chemistry

Mustard gas

Mustard gas is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mustard gas rather than just read about it. In short: Mustard gas or sulfur mustard are names commonly used for the organosulfur chemical compound bis(2-chloroethyl) sulfide, which has the chemical structure S(CH2CH2Cl)2, as well as other species. In the wider sense, compounds with the substituents −SCH2CH2X or −N(CH2CH2X)2 are known as sulfur mustards or nitrogen mustards, respectively, where X = Cl or Br.

Key takeaways

Mustard gas belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mustard gas to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mustard gas from memory before moving on to harder problems.

Reference excerpt

Mustard gas or sulfur mustard are names commonly used for the organosulfur chemical compound bis(2-chloroethyl) sulfide, which has the chemical structure S(CH2CH2Cl)2, as well as other species. In the wider sense, compounds with the substituents −SCH2CH2X or −N(CH2CH2X)2 are known as sulfur mustards or nitrogen mustards, respectively, where X = Cl or Br. Such compounds are potent alkylating agents, making mustard gas acutely and severely toxic. Mustard gas is a carcinogen. There is no preventive agent against mustard gas, with protection depending entirely on skin and airways protection, and no antidote exists for mustard poisoning. Also known as mustard agents, this family of compounds comprises infamous cytotoxins and blister agents with a long history of use as chemical weapons. The name mustard gas is technically incorrect; the substances, when dispersed, are often not gases but a fine mist of liquid droplets that can be readily absorbed through the skin and by inhalation. The skin can be affected by contact with either the liquid or vapor. The rate of penetration into skin is proportional to dose, temperature and humidity. Sulfur mustards are viscous liquids at room temperature and have an odor resembling mustard plants, garlic, or horseradish, hence the name. When pure, they are colorless, but when used in impure forms, such as in warfare, they are usually yellow-brown. Mustard gases form blisters on exposed skin and in the lungs, often resulting in prolonged illness ending in death.

Etymology The name of mustard gas derived from its yellow color, smell of mustard, and burning sensation on eyes. The term was first used in 1917 during World War I when Germans used the chemical in combat.

History as chemical weapons Sulfur mustard is a type of chemical warfare agent. As a chemical weapon, mustard gas has been used in several armed conflicts since World War I, including the Iran–Iraq War. Sulfur-based and nitrogen-based mustard agents are regulated under Schedule 1 of the 1993 Chemical Weapons Convention, as substances with few uses other than in chemical warfare. Mustard agents can be deployed by means of artillery shells, aerial bombs, rockets, or by spraying from aircraft.

Adverse health effects

Mustard gases have powerful blistering effects on victims. They are also carcinogenic and mutagenic alkylating agents. Their high lipophilicity accelerates their absorption into the body. Because mustard agents often do not elicit immediate symptoms, contaminated areas may appear normal. Within 24 hours of exposure, victims experience intense itching and skin irritation. If this irritation goes untreated, blisters filled with pus can form wherever the agent contacted the skin. As chemical burns, these are severely debilitating. Mustard gas can have the effect of turning a patient's skin different colors due to melanogenesis. If the victim's eyes were exposed, then they become sore, starting with conjunctivitis (also known as pink eye), after which the eyelids swell, resulting in temporary blindness. Extreme ocular exposure to mustard gas vapors may result in corneal ulceration, anterior chamber scarring, and neovascularization. In these severe and infrequent cases, corneal transplantation has been used as a treatment. If inhaled in high concentrations, mustard agents cause bleeding and blistering within the respiratory system, damaging mucous membranes and causing pulmonary edema. Depending on the level of contamination, mustard agent burns can vary between first and second degree burns. They can also be as severe, disfiguring, and dangerous as third degree burns. Some 80% of sulfur mustard in contact with the skin evaporates, while 10% stays in the skin and 10% is absorbed and circulated in the blood. The carcinogenic and mutagenic effects of exposure to mustard gas increase the risk of developing cancer later in life. In a study of patients 25 years after wartime exposure to chemical weaponry, c-DNA microarray profiling indicated that 122 genes were significantly mutated in the lungs and airways of mustard gas victims. Those genes all correspond to functions commonly affected by mustard gas exposure, including apoptosis, inflammation, and stress responses.

Symptoms of exposure have been extensively documented. There is a considerable amount of information about the effects of exposure to sulfur mustard in humans and animals from the last century from wartime exposures and laboratory testing. Substantial information in the original documents is not readily available. There are numerous reviews of the literature that include early data as well as recent information.

Medical management In a rinse-wipe-rinse sequence, skin is decontaminated of mustard gas by washing with liquid soap and water, or an absorbent powder. The eyes should be thoroughly rinsed using saline or clean water. A topical analgesic is used to relieve skin pain during decontamination. For skin lesions, topical treatments, such as calamine lotion, steroids, and oral antihistamines are used to relieve itching. Larger blisters are irrigated repeatedly with saline or soapy water, then treated with an antibiotic and petroleum gauze. Mustard agent burns do not heal quickly and (as with other types of burns) present a risk of sepsis caused by pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. The mechanisms behind mustard gas's effect on endothelial cells are still being studied, but recent studies have shown that high levels of exposure can induce high rates of both necrosis and apoptosis. In vitro tests have shown that at low concentrations of mustard gas, where apoptosis is the predominant result of exposure, pretreatment with 50 mM N-acetyl-L-cysteine (NAC) was able to decrease the rate of apoptosis. NAC protects actin filaments from reorganization by mustard gas, demonstrating that actin filaments play a large role in the severe burns observed in victims. A British nurse treating soldiers with mustard agent 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.

Mechanism of cellular toxicity

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Mustard gas

Start with the simplest possible case. Write down what Mustard gas claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mustard gas before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mustard gas ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mustard gas

In research: Mustard gas appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mustard gas in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mustard gas is common in secondary-school and first-year university syllabi. It links to neighbouring topics Blister agents, Chemical weapons in World War I, Chloroethyl compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Mustard gas outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mustard gas in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mustard gas means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mustard gas out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mustard gas in simple terms?

Why does Mustard gas matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mustard gas?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mustard gas.