Mustard gas

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Chemical Structure of Mustard Gas Compound
Chemical Structure of Mustard Gas Compound

Mustard gas (HD) is a chemical compound that was first used as a chemical weapon in World War I. In pure form, it is a colorless, odorless, viscous liquid at room temperature and causes blistering of the skin. The name comes from impure mustard gas, which is usually yellow-brown in color and has an odor resembling mustard, garlic or horseradish. It is otherwise not related to mustard in any way.

It 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 would publish a paper in 1886 describing a synthesis which produced good yields. The abbreviation LOST comes from LOmmel and STeinkopf who developed a process for mass-producing the gas for war use at the German company Bayer AG.

Other names for mustard gas include HD, senfgas, sulfur mustard, blister gas, S-LOST, and Kampfstoff LOST or Yperite or Yperiet. "mustine" as shown in older medical dictionaries a substance used in chemotherapy to treat/cure cancer.The use of mustard gas in chemotherapy has ceased in most countries in recent years.

Mustard gas is now listed in schedule 1 of the Chemical Weapons Convention: its production is prohibited.

Contents

Chemistry

This article forms part of the series
(A subset of Weapons of mass destruction)
Lethal agents
Blood agents
Cyanogen chloride
Hydrogen cyanide
Blister agents
Lewisite
Sulfur mustard gas (HD and THD, HT)
Nerve agents
G-Agents
GA (tabun), GB (sarin)
GD (soman), GF (cyclosarin)
V-Agents
VE, VG, VM, VX
Pulmonary agents
Chlorine
Chloropicrin (PS)
Phosgene (DP)
Diphosgene (CG)
Non-lethal agents
Incapacitating agents
BZ / Agent 15
KOLOKOL-1
Riot control agents
Pepper spray (OC)
CS gas
CN gas
CR gas

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

Mustard gas is a strong vesicant (a compound that causes blisters). Those exposed usually suffer no immediate symptoms. The exposure develops (in 4 to 24 hours) 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 leading 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, common bleach (NaOCl-) can be used or decontamination solution "DS2" (2% NaOH, 70% diethylenetriamine, 28% ethylene glycol monomethyl ether). 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 colour and a distinctive odour. 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 by:

Also, in 1943 a US 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. 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 amber, 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; 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 they only know the rough whereabouts of half of them.

The largest stockpile of mustard gas in the United States was stored at the Edgewood Arsenal, Aberdeen Proving Ground in Maryland. Mustard gas was stored in several 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 its proximity to several populated areas and schools in the area. 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. Unexploded shells containing mustard gas 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 smaller stockpiles are awaiting neutralization in compliance with international chemical weapons treaties.

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This reference has several errors in it:
  1. The Fredrick Guthrie synthesis should be from ethylene and SCl2, not ethylene and Cl2 as stated.
  2. The hydrolysis reaction pathway produces two molecules of HCl and the last one produced is H2O, not three molecules of HCl as shown in the reference.
  3. The molecular structure given for nitrogen mustard (N-mustard) is not correct. The nitrogen atom should have a hydrogen bonded to it.
This reference also has an error in it.
In the sentence on synthesis of mustard gas, the phrase "sulfur monochloride, S2Cl2" should be "sulfur dichloride, SCl2"
  • Organization for the Prohibition of Chemical Weapons - Mustard Agents [1]
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