Editing Sarin (section)

==Production and structure==
Sarin is a [[chirality (chemistry)|chiral]] molecule because it has four chemically distinct [[substituents]] attached to the [[tetrahedral molecular geometry|tetrahedral]] phosphorus center.<ref>{{cite book |last=Corbridge |first=D. E. C. |title=Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology |publisher=[[Elsevier]] |location=Amsterdam, Netherlands |date=1995 |isbn=0-444-89307-5}}</ref> The ''S<sub>P</sub> ''form (the [[Dextrorotation|(–) optical isomer]]) is the more active [[enantiomer]] due to its greater [[binding affinity]] to [[acetylcholinesterase]].<ref name=enantiomers1>{{cite journal |last1=Kovarik |first1=Zrinka |last2=Radić |first2=Zoran |last3=Berman |first3=Harvey A. |last4=Simeon-Rudolf |first4=Vera |last5=Reiner |first5=Elsa |last6=Taylor |first6=Palmer |title=Acetylcholinesterase active centre and gorge conformations analysed by combinatorial mutations and enantiomeric phosphonates |journal=[[Biochemical Journal]] |publisher=[[Portland Press]] |location=London, England |date=March 2003 |volume=373 |pages=33–40 |pmid=12665427 |issue=Pt. 1 |pmc=1223469 |doi=10.1042/BJ20021862}}</ref><ref name=enantiomers2>{{cite journal |title=Nerve agent stereoisomers: analysis, isolation and toxicology |last1=Benschop |first1=H. P. |last2=De Jong |first2=L. P. A. |journal=[[Accounts of Chemical Research]] |publisher=[[American Chemical Society]] |location=Washington DC |date=1988 |volume=21 |issue=10 |pages=368–374 |doi=10.1021/ar00154a003}}</ref> The P-F bond is easily broken by [[nucleophile|nucleophilic]] agents, such as water and hydroxide. At high [[pH|p''H'']], sarin decomposes rapidly to nontoxic [[phosphonic acid]] derivatives.<ref name=FAS/>

It is almost always manufactured as a [[racemic mixture]] (a 1:1 mixture of its enantiomeric forms) as this involves a much simpler [[chemical synthesis|synthesis]] while providing an adequate weapon.<ref name=enantiomers1/><ref name=enantiomers2/>

A number of production pathways can be used to create sarin. The final reaction typically involves attachment of the isopropoxy group to the phosphorus with an [[alcoholysis]] with [[isopropyl alcohol]]. Two variants of this final step are common. One is the reaction of [[methylphosphonyl difluoride]] with isopropyl alcohol, which produces a racemic mixture of sarin enantiomers with [[hydrofluoric acid]] as a byproduct:<ref name=FAS/>

:[[File:Sarin synth with racemic stereochemistry.png|class=skin-invert-image|415px]]

The second process, known as the "Di-Di" process, uses equimolar quantities of [[methylphosphonyl difluoride]] (Difluoro) and [[methylphosphonyl dichloride]] (Dichloro). This reaction gives sarin, [[hydrochloric acid]] and others minors byproducts. The Di-Di process was used by the United States for the production of its unitary sarin stockpile.<ref name=FAS>{{cite book |chapter=Chemical Weapons Technology |chapter-url=https://irp.fas.org/threat/mctl98-2/p2sec04.pdf |via=[[Federation of American Scientists]] |title=The Militarily Critical Technologies List Part II: Weapons of Mass Destruction Technologies (ADA 330102) |publisher=[[U.S. Department of Defense]] |author=Office of the Under Secretary of Defense for Acquisition and Technology |date=February 1998 |access-date=September 4, 2020}}</ref>

The scheme below shows a generic example that employs the Di-Di method as the final esterification step; in reality, the selection of reagents and reaction conditions dictate both product structure and yield. The choice of enantiomer of the mixed chloro fluoro intermediate displayed in the diagram is arbitrary, but the final substitution is selective for chloro over fluoro as the [[leaving group]]. Inert atmosphere and anhydrous conditions ([[Schlenk line#Techniques|Schlenk techniques]]) are used for synthesis of sarin and other organophosphates.<ref name=FAS/>

:[[File:Sarin-di-di-process-by-AHRLS-2011.png|class=skin-invert-image|500x500px|An example of "di-di" process using arbitrary reagents.|left|frameless]]{{clear-left}}

As both reactions leave considerable acid in the product, sarin produced in bulk by these methods has a short half life without further processing, and would be corrosive to containers and damaging to weapons systems. Various methods have been tried to resolve these problems. In addition to industrial [[refining]] techniques to purify the chemical itself, various additives have been tried to combat the effects of the acid, such as:
* [[Tributylamine]] was added to US sarin produced at [[Rocky Mountain Arsenal]].<ref name="auto">{{cite journal |title=Nerve Gas: America's Fifteen Year Struggle for Modern Chemical weapons |last=Kirby |first=Reid |date=January 2006 |journal=[[Army Chemical Review]] |url=http://www.wood.army.mil/chmdsd/images/pdfs/Jan-June%202006/Kirby-Nerve%20Gas.pdf |access-date=December 29, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20170211021417/http://www.wood.army.mil/chmdsd/images/pdfs/Jan-June%202006/Kirby-Nerve%20Gas.pdf |archive-date=February 11, 2017}}</ref>
* [[Triethylamine]] was added to UK sarin, with relatively poor success.<ref>{{cite book |title=The Determination of Free Base in Stabilised GB |publisher=UK Ministry of Supply |year=1956 |location=United Kingdom |url=https://apps.dtic.mil/sti/tr/pdf/AD0090924.pdf |url-status=live |access-date=March 20, 2024 |archive-url=https://web.archive.org/web/20140828035415/http://www.dtic.mil/dtic/tr/fulltext/u2/090924.pdf |archive-date=August 28, 2014}}</ref> The [[Aum Shinrikyo]] cult experimented with triethylamine as well.<ref>{{cite web |title=New Information Revealed By Aum Shinrikyo Death Row Inmate Dr. Tomomasa Nakagawa |last=Tu |first=Anthony |url=http://www.foi.se/Global/V%C3%A5ra%20tj%C3%A4nster/Konferenser%20och%20seminarier/CBW%20symposium/Proceedings/Tu.pdf}}</ref>
* [[N,N-Diethylaniline|''N'',''N''-Diethylaniline]] was used by Aum Shinrikyo for acid reduction.<ref>{{cite news |title=The Sarin Gas Attack in Japan and the Related Forensic Investigation |date=June 2001 |publisher=OPCW |last=Seto |first=Yasuo |url=https://www.opcw.org/media-centre/news/2001/06/sarin-gas-attack-japan-and-related-forensic-investigation}}</ref>
* [[N,N'-Diisopropylcarbodiimide|''N'',''N′''-Diisopropylcarbodimide]] was added to sarin produced at Rocky Mountain Arsenal to combat corrosion.<ref name="Chemical Agent Disposal">{{cite book |title=Chemical agent and munition disposal summary of the U.S. army's experience |publisher=United States Army |year=1987 |pages=B-30 |url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a193351.pdf |url-status=live |archive-url=https://web.archive.org/web/20150719010335/http://www.dtic.mil/dtic/tr/fulltext/u2/a193351.pdf |archive-date=July 19, 2015}}</ref>
* [[Isopropylamine]] was included as part of the [[M687]] 155&nbsp;mm field artillery shell, which was a [[binary chemical weapon|binary]] sarin weapon system developed by the US Army.<ref>{{cite news |last=Hedges |first=Michael |date=May 18, 2004 |title=Shell said to contain sarin poses questions for U.S. |work=[[Houston Chronicle]] |page=A1 |url=https://www.chron.com/news/nation-world/article/artillery-shell-with-sarin-poses-dilemma-for-u-s-1974450.php |access-date=December 30, 2015 |url-status=live |archive-url=https://web.archive.org/web/20151012210347/http://www.chron.com/news/nation-world/article/Artillery-shell-with-sarin-poses-dilemma-for-U-S-1974450.php |archive-date=October 12, 2015}}</ref>

Another byproduct of these two chemical processes is [[diisopropyl methylphosphonate]], formed when a second isopropyl alcohol reacts with the sarin itself and from disproportionation of sarin, when distilled incorrectly. The factor of its formation in esterification is that as the concentration of DF-DCl decreases, the concentration of sarin increases, the probability of DIMP formation is greater. DIMP is a natural impurity of sarin, that is almost impossible to be eliminated, mathematically, when the reaction is a 1 mol-1 mol "one-stream".<ref>cit-OPDC. The preparatory manual to chemical warfare. Vol 1: Sarin.</ref>

:{{chem2 | (CH3)2CHO- + CH3P(O)FOCH(CH3)2 -> CH3P(O)(OCH(CH3)2)2 + F- }}

This chemical degrades into isopropyl methylphosphonic acid.<ref>{{cite web |work=[[Agency for Toxic Substances and Disease Registry]] |title=Toxic Substances Portal – Diisopropyl Methylphosphonate (DIMP) |url=https://wwwn.cdc.gov/TSP/PHS/PHSLanding.aspx?id=967&tid=203}}</ref>