chemistry

Methanethiol

Methanethiol 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 Methanethiol rather than just read about it. In short: Methanethiol ( METH-ayn-THY-ol), also called methyl mercaptan, is an organosulfur compound with the chemical formula CH3SH. It is a colorless flammable gas with a distinctive putrid smell.

Key takeaways

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

Reference excerpt

Methanethiol ( METH-ayn-THY-ol), also called methyl mercaptan, is an organosulfur compound with the chemical formula CH3SH. It is a colorless flammable gas with a distinctive putrid smell. In small amounts, it is pervasive in nature and found in certain foods, such as some nuts and cheese. It contributes to many odors, including the emissions from pulp mills, bad breath, and flatus. Methanethiol is the simplest thiol and is sometimes abbreviated as MeSH.

Structure and reactions The molecule is tetrahedral at the carbon atom, like methanol. It is a weak acid, with a pKa of ~10.4, but is about a hundred thousand times more acidic than methanol. The colorless salt can be obtained by treatment with sodium methoxide:

CH3SH + CH3ONa → CH3SNa + CH3OH The thiolate anion in sodium methanethiolate is a strong nucleophile. It can be methylated to dimethyl disulfide:

2 CH3SH + [O] → CH3SSCH3 + H2O Further oxidation takes the disulfide to two molecules of methanesulfonic acid, which is odorless. Bleach deodorizes methanethiol in this way.

Occurrence Methanethiol (MeSH) is released as a by-product of kraft pulping in pulp mills. In kraft pulping, lignin is depolymerized by nucleophilic attack with the strongly nucleophilic hydrosulfide ion (HS−) in a highly alkaline medium. However, in a side reaction, HS− attacks methoxyl groups (OMe) in lignin, demethylating them to give free phenolate groups (PhO−) and releasing MeSH. Due to alkalinity, MeSH is readily deprotonated (MeSNa), and the formed MeS− ion is also a strong nucleophile, reacting further to dimethyl sulfide. The compounds remain in the liquor and are burned in the recovery boiler, where the sulfur is recovered as sodium sulfide. Methanethiol is released from decaying organic matter in marshes and is present in the natural gas of certain regions, in coal tar, and in some crude oils. It occurs in various plants and vegetables, such as radishes. In surface seawater, methanethiol is the primary breakdown product of the algal metabolite dimethylsulfoniopropionate (DMSP). Marine bacteria appear to obtain most of the sulfur in their proteins by the breakdown of DMSP and incorporation of methanethiol, despite the fact that methanethiol is present in seawater at much lower concentrations than sulfate (~0.3 nM vs. 28 mM). Bacteria in environments both with and without oxygen can also convert methanethiol to dimethyl sulfide (DMS), although most DMS in surface seawater is produced by a separate pathway. Both DMS and methanethiol can be used by certain microbes as substrates for methanogenesis in some anaerobic soils. Methanethiol is a byproduct of asparagus metabolism. The production of methanethiol in urine after eating asparagus was once thought to be a genetic trait. More recent research suggests that the peculiar odor is in fact produced by all humans after consuming asparagus, while the ability to detect it (methanethiol being one of many components in "asparagus pee") is in fact the genetic trait. The chemical components responsible for the change in the odor of urine show as soon as 15 minutes after eating asparagus.

Preparation Methanethiol is prepared commercially by the reaction of methanol with hydrogen sulfide gas over an aluminium oxide catalyst:

CH3OH + H2S → CH3SH + H2O Although impractical, it can be prepared by the reaction of methyl iodide with thiourea.

Uses

Methanethiol is mainly used to produce the essential amino acid methionine, which is used as a dietary component in poultry and animal feed. Methanethiol is also used in the plastic industry as a moderator for free-radical polymerizations and as a precursor in the manufacture of pesticides including isomalathion. This chemical is also used in the natural gas industry as an odorant, as it mixes well with methane. The characteristic rotting vegetation smell of the mix is widely known by natural gas customers as an indicator of a possible gas leak, even a minor one.

Safety The safety data sheet (SDS) lists methanethiol as a colorless, flammable gas with an extremely strong and repulsive smell. At very high concentrations it is highly toxic and affects the central nervous system. Its penetrating odor provides warning at dangerous concentrations. An odor threshold of 1 ppb has been reported. The United States OSHA Ceiling Limit is listed as 10 ppm.

Accidents In 2001 a rail car fire of 25,000 US gallons (95,000 L) near Trenton, Michigan left three people dead and nine injured. On November 15, 2014, at DuPont's La Porte, Texas facility, 24,000 lb (11,000 kg) of methyl mercaptan were released and travelled downwind into surrounding areas, killing four and injuring one other. In 2023, DuPont pleaded guilty to criminal negligence for its role in the leak. The company was ordered to pay a $12 million fine and donate an additional $4 million to the National Fish and Wildlife Foundation. On July 14, 2022, an accidental release in Charlotte, North Carolina led to the temporary closure of local government offices. On April 10, 2024, an accidental release of a higher-than-expected level of methyl mercaptan into the natural gas supply was attributed to an "upstream supplier" for Columbia Gas. This release was noticed by residents in at least Richland, Ashland, and Lorain counties in Ohio. Numerous schools cancelled their school days and numerous evacuations took place.

References

External links NLM Hazardous Substances Databank – Methyl mercaptan CDC - NIOSH Pocket Guide to Chemical Hazards

Illustrations

Worked examples

Example 1 — a first encounter with Methanethiol

Start with the simplest possible case. Write down what Methanethiol 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 Methanethiol 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 Methanethiol 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 Methanethiol

In research: Methanethiol 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 Methanethiol 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: Methanethiol is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkanethiols, Flatulence, Foul-smelling chemicals, so understanding it makes those chapters shorter.
In everyday life: Look for Methanethiol 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 Methanethiol in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Methanethiol 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 Methanethiol out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Methanethiol in simple terms?

Methanethiol ( METH-ayn-THY-ol), also called methyl mercaptan, is an organosulfur compound with the chemical formula CH3SH. It is a colorless flammable gas with a distinctive putrid smell.

Why does Methanethiol 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 Methanethiol?

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 Methanethiol.