Lewisite (L) (A-243) is an organoarsenic compound. It was once manufactured in the United States, Japan, Germany and the Soviet Union for use as a chemical weapon, acting as a vesicant (blister agent) and lung irritant. Although 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. Lewisite is named after the US chemist and soldier Winford Lee Lewis (1878–1943). Lewisite has no applications other than use as a chemical weapon, with a chemist from the United States Army's chemical warfare laboratories stating that "no one has ever found any use for the compound".
Chemical reactions The compound is prepared by the addition of arsenic trichloride to acetylene in the presence of a suitable catalyst:
AsCl3 + C2H2 → ClCH=CHAsCl2 (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):
ClCH=CHAsCl2 + 2 H2O → ClCH=CHAs(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.
Applications 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 to deal with existing stockpiles of lewisite (around 500 cubic meters at the time) by "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). The report, however, concluded that "the engineering and scale up of the process to a production level may be prohibitively difficult" and that "unless other metallic impurities which are likely to be found in Lewisite are removed, the high purity required for chip application may require additional steps", noting that worldwide demand for arsenic compounds (already declining at the time) was projected to shrink further, and that the proposed economics of the conversion process did not align with then-current prices for gallium arsenide.
Mechanism of action Lewisite is a suicide inhibitor of 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. Peripheral nervous system pathology usually arises from Lewisite exposure as the nervous system essentially relies on glucose as its only catabolic fuel.
It can easily penetrate ordinary clothing and latex rubber gloves. Upon skin contact it causes immediate stinging, burning pain and itching that can last for 24 hours. Within minutes, a rash develops and the agent is absorbed through the skin. Large, fluid-filled blisters (similar to those caused by mustard gas exposure) develop after approximately 12 hours and cause pain for 2–3 days. These are severe chemical burns and begin with small blisters in the red areas of the skin within 2–3 hours and grow worse, encompassing the entire red area, for the ensuing 12–18 hours after initial exposure. Liquid lewisite has faster effects than lewisite vapor. Sufficient absorption can cause deadly liver necrosis. Those exposed to lewisite can develop refractory hypotension (low blood pressure) known as Lewisite shock, with some features of arsenic toxicity. Lewisite damages capillaries, which then become leaky, reducing blood volume required to maintain blood pressure, a condition called hypovolemia. When the blood pressure is low, the kidneys may not receive enough oxygen and can be damaged. Inhalation, the most common route of exposure, causes burning pain and irritation throughout the respiratory tract, nosebleed (epistaxis), laryngitis, sneezing, coughing, vomiting, difficult breathing (dyspnea), and in severe cases of exposure, can cause fatal pulmonary edema, pneumonitis, or respiratory failure. Ingestion results in severe pain, nausea, vomiting, and tissue damage. The results of eye exposure can range from stinging, burning pain, and strong irritation to blistering and scarring of the cornea, along with blepharospasm, lacrimation, and edema of the eyelids and periorbital area. The eyes can swell shut, which can keep the eyes safe from further exposure. The most severe consequences of eye exposure to lewisite are globe perforation and blindness. Generalised symptoms also include restlessness, weakness, hypothermia, and low blood pressure. It is possible that Lewisite is carcinogenic: 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 causes damage to the respiratory tract at levels lower than the odor detection threshold. Early tissue damage causes pain. Hydrolysis leads to chlorovinylarsonous acid, CVAA.
Treatment Dimercaprol, also known as "British anti-lewisite", is the antidote for lewisite. It can be injected to prevent systemic toxicity, but will not prevent injury to the skin, eyes, or mucous membranes. Chemically, dimercaprol binds to the arsenic in lewisite. It is contraindicated in those with peanut allergies as it is usually formulated in peanut oil. Other treatment for lewisite exposure is primarily supportive. First aid of lewisite exposure consists of decontamination and irrigation of any areas that have been exposed. Other measures can be used as necessary, such as airway management, assisted ventilation, and monitoring of vital signs. In an advanced care setting, supportive care can include fluid and electrolyte replacement. Because the tube may injure or perforate the esophagus, gastric lavage is contraindicated.
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