Methanethiol

The molecule is tetrahedral at the carbon atom, like methanol. It is a weak acid, with a pK_a 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 oxidized to dimethyl disulfide:

:2CH₃SH + [O] → CH₃SSCH₃ + H₂O

Further oxidation takes the disulfide to two molecules of methanesulfonic acid, which is odorless. Bleach deodorizes methanethiol in this way.

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.Sixta, H.; Potthast, A.; Krotschek, A. W., Chemical Pulping Processes. In Handbook of Pulp, Sixta, H., Ed. Wiley-VCH Verlag GmbH & Co.: Weinheim, 2006; Vol. 1, p 169 (109–510).

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).Charel Wohl, Julián Villamayor and Martí Galí et al. ,Marine emissions of methanethiol increase aerosol cooling in the Southern Ocean.Sci. Adv.10,eadq2465(2024).DOI:10.1126/sciadv.adq2465 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.Kiene, R.P., and Service, S. [https://www.jstor.org/stable/24825568 "Decomposition of DMSP and DMS in Estuarine Waters: dependence on temperature and substrate concentration"]," Marine Ecology Progress Series. September, 1991 Both DMS and methanethiol can be used by certain microbes as substrates for methanogenesis in some anaerobic soils.

Methanethiol is a byproduct of the metabolism of asparagus.Richer, Decker, Belin, Imbs, Montastruc, Giudicelli: [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1379934/ "Odorous urine in man after asparagus"], British Journal of Clinical Pharmacology, May 1989 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.{{cite journal |journal=Br Med J |volume=281 |pages=1676–8 |year= 1980 |vauthors=Lison M, Blondheim SH, Melmed RN |title=A polymorphism of the ability to smell urinary metabolites of asparagus |pmid=7448566 |doi= 10.1136/bmj.281.6256.1676 |issue=6256 |pmc=1715705}} The chemical components responsible for the change in the odor of urine show as soon as 15 minutes after eating asparagus.[http://www.discovery.com/area/skinnyon/skinnyon970115/skinny1.html Skinny On: Discovery Channel] {{webarchive|url=https://web.archive.org/web/20080229081018/http://www.discovery.com/area/skinnyon/skinnyon970115/skinny1.html |date=2008-02-29 }}

Methanethiol is prepared commercially by the reaction of methanol with hydrogen sulfide gas over an aluminium oxide catalyst:{{cite book |last1=Norell |first1=John |last2=Louthan |first2=Rector P. |title=Kirk-Othmer Concise Encyclopedia of Chemical Technology |edition=3rd |year=1988 |publisher= John Wiley & Sons, Inc.|location=New York|isbn=978-0471801047|pages=946–963 |chapter=Thiols}}

:CH₃OH + H₂S → CH₃SH + H₂O

Although impractical, it can be prepared by the reaction of methyl iodide with thiourea.{{cite book |last1= Reid|first1= E. Emmet |title= Organic Chemistry of Bivalent Sulfur |volume= 1|year=1958 |publisher=Chemical Publishing Company, Inc. |location= New York |pages=32–33, 38}}

File:Methanethiol cylinder.jpg

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.[http://www.safegas.org/about/about.html SafeGase: About Natural Gas:]

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.{{cite book|last=Devos|first=M|title=Standardized Human Olfactory Thresholds|year=1990|publisher=IRL Press |location=Oxford |isbn=0199631468 |page=101|author2=F. Patte |author3=J. Rouault |author4=P. Lafort |author5=L. J. Van Gemert}} The United States OSHA Ceiling Limit is listed as 10 ppm.

In 2001 a rail car fire of {{Convert|25000|gal|L}} near Trenton, Michigan left three people dead and nine injured.{{Cite web |title=Deadly Explosion At Chemical Plant |url=https://www.cbsnews.com/news/deadly-explosion-at-chemical-plant/ |access-date=2022-05-25 |website=www.cbsnews.com |date=14 July 2001 |language=en-US}}

On November 15, 2014, at DuPont's La Porte, Texas facility, 24,000 lb (10,886 kg) of methyl mercaptan were released and travelled downwind into surrounding areas, killing four and injuring one other.{{Cite web |title=DuPont La Porte Facility Toxic Chemical Release {{!}} CSB |url=https://www.csb.gov/dupont-la-porte-facility-toxic-chemical-release-/#:~:text=Accident%20Description&text=The%20accident%20at%20DuPont%27s%20facility,fungicide%20manufacturing%20process,%20was%20released. |access-date=2022-06-02 |website=www.csb.gov}}{{cite web |author1=US Chemical Safety Board |title=Animation of Chemical Release at DuPont's La Porte Facility |url=https://www.youtube.com/watch?v=pbFzuS8Bdhw&pp=ygUQbWV0aHlsIG1lcmNhcHRhbg%3D%3D |website=Youtube |access-date=8 October 2023 |format=Video |date=30 September 2015}} 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.{{Cite web |date=2023-04-24 |title=Southern District of Texas {{!}} DuPont and former employee sentenced for gas release that killed four {{!}} United States Department of Justice |url=https://www.justice.gov/usao-sdtx/pr/dupont-and-former-employee-sentenced-gas-release-killed-four |access-date=2023-11-13 |website=www.justice.gov |language=en}}{{Cite web |date=2023-04-24 |title=DuPont ordered to pay $16M in Texas plant leak that killed 4 |url=https://fox5sandiego.com/news/business/ap-business/dupont-ordered-to-pay-16m-in-texas-plant-leak-that-killed-4/ |access-date=2023-04-24 |website=FOX 5 San Diego |language=en-US}}

On July 14, 2022, an accidental release in Charlotte, North Carolina led to the temporary closure of local government offices.{{Cite news |last=Limehouse |first=Jonathan |date=2022-07-14 |title=What is the strong natural gas odor smell in Charlotte NC? |work=Charlotte Observer |url=https://www.charlotteobserver.com/news/local/article263462253.html |access-date=2022-07-14 |archive-url=https://web.archive.org/web/20220715063619/https://www.charlotteobserver.com/news/local/article263462253.html |archive-date=2022-07-15}}

On April 10, 2024, an accidental release{{cite web |last1=Carr |first1=Dillon |title=Mansfield-area schools back to normal following natural gas scare |url=https://www.richlandsource.com/2024/04/10/area-schools-back-to-normal-following-natural-gas-scare/ |website=Richland Source |date=10 April 2024 |access-date=2024-04-11}} 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 day and numerous evacuations took place out.

{{Reflist|2}}

• [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+Methanethiol NLM Hazardous Substances Databank – Methyl mercaptan]
• [https://www.cdc.gov/niosh/npg/npgd0425.html CDC - NIOSH Pocket Guide to Chemical Hazards]

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Category:Flatulence

Category:Foul-smelling chemicals

Category:Organic compounds with 1 carbon atom