|Jmol-3D images||Image 1|
|Molar mass||207.32 g/mol|
|Melting point||−18 °C (0 °F; 255 K)|
|Boiling point||190 °C (374 °F; 463 K)|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Lewisite is an organoarsenic compound. It was once manufactured in the U.S., Japan, and Germany for use as a chemical weapon, acting as a vesicant (blister agent) and lung irritant. Although colorless and odorless, impure samples of lewisite are a yellow or brown liquid with a distinctive odor that has been described as similar to scented geraniums.
The compound is prepared by the addition of arsenic trichloride to acetylene in the presence of a suitable catalyst:
- AsCl3 + C2H2 → ClCHCHAsCl2
Lewisite, like other arsenous chlorides, hydrolyses in water to form hydrochloric acid:
- ClCHCHAsCl2 + 2 H2O → ClCHCHAs(OH)2 + 2 HCl
This reaction is accelerated in alkaline solutions, with poisonous (but non-volatile) alkali arsenite being the coproduct.
Mode of action as chemical weapon
Arsenite inhibits important biochemical pathways of the human body. Arsenite poisoning specifically targets the E3 component of pyruvate dehydrogenase. As an efficient method to produce ATP, pyruvate dehydrogenase is involved in the conversion of pyruvate to Acetyl-CoA. The latter subsequently enters the TCA cycle. Arsenite has a high affinity for dihydrolipoamide; E3 component of the pyruvate dehydrogenase. Binding results in inhibition of the enzyme and can lead to dire consequences. Nervous pathology usually arises from arsenite poisoning as the nervous system essentially relies on glucose as its only catabolic fuel. There is evidence that at high concentrations other enzymes are attacked as well, but the pyruvate oxidase system is the first point of attack by arsenicals such as lewisite. 
It can easily penetrate ordinary clothing and even rubber; upon skin contact it causes immediate pain and itching with a rash and swelling. Large, fluid-filled blisters (similar to those caused by mustard gas exposure) develop after approximately 12 hours. These are severe chemical burns. Sufficient absorption can cause systemic poisoning leading to liver necrosis or death.
Those exposed to lewisite can develop refractory hypotension known as Lewisite shock, as well as some features of arsenic toxicity. 
Inhalation causes a burning pain, sneezing, coughing, vomiting, and possibly pulmonary edema. Ingestion results in severe pain, nausea, vomiting, and tissue damage. The results of eye exposure can range from stinging and strong irritation to blistering and scarring of the cornea. Generalised symptoms also include restlessness, weakness, subnormal temperature and low blood pressure.
It is possible that Lewisite may be a carcinogen since arsenic is categorized as a respiratory carcinogen by the International Agency for Research on Cancer, though it has not been confirmed that Lewisite is a carcinogen. 
Lewisite is usually found as a mixture, of 2-chlorovinylarsonous dichloride as well as bis(2-chloroethenyl)arsinous chloride ("lewisite 2"), and tris(2-chlorovinyl)arsine ("lewisite 3").
Lewisite was first synthesised in 1904 by Julius Arthur Nieuwland during studies for his PhD. Within his doctoral thesis he described a reaction between acetylene and arsenic trichloride, which led to the formation of lewisite. Exposure to the resulting compound made Nieuwland so ill he was hospitalized for a number of days.
Lewisite is named after the US chemist and soldier Winford Lee Lewis (1878–1943). In 1918 Dr John Griffin (Julius Arthur Nieuwland's thesis advisor) drew Lewis's attention to Nieuwland's thesis at Maloney Hall, a chemical laboratory at The Catholic University of America, Washington D.C.. Lewis then attempted to purify the compound through distillation but found that the mixture exploded on heating until it was washed with HCl.
Lewisite was developed into a secret weapon (at a facility located in Cleveland, Ohio (The Cleveland Plant) at East 131st Street and Taft Avenue) and given the name "G-34" (which had previously been the code for mustard gas) in order to confuse its development with mustard gas. Production began at a plant in Willoughby, Ohio on November 1, 1918. It was not used in World War I, but experimented with in the 1920s as the "Dew of Death."
After World War I, the US became interested in lewisite because it was not flammable. It had the military symbol of "M1" up into World War II, when it was changed to "L". Field trials with lewisite during World War II demonstrated that casualty concentrations were not achievable under high humidity due to its rate of hydrolysis and its characteristic odor and lacrymation forced troops to don masks and avoid contaminated areas. The United States produced about 20,000 tons of lewisite, keeping it on hand primarily as an antifreeze for mustard gas or to penetrate protective clothing in special situations.
It was replaced by the mustard gas variant HT (a 60:40 mixture of sulfur mustard and O Mustard), and declared obsolete in the 1950s. It is effectively treated with British anti-lewisite (dimercaprol). Most stockpiles of lewisite were neutralised with bleach and dumped into the Gulf of Mexico, but some remained at the Deseret Chemical Depot located outside of Salt Lake City, Utah , although as of January 18, 2012 the last of the global stockpile there was destroyed.
In 2001, lewisite was found in a World War I weapons dump in Washington, D.C.
Controversy over Japanese depots of lewisite in China
In mid-2006, China and Japan were negotiating disposal of stocks of lewisite in northeastern China, left by Japanese military during World War II. Residents of China have died over the past twenty years from accidental exposure to these stockpiles.
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