Editing Methanethiol (section)

==Occurrence==
Methanethiol (MeSH) is released as a by-product of [[kraft pulping]] in [[pulp (paper)|pulp mill]]s. In kraft pulping, [[lignin]] is [[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 [[lignin]], demethylating them to give free [[phenolate]] groups (PhO<sup>−</sup>) and releasing MeSH. Due to alkalinity, MeSH is readily deprotonated ([[sodium methanethiolate|MeSNa]]), and the formed MeS<sup>−</sup> 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]].<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 [[marsh]]es and is present in the [[natural gas]] of certain regions, in [[coal tar]], and in some [[crude oil]]s. It occurs in various plants and vegetables, such as radishes.

In surface [[seawater]], methanethiol is the primary breakdown product of the [[Algae|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).<ref>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</ref> 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.<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 [[methanogenesis]] in some anaerobic soils.

Methanethiol is a byproduct of the metabolism of [[asparagus]].<ref>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</ref> The production of methanethiol in [[urine]] after eating asparagus was once thought to be a [[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>