosgene as Studied by Gas Electron Diffraction and Microwave Spectroscopy. The ''r<sub>z</sub>'' Structure and Isotope Effect |journal= [[Journal of Molecular Spectroscopy]] |year= 1980 |volume= 83 |pages= 105–117 |doi=10.1016/0022-2852(80)90314-8}}</ref> Phosgene is a [[carbon oxohalide]] and it can be considered one of the simplest acyl chlorides, being formally derived from [[carbonic acid]].{{cn|date=April 2025}}

== Production ==
Industrially, phosgene is produced by passing purified [[carbon monoxide]] and [[chlorine]] gas through a bed of porous [[activated carbon]], which serves as a [[catalyst]]:<ref name=Ullmann/>
:{{chem2|CO + Cl2 → COCl2}} (Δ''H''<sub>rxn</sub> = −107.6 kJ/mol)

This reaction is exothermic and is typically performed between 50 and 150&nbsp;°C. Above 200&nbsp;°C, phosgene reverts to carbon monoxide and chlorine, ''K''<sub>eq</sub>(300&nbsp;K) = 0.05. World production of this compound was estimated to be 2.74 million tonnes in 1989.<ref name=Ullmann/>

Phosgene is fairly simple to produce, but is listed as a [[List of Schedule 3 substances (CWC)|Schedule 3 substance]] under the [[Chemical Weapons Convention]]. As such, it is usually considered too dangerous to transport in [[Bulk cargo|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. Some batch production does still take place, but efforts are made to reduce the amount of phosgene stored.<ref>{{cite journal |last=Gowland |first=Richard |title=Applying inherently safer concepts to a phosgene plant acquisition |journal=Process Safety Progress |date=1996 |volume=15 |issue=1 |pages=52–57 |s2cid=110707551 |doi=10.1002/prs.680150113}}</ref>

=== Inadvertent generation ===
====Atmospheric chemistry====
Simple [[organochloride]]s slowly convert into phosgene when exposed to [[ultraviolet]] (UV) irradiation in the presence of [[oxygen]].<ref name=Singh>{{cite journal |last=Singh |first=Hanwant Bir |title=Phosgene in the ambient air |journal=Nature |date=December 1976 |volume=264 |issue=5585 |pages=428–429 |pmid=1004568 |bibcode=1976Natur.264..428S |s2cid=4209599 |doi=10.1038/264428a0}}</ref> Before the discovery of the [[ozone hole]] in the late 1970s large quantities of organochlorides were routinely used by industry, which inevitably led to them entering the atmosphere. In the 1970-80s phosgene levels in the [[troposphere]] were around 20-30 [[Parts-per notation#Mass fraction vs. mole fraction vs. volume fraction|parts per trillion]] by volume (peak 60 parts per trillion by volume).<ref name=Singh /> These levels had not decreased significantly nearly 30 years later,<ref>{{cite journal |last1=Fu |first1=Dejian |last2=Boone |first2=Chris D. |last3=Bernath |first3=Peter F. |last4=Walker |first4=Kaley A. |last5=Nassar |first5=Ray |last6=Manney |first6=Gloria L. |last7=McLeod |first7=Sean D. |title=Global phosgene observations from the Atmospheric Chemistry Experiment (ACE) mission |journal=Geophysical Research Letters |date=14 September 2007 |volume=34 |issue=17 |pages=L17815 |doi=10.1029/2007GL029942|bibcode=2007GeoRL..3417815F |s2cid=44164908 |doi-access=free }}</ref> despite organochloride production becoming restricted under the [[Montreal Protocol]].

Phosgene in the troposphere can last up to about 70 days and is removed primarily by hydrolysis with ambient humidity or cloudwater.<ref>{{cite journal |last1=Kindler |first1=T.P. |last2=Chameides |first2=W.L. |last3=Wine |first3=P.H. |last4=Cunnold |first4=D.M. |last5=Alyea |first5=F.N. |last6=Franklin |first6=J.A. |title=The fate of atmospheric phosgene and the stratospheric chlorine loadings of its parent compounds: CCl 4, C 2 Cl 4, C 2 HCl 3, CH 3 CCl 3, and CHCl 3 |journal=Journal of Geophysical Research: Atmospheres |date=20 January 1995 |volume=100 |issue=D1 |pages=1235–1251 |doi=10.1029/94JD02518|bibcode=1995JGR...100.1235K }}</ref> Less than 1% makes it to the [[stratosphere]], where it is expected to have a lifetime of several years, since this layer is much drier and phosgene decomposes slowly through UV [[Photodissociation|photolysis]]. It plays a minor part in [[ozone depletion]].

====Combustion====
[[Carbon tetrachloride]] ({{chem2|CCl4}}) can turn into phosgene when exposed to heat in air. This was a problem as carbon tetrachloride is an effective fire suppressant and was formerly in widespread use in [[fire extinguisher]]s.<ref name="Burke">{{cite book |last=Burke |first=Robert |title=Fire Protection: Systems and Response |date=2007-11-06 |publisher=CRC Press |isbn=978-0-203-48499-9 |pages=209}}</ref> There are reports of fatalities caused by its use to fight fires in [[confined space]]s.<ref>{{cite journal |last1=Fieldner |first1=A. C. |last2=Katz |first2=S. H. |last3=Kinney |first3=S. P. |last4=Longfellow |first4=E. S. |date=1920-10-01 |title=Poisonous gases from carbon tetrachloride fire extinguishers |url=https://www.sciencedirect.com/science/article/pii/S0016003220914941 |access-date=2022-02-03 |journal=Journal of the Franklin Institute |volume=190 |issue=4 |pages=543–565 |language=en |doi=10.1016/S0016-0032(20)91494-1|url-access=subscription }}</ref> Carbon tetrachloride's generation of phosgene and its own toxicity mean it is no longer used for this purpose.<ref name="Burke" />

====Biologically====
Phosgene is also formed as a metabolite of [[chloroform]], likely via the action of [[cytochrome P-450]].<ref>{{cite journal |last1=Pohl |first1=Lance R. |last2=Bhooshan |first2=B. |last3=Whittaker |first3=Noel F. |last4=Krishna |first4=Gopal |title=Phosgene: A metabolite of chloroform |journal=Biochemical and Biophysical Research Communications |date=December 1977 |volume=79 |issue=3 |pages=684–691 |pmid=597296 |doi=10.1016/0006-291X(77)91166-4}}</ref>

==History==
Phosgene was synthesized by the [[Cornish people|Cornish]] chemist [[John Davy (chemist)|John Davy]] (1790–1868) in 1812 by exposing a mixture of carbon monoxide and chlorine to [[sunlight]]. He named it "phosgene" from [[Greek language|Greek]] {{lang|grc|φῶς}} ({{lang|grc-Latn|phos}}, light) and {{lang|grc|γεννάω}} ({{lang|grc-Latn|gennaō}}, to give birth) in reference of the use of light to promote the reaction.<ref>{{cite journal |title= On a gaseous compound of carbonic oxide and chlorine |author= John Davy |journal= Philosophical Transactions of the Royal Society of London |volume= 102 |year= 1812 |pages= 144–151 |url= https://babel.hathitrust.org/cgi/pt?id=mdp.39015034564289;view=1up;seq=162 |doi= 10.1098/rstl.1812.0008 |jstor=107310|doi-access= free }} 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 {{lang|grc|φως}}, light, {{lang|grc|γινομαι}}, to produce, which signifies formed by light; ... "</ref> 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'''.<ref name=Ullmann/> Phosgenation of [[diol]]s give carbonates (R = [[Hydrogen|H]], [[alkyl]], [[aryl]]), which can be either linear or cyclic:
:{{chem2|''n'' HO\sCR2\sX\sCR2\sOH + ''n'' COCl2 → [\sO\sCR2\sX\sCR2\sO\sC(\dO)\s]_{''n''} + 2''n'' HCl}}
An example is the reaction of phosgene with [[bisphenol A]] to form [[polycarbonate]]s.<ref name="Ullmann" /> Phosgenation of diamines gives di-isocyanates, like [[toluene diisocyanate]] (TDI), [[methylene diphenyl diisocyanate]] (MDI), [[hexamethylene diisocyanate]] (HDI), and [[isophorone diisocyanate]] (IPDI). In these conversions, phosgene is used in excess to increase yield and minimize 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. Diisocyanates are precursors to [[polyurethanes]]. More than 90% of the 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 also used to produce monoisocyanates, used as pesticide precursors (''e.g.'' [[methyl isocyanate]] (MIC).

Aside from the widely used reactions described above, phosgene is also used to produce [[acyl chloride]]s from [[carboxylic acid]]s:
:{{chem2|R\sC(\dO)\sOH + COCl2 → R\sC(\dO)\sCl + HCl + CO2}}
For this application, [[thionyl chloride]] is commonly used instead of phosgene.

===Laboratory uses===
The synthesis of [[isocyanate]]s from amines illustrates the [[electrophilic]] character of this reagent and its use in introducing the equivalent [[synthon]] "CO<sup>2+</sup>":<ref>{{OrgSynth |author= R. L. Shriner, W. H. Horne, and R. F. B. Cox |title= p-Nitrophenyl Isocyanate |collvol= 2 |collvolpages= 453 |year= 1943 |prep= CV2P0453}}</ref>
:{{chem2|R\sNH2 + COCl2 → R\sN\dC\dO + 2 HCl}}, where R = [[alkyl]], [[aryl]]
Such reactions are conducted on laboratory scale in the presence of a base such as [[pyridine]] that neutralizes the [[hydrogen chloride]] side-product.

Phosgene is used to produce [[chloroformate]]s such as [[benzyl chloroformate]]:
:{{chem2|R\sOH + COCl2 → R\sO\sC(\dO)\sCl + HCl}}
In these syntheses, phosgene is used in excess to prevent formation of the corresponding [[carbonate ester]].

With [[amino acid]]s, phosgene (or its trimer) reacts to give [[amino acid N-carboxyanhydride]]s. More generally, phosgene acts to link two nucleophiles by a carbonyl group. For this purpose, alternatives to phosgene such as [[carbonyldiimidazole]] (CDI) are safer, albeit expensive.<ref>{{cite journal |last1=Bigi |first1=Franca |last2=Maggi |first2=Raimondo |last3=Sartori |first3=Giovanni |title=Selected syntheses of ureas through phosgene substitutes |journal=Green Chemistry |date=2000 |volume=2 |issue=4 |pages=140–148 |doi=10.1039/B002127J}}</ref> CDI itself is prepared by reacting phosgene with [[imidazole]].

Phosgene is stored in [[Gas cylinder|metal cylinders]]. In the US, the cylinder valve outlet is a tapered thread known as "[[Gas cylinder#Connection|CGA]] 160" that is used only for phosgene.

===Alternatives to phosgene===
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.<ref>Hamley, P. "Phosgene" ''Encyclopedia of Reagents for Organic Synthesis'', 2001 John Wiley, New York. {{doi |10.1002/047084289X.rp149}}</ref>

===Other reactions===
Phosgene reacts with [[water]] to release [[hydrogen chloride]] and [[carbon dioxide]]:
:{{chem2|COCl2 + H2O → CO2 + 2 HCl}}

Analogously, upon contact with ammonia, it converts to [[urea]]:
:{{chem2|COCl2 + 4 NH3 → CO(NH2)2 + 2 [NH4]Cl}}

Halide exchange with [[nitrogen trifluoride]] and [[aluminium tribromide]] gives [[carbonyl fluoride|{{chem2|COF2}}]] and [[carbonyl bromide|{{chem2|COBr2}}]], respectively.<ref name=Ullmann/>

===Chemical warfare===
{{Further|Chemical weapons in World War I|Second Italo-Ethiopian War}}
[[File:"Phosgene, smells like musty hay" (OHA 365), National Museum of Health and Medicine (5404773309).jpg|thumb|upright|US Army phosgene identification poster from [[World War II]]]]

It is listed on [[list of Schedule 3 substances (CWC)|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 Annex on Implementation and Verification ("Verification Annex")<!-- Bot generated title -->] {{webarchive|url=https://web.archive.org/web/20060515151142/http://www.opcw.org/html/db/cwc/eng/cwc_annex_verification_part_VIII.html |date=2006-05-15}}.</ref> Although less toxic than many other [[chemical weapon]]s 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 [[tabun (nerve agent)|tabun]], a first-generation [[nerve agent]].<ref>https://itportal.decc.gov.uk/cwc_files/S2AAD_guidance.pdf {{Webarchive|url=https://web.archive.org/web/20160304042624/https://itportal.decc.gov.uk/cwc_files/S2AAD_guidance.pdf |date=2016-03-04 }}.</ref>

Phosgene was first deployed as a chemical weapon by the French in 1915 in World War I.<ref>{{cite book |first=Mary Jo |last=Nye |year=1999 |page=193 |title=Before big science: the pursuit of modern chemistry and physics, 1800–1940 |publisher=Harvard University Press |isbn=0-674-06382-1}}</ref> It was also used in a mixture with an equal volume of chlorine, with the chlorine helping to spread the denser phosgene.<ref name="cbwinfo">{{cite web |author=Staff |year=2004 |url=http://cbwinfo.com/Chemical/Pulmonary/CG.shtml |title=Choking Agent: CG |publisher=CBWInfo |access-date=2007-07-30 |url-status=dead |archive-url=https://web.archive.org/web/20060218124704/http://cbwinfo.com/Chemical/Pulmonary/CG.shtml |archive-date=2006-02-18 }}</ref><ref>{{cite book |author=Kiester, Edwin |title=An Incomplete History of World War I |page=74 |volume=1 |publisher=Murdoch Books |year=2007 |isbn=978-1-74045-970-9 |display-authors=etal}}</ref> Phosgene was more potent than chlorine, though some symptoms took 24 hours or more to manifest.

Following the extensive use of phosgene during [[World War I]], it was stockpiled by various countries.<ref>[https://archive.today/20120713033614/http://lithgow.yourguide.com.au/news/local/news/general/chemical-warfare-left-its-legacy/1237570.aspx Base's phantom war reveals its secrets], ''Lithgow Mercury'', 7/08/2008</ref><ref>[http://lithgow.yourguide.com.au/news/local/news/general/chemical-warfare-left-its-legacy/1266856.aspx Chemical warfare left its legacy] {{Webarchive|url=https://web.archive.org/web/20081205064323/http://lithgow.yourguide.com.au/news/local/news/general/chemical-warfare-left-its-legacy/1266856.aspx |date=2008-12-05 }}, ''Lithgow Mercury'', 9/09/2008</ref><ref>[http://www.mustardgas.org/wp-content/uploads/Chemical-Warfare-Left-Its-Legacy.pdf Chemical bombs sit metres from Lithgow families for 60 years], ''The Daily Telegraph'', September 22, 2008</ref>

Phosgene was then only infrequently used by the [[Imperial Japanese Army]] against the [[Republic of China (1912–1949)|Chinese]] during the [[Second Sino-Japanese War]].<ref>Yuki Tanaka, "Poison Gas, the Story Japan Would Like to Forget", ''Bulletin of the Atomic Scientists'', October 1988, pp. 16–17</ref> Gas weapons, such as phosgene, were produced by the IJA's [[Unit 731]].

==Toxicology and safety==
[[File:Smelling Case of War Gases, Clifton Park Museum.jpg|thumb|A sample case of toxic gases used in chemical warfare; the leftmost contains phosgene in a sealed capillary]]
Phosgene is an insidious poison as the odor may not be noticed and symptoms may be slow to appear.<ref>{{cite journal |title= Phosgene exposure: mechanisms of injury and treatment strategies |author1=Borak J. |author2=Diller W. F. |journal= Journal of Occupational and Environmental Medicine |year= 2001 |volume= 43 |issue= 2 |pages= 110–9 |pmid= 11227628 |doi= 10.1097/00043764-200102000-00008|s2cid=41169682 }}</ref>

At low concentrations,  phosgene may have a pleasant odor of freshly mown hay or green corn,<ref>{{Cite web |last=CDC |date=2023-08-31 |title=Facts About Phosgene |url=https://emergency.cdc.gov/agent/phosgene/basics/facts.asp |access-date=2024-06-28 |website=emergency.cdc.gov |language=en-us}}</ref> but has also been described as sweet, like rotten banana peels.
The [[odor detection threshold]] for phosgene is 0.4 ppm, four times the [[threshold limit value]] (time weighted average). Its high [[toxicity]] arises from the action of the phosgene on the {{chem2|\sOH}}, {{chem2|\sNH2}} and {{chem2|\sSH}} groups of the [[protein]]s in pulmonary [[Pulmonary alveolus|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.<ref name=":0" /> Dose can be approximately calculated as "concentration" × "duration of exposure".<ref name=":0">Werner F. Diller, Early Diagnosis of Phosgene Overexposure.''Toxicology and Industrial Health, Vol.1, Nr.2, April 1985, p. 73 -80''</ref><ref>W. F. Diller, R. Zante : Zentralbl. Arbeitsmed. Arbeitsschutz Prophyl. Ergon. 32, (1982) 60 -368</ref> Therefore, persons in workplaces where there exists risk of accidental phosgene release usually wear indicator badges close to the nose and mouth.<ref name=":1" /> Such badges indicate the approximate inhaled dose, which allows for immediate treatment if the monitored dose rises above safe limits.<ref name=":1">W. F.Diller, E.Drope, E. Reichold: ''Ber. Int. Kolloq. Verhütung von Arbeitsunfällen und Berufskrankheiten Chem. Ind.6 th (1979) Chem. Abstr. 92 (1980) 168366x''</ref>

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 be detected by [[Radiography|X-ray imaging]] and regressive [[Oxygen saturation (medicine)|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 (nerve agent)|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.<ref>W. F. Diller: ''Radiologische Untersuchungen zur verbesserten Frühdiagnose von industriellen Inhalationsvergiftungen mit verzögertem Wirkungseintritt, Verlag für Medizin Dr. E. Fischer, Heidelberg. Zentralbatt für Arbeitsmedizin, Arbeitsschutz und Ergonomie, Nr. 3, Mai 2013, p. 160 - 163''</ref> Nearly 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.<ref>W.F. Diller, F. Schnellbächer, F. Wüstefeld : Zentralbl. Arbeitsmed. Arbeitsschutz Prophyl. 29 (1979) p.5-16</ref><ref>Results From the US Industry-Wide Phosgene Surveillance "The Diller Registry" : Journal of Occ. and Env. Med., March 2011-Vol.53-iss. 3 p.239- 244</ref> 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#Later years|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.<ref>{{cite web |publisher= [[International Programme on Chemical Safety]] |title= Phosgene: Health and Safety Guide |year= 1998 |url= http://www.inchem.org/documents/hsg/hsg/hsg106.htm}}</ref>

==Accidents==
* The first major phosgene-related incident happened in May 1928 when eleven tons of phosgene escaped from a war surplus store in central [[Hamburg]].<ref name=Ryan154/> Three hundred people were poisoned, of whom ten died.<ref name=Ryan154>{{cite book |title=Phosgene and Related Carbonyl Halides |url=https://archive.org/details/phosgenerelatedc00tary |url-access=limited |last=Ryan |first=T.Anthony |year=1996 |publisher= Elsevier |isbn=0444824456 |pages=[https://archive.org/details/phosgenerelatedc00tary/page/n200 154]–155}}</ref>
* In the second half of 20th century several fatal incidents implicating phosgene occurred in Europe, Asia and the US. Most of them have been investigated by authorities and the outcome made accessible to the public. For example, phosgene was initially [[blamed]] for the [[Bhopal disaster]], but investigations proved [[methyl isocyanate]] to be responsible for the numerous poisonings and fatalities.
* Recent major incidents happened in January 2010 and May 2016. An accidental release of phosgene gas at a [[DuPont (1802–2017)|DuPont]] facility in [[West Virginia]] killed one employee in 2010.<ref>{{Cite web|url=https://www.csb.gov/dupont-corporation-toxic-chemical-releases/|title=DuPont Corporation Toxic Chemical Releases &#124; CSB}}</ref> The [[U.S. Chemical Safety Board|US Chemical Safety Board]] released a video detailing the accident.<ref>{{Citation|title=Fatal Exposure: Tragedy at DuPont| date=22 September 2011 |url=https://www.youtube.com/watch?v=ISNGimMXL7M|language=en|access-date=2021-07-02}}</ref> Six years later, a phosgene leak occurred in a [[BASF]] plant in [[South Korea]], where a contractor inhaled a lethal dose of phosgene.<ref>Archived at [https://ghostarchive.org/varchive/youtube/20211205/ISNGimMXL7M Ghostarchive]{{cbignore}} and the [https://web.archive.org/web/20130104204718/http://www.youtube.com/watch?v=ISNGimMXL7M&feature=youtube_gdata Wayback Machine]{{cbignore}}: {{cite web| url = https://www.youtube.com/watch?v=ISNGimMXL7M| title = Fatal Exposure: Tragedy at DuPont | website=[[YouTube]]| date = 22 September 2011 }}{{cbignore}}</ref>
* [[2023 Ohio train derailment]]: A freight train carrying [[vinyl chloride]] derailed and burned in [[East Palestine, Ohio]], releasing phosgene and [[hydrogen chloride]] into the air and contaminating the [[Ohio River]].<ref>{{Cite web |date=February 11, 2023 |title=Ohio catastrophe is 'wake-up call' to dangers of deadly train derailments |url=https://www.theguardian.com/us-news/2023/feb/11/ohio-train-derailment-wake-up-call |website=The Guardian |access-date=February 13, 2023 |archive-date=February 13, 2023 |archive-url=https://web.archive.org/web/20230213091852/https://www.theguardian.com/us-news/2023/feb/11/ohio-train-derailment-wake-up-call |url-status=live }}</ref>

==See also==
{{Div col}}
* [[Bis(trifluoromethyl) disulfide]]
* [[Carbonyl bromide]]
* [[Carbonyl fluoride]]
* [[Oxalyl chloride]]
* [[Perfluoroisobutene]]
* [[Thionyl chloride]]
* [[Thiophosgene]]
{{Div col end}}

==References==

{{Reflist}}

==External links==
* [http://web.lemoyne.edu/~giunta/jdavy.html Davy's account of his discovery of phosgene]
* [http://www.inchem.org/documents/icsc/icsc/eics0007.htm International Chemical Safety Card 0007]
* [https://www.cdc.gov/niosh/topics/phosgene/ CDC - Phosgene - NIOSH Workplace Safety and Health Topic]
* [https://www.cdc.gov/niosh/npg/npgd0504.html NIOSH Pocket Guide to Chemical Hazards]
* [https://web.archive.org/web/20051017210254/http://www.bt.cdc.gov/agent/phosgene/ U.S. CDC Emergency Preparedness & Response]
* [https://web.archive.org/web/20040928025934/http://www.epa.gov/oppt/aegl/results7.htm U.S. EPA Acute Exposure Guideline Levels]
* [https://web.archive.org/web/20060515151142/http://www.opcw.org/html/db/cwc/eng/cwc_annex_verification_part_VIII.html Regime For Schedule 3 Chemicals And Facilities Related To Such Chemicals], OPCW website
* [https://web.archive.org/web/20081202060713/http://cbwinfo.com/Chemical/Pulmonary/CG.shtml CBWInfo website]
* [http://www.jlaw.com/Articles/NaziMedEx.html Use of Phosgene in WWII and in modern-day warfare]
* [https://www.youtube.com/watch?v=ISNGimMXL7M US Chemical Safety Board Video on accidental release at DuPont facility in West Virginia]

{{Chemical agents}}
{{U.S. chemical weapons}}
{{Authority control}}

[[Category:Acyl chlorides]]
[[Category:Inorganic carbon compounds]]
[[Category:Nonmetal halides]]
[[Category:Oxychlorides]]
[[Category:Carbon oxohalides]]
[[Category:Pulmonary agents]]
[[Category:Reagents for organic chemistry]]
[[Category:Chemical weapons in World War I]]