Editing Phosgene (section)

==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===
[[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]]]]
{{Further|Chemical weapons in World War I|Second Italo-Ethiopian War}}

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]].