View source for CS gas

{{Short description|Chemical compound}}
{{About|the tear gas|the compound with the molecular formula CS|Carbon monosulfide}}
{{Good article}}
{{Use dmy dates|date=June 2020}}
{{Use British English|date=November 2013}} 
{{Chembox
| data page pagename = none
| Watchedfields = changed
| verifiedrevid = 451284250
| ImageFile = CS gas.svg
| ImageClass = skin-invert-image
| ImageSize = 
| ImageName = Skeletal formula of CS gas
| ImageFile1 = CS-gas-3D-vdW.png
| ImageClass1 = bg-transparent
| ImageSize1 = 
| ImageName1 = Space-filling model of CS gas
| PIN = [(2-Chlorophenyl)methylidene]propanedinitrile
| OtherNames = 2-(2-Chlorobenzylidene)malononitrile<br />2-Chlorobenzalmalononitrile<br />''o''-Chlorobenzylidene malononitrile<br />Tear gas<!--OCBM <br />TL-238 <br />EA-1779 unchecked unsourced-->
<!-- 2022-01-05: from CS gas (data page), unchecked unsourced so no showing here. {{ubl|2-Chlorobenzalmalononitrile|(''o''-Chlorobenzal)malononitrile|''o''-Chlorobenzylidenemalonic nitrile|2-Chlorobenzylidenemaloninitrile|(''o''-Chlorobenzylidene)malonitrile|2-Chlorobenzylidenemalononitrile|2-(2-Chlorobenzylidene)malononitrile|(''o''-Chlorobenzylidene)malononitrile|''ortho''-Chlorobenzylidenemalononitrile|2-2-Chlorobenzylidenepropanedinitrile|2-Chloro BMN|β,β-Dicyano-''o''-chlorostyrene|NCI-C55118|Tear gas|USAF KF-11}} --->
|Section1={{Chembox Identifiers
| IUPHAR_ligand = 4158
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 16644
| PubChem = 17604
| EC_number = 220-278-9
| RTECS = OO3675000
| UNNumber = 2810, 3276, 2811
| UNII = D8317IAV7Q
| ChEMBL = 1256101
| InChI = 1/C10H5ClN2/c11-10-4-2-1-3-9(10)5-8(6-12)7-13/h1-5H
| InChIKey = JJNZXLAFIPKXIG-UHFFFAOYAA
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 2698-41-1
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C10H5ClN2/c11-10-4-2-1-3-9(10)5-8(6-12)7-13/h1-5H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = JJNZXLAFIPKXIG-UHFFFAOYSA-N
| SMILES = Clc1ccccc1\C=C(/C#N)C#N
}}
|Section2={{Chembox Properties
| Formula = C<sub>10</sub>H<sub>5</sub>ClN<sub>2</sub><ref name="USArmy">{{cite web | last = Williams | first = Kenneth E. | name-list-style = vanc | url = http://www.waco93.com/detcs.pdf | archive-url = https://web.archive.org/web/20070926011533/http://www.waco93.com/detcs.pdf  | archive-date = 26 September 2007 | title = Detailed Facts About Tear Agent O-Chlorobenzylidene Malononitrile (CS)] | work = U.S. Army Center for Health Promotion and Preventive Medicine }}</ref>
| MolarMass = 188.6&nbsp;g/mol<ref name=UweHeinrich>{{cite web | vauthors = Heinrich U | url = http://www.veritagiustizia.it/docs/gas_cs/CS_Effects_Waco.pdf | title = Possible lethal effects of CS tear gas on Branch Davidians during the FBI raid on the Mount Carmel compound near Waco, Texas | date = September 2000 | access-date = 23 September 2007 | archive-date = 25 December 2014 | archive-url = https://web.archive.org/web/20141225230238/http://www.veritagiustizia.it/docs/gas_cs/CS_Effects_Waco.pdf | url-status = live }}</ref>
| Appearance = White crystalline powder<br />Colourless gas when burned
| Odor = Pepper-like<ref name=PGCH />
| Density = 1.04&nbsp;g/cm<sup>3</sup>
| MeltingPtC = 93
| MeltingPt_notes =
| BoilingPtC = 310
| BoilingPt_ref = <ref>{{cite book|url=https://books.google.com/books?id=y2FwGRVMW5kC&pg=PA138|page=138|title=Compendium of Chemical Warfare Agents|author=Hoenig, Steven L.|publisher=Springer|year=2006|isbn=978-0-387-34626-7}}</ref>
| VaporPressure = 3.4×10<sup>−5</sup>{{nbsp}}[[mmHg]] at 20&nbsp;°C
| Solubility = Insoluble
 }}
|Section7={{Chembox Hazards
| NFPA-H = 2
| NFPA-F = 1
| NFPA-R = 0
| GHSPictograms = {{GHS05}}{{GHS06}}{{GHS07}}{{GHS08}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|302|314|330|335|372|410}}
| PPhrases = {{P-phrases|260|261|264|270|271|273|280|284|301+312|301+330+331|303+361+353|304+340|305+351+338|310|312|314|320|321|330|363|391|403+233|405|501}}
| PEL = TWA 0.05{{nbsp}}ppm (0.4{{nbsp}}mg/m<sup>3</sup>)<ref name=PGCH>{{PGCH|0122}}</ref>
| IDLH = 2{{nbsp}}mg/m<sup>3</sup><ref name=PGCH />
| REL = C 0.05{{nbsp}}ppm (0.4{{nbsp}}mg/m<sup>3</sup>) [skin]<ref name=PGCH />
| LCLo = {{ubl
 | 1806{{nbsp}}mg/m<sup>3</sup> (rat, 45{{nbsp}}min)
 | 2753{{nbsp}}mg/m<sup>3</sup> (mouse, 20{{nbsp}}min)
 | 1802{{nbsp}}mg/m<sup>3</sup> (rabbit, 10{{nbsp}}min)
 | 2326{{nbsp}}mg/m<sup>3</sup> (guinea pig, 10{{nbsp}}min)<ref>{{IDLH|2698411|o-Chlorobenzylidene malononitrile}}</ref>
 }}
}}
|Section8={{Chembox Related
| OtherCompounds = [http://www.aist.go.jp/RIODB/SDBS/cgi-bin/direct_frame_top.cgi?lang=eng SDBS]
5-chloro-2-quinolinecarbonitrile <br /> 6-chloro-2-quinolinecarbonitrile <br /> 7-chloro-2-quinolinecarbonitrile}}
}}

The compound '''2-chlorobenzalmalononitrile''' (also called '''''o''-chlorobenzylidene malononitrile'''; chemical formula: C<sub>10</sub>H<sub>5</sub>ClN<sub>2</sub>), a [[cyanocarbon]], is the defining component of the [[lachrymatory agent]] commonly referred to as '''CS gas''', a [[tear gas]] which is used as a [[riot control agent]], and is banned for use in warfare due to the [[1925 Geneva Protocol]].

Exposure causes a burning sensation and tearing of the eyes to the extent that the subject cannot keep their eyes open, and a burning irritation of the mucous membranes of the nose, mouth and throat, resulting in profuse coughing, nasal mucus discharge, disorientation, and difficulty breathing, partially incapacitating the subject. CS gas is an [[aerosol]] of a [[volatility (chemistry)|volatile]] [[solvent]] (a substance that dissolves other active substances and that easily evaporates) and 2-chlorobenzalmalononitrile, which is a solid compound at room temperature. CS gas is generally accepted as being [[Non-lethal force|non-lethal]].

==History==
CS gas was first [[Chemical synthesis|synthesized]] by two Americans, Ben Corson and Roger Stoughton,<ref name=corson28>{{cite journal| last1 = Corson| first1 = Ben B.| last2 = Stoughton| first2 = Roger W. | name-list-style = vanc | year = 1928| title = Reactions of Alpha, Beta-Unsaturated Dinitriles| journal = Journal of the American Chemical Society| volume = 50| issue = 10| pages = 2825–2837 | doi = 10.1021/ja01397a037}}</ref> at [[Middlebury College]] in [[Vermont]] in 1928, and the chemical's name is derived from the first letters of the scientists' surnames.<ref>{{OED|CS}}</ref><ref name="Name">"[http://columbia.thefreedictionary.com/Cs CS, chemical compound] {{Webarchive|url=https://web.archive.org/web/20051219182423/http://columbia.thefreedictionary.com/Cs |date=19 December 2005 }}". [http://columbia.thefreedictionary.com/ columbia.thefreedictionary.com] {{Webarchive|url=https://web.archive.org/web/20050729031936/http://columbia.thefreedictionary.com/ |date=29 July 2005 }}. Retrieved on 23 September 2007.</ref>

CS was developed and tested secretly at [[Porton Down]] in [[Wiltshire]], UK, in the 1950s and '60s. CS was used first on animals, and subsequently on [[British Army]] servicemen volunteers. CS has less effect on animals because they have different tear ducts and, in the case of non-human mammals, their fur inhibits the free entry of the gas.<ref name=Zarc>"[http://www.zarc.com/english/tear_gases/csmain.html Orthochlorobenzylidenemalononitrile ClC6H4CHCCN(CN)2] {{Webarchive|url=https://web.archive.org/web/20061128091426/http://www.zarc.com/english/tear_gases/csmain.html |date=28 November 2006 }}". Zarc International. Retrieved on 23 September 2007</ref>

As recently as 2002, the U.S. State Department [[Bureau of International Security and Nonproliferation]] of [[Colin Powell]] made a firm distinction between "riot-control agents" such as CS gas, and "lethal chemical weapons." The Bureau cited support for this position from the U.K. and Japan.<ref name=s2002>{{cite web |url=https://2009-2017.state.gov/t/isn/4784.htm |title=Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases and of Bacteriological Methods of Warfare (Geneva Protocol) |publisher=U.S. Department of State |date=25 September 2002 |access-date=24 August 2013}}</ref>

The use of CS in warfare has been prohibited under the [[Chemical Weapons Convention]].<ref>{{Cite web |title=Article II – Definitions and Criteria |url=https://www.opcw.org/chemical-weapons-convention/articles/article-ii-definitions-and-criteria |access-date=2024-11-25 |website=OPCW |language=en}}</ref> The [[OPCW]] (the governing body of the convention) has observed its use in the [[Russo-Ukrainian War]] in 2024.<ref>{{Cite web |title=OPCW issues report on its Technical Assistance Visit to Ukraine following an alleged incident of use of toxic chemicals as a weapon |url=https://www.opcw.org/media-centre/news/2024/11/opcw-issues-report-its-technical-assistance-visit-ukraine-following |access-date=2024-11-25 |website=OPCW |language=en}}</ref><ref>{{Cite web |date=2024-11-18 |title=Tear gas used on Ukraine battlefield, chemical weapons agency finds |url=https://www.reuters.com/world/europe/tear-gas-used-ukraine-battlefield-chemical-weapons-agency-finds-2024-11-18/ |publisher=[[Reuters]]}}</ref>

== Production ==
CS is [[Chemical synthesis|synthesized]] by the reaction of [[2-Chlorobenzaldehyde|2-chlorobenzaldehyde]] and [[malononitrile]] via the [[Knoevenagel condensation]]:
[[File:CS-Gas-Synthese.svg|422x422px|thumb|Preparation of CS|left]]
::ClC<sub>6</sub>H<sub>4</sub>CHO + [[Malononitrile|H<sub>2</sub>C(CN)<sub>2</sub>]] → ClC<sub>6</sub>H<sub>4</sub>CHC(CN)<sub>2</sub> + H<sub>2</sub>O

The reaction is catalysed with a weak base like [[piperidine]] or [[pyridine]]. The production method has not changed since the substance was discovered by Corson and Stoughton.<ref name="corson">{{cite journal|vauthors= Corson BB, Stoughton RW| title=Reactions of Alpha, Betha-Unsaturated Dinitriles|journal=J Am Chem Soc|year= 1928|volume=50|pages=2825–2837|doi=10.1021/ja01397a037|issue= 10}}</ref> Other bases, solvent free methods and [[microwave]] promotion have been suggested to improve the production of the substance.<ref>{{cite journal|vauthors= Pande A, Ganesan K, Jain AK, Gupta PK, Malhotr RC| title=Novel Eco-Friendly Process for the Synthesis of 2-Chlorobenzylidenemalononitrile and ITS Analogues Using Water As a Solvent|journal=Org Proc Res Develop|year= 2005|volume=9|pages=133–136| doi=10.1021/op0498262|issue= 2}}</ref>

The physiological properties had been discovered already by the chemists first synthesising the compound in 1928:
"Physiological Properties. Certain of these dinitriles have the effect of sneeze and tear gases. They are harmless when wet but to handle the dry powder is disastrous."<ref name="corson" />

=== Use as an aerosol ===

As 2-chlorobenzalmalononitrile is a solid at room temperature, not a [[gas]], a variety of techniques have been used to make this solid usable as an [[aerosol]]:

* Melted and sprayed in the molten form.
* Dissolved in organic solvent.
* CS2 dry powder (CS2 is a [[Adsorption#Silica_gel|siliconized]], micro-pulverized form of CS).
* CS from thermal grenades by generation of hot gases.<ref name=UweHeinrich />

In the [[Waco Siege]] in the United States, CS was dissolved in the organic solvent [[dichloromethane]] (also known as methylene chloride). The solution was dispersed as an [[aerosol]] via explosive force and when the highly volatile dichloromethane evaporated, CS crystals precipitated and formed a fine dispersion in the air.<ref name=UweHeinrich />

== Effects ==
[[File:Tear gas shells used in istanbul in 2013.jpg|250px|thumb|CS gas shells used in Taksim Gezi Park, Istanbul in May 2013]]
Many types of tear gas and other riot control agents have been produced with effects ranging from mild tearing of the eyes to immediate [[nausea|vomiting]] and [[prostration]]. [[CN gas|CN]] and CS are the most widely used and known, but around 15 different types of tear gas have been developed worldwide, e.g. [[adamsite]] or [[bromoacetone]], CNB, and CNC. CS has become the most popular due to its strong effect. The effect of CS on a person will depend on whether it is packaged as a solution or used as an [[aerosol]]. The size of solution droplets and the size of the CS [[particulate]]s after evaporation are factors determining its effect on the human body.<ref name="Ineffective">"[https://web.archive.org/web/20060524072325/http://www.ipcc.gov.uk/safer_restraint_june2003.pdf Safer Restraint: A report of the conference held in April 2002 at Church House, Westminster]." ''Police Complaints Authority.'' Retrieved on 23 September 2007</ref>

The chemical reacts with moisture on the skin and in the eyes, causing a burning sensation and the immediate forceful and uncontrollable shutting of the eyes. Effects usually include tears streaming from the eyes, profuse coughing, exceptional nasal discharge that is full of mucus, burning in the eyes, eyelids, nose and throat areas, disorientation, dizziness and restricted breathing. It will also burn the skin where sweaty or sunburned. In highly concentrated doses, it can also induce severe coughing and vomiting. Most of the immediate effects wear off within a few hours (such as exceptional nasal discharge and profuse coughing), although respiratory, gastrointestinal, and oral symptoms may persist for months.<ref>{{cite journal | vauthors = Karagama YG, Newton JR, Newbegin CJ | title = Short-term and long-term physical effects of exposure to CS spray | journal = Journal of the Royal Society of Medicine | volume = 96 | issue = 4 | pages = 172–4 | date = April 2003 | pmid = 12668703 | pmc = 539444 | doi = 10.1177/014107680309600404 }}</ref><ref>{{cite journal | vauthors = Torgrimson-Ojerio BN, Mularski KS, Peyton MR, Keast EM, Hassan A, Ivlev I | title = Health issues and healthcare utilization among adults who reported exposure to tear gas during 2020 Portland (OR) protests: a cross-sectional survey | journal = BMC Public Health | volume = 21 | issue = 1 | pages = 803 | date = April 2021 | pmid = 33902512 | pmc = 8074355 | doi = 10.1186/s12889-021-10859-w | doi-access = free }}</ref> Excessive exposure can cause chemical burns resulting in permanent scarring.<ref>[http://news.bbc.co.uk/2/hi/uk_news/england/dorset/4674350.stm "CS spray man 'scarred for life'"] {{Webarchive|url=https://web.archive.org/web/20160305124551/http://news.bbc.co.uk/2/hi/uk_news/england/dorset/4674350.stm |date=5 March 2016 }}. ''[[BBC News]].'' 2 February 2006. Retrieved on 23 September 2007</ref>

Adults exposed to tear gas during the 2020 protests in Portland, Oregon, US also reported menstrual changes (899; 54.5% of 1650 female respondents). Exposure to tear gas is associated with avoidable healthcare utilization.<ref>{{cite journal | vauthors = Torgrimson-Ojerio BN, Mularski KS, Peyton MR, Keast EM, Hassan A, Ivlev I | title = Health issues and healthcare utilization among adults who reported exposure to tear gas during 2020 Portland (OR) protests: a cross-sectional survey | journal = BMC Public Health | volume = 21 | issue = 1 | pages = 803 | date = April 2021 | pmid = 33902512 | pmc = 8074355 | doi = 10.1186/s12889-021-10859-w | doi-access = free }}</ref>

=== Secondary effects ===
People or objects contaminated with CS gas can cause secondary exposure to others, including healthcare professionals and [[police]]. In addition, repeated exposure may cause [[Sensitization|sensitisation]].<ref>{{cite journal | vauthors = Carron PN, Yersin B | title = Management of the effects of exposure to tear gas | journal = BMJ | volume = 338 | pages = b2283 | date = June 2009 | pmid = 19542106 | doi = 10.1136/bmj.b2283 | s2cid = 7870564 }}</ref>

== Toxicity ==

[[TRPA1]] (Transient Receptor Potential-Ankyrin 1) ion channel expressed on [[nociceptors]] (especially [[trigeminal]]) has been implicated as the site of action for CS gas in rodent models.<ref>{{cite journal | vauthors = Bessac BF, Sivula M, von Hehn CA, Caceres AI, Escalera J, Jordt SE | title = Transient receptor potential ankyrin 1 antagonists block the noxious effects of toxic industrial isocyanates and tear gases | journal = FASEB Journal | volume = 23 | issue = 4 | pages = 1102–14 | date = April 2009 | pmid = 19036859 | pmc = 2660642 | doi = 10.1096/fj.08-117812 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Brône B, Peeters PJ, Marrannes R, Mercken M, Nuydens R, Meert T, Gijsen HJ | title = Tear gasses CN, CR, and CS are potent activators of the human TRPA1 receptor | journal = Toxicology and Applied Pharmacology | volume = 231 | issue = 2 | pages = 150–6 | date = September 2008 | pmid = 18501939 | doi = 10.1016/j.taap.2008.04.005 }}</ref>

Although described as a [[non-lethal weapon]] for crowd control, studies have raised doubts about this classification. CS can cause severe [[pulmonary]] damage and can also significantly damage the heart and liver.<ref name="AMA">{{cite journal | vauthors = Hu H, Fine J, Epstein P, Kelsey K, Reynolds P, Walker B | title = Tear gas--harassing agent or toxic chemical weapon? | journal = JAMA | volume = 262 | issue = 5 | pages = 660–3 | date = August 1989 | pmid = 2501523 | doi = 10.1001/jama.1989.03430050076030 }}</ref>

On 28 September 2000, Prof. Dr. Uwe Heinrich released a study commissioned by [[John C. Danforth]], of the [[United States Office of Special Counsel]], to investigate the use of CS by the FBI at the [[Branch Davidians]]' Mount Carmel compound. He said no human deaths had been reported, but concluded that the lethality of CS used would have been determined mainly by two factors: whether gas masks were used and whether the occupants were trapped in a room. He suggests that if no gas masks were used and the occupants were trapped, then, "there is a distinct possibility that this kind of CS exposure can significantly contribute to or even cause lethal effects".<ref name=UweHeinrich />

CS gas can have a [[clastogen]]ic effect (abnormal chromosome change) on mammalian cells, but no studies have linked it to miscarriages or stillbirths.<ref name=AMA /><!-- Quote: "Only one study (27) has assessed the effect of CS on pregnancy in animals and itfound no significant effect. The Himsworth committee (5) found no signficant increase in abortions, stillbirths, or congenital abnormalities in geographic districts of tear gas use, comparing a 9-month period of heavy tear gas exposure to aprevious 9-month period. " --> In Egypt, CS gas was reported to be the cause of death of several protesters in Mohamed Mahmoud Street near [[Tahrir Square|Tahrir square]] during the November 2011 protests. The solvent in which CS is dissolved, [[methyl isobutyl ketone]] (MIBK), is classified as harmful by inhalation; irritating to the eyes and respiratory system; and repeated exposure may cause skin dryness or cracking.<ref>{{cite web|title=MSDS for 99% 4-Methyl-2-pentanone (MIBK)|url=https://www.alfa.com/en/content/msds/british/A11618.pdf|publisher=Alfa Aesar|access-date=7 January 2013|archive-url=https://web.archive.org/web/20180816093639/https://www.alfa.com/en/content/msds/british/A11618.pdf|archive-date=16 August 2018}}</ref>

== See also ==

* [[List of parties to the Chemical Weapons Convention]]
* [[List of uses of CS gas by country]]
* [[CR gas]]
* [[Phenacyl chloride|CN gas]]
* [[Pepper spray]]
* [[Chemical Weapons Convention]]
* [[Hand grenade]]s

== References ==

{{Reflist}}

== External links ==
{{Commons category|CS gas}}
* {{cite journal | vauthors=Carron PN, Yersin B | title=Management of the effects of exposure to tear gas | journal=BMJ | volume=338 | issue=7710 | pages=b2283 | date=June 2009 | pmid=19542106 | doi=10.1136/bmj.b2283 | s2cid=7870564 |ref=none}}
* Hout J, Hook G, LaPuma P, White D (June 2010). [https://www.ncbi.nlm.nih.gov/pubmed/20391049 "Identification of compounds formed during low temperature thermal dispersion of encapsulated o-chlorobenzylidene malononitrile (CS riot control agent)"]. ''Journal of Occupational and Environmental Hygiene''].
* Salem H, Gutting B, Kluchinsky T, Boardman C, Tuorinsky S, Hout J (2008). [https://web.archive.org/web/20130217101050/https://ke.army.mil/bordeninstitute/published_volumes/chemwarfare/Ch13_Pg441_484.pdf Medical Aspects of Chemical Warfare, Chapter 13 Riot Control Agents]. US Army Medical Institute, Borden Institute, pp. 441–484.
* [http://webbook.nist.gov/cgi/cbook.cgi?ID=C2698411&Units=SI&Mask=2000#Gas-Chrom Gas Chromatography]—[[NIST]]
* [https://www.cdc.gov/niosh/npg/npgd0122.html CDC – NIOSH Pocket Guide to Chemical Hazards – o-Chlorobenzylidene malononitrile]
* [https://web.archive.org/web/20150924065113/http://www.patfinucanecentre.org/policing/plastic/phase1rp.pdf Patten report recommendations 69 and 70 relating to public order equipment]—A paper prepared by the Steering Group led by the Northern Ireland Office (April 2001)
* [https://web.archive.org/web/20060111102425/http://www.advisorybodies.doh.gov.uk/pub/docs/doh/csgas.pdf Committees on toxicity, mutagenicity and carcinogenicity of chemicals in food, consumer products and the environment]. Statement on 2-chlorobenzylidene malononitrile (CS) and CS spray, September 1999 (PDF).
* [http://ejmas.com/jnc/jncart_edwardson_0103.htm Noxious Tear-Gas Bomb Mightier in Peace than in War]. Journal of Non-lethal Combatives, January 2003
* [https://web.archive.org/web/20060225100529/http://www.europarl.eu.int/stoa/publi/pdf/99-14-01-a_annex_en.pdf "Crowd Control Technologies: An Assessment Of Crowd Control Technology Options For The European Union"] – The Omega Foundation (PDF)
* [http://www.emedicine.com/emerg/topic914.htm eMedicine Information on irritants: Cs, Cn, Cnc, Ca, Cr, Cnb, PS]

{{Chemical warfare}}
{{Transient receptor potential channel modulators}}

[[Category:2-Chlorophenyl compounds]]
[[Category:Chemical weapons]]
[[Category:Lachrymatory agents]]
[[Category:Nitriles]]
[[Category:Riot control agents]]