Methanethiol

Methanethiol

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Encyclopedia
Methanethiol is a colorless gas with a smell like rotten cabbage
Cabbage
Cabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae and is a leafy green vegetable...

. It is a natural substance found in the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 and brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 of humans and other animal as well as plant tissues. It is disposed of through animal feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...

. It occurs naturally in certain foods, such as some nut
Nut (fruit)
A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts...

s and cheese
Cheese
Cheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....

. It is also one of the main chemicals responsible for bad breath
Halitosis
Halitosis is a term used to describe noticeably unpleasant odors exhaled in breathing. Halitosis is estimated to be the third most frequent reason for seeking dental aid, following tooth decay and periodontal disease.- General :...

 and the smell of flatus. The chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 for methanethiol is CH3SH
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...

; it is classified as a thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...

. It is sometimes abbreviated as MeSH.

Occurrence


Methanethiol is released from decaying organic matter in marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....

es and is present in the natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 of certain regions, in coal tar
Coal tar
Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons. Coal tar is among the by-products when coal iscarbonized to make coke or gasified to make coal gas...

, and in some crude oils.

In surface seawater, methanethiol is the primary breakdown product of the algal metabolite dimethylsulfoniopropionate
Dimethylsulfoniopropionate
Dimethylsulfoniopropionate , is an organosulfur compound with the formula 2S+CH2CH2COO−. This zwitterionic metabolite found in marine phytoplankton, seaweeds, and some species of terrestrial and aquatic vascular plants...

 (DMSP). Marine bacteria appear to obtain most of their protein sulfur 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 oxic and anoxic environments can also convert methanethiol to dimethyl sulfide
Dimethyl sulfide
Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...

 (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
Methanogenesis
Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with...

 in some anaerobic soils.

Methanethiol is a weak acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

, with a pKa
PKA
PKA, pKa, or other similar variations may stand for:* pKa, the symbol for the acid dissociation constant at logarithmic scale* Protein kinase A, a class of cAMP-dependent enzymes* Pi Kappa Alpha, the North-American social fraternity...

 of ~10.4. This acidic property makes it reactive with dissolved metals in aqueous solutions. The environmental chemistry
Environmental chemistry
Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source...

 of these interactions in seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...

 or fresh water environments such as lakes has yet to be fully investigated.

The United States material safety data sheet
Material safety data sheet
A Material Safety Data Sheet is a form with data regarding the properties of a particular substance....

 (MSDS) 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 0.002 ppm has been reported. The United States OSHA
Occupational Safety and Health Administration
The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M. Nixon, on December 29, 1970...

 Ceiling Limit is listed as 10 ppm.

Uses



Methanethiol is mainly used to produce methionine
Methionine
Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...

, which is used as a dietary component in poultry and animal feed. Methanethiol is also used in the plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

s industry and as a precursor in the manufacture of pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s. It is also released as a decay product of wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

 in pulp mill
Pulp mill
A pulp mill is a manufacturing facility that converts wood chips or other plant fibre source into a thick fibre board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical or fully chemical methods...

s. Due to the extremely low odor threshold of thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...

s in general, they may be added to otherwise odorless gases such as natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

, enabling people to detect leaks by smell. It is also used by the mining industry, where it is injected into fresh-air intakes of a mine to warn miners of any emergencies that require evacuation.

St. Petersburg incident



On December 26, 2005, dozens of people at a St. Petersburg, Russia Maksidom home supplies store became ill when gas suspected to be methanethiol was released. The store had received letters threatening to disrupt business during the Christmas season
Christmas season
Christmastide is one of the seasons of the liturgical year of most Christian churches. It tends to be defined as the period from Christmas Eve to the evening of 5 January, the day before Epiphany...

. Three other stores belonging to the same chain found boxes with glass containers and timers that also might have been rigged to release the gas.

Milan incident


In 2004, an exhausted methanethiol canister used by a natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 distributor was being returned to a supplier for refilling. The canister sprang a leak while in transit at a road deliveries company in Sesto San Giovanni
Sesto San Giovanni
Sesto San Giovanni is a comune in the Milan metropolitan area, located in the province of Milan and region of Lombardy in Italy. Its railway station is the northernmost stop on the Milan Metro M1 line. The city is informally referred to as "Sesto"...

, a town just north of Milan
Milan
Milan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...

, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

. Gas was carried by winds across the eastern half of the city of Milan, causing residents as far as 12 kilometers from the canister to make thousands of calls that overwhelmed emergency services for four hours, and risked hiding actual gas leaks.

San Francisco Bay Area Incident


On November 12, 2009, an out-of-state natural gas supplier injected too much methanethiol into the local supply lines. The resulting odor alarmed many thousands of customers, who called emergency services to report what they thought were leaks.

Asparagus


Methanethiol is a byproduct produced by the metabolism of asparagus
Asparagus
Asparagus officinalis is a spring vegetable, a flowering perennialplant species in the genus Asparagus. It was once classified in the lily family, like its Allium cousins, onions and garlic, but the Liliaceae have been split and the onion-like plants are now in the family Amaryllidaceae and...

. The ability to produce methanethiol in urine after eating asparagus was once thought to be a genetic trait. However 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.

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