View source for Chemistry:Organomercury

{{Short description|Group of chemical compounds containing mercury}}
[[File:Organomercury-Logo.svg|150px|thumb|right|Organomercury compounds contain at least one carbon bonded to a mercury atom, shown here.]]'''Organomercury''' refers to the group of organometallic compounds that contain mercury. Typically the Hg–C bond is stable toward air and moisture but sensitive to light. Important organomercury compounds are the methylmercury(II) cation, CH<sub>3</sub>Hg<sup>+</sup>; ethylmercury(II) cation, C<sub>2</sub>H<sub>5</sub>Hg<sup>+</sup>; dimethylmercury, (CH<sub>3</sub>)<sub>2</sub>Hg, diethylmercury and merbromin ("Mercurochrome"). [[Chemistry:Thiomersal|Thiomersal]] is used as a preservative for vaccines and intravenous drugs.

The toxicity of organomercury compounds<ref>{{cite book|last=Hintermann|first=H.|title=Organomercurials. Their Formation and Pathways in the Environment|publisher=RSC publishing| location=Cambridge|year=2010|series=Metal Ions in Life Sciences|volume=7|pages=365–401|isbn=978-1-84755-177-1}}</ref><ref>{{cite book|last=Aschner|first=M.|author2=Onishchenko, N. |author3=Ceccatelli, S. |title=Toxicology of Alkylmercury Compounds|publisher=RSC publishing|location=Cambridge|year=2010|series=Metal Ions in Life Sciences|volume=7|pages=403–434|doi=10.1515/9783110436600-017|pmid=20877814|isbn=978-1-84755-177-1}}</ref> presents both dangers and benefits.  Dimethylmercury in particular, is notoriously toxic, but found use as an antifungal agent and [[Biology:Insecticide|insecticide]]. Merbromin and [[Chemistry:Phenylmercuric borate|phenylmercuric borate]] are used as topical antiseptics, while [[Chemistry:Nitromersol|nitromersol]] is used as a preservative for vaccines and antitoxins.

==Synthesis==
Organomercury compounds are generated by many methods, including the direct reaction of hydrocarbons and mercury(II) salts.  In this regard, organomercury chemistry more closely resembles organopalladium chemistry and contrasts with organocadmium compounds.

===Mercuration of aromatic rings===
Electron-rich arenes undergo '''mercuration''' upon treatment with [[Chemistry:Mercury(II) acetate|Hg(O<sub>2</sub>CCH<sub>3</sub>)<sub>2</sub>]]. The one acetate group that remains on mercury can be displaced by chloride:<ref>{{OrgSynth | vauthors = Whitmore FC, Hanson ER | title = o-Chloromercuriphenol | volume = 4 | pages = 13 | year = 1925 | doi = 10.15227/orgsyn.004.0013}}</ref>
:C<sub>6</sub>H<sub>5</sub>OH + Hg(O<sub>2</sub>CCH<sub>3</sub>)<sub>2</sub> → C<sub>6</sub>H<sub>4</sub>(OH)–2-HgO<sub>2</sub>CCH<sub>3</sub> + CH<sub>3</sub>CO<sub>2</sub>H

:C<sub>6</sub>H<sub>4</sub>(OH)–2–HgO<sub>2</sub>CCH<sub>3</sub> + NaCl → C<sub>6</sub>H<sub>4</sub>(OH)–2-HgCl + NaO<sub>2</sub>CCH<sub>3</sub>

The first such reaction, including a mercuration of [[Chemistry:Benzene|benzene]] itself, was reported by Otto Dimroth between 1898 and 1902.<ref>{{cite journal | title = Directe Einführung von Quecksilber in aromatische Verbindungen | journal = Berichte der deutschen chemischen Gesellschaft | volume = 31 | issue = 2 | year = 1898 | pages = 2154–2156 | author = Otto Dimroth | doi = 10.1002/cber.189803102162| url = https://zenodo.org/record/1425906}}</ref><ref>{{cite journal | title = Ueber die Einwirkung von Quecksilberoxydsalzen auf aromatische Verbindungen | journal = Berichte der deutschen chemischen Gesellschaft | volume = 32 | issue = 1 | year = 1899 | pages = 758–765 | author = Otto Dimroth | doi = 10.1002/cber.189903201116| url = https://zenodo.org/record/1425926}}</ref><ref>{{cite journal | title = Ueber die Mercurirung aromatischer Verbindungen | journal = Berichte der deutschen chemischen Gesellschaft | volume = 35 | issue = 2 | year = 1902 | pages = 2032–2045 | author = Otto Dimroth | doi = 10.1002/cber.190203502154| url = https://zenodo.org/record/1426050}}</ref>

===Addition to alkenes===
The Hg<sup>2+</sup> center binds to alkenes, inducing the addition of [[Chemistry:Hydroxide|hydroxide]] and [[Chemistry:Alkoxide|alkoxide]].  For example, treatment of [[Chemistry:Methyl acrylate|methyl acrylate]] with mercuric acetate in [[Chemistry:Methanol|methanol]] gives an α--mercuri ester:<ref>{{OrgSynth|vauthors=Carter HE, West HD |title=dl-Serine |collvol=3 |collvolpages=774 |year=1955 |prep = cv3p0774}}</ref>

:Hg(O<sub>2</sub>CCH<sub>3</sub>)<sub>2</sub> + CH<sub>2</sub>=CHCO<sub>2</sub>CH<sub>3</sub> → CH<sub>3</sub>OCH<sub>2</sub>CH(HgO<sub>2</sub>CCH<sub>3</sub>)CO<sub>2</sub>CH<sub>3</sub>

The resulting Hg-C bond can be cleaved with [[Chemistry:Bromine|bromine]] to give the corresponding [[Chemistry:Alkyl|alkyl]] bromide:

:CH<sub>3</sub>OCH<sub>2</sub>CH(HgO<sub>2</sub>CCH<sub>3</sub>)CO<sub>2</sub>CH<sub>3</sub> + Br<sub>2</sub> → CH<sub>3</sub>OCH<sub>2</sub>CHBrCO<sub>2</sub>CH<sub>3</sub> + BrHgO<sub>2</sub>CCH<sub>3</sub>

This reaction is called the '''Hofmann-Sand Reaction'''.<ref>{{cite journal|first1=K. A. |last1=Hofmann |first2=J. |last2=Sand |journal=Berichte der deutschen chemischen Gesellschaft |title=Ueber das Verhalten von Mercurisalzen gegen Olefine |volume=33 |issue=1 |pages=1340–1353 |date=January–April 1900 |doi=10.1002/cber.190003301231|url=https://zenodo.org/record/1425962}}</ref>

===Reaction of Hg(II) compounds with carbanion equivalents===
A general synthetic route to organomercury compounds entails alkylation with [[Chemistry:Grignard reagent|Grignard reagent]]s and organolithium compounds. Diethylmercury results from the reaction of [[Chemistry:Mercury(II) chloride|mercury chloride]] with two equivalents of ethylmagnesium bromide, a conversion that would typically be conducted in [[Chemistry:Diethyl ether|diethyl ether]] solution.<ref>{{cite book | title = Synthetic Methods of Organometallic and Inorganic Chemistry Volume 5, Copper, Silver, Gold, Zinc, Cadmium, and Mercury | editor = W.A. Herrmann | isbn = 3-13-103061-5| year = 1996}}</ref> The resulting (CH<sub>3</sub>CH<sub>2</sub>)<sub>2</sub>Hg is a [[Physics:Density|dense]] liquid (2.466 g/cm<sup>3</sup>) that [[Physics:Boiling point|boils]] at 57&nbsp;°C at 16 [[Torr|torr]]. The compound is slightly soluble in ethanol and soluble in ether.

Similarly, diphenylmercury (m.p.&nbsp;121–123&nbsp;°C) can be prepared by reaction of mercury chloride and [[Chemistry:Phenylmagnesium bromide|phenylmagnesium bromide]]. A related preparation entails formation of [[Chemistry:Phenylsodium|phenylsodium]] in the presence of mercury(II) salts.<ref>{{OrgSynth | author = Calvery, H. O. | title = Diphenylmercury | collvol = 1 | collvolpages = 228 | year = 1941 | prep = CV1P0228}}</ref>

===Other methods===
Hg(II) can be alkylated by treatment with diazonium salts in the presence of copper metal.  In this way 2-chloromercuri-naphthalene has been prepared.<ref>{{OrgSynth | author = Nesmajanow, A. N. | title = β-Naphthylmercuric Chloride | collvol = 2 | collvolpages = 432 | year = 1943 | prep = CV2P0432}}</ref>

[[Chemistry:Phenyl(trichloromethyl)mercury|Phenyl(trichloromethyl)mercury]] can be prepared by generating dichlorocarbene in the presence of phenylmercuric chloride.  A convenient carbene source is [[Chemistry:Sodium trichloroacetate|sodium trichloroacetate]].<ref>{{OrgSynth | author = Logan, T. J. | title = Phenyl(trichloromethyl)mercury | collvol = 5 | collvolpages = 969 | year = 1973 | prep = cv5p0969}}</ref> This compound on heating releases [[Chemistry:Dichlorocarbene|dichlorocarbene]]:
:C<sub>6</sub>H<sub>5</sub>HgCCl<sub>3</sub>  →  C<sub>6</sub>H<sub>5</sub>HgCl  +  CCl<sub>2</sub>

==Reactions==
Organomercury compounds are versatile synthetic intermediates due to the well controlled conditions under which they undergo cleavage of the Hg-C bonds.  [[Chemistry:Diphenylmercury|Diphenylmercury]] is a source of the phenyl radical in certain syntheses.  Treatment with aluminium gives triphenyl aluminium:

:3 Ph<sub>2</sub>Hg + 2 Al → (AlPh<sub>3</sub>)<sub>2</sub> + 3 Hg

As indicated above, organomercury compounds react with halogens to give the corresponding organic halide.
Organomercurials are commonly used in [[Chemistry:Transmetalation|transmetalation]] reactions with lanthanides and alkaline-earth metals.

Cross coupling of organomercurials with organic halides is catalyzed by palladium, which provides a method for C-C bond formation.
Usually of low selectivity, but if done in the presence of halides, selectivity increases.  Carbonylation of lactones has been shown to employ Hg(II) reagents under palladium catalyzed conditions. (C-C bond formation and Cis ester formation).<ref>"Reactivity control in palladium-catalyzed reactions: a personal account" Pavel Kocovsky J. Organometallic Chemistry 687 (2003) 256-268. {{doi|10.1016/j.jorganchem.2003.07.008}}</ref>

==Applications==
Due to their toxicity and low nucleophilicity, organomercury compounds find limited use. The [[Chemistry:Oxymercuration reaction|oxymercuration reaction]] of alkenes to alcohols using mercuric acetate proceeds via organomercury intermediates. A related reaction forming phenols is the [[Chemistry:Wolffenstein–Böters reaction|Wolffenstein–Böters reaction]]. The toxicity is useful in antiseptics such as thiomersal and merbromin, and fungicides such as [[Chemistry:Ethylmercury|ethylmercury]] chloride and [[Chemistry:Phenylmercury acetate|phenylmercury acetate]].

thumb|right|220px|Thiomersal (Merthiolate) is a well-established [[antiseptic and antifungal agent.]]

[[Chemistry:Mercurial diuretic|Mercurial diuretic]]s such as mersalyl acid were once in common use, but have been superseded by the [[Chemistry:Thiazide|thiazide]]s and loop diuretics, which are safer and longer-acting, as well as being orally active.

===Thiol affinity chromatography===
[[Chemistry:Thiol|Thiol]]s are also known as mercaptans due to their propensity for ''mer''cury ''capt''ure. Thiolates (R-S<sup>−</sup>) and [[Chemistry:Thioketone|thioketone]]s (R<sub>2</sub>C=S), being [[Chemistry:HSAB theory|soft]] [[Chemistry:Nucleophile|nucleophile]]s, form strong coordination complexes with mercury(II), a soft electrophile.<ref>{{cite book|author1=Jonathan Clayden|author2=Nick Greeves|author3=Stuart Warren|title=Organic Chemistry|url=https://books.google.com/books?id=kQgu2j_ber0C&pg=PA658|date=2012-03-15|publisher=OUP Oxford|isbn=978-0-19-927029-3|pages=658}}</ref>  This mode of action makes them useful for [[Physics:Affinity chromatography|affinity chromatography]] to separate thiol-containing compounds from complex mixtures. For example, organomercurial agarose gel or gel beads are used to isolate thiolated compounds (such as thiouridine) in a biological sample.<ref>{{cite journal |author1=Masao Ono  |author2=Masaya Kawakami  |name-list-style=amp | title = Separation of Newly-Synthesized RNA by Organomercurial Agarose Affinity Chromatography | journal = J. Biochem. | year = 1977 | volume = 81 | issue = 5 | pages = 1247–1252 | pmid = 19428}}</ref>

==See also==
*Heavy metal poisoning
*[[Medicine:Mercury poisoning|Mercury poisoning]]
*Minamata disease

==References==
{{Reflist}}

==External links==
* {{cite web | publisher = International Programme on Chemical Safety | title = 1967 Evaluations of some Pesticide Residues in Food: Organomercury compounds | url = http://www.inchem.org/documents/jmpr/jmpmono/v067pr27.htm}}
* {{cite web |title= Organomercury Compounds |work= Comparative Toxicogenomics Database | url = http://ctdbase.org/detail.go?type=chem&acc=D009941 | publisher = Mount Desert Island Biological Laboratory}}
* Safety data for a typical organomercury compound: {{cite web |url=https://www.sigmaaldrich.com/GB/en/sds/aldrich/p27127 |title=Safety data sheet for phenylmercuric acetate |publisher=Merck |date=2022-07-22 |access-date=2022-08-19 }}

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[[Category:Organomercury compounds| ]]
[[Category:Obsolete pesticides]]

{{Sourceattribution|Organomercury|1}}