|Jmol-3D images||Image 1|
|Molar mass||159.08 g mol−1|
|Appearance||Colorless if pure.
Normally ranges from
pale yellow to dark brown.
Slight garlic or horseradish type odour
|Density||1.27 g/mL, liquid|
14.4 °C, 287.6 K, 57.9 °F
218 °C, 491 K, 424 °F (begins to decompose at 217 °C and boils at 218 °C)
|Solubility in water||Negligible|
|Solubility||soluble in ether, benzene, fat, alcohol, THF|
|EU classification||Very toxic (T+)
Dangerous for the environment (N)
Carc. Cat 1
|Main hazards||Poison, contact hazard, inhalation hazard, corrosive, environmental hazard, carcinogenic, possibly mutagenic|
|Flash point||105 °C|
|Related compounds||Nitrogen mustard|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
The sulfur mustards, or sulphur mustards, commonly known as mustard gas, are a class of related cytotoxic and vesicant chemical warfare agents with the ability to form large blisters on the exposed skin and in the lungs. Pure sulfur mustards are colorless, viscous liquids at room temperature. When used in impure form, such as warfare agents, they are usually yellow-brown in color and have an odor resembling mustard plants, garlic, or horseradish, hence the name. Mustard gas was originally assigned the name LOST, after the scientists Wilhelm Lommel and Wilhelm Steinkopf, who developed a method for the large-scale production of mustard gas for the Imperial German Army in 1916.
Mustard agents 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 Schedule 1, as substances with no use other than in chemical warfare. Mustard agents could be deployed on the battlefield by means of artillery shells, aerial bombs, rockets, or by spraying from warplanes.
- SCl2 + 2 C2H4 → (Cl-CH2CH2)2S
- 8 S2Cl2 + 16 C2H4 → 8 (Cl-CH2CH2)2S + S8
- 3 (HO-CH2CH2)2S + 2 PCl3 → 3 (Cl-CH2CH2)2S + 2 P(OH)3
In the Meyer-Clarke method, concentrated hydrochloric acid (HCl) instead of PCl3 is used as the chlorinating agent:
- (HO-CH2CH2)2S + 2 HCl → (Cl-CH2CH2)2S + 2 H2O
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 (424.4 °F).
Mechanism of toxicity
The compound readily eliminates a chloride ion by intramolecular nucleophilic substitution to form a cyclic sulfonium ion. This very reactive intermediate tends to permanently alkylate the guanine nucleotide in DNA strands, which prevents cellular division and generally leads directly to programmed cell death, or, if cell death is not immediate, the damaged DNA may lead to the development of cancer. Sulfur mustard 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 (sulfonium, ammoniums, etc.) that are good alkylating agents. Examples are bis(2-chloroethyl)ether, the (2-haloethyl)amines (nitrogen mustards), and sulfur sesquimustard, which has two α-chloroethyl thioether groups (ClH2C-CH2-S-) connected by an ethylene (-CH2CH2-) group. These compounds have a similar ability to alkylate DNA, but their physical properties, e.g. melting point, vary.
Mustard gas has extremely powerful vesicant effects on its victims. In addition, it is strongly mutagenic and carcinogenic, due to its alkylating properties. It is also lipophilic. Because people exposed to mustard gas rarely suffer immediate symptoms, and mustard-contaminated areas may appear completely normal, victims can unknowingly receive high dosages. Within 24 hours of exposure to mustard agent, victims experience intense itching and skin irritation, which gradually turns into large blisters filled with yellow fluid wherever the mustard agent contacted the skin. These are chemical burns and are very debilitating. Mustard gas vapour easily penetrates clothing fabrics such as wool or cotton, so it is not only the exposed skin of victims that gets burned. If the victim's eyes were exposed then they become sore, starting with conjunctivitis, after which the eyelids swell, resulting in temporary blindness. Miosis may also occur, which is probably the result from the cholinomimetic activity of mustard. At very high concentrations, if inhaled, mustard agent causes bleeding and blistering within the respiratory system, damaging mucous membranes and causing pulmonary edema. Depending on the level of contamination, mustard gas burns can vary between first and second degree burns, though they can also be every bit as severe, disfiguring and dangerous as third degree burns. Severe mustard gas burns (i.e. where more than 50% of the victim's skin has been burned) are often fatal, with death occurring after some days or even weeks have passed. Mild or moderate exposure to mustard agent is unlikely to kill, though victims require lengthy periods of medical treatment and convalescence before recovery is complete. The mutagenic and carcinogenic effects of mustard agent mean that victims who recover from mustard gas burns have an increased risk of developing cancer in later life.
Skin damage can be reduced if povidone-iodine in a base of glycofurol is rapidly applied, but since mustard agent initially has no symptoms, exposure is usually not recognised until skin irritation begins, at which point it is too late for countermeasures. The vesicant property of mustard gas can be neutralised by oxidation or chlorination, using household bleach (sodium hypochlorite), or by nucleophilic attack using e.g. decontamination solution "DS2" (2% NaOH, 70% diethylenetriamine, 28% ethylene glycol monomethyl ether). After initial decontamination of the victim's wounds is complete, medical treatment is similar to that required by any conventional burn. The amount of pain and discomfort suffered by the victim is comparable as well. Mustard gas burns heal slowly, and, as with other types of burn, there is a risk of sepsis caused by pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa.
A British nurse treating soldiers with mustard gas burns during World War I commented:
They cannot be bandaged or touched. We cover them with a tent of propped-up sheets. Gas burns must be agonizing because usually the other cases do not complain, even with the worst wounds, but gas cases are invariably beyond endurance and they cannot help crying out.
In its history, various types and mixtures of sulfur mustard have been employed. These include:
- H – Also known as HS ("Hun Stuff") or Levinstein mustard. This is named after the inventor of the quick but dirty Levinstein Process for manufacture, 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. Also, as it decomposes, it increases in vapor pressure, making the munition it is contained in likely to split, especially along a seam, releasing the agent to the atmosphere
- HD – Codenamed Pyro by the British, and Distilled Mustard by the US. Distilled sulfur mustard (bis(2-chloroethyl) sulfide); approximately 96% pure. The term "mustard gas" usually refers to this variety of sulfur mustard. A much-used path of synthesis was based upon the reaction of thiodiglycol with hydrochloric acid.
- HT – Codenamed Runcol by the British, and Mustard T- mixture by the US. A mixture of 60% sulfur mustard (HD) and 40% T (bis[2-(2-chloroethylthio)ethyl] ether), a related vesicant with lower freezing point, lower volatility and similar vesicant characteristics.
- HL – A blend of distilled mustard (HD) and Lewisite (L), originally intended for use in winter conditions due to its lower freezing point compared to the pure substances. The Lewisite component of HL was used as a form of antifreeze.
- HQ – A blend of distilled mustard (HD) and sesquimustard (Q) (Gates and Moore 1946).
Sulfur mustard agents (class)
The complete list of effective sulfur mustard agents commonly stockpiled is as follows:
|Chemical||Code||Trivial name||CAS number||PubChem||Structure|
|2-Chloroethyl chloromethyl sulfide||2625-76-5|
Mustard gas was possibly developed as early as 1822 by César-Mansuète Despretz (1798–1863). Despretz described the reaction of sulfur dichloride and ethylene but never made mention of any irritating properties of the reaction product, which makes the claim doubtful. In 1854, another French chemist, Alfred Riche (1829–1908), repeated this procedure but he did not describe any adverse physiological properties. In 1860, the British scientist Frederick Guthrie synthesized and characterized the mustard gas compound, and he also noted its irritating properties, especially in tasting. In 1860, chemist Albert Niemann, known as a pioneer in cocaine chemistry, repeated the reaction, and recorded blister-forming properties. In 1886, Viktor Meyer published a paper describing a synthesis that produced good yields. He combined 2-chloroethanol with aqueous potassium sulfide, and then treated the resulting thiodiglycol with phosphorus trichloride. The purity of this compound was much higher, and so were the adverse health effects on exposure much more severe. These symptoms presented themselves in his assistant, and in order to rule out the possibility that his assistant was suffering from a mental illness (psychosomatic symptoms), Meyer had this compound tested on laboratory rabbits, most of which died. In 1913, the English chemist Hans Thacher Clarke (known for the Eschweiler-Clarke reaction) replaced the phosphorus trichloride with hydrochloric acid in Meyer's formulation while working with Emil Fischer in Berlin. Clarke was hospitalized for two months for burns after one of his flasks broke. According to Meyer, Fischer's report on this accident to the German Chemical Society sent the German Empire on the road to chemical weapons. The German Empire during World War I relied on the Meyer-Clarke method with the 2-chloroethanol chemical structure already available from the German chemical dye industry of that time.
Mustard gas was first used effectively in World War I by the German army against British and Canadian soldiers near Ypres, Belgium, in 1917 and later also against the French Second Army. The name Yperite comes from its usage by the German army near the town of Ypres. The Allies did not use mustard gas until November 1917 at Cambrai, France, after the armies had captured a stockpile of German mustard-gas shells. It took the British more than a year to develop their own mustard gas weapon. (The only option available to the British was the Despretz–Niemann–Guthrie process). This was used first 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 has also been dispersed in such munitions as aerial bombs, land mines, mortar rounds, artillery shells, and rockets. Exposure to mustard gas was lethal in about one percent of cases. Its effectiveness was as an incapacitating agent. The early countermeasures against mustard gas were relatively ineffective, since a soldier wearing a gas mask was not protected against absorbing it through his skin and being blistered.
Mustard gas is a persistent weapon that remains on the ground for days and weeks, and it continues to cause ill effects. If mustard gas contaminates a soldier's clothing and equipment, then the other soldiers that he comes into contact with are also poisoned. Towards the end of World War I, mustard gas was used in high concentrations as an area-denial weapon that forced troops to abandon heavily-contaminated areas.
Since World War I, mustard gas has been used in several wars or other conflicts, usually against people who cannot retaliate in kind:
- United Kingdom against the Red Army in 1919
- Spain and France against the Rifian resistance in Morocco during 1921–27
- Italy in Libya during 1930
- The Soviet Union in Xinjiang, Republic of China, during the Soviet Invasion of Xinjiang against the 36th Division (National Revolutionary Army) in 1934, and also in the Xinjiang War (1937) during 1936–37
- Italy against Abyssinia (now Ethiopia) from 1935 to 1940
- Nazi Germany against Poland and the Soviet Union in a few incidents during World War II
- Poland against Germany in 1939 during an isolated incident, using a British product
- The Japanese Empire against China during 1937–45
- Egypt against North Yemen during 1963–67
- Iraq against Iran and the Kurds during 1983–88
- Possibly Sudan against insurgents in the civil war, in 1995 and 1997
In 1943, during the Second World War, an American shipment of mustard gas exploded aboard a supply ship that was bombed during an air raid in the harbor of Bari, Italy. Eighty-three of the 628 hospitalized victims who had been exposed to the mustard gas died. The deaths and incident were partially classified for many years.
From 1943 to 1944, mustard gas experiments were performed on Australian service volunteers in tropical Queensland, Australia, by British Army and American experimenters, resulting in some severe injuries. One test site, the Brook Islands National Park, was chosen to simulate Pacific islands held by the Imperial Japanese Army.
The use of poison gases, including mustard gas, during warfare is known as chemical warfare, and this kind of warfare was prohibited by the Geneva Protocol of 1925, and also by the later Chemical Weapons Convention of 1993. The latter agreement also prohibits the development, production, stockpiling, and sale of such weapons.
Development of the first chemotherapy drug
As early as 1919 it was known that mustard gas was a suppressor of hematopoiesis. In addition, autopsies performed on 75 soldiers who had died of mustard gas during World War I were done by researchers from the University of Pennsylvania who reported decreased counts of white blood cells. This led the American Office of Scientific Research and Development (OSRD) to finance the biology and chemistry departments at Yale University to conduct research on the use of chemical warfare during World War II. As a part of this effort, the group investigated nitrogen mustard as a therapy for Hodgkin's lymphoma and other types of lymphoma and leukemia, and this compound was tried out on its first human patient in December 1942. The results of this study were not published until 1946, when they were declassified. In a parallel track, after the air raid on Bari in December 1943, the doctors of the U.S. Army noted that white blood cell counts were reduced in their patients. Some years after World War II was over, the incident in Bari and the work of the Yale University group with nitrogen mustard converged, and this prompted a search for other similar chemical compounds. Due to its use in previous studies, the nitrogen mustard called "HN2" became the first cancer chemotherapy drug, mustine, to be used.
Most of the sulfur mustard gas found in Nazi Germany after World War II was dumped into the Baltic Sea. Between 1966 and 2002, fishermen have found about 700 chemical weapons in the region of Bornholm, most of which contain sulfur mustard. One of the more frequently-dumped weapons was the "Sprühbüchse 37" (SprüBü37, Spray Can 37, 1937 being the year of its fielding with the German Army). These weapons contain sulfur mustard mixed with a thickener, which gives it a tar-like viscosity. When the content of the SprüBü37 comes in contact with water, only the sulfur mustard in the outer layers of the lumps of viscous mustard hydrolyzes, leaving behind amber-colored residues that still contain most of the active sulfur mustard. On mechanically breaking these lumps, e.g., with the drag board of a fishing net or by the human hand, the enclosed sulfur mustard is still as active as it had been at the time the weapon was dumped. These lumps, when washed ashore, can be mistaken for amber, which can lead to severe health problems. Artillery shells containing sulfur mustard and other toxic ammunition from World War I (as well as conventional explosives) can still be found in France and Belgium. These were formerly disposed of by explosion undersea, but since the current environmental regulations prohibit this, the French government is building an automated factory to dispose of the accumulation of chemical shells.
In 1972, the U.S. Congress banned the practice of disposing of chemical weapons into the ocean by the United States. 64 million pounds of nerve and mustard agents had already been dumped into the ocean off the United States by the U.S. Army. According to a report created in 1998 by William Brankowitz, a deputy project manager in the U.S. Army Chemical Materials Agency, the army created at least 26 chemical weapons dumping sites in the ocean offshore from at least 11 states on both the East Coast and the West Coast (in Operation CHASE, Operation Geranium, etc.). In addition, due to poor recordkeeping, about one-half of the sites have only their rough locations known.
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 1,621 tons of mustard agent were stored in one-ton containers on the base under heavy guard. An incineration plant built on the proving ground neutralized the last of this stockpile in February 2005. This stockpile had priority because of the potential for quick reduction of risk to the community. The nearest schools were fitted with overpressurization machinery to protect the students and faculty 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 program of the Army and the Federal Emergency Management Agency (FEMA). Unexploded shells containing mustard agent and other chemical agents are still present in several test ranges in proximity to schools in the Edgewood area, but the smaller amounts of poison gas (four to 14 pounds) present considerably lower risks. These remnants are being detected and excavated systematically for disposal. The U.S. Army Chemical Materials Agency oversaw disposal of several other chemical weapons stockpiles located across the United States in compliance with international chemical weapons treaties. These include the complete incineration of the chemical weapons stockpiled in Alabama, Arkansas, Indiana, and Oregon. Earlier, this agency had also completed destruction of the chemical weapons stockpile located on Johnston Atoll located south of Hawaii in the Pacific Ocean. The largest mustard gas stockpile, of about 6,196 tons, was stored at the Deseret Chemical Depot in northern Utah. The incineration of this stockpile began in 2006. In May 2011, the last one-ton tank of mustard gas was incinerated at the Deseret Chemical Depot, and the last mustard gas artillery shells at Deseret were incinerated in January 2012.
The storage and incineration of mustard gas and other poison gases was carried out by the U.S. Army Chemical Materials Agency. Disposal projects at the two remaining American chemical weapons sites, will be carried out at their sites near Richmond, Kentucky, and Pueblo, Colorado,
In 2008, many empty mustard gas aerial bombs were found in an excavation at the Marrangaroo Army Base just west of Sydney, Australia. In 2009, a mining survey near Chinchilla, Queensland, uncovered 144 105-millimeter howitzer shells, some containing "Mustard H", that had been buried by the U.S. Army during World War II.
In 2010, a clamming boat pulled up some old artillery shells of World War I from the Atlantic Ocean south of Long Island, New York. Multiple fishermen suffered from skin blistering and respiratory irritation severe enough to require their hospitalization.
Detection in biological fluids
Urinary concentrations of the thiodiglycol hydrolysis products of sulfur mustard have been used to confirm a diagnosis of chemical poisoning in hospitalized victims. The presence in urine of 1,1'-sulfonylbismethylthioethane (SBMTE), a conjugation product with glutathione, is considered a more specific marker, since this metabolite is not found in specimens from unexposed persons. Intact sulfur mustard was detected in postmortem fluids and tissues of a man who died one week post-exposure.
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|Wikimedia Commons has media related to Sulfur mustard.|
- Textbook of Military Medicine – Intensive overview of mustard gas Includes many references to scientific literature
- Detailed information on physical effects and suggested treatments
- Iyriboz Y (2004). "A Recent Exposure to Mustard Gas in the United States: Clinical Findings of a Cohort (n = 247) 6 Years After Exposure". MedGenMed 6 (4): 4. PMC 1480580. PMID 15775831. Shows photographs taken in 1996 showing people with mustard gas burns.
- An overview of the sulfur and nitrogen mustard agents (Caution: contains graphic images)
- Questions and Answers for Mustard Gas
- UMDNJ-Rutgers University CounterACT Research Center of Excellence A research center studying sulfur mustard, includes searchable reference library with many early references on sulfur mustard.
- Treatment of Mustard Gas Burns – published in the BMJ in 1946
- Nightmare in Bari
- surgical treatment of Sulfur Mustard Burns
- UK Ministry of Defence Report on disposal of weapons at sea and incidents arising
- Rhydymwyn Valley History Society