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Methanethiol
Methanethiol
Ball-and-stick model of the methanethiol molecule
Space-filling model of the methanethiol molecule
IUPAC name
Other names methyl mercaptan
mercaptomethane
thiomethyl alcohol
Identifiers
CAS number 74-93-1 Yes check.svgY
SMILES
Properties
Molecular formula CH4S
Molar mass 48.11 g·mol−1
Melting point

-123 °C, 150 K, -189 °F

Boiling point

5.95 °C, 279 K, 43 °F

Acidity (pKa) ~10.4
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Methanethiol (also known as methyl mercaptan) is a colorless gas with a smell like rotten cabbage. It is a natural substance found in the blood, brain, and other animal as well as plant tissues. It is disposed of through animal feces. It occurs naturally in certain foods, such as some nuts and cheese. It is also one of the main chemicals responsible for bad breath and the smell of flatus. The chemical formula for methanethiol is CH3SH; it is classified as a thiol.

Contents

Occurrence

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.

In surface seawater, methanethiol is the primary breakdown product of the algal metabolite dimethylsulfoniopropionate (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 (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 anoxic sediments.

Methanethiol is a weak acid, with a pKa of ~10.4. This acidic property makes it reactive with dissolved metals in aqueous solutions. The environmental chemistry of these interactions in seawater or fresh water environments such as lakes has yet to be fully investigated.

The United States material safety data sheet (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 Permissible Exposure Limit is listed as 10 ppm.

Uses

Cylinder of methanethiol gas

Methanethiol is mainly used to produce methionine, which is used as a dietary component in poultry and animal feed. Methanethiol is also used in the plastics industry and as a precursor in the manufacture of pesticides. It is also released as a decay product of wood in pulp mills. Due to the extremely low odor threshold of thiols in general, they may be added to otherwise odorless gases such as natural gas, enabling people to detect leaks by smell.

Incidents

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.[1] The store had received letters threatening to disrupt business during the Christmas season. 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 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, a town just north of Milan, Italy. 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.[2] The ability to detect the presence of methanethiol is a genetic trait.[3] It is responsible for a noticeable change in the odor of urine, as soon as a few hours after eating asparagus.[4]

See also

External links

References

  1. ^ "Gas Sickens 78 in Russia". FOXNews.com. 2005-12-26. http://www.foxnews.com/story/0,2933,179741,00.html. Retrieved 2007-02-22.  
  2. ^ C. RICHER1, N. DECKER2, J. BELIN3, J. L. IMBS2, J. L. MONTASTRUC3 & J. F. GIUDICELLI (May 1989). "Odorous urine in man after asparagus"
  3. ^ Richer, Decker, Belin, Imbs, Montastruc, Giudicelli: "Odorous urine in man after asparagus", British Journal of Clinical Pharmacology, May 1989
  4. ^ Skinny On : Discovery Channel







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