Lewisite

Lewisite (L) (A-243) is an organoarsenic compound. It was once manufactured in the U.S., Japan, Germany and the Soviet Union for use as a chemical weapon, acting as a vesicant (blister agent) and lung irritant. Although the substance is colorless and odorless in its pure form, impure samples of lewisite are a yellow, brown, violet-black, green, or amber oily liquid with a distinctive odor that has been described as similar to geraniums. Apart from its use as a weapon of war, lewisite is useless; a chemist from the United States Army's chemical warfare laboratories said that "no one has ever found any use for the compound". The compound is prepared by the addition of arsenic trichloride to acetylene in the presence of a suitable catalyst: AsCl3 + C2H2 → ClCHCHAsCl2 (Lewisite) This chemical process can occur a second or third time, giving lewisite 2 and lewisite 3 as byproducts. Lewisite, like other arsenous chlorides, hydrolyses in water to form hydrochloric acid and chlorovinylarsenous oxide (a less-powerful blister agent): ClCHCHAsCl2 + 2 H2O → ClCHCHAs(OH)2 + 2 HCl This reaction is accelerated in alkaline solutions, and forms acetylene and trisodium arsenate. Lewisite reacts with metals to form hydrogen gas. It is combustible, but difficult to ignite. Apart from deliberately injuring and killing people, lewisite has no commercial, industrial, or scientific applications. In a 1959 paper regarding the development of a batch process for lewisite synthesis, Gordon Jarman of the United States Army Chemical Warfare Laboratories said: The manufacture can be one of the easiest and most economical in the metal-organic field, and it is regretted that no one has ever found any use for the compound. It is a pity to waste such a neat process. While the compound itself has no useful application, a 1993 report from the US Defense Nuclear Agency detailed attempts by Russian chemists in "exploring processes for the conversion of these agents to marketable products", including the extraction of high-purity arsenic for use in semiconductor doping (as gallium arsenide).