View source for Chemistry:Methanethiol

{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 444011638
| Name = Methanethiol
| ImageFile_Ref = {{chemboximage|correct|??}}
| ImageFile = Methanethiol.svg
| ImageSize = 150px
| ImageName = Methanethiol
| ImageFileL1 = Methanethiol-3D-balls.png
| ImageNameL1 = Ball-and-stick model of the methanethiol molecule
| ImageFileR1 = Methanethiol-3D-vdW.png
| ImageNameR1 = Space-filling model of the methanethiol molecule
| PIN = Methanethiol
| OtherNames = Methyl mercaptan<br />Mercaptomethane<br />Methiol<br />Thiomethyl alcohol/Thiomethanol<br />Methylthiol
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspiders}}
| ChemSpiderID = 855
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 2X8406WW9I
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C00409
| PubChem = 878
| InChI = 1/CH3SH/c1-2/h2H,1H3
| InChIKey = LSDPWZHWYPCBBB-UHFFFAOYAW
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/CH3SH/c1-2/h2H,1H3
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = LSDPWZHWYPCBBB-UHFFFAOYSA-N
| CASNo = 74-93-1
| CASNo_Ref = {{cascite|correct|CAS}}
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 16007
| DTXSID = DTXSID5026382
| RTECS = PB4375000
| UNNumber = 1064
| EINECS = 200-822-1
| 3DMet = B00105
| SMILES = SC
}}
|Section2={{Chembox Properties
| Formula = CH<sub>3</sub>SH
| MolarMass = 48.11&nbsp;g·mol<sup>&minus;1</sup>
| Appearance = colorless gas<ref name=PGCH/>
| Odor = Distinctive, like that of rotten cabbage or eggs 
| MeltingPtC = -123
| BoilingPtC = 5.95
| Solubility = 2%
| Solvent =
| SolubleOther = alcohol, ether
| pKa = ~10.4
| VaporPressure = 1.7 atm (20°C)<ref name=PGCH/>
| Density = 0.9 g/mL (liquid at 0°C)<ref name=PGCH/>
  }}
|Section3={{Chembox Hazards
| GHSPictograms = {{GHS02}}{{GHS06}}{{GHS08}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|220|331|410}}
| PPhrases = {{P-phrases|210|261|271|273|304+340|311|321|377|381|391|403|403+233|405|501}}
| NFPA-H = 4
| NFPA-F = 4
| NFPA-R = 1
| IDLH = 150 ppm<ref name=PGCH>{{PGCH|0425}}</ref>
| LC50 = 3.3 ppm (mouse, 2 hr)<br/>675 ppm (rat, 4 hr)<ref name=IDLH>{{IDLH|74931|Methyl mercaptan}}</ref>
| LD50 = 60.67 mg/kg (mammal)<ref name=IDLH/>| PEL = C 10 ppm (20 mg/m<sup>3</sup>)<ref name=PGCH/>
| REL = C 0.5 ppm (1 mg/m<sup>3</sup>) [15-minute]<ref name=PGCH/>
| FlashPtF = 0
| FlashPt_ref = <ref name=PGCH/>
| AutoignitionPtF = 687
| AutoignitionPt_ref = <ref>{{cite web |title=Sigma Aldrich Methanethiol SDS |url=https://www.sigmaaldrich.com/US/en/sds/aldrich/742805 | website=Sigma Aldrich |publisher=Millipore Sigma |access-date=Nov 1, 2022}}</ref>
| ExploLimits = 3.9%-21.8%<ref name=PGCH/>  }}
|Section4={{Chembox Related
| OtherCompounds = [[Chemistry:Ethanethiol|Ethanethiol]] 
[[Chemistry:Hydrogen sulfide|Hydrogen sulfide]]
  }}
}}

'''Methanethiol''' {{IPAc-en|ˌ|m|ɛ|θ|.|eɪ|n|.|ˈ|θ|aɪ|.|ɒ|l}} (also known as '''methyl mercaptan''') is an organosulfur compound with the [[Chemistry:Chemical formula|chemical formula]] {{Chem|CH|3|SH}}. It is a colorless gas with a distinctive putrid smell. It is a natural substance found in the [[Biology:Blood|blood]], [[Biology:Brain|brain]] and [[Biology:Feces|feces]] of animals (including humans), as well as in [[Biology:Tissue#Plant tissue|plant tissues]]. It also occurs naturally in certain foods, such as some [[Biology:Nut (fruit)|nuts]] and cheese. It is one of the chemical compounds responsible for bad breath and the smell of flatus. Methanethiol is the simplest [[Chemistry:Thiol|thiol]] and is sometimes abbreviated as '''MeSH'''. It is very flammable.

==Structure and reactions==
The molecule is tetrahedral at the carbon atom, like [[Chemistry:Methanol|methanol]]. It is a [[Chemistry:Weak acid|weak acid]], with a p''K''<sub>a</sub> of ~10.4, but is about a hundred thousand times more acidic than methanol. The colorless salt can be obtained in this way:
:CH<sub>3</sub>SH + [[Chemistry:Sodium methoxide|CH<sub>3</sub>ONa]] → [[Chemistry:Sodium methanethiolate|CH<sub>3</sub>SNa]] + CH<sub>3</sub>OH
The resulting thiolate anion is a strong [[Chemistry:Nucleophile|nucleophile]].

It can be oxidized to [[Chemistry:Dimethyl disulfide|dimethyl disulfide]]:
:2CH<sub>3</sub>SH + [O] → CH<sub>3</sub>SSCH<sub>3</sub> + H<sub>2</sub>O
Further oxidation takes the [[Biology:Disulfide|disulfide]] to two molecules of [[Chemistry:Methanesulfonic acid|methanesulfonic acid]], which is odorless. [[Chemistry:Bleach|Bleach]] deodorizes methanethiol in this way.

==Occurrence==
Methanethiol (MeSH) is released as a by-product of kraft pulping in [[Chemistry:Pulp (paper)|pulp mill]]s. In kraft pulping, [[Biology:Lignin|lignin]] is [[Chemistry:Depolymerization|depolymerized]] by nucleophilic attack with the strongly nucleophilic hydrosulfide ion (HS<sup>−</sup>) in a highly alkaline medium. However, in a side reaction, HS<sup>−</sup> attacks methoxyl groups (OMe) in [[Biology:Lignin|lignin]], demethylating them to give free phenolate groups (PhO<sup>−</sup>) and releasing MeSH. Due to alkalinity, MeSH is readily deprotonated ([[Chemistry:Sodium methanethiolate|MeSNa]]), and the formed MeS<sup>−</sup> ion is also a strong nucleophile, reacting further to [[Chemistry:Dimethyl sulfide|dimethyl sulfide]]. The compounds remain in the liquor and are burned in the [[Engineering:Recovery boiler|recovery boiler]], where the sulfur is recovered as [[Chemistry:Sodium sulfide|sodium sulfide]].<ref>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).</ref>

Methanethiol is released from decaying organic matter in [[Earth:Marsh|marsh]]es and is present in the [[Chemistry:Natural gas|natural gas]] of certain regions, in [[Chemistry:Coal tar|coal tar]], and in some crude oils. It occurs in various plants and vegetables, such as radishes.

In surface [[Earth:Seawater|seawater]], methanethiol is the primary breakdown product of the [[Biology:Algae|algal]] [[Biology:Metabolite|metabolite]] [[Chemistry:Dimethylsulfoniopropionate|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 [[Chemistry:Dimethyl sulfide|dimethyl sulfide]] (DMS), although most DMS in surface seawater is produced by a separate pathway.<ref> 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  </ref> Both DMS and methanethiol can be used by certain microbes as substrates for [[Engineering:Methanogenesis|methanogenesis]] in some anaerobic soils.

Methanethiol is a byproduct of the metabolism of [[Biology:Asparagus|asparagus]].<ref>Richer, Decker, Belin, Imbs, Montastruc, Giudicelli: [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1379934 "Odorous urine in man after asparagus"], ''British Journal of Clinical Pharmacology'', May 1989</ref> The production of methanethiol in [[Biology:Urine|urine]] after eating asparagus was once thought to be a [[Biology:Genetics|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.<ref>{{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}}</ref> The chemical components responsible for the change in the odor of urine show as soon as 15 minutes after eating asparagus.<ref>[http://www.discovery.com/area/skinnyon/skinnyon970115/skinny1.html Skinny On: Discovery Channel<!-- Bot generated title -->] {{webarchive|url=https://web.archive.org/web/20080229081018/http://www.discovery.com/area/skinnyon/skinnyon970115/skinny1.html |date=2008-02-29 }}</ref>

==Preparation==
Methanethiol is prepared commercially by the reaction of [[Chemistry:Methanol|methanol]] with [[Chemistry:Hydrogen sulfide|hydrogen sulfide]] gas over an [[Chemistry:Aluminium oxide|aluminium oxide]] catalyst:<ref name="John Wiley & Sons, Inc">{{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}}</ref>
:CH<sub>3</sub>OH + H<sub>2</sub>S → CH<sub>3</sub>SH + H<sub>2</sub>O
Although impractical, it can be prepared by the reaction of [[Chemistry:Methyl iodide|methyl iodide]] with [[Chemistry:Thiourea|thiourea]].<ref Name="Reid">{{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}}</ref>

==Uses==
[[File:Methanethiol cylinder.jpg|thumb|Cylinder of methanethiol gas]]
Methanethiol is mainly used to produce the essential amino acid [[Chemistry:Methionine|methionine]], which is used as a dietary component in poultry and animal feed.<ref name="John Wiley & Sons, Inc"/> Methanethiol is also used in the plastic industry as a moderator for [[Chemistry:Radical polymerization|free-radical polymerizations]]<ref name="John Wiley & Sons, Inc" /> and as a precursor in the manufacture of [[Biology:Pesticide|pesticide]]s.

This chemical is also used in the [[Chemistry:Natural gas|natural gas]] industry as an [[Chemistry:Aroma compound|odorant]], as it mixes well with [[Chemistry:Methane|methane]]. The characteristic rotting vegetation smell of the mix is widely known by natural gas customers as an indicator of a possible [[Physics:Gas leak|gas leak]], even a very minor one.<ref>[http://www.safegas.org/about/about.html SafeGase: About Natural Gas:]</ref>

==Safety==
The [[Chemistry:Safety data sheet|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&nbsp;ppb has been reported.<ref name= "Devos">{{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}}</ref> The United States [[Organization:Occupational Safety and Health Administration|OSHA]] Ceiling Limit is listed as 10&nbsp;ppm.

=== Accidents ===
In 2001 a rail car fire of {{Convert|25000|gal|L}} near Trenton, Michigan left three people dead and nine injured.<ref>{{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}}</ref>

On November 15, 2014, at [[Company:DuPont|DuPont]]'s La Porte, Texas facility, a deadly release of methyl mercaptan occurred in a confined space, killing four and injuring one other.<ref>{{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}}</ref><ref name="CSB Video">{{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 |publisher=Youtube |access-date=8 October 2023 |format=Video |date=30 September 2015}}</ref>

On July 14, 2022, there was an accidental release of methanethiol in Charlotte, North Carolina. While there were no injuries, a rare weather event caused the odor to persist for several hours. Many believed they were experiencing a natural gas leak, which led to a high volume of emergency calls and the closure of several local government offices.<ref>{{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}}</ref>

==References==
{{Reflist|2}}

==External links==
*[http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+Methanethiol NLM Hazardous Substances Databank &ndash; Methyl mercaptan]
*[https://www.cdc.gov/niosh/npg/npgd0425.html CDC - NIOSH Pocket Guide to Chemical Hazards]
{{Molecules detected in outer space}}


[[Category:Alkanethiols|1]]
[[Category:Flatulence]]
[[Category:Foul-smelling chemicals]]
[[Category:Organic compounds with 1 carbon atom]]

{{Sourceattribution|Methanethiol}}