The compound2-chlorobenzalmalononitrile (also calledo-chlorobenzylidene malononitrile; chemical formula: C10H5ClN2), acyanocarbon, is the defining component of the lachrymatory agent commonly calledCS gas, atear gas used as ariot control agent, and is banned for use in warfare pursuant to the 1925Geneva 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 anaerosol of avolatilesolvent (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 anon-lethal weapon.
CS gas was firstsynthesized by two Americans, Ben Corson and Roger Stoughton,[6] atMiddlebury College inVermont in 1928, and the chemical's name is derived from the first letters of the scientists' surnames.[7][8]
CS was developed and tested secretly atPorton Down inWiltshire, UK, in the 1950s and 1960s. CS was used first on animals, and subsequently onBritish 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.[9]
As recently as 2002, the U.S. State DepartmentBureau of International Security and Nonproliferation 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.[10]
The reaction is catalysed with a weak base likepiperidine orpyridine. The production method has not changed since the substance was discovered by Corson and Stoughton.[14] Other bases, solvent free methods andmicrowave promotion have been suggested to improve the production of the substance.[15]
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."[14]
As 2-chlorobenzalmalononitrile is a solid at room temperature, not agas, a variety of techniques have been used to make this solid usable as anaerosol:
Melted and sprayed in the molten form.
Dissolved in organic solvent.
CS2 dry powder (CS2 is asiliconized, micro-pulverized form of CS).
CS from thermal grenades by generation of hot gases.[2]
In the 1993Waco siege in the United States, CS was dissolved in the organic solventdichloromethane (also known as methylene chloride). The solution was dispersed as anaerosol via explosive force and when the highly volatile dichloromethane evaporated, CS crystals precipitated and formed a fine dispersion in the air.[2]
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 immediatevomiting andprostration.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 orbromoacetone, 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 anaerosol. The size of solution droplets and the size of the CSparticulates after evaporation are factors determining its effect on the human body.[16]
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.[17][18] Excessive exposure can cause chemical burns resulting in permanent scarring.[19]
Adults exposed to tear gas during the 2020 protests inPortland, Oregon, also reported menstrual changes (899; 54.5% of 1650 female respondents). Exposure to tear gas is associated with avoidable healthcare utilization.[20]
People or objects contaminated with CS gas can cause secondary exposure to others, including healthcare professionals andpolice. In addition, repeated exposure may causesensitisation.[21]
TRPA1 (Transient Receptor Potential-Ankyrin 1) ion channel expressed onnociceptors, especially [thetrigeminal nerve, has been implicated as the site of action for CS gas in rodent models.[22][23]
Although described as anon-lethal weapon for crowd control, studies have raised doubts about this classification. CS can cause severelung damage and can also significantly damage the heart and liver.[24]
On 28 September 2000, Prof. Dr. Uwe Heinrich released a study commissioned byJohn Danforth, of theUnited States Office of Special Counsel, to investigate the use of CS by the F.B.I at theBranch 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".[2]
CS gas can have aclastogenic effect (abnormal chromosome change) on mammalian cells, but no studies have linked it to miscarriages or stillbirths.[24] In Egypt, CS gas was reported to be the cause of death of several protesters in Mohamed Mahmoud Street nearTahrir 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.[25]
^Corson BB, Stoughton RW (1928). "Reactions of Alpha, Beta-Unsaturated Dinitriles".Journal of the American Chemical Society.50 (10):2825–2837.doi:10.1021/ja01397a037.
^abCorson BB, Stoughton RW (1928). "Reactions of Alpha, Betha-Unsaturated Dinitriles".J Am Chem Soc.50 (10):2825–2837.doi:10.1021/ja01397a037.
^Pande A, Ganesan K, Jain AK, Gupta PK, Malhotr RC (2005). "Novel Eco-Friendly Process for the Synthesis of 2-Chlorobenzylidenemalononitrile and ITS Analogues Using Water As a Solvent".Org Proc Res Develop.9 (2):133–136.doi:10.1021/op0498262.
^Brône B, Peeters PJ, Marrannes R, Mercken M, Nuydens R, Meert T, Gijsen HJ (September 2008). "Tear gasses CN, CR, and CS are potent activators of the human TRPA1 receptor".Toxicology and Applied Pharmacology.231 (2):150–6.doi:10.1016/j.taap.2008.04.005.PMID18501939.
^abHu H, Fine J, Epstein P, Kelsey K, Reynolds P, Walker B (August 1989). "Tear gas--harassing agent or toxic chemical weapon?".JAMA.262 (5):660–3.doi:10.1001/jama.1989.03430050076030.PMID2501523.
