Article: Sulfur mustard

Sulfur mustard (HD)
General
Systematic name	Bis (2-chloroethyl) sulfide
Other names	Iprit Kampstoff "Lost" Lost Mustard gas Senfgas Yellow Cross Liquid Yperite
Molecular formula	C4H8Cl2S
Molar mass	159 g/mol
Appearance	Colorless if pure. Normally ranges from pale yellow to dark brown. Slight garlic type odor.
CAS numbers	[505-60-2] [39472-40-7] [68157-62-0]
Properties
Density and phase	1.27 g/ml, liquid
Solubility in water	Negligible
Melting point	14.4 °C
Boiling point	217 °C
Vapor pressure	0.11 mmHg @ 25 °C
Hazards
MSDS	External MSDS
Main hazards	Vesicant
NFPA 704	1 4 1
0.003 mg/m3
Flash point	105 °C
Related compounds
Related compounds	Nitrogen mustard
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

The sulfur mustards, of which mustard gas is a member, are a class of related cytotoxic, vesicant chemical warfare agents with the ability to form large blisters on exposed skin. In their pure form most sulfur mustards are colorless, odorless, viscous liquids at room temperature. When used as warfare agents they are usually yellow-brown in color and have an odor resembling mustard plants, garlic or horseradish, which is how they got their name. However, these compounds have absolutely no relation whatsoever to culinary mustard.

Sulfur mustards are variations of "mustard gas" (bis-(2-chloroethyl) sulfide), which was first synthesised by Frederick Guthrie in 1860, though it is possible that it was developed as early as 1822 by M Depretz. V Meyer published a paper in 1886 describing a synthesis which produced good yields. Mustard gas is referred to by numerous other names, including HD, senfgas, sulfur mustard, blister gas, s-lost, lost, Kampfstoff LOST, yellow cross liquid, and yperite. The abbreviation LOST comes from the names Lommel and Steinkopf, who developed a process for mass producing the gas for war use at the German company Bayer AG. This involved reacting thiodiglycol with hydrochloric acid.

Mustard agents, including sulfur mustard, are regulated under the 1993 Chemical Weapons Convention (CWC). Three classes of chemicals are monitored under this Convention, with sulfur and nitrogen mustard grouped in the highest risk class, "schedule 1".

In its history, several varieties and mixtures of sulfur mustard have been employed. Some of those varieties are listed below:

• H – Also known as HS or Levinstein mustard. Manufactured by reacting dry ethylene with sulfur monochloride under controlled conditions. Undistilled sulfur mustard contains 20–30% impurities, for which reason it does not store as well as HD.
• HD – Codenamed Pyro by the British. Distilled sulfur mustard (bis-(2-chloroethyl) sulfide); approximately 96% pure. The term "mustard gas" usually refers to this variety of sulfur mustard.
• HT – Codenamed Runcol by the British. A blend of 60% sulfur mustard (HD) and 40% T (nitrogen mustard, a related vesicant with lower freezing point lower volatility and similar vesicant characteristics)
• HL – A blend of distilled mustard (HD) and lewisite (L)
• HQ – A blend of distilled mustard (HD) and sesquimustard (Q) (Gates and Moore 1946)

Chemistry

Chemically, it is a thioether with the formula C₄H₈Cl₂S. Its structure can be described as 1,1-thio-bis-[2-chloroethane], (ClCH₂CH₂)₂S, 2,2′-dichlorodiethyl sulfide or bis-(2-chloroethyl)-sulfide. Mustard gas can be synthesized by reacting sulfur dichloride (SCl₂) with two moles of ethylene (C₂H₄).

Although the compound is commonly known as "mustard gas", it is a viscous liquid at normal temperatures. The pure compound has a melting point of 14°C (57°F) and decomposes before boiling at 218°C (423°F).

The compound readily eliminates chloride ion by intramolecular nucleophilic substitution to form a cyclic sulfonium ion. This very reactive intermediate is particularly detrimental to cellular health as it has a strong tendency to bond to the guanine nitrogen in DNA strands. This leads to either immediate cellular death or, as recent research has found, cancer. Mustard gas is not very soluble in water but is very soluble in fat, contributing to its rapid absorption into the skin.

In the wider sense, compounds with the structural element BCH₂CH₂X, where X is any leaving group and B is a Lewis base are known as mustards. Such compounds can form cyclic onium ions that readily react with nucleophiles. Examples are bis-(2-chloroethyl)ether or the (2-haloethyl)amines.

Physiological effects

A soldier with mustard gas burns sustained during World War I.

Mustard gas is a strong vesicant (blister-causing agent). Those exposed usually suffer no immediate symptoms. Within 4 to 24 hours the exposure develops into deep, itching or burning blisters wherever the mustard contacted the skin; the eyes (if exposed) become sore and the eyelids swollen, possibly leading to conjunctivitis and blindness. At very high concentrations, if inhaled, it causes bleeding and blistering within the respiratory system, damaging the mucous membrane and causing to pulmonary edema. Blister agent exposure over more than 50% body surface area is usually fatal.

Skin damage can be reduced if povidone iodine in a base of glycofurol is rapidly applied, but since mustard initially has no symptoms, the exposure is usually not identified until the blisters rise. The vesicant property can be neutralised by oxidation or chlorination; household bleach (sodium hypochlorite) or decontamination solution "DS2" (2% NaOH, 70% diethylenetriamine, 28% ethylene glycol monomethyl ether) can be used. Mustard gas is also carcinogenic (cancer causing) and mutagenic (causing damage to DNA of exposed cells).

History

After a failed attempt on the Eastern front, it was first used effectively in World War I by the German army against Canadian soldiers in 1917 and later also against the French – the name Yperite comes from its usage by the German army near the city of Ypres. It took the British over a year to develop their own mustard gas weapon, first using it in September 1918 during the breaking of the Hindenburg Line.

Mustard gas was dispersed as an aerosol in a mixture with other chemicals, giving it a yellow-brown color and a distinctive odor. Mustard gas was lethal in only about 1% of cases. Its effectiveness was as an incapacitating agent: a wounded soldier slows an advancing army much more than a dead one. The countermeasures against the gas were quite ineffective, since a soldier wearing a gas mask was not protected against absorbing it through the skin.

Furthermore, mustard gas was a persistent agent which would remain in the environment for days and continue to cause sickness. If mustard gas contaminated a soldier's clothing and equipment, then other soldiers he came into contact with would also be poisoned. Towards the end of the war it was even used in high concentrations as an area-denial weapon, which often forced soldiers to abandon heavily contaminated positions.

Since then, mustard gas has also been reportedly used in several wars, often where the side it is used against cannot retaliate^[1]:

• United Kingdom against Bolsheviks in 1919^[2];
• United Kingdom against rebels in Iraq in 1920^[3];
• United Kingdom against rebels in Afghanistan in the 1920s;
• Spain against Rif insurgents in Morocco in 1921-1927^[4][5];
• Italy in Libya in 1930^[6];
• Soviet Union in Xinjiang, China in 1934 and 1936-1937^[7][8];
• Italy in Abyssina (now Ethiopia) in 1935-1940^[9];
• Poland against Germany in 1939 during an isolated incident^[10];
• Germany against Poland and the Soviet Union in a few erroneous uses during the Second World War^[11];
• Japan against China in 1937-1945;
• Egypt against North Yemen in 1963-1967^[12];
• Iraq against Iran in 1981 and 1983-1988^[13];
• Iran against Iraq in 1987-1988, possibly using captured Iraqi munitions^[14];
• Iraq against Kurds in 1988^[15];
• Possibly Sudan against insurgents in the civil war, in 1995 and 1997^[16]

Also, in 1943 a U.S. stockpile was bombed in Bari, Italy, accidentally exposing thousands of civilians and 628 friendly troops. It was noted by medical workers that the white cell counts of exposed soldiers were decreased, and mustard gas was investigated as a therapy for Hodgkin's lymphoma, a form of cancer. Study of the use of similar chemicals as agents for the treatment of cancers led to the discovery of mustine, and the birth of anticancer chemotherapy.

Disposal of Mustard Gas

Most of the mustard gas found in Germany after World War II was dumped into the Baltic Sea. Between 1966 and 2002, fishers have found around 700 chemical weapons outside Bornholm, most of which were mustard gas bombs ^{[citation needed]}. When mustard gas is exposed to seawater, it forms a tar-like gel and maintains its lethality for at least five years. It is possible to mistake a piece of polymerised mustard gas for ambergris, which can lead to severe health problems. Shells containing mustard gas and other toxic ammunition from World War I (as well as conventional explosives) can still occasionally be found in France and Belgium; they used to be disposed of by explosion at sea, but current environmental regulations prohibit this and so the French government is building an automated factory to dispose of the backlog of shells.

In 1972, The United States Congress banned the practice of disposing chemical weapons into the ocean. However by this point, 64 million pounds of nerve and mustard agents had already been dumped into the ocean waters off of the United States by the U.S. Army. According to a 1998 report created by William Brankowitz, a deputy project manager in the U.S. Army Chemical Materials Agency, the Army created at least 26 chemical weapons dumpsites in the ocean off of at least 11 states on both the west and east coasts. Additionally due to poor records, they currently only know the rough whereabouts of half of them.

A significant portion of the stockpile of mustard agent in the United States was stored at the Edgewood Area of Aberdeen Proving Ground in Maryland. Approximately 1621 tons of mustard agent was stored in one-ton (900 kg) containers on the base under heavy guard. A disposal plant built on site neutralized the last of this stockpile in February, 2005. This stockpile had priority due to the potential for quick reduction of risk to the community. The closest schools were fitted with overpressurization units to protect the students and staff in the event of a catastrophic explosion and fire at the site. These projects, as well as planning, equipment, and training assistance, were provided to the surrounding community as a part of the Chemical Stockpile Emergency Preparedness Program (CSEPP), a joint US Army and Federal Emergency Management Agency program (http://www.fema.gov/government/grant/csepp1.shtm). Unexploded shells containing mustard agent and other chemical agents are still present in several test ranges in proximity to Edgewood area schools, but the smaller amounts (4–14 pounds; 2–6 kg) present considerably less risk. They are being systematically detected and excavated for disposal. There are several other sites in the United States where the remaining US stockpiles of chemical agents are awaiting destruction in compliance with international chemical weapons treaties; the largest mustard agent stockpile, approximately 6196 tons, is stored at the Deseret Chemical Depot in Utah with destruction anticipated to begin in 2006. US mustard agent and other chemical agent storage is managed by the US Army's Chemical Materials Agency (http://www.cma.army.mil/home.aspx). The Chemical Materials Agency (CMA) manages disposal operations at five of the remaining seven stockpile sites, located in Alabama, Arkansas, Indiana, Utah, and Oregon; disposal projects at the other two sites, located in Kentucky and Colorado, are managed by the Program Manager Assembled Chemical Weapons Alternatives (ACWA) (http://www.pmacwa.army.mil/).

See also

• Blister agent
• Nitrogen mustard