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 cation, CH3Hg+; ethylmercury cation, C2H5Hg+; dimethylmercury, (CH3)2Hg, diethylmercury, and merbromin ("Mercurochrome"). Thiomersal is used as a preservative for vaccines and intravenous drugs.
The toxicity of organomercury compounds12 presents both dangers and benefits. Dimethylmercury in particular, is notoriously toxic, but has found use as an antifungal agent and insecticide. Merbromin and phenylmercuric borate are used as topical antiseptics, while Nitromersol is used as a preservative for vaccines and antitoxins.
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.
- C6H5OH + Hg(O2CCH3)2 → C6H4(OH)–2-HgO2CCH3 + CH3CO2H
- C6H4(OH)–2–HgO2CCH3 + NaCl → C6H4(OH)–2-HgCl + NaO2CCH3
- Hg(O2CCH3)2 + CH2=CHCO2CH3 → CH3OCH2CH(HgO2CCH3)CO2CH3
- CH3OCH2CH(HgO2CCH3)CO2CH3 + Br2 → CH3OCH2CHBrCO2CH3 + BrHgO2CCH3
This reaction is called the Hofmann-Sand Reaction.8
A general synthetic route to organomercury compounds entails alkylation with Grignard reagents and organolithium compounds. Diethylmercury results from the reaction of mercury chloride with two equivalents of ethylmagnesium bromide, a conversion that would typically be conducted in diethyl ether solution.9 The resulting (CH3CH2)2Hg is a dense liquid (2.466 g/cm3) that boils at 57 °C at 16 torr. The compound is slightly soluble in ethanol and soluble in ether.
Similarly, diphenylmercury (m.p. 121–123 °C) can be prepared by reaction of mercury chloride and phenylmagnesium bromide. A related preparation entails formation of phenylsodium in the presence of mercury(II) salts.10
Phenyl(trichloromethyl)mercury compounds can be prepared by generating dichlorocarbene in the presence of phenylmercuric chloride. A convenient carbene source is sodium trichloroacetate.12 This compound on heating releases dichlorocarbene:
- C6H5HgCCl3 → C6H5HgCl + CCl2
Organomercury compounds are versatile synthetic intermediates due to the well controlled conditions under which they undergo cleavage of the Hg-C bonds. Diphenylmercury is a source of the phenyl radical in certain syntheses. Treatment with aluminium gives triphenyl aluminium:
- 3 Ph2Hg + 2 Al → (AlPh3)2 + 3 Hg
As indicated above, organomercury compounds react with halogens to give the corresponding organic halide. Organomercurials are commonly used in 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).13
Due to their toxicity and low nucleophilicity, organomercury compounds find limited use. The oxymercuration reaction of alkenes to alcohols using mercuric acetate proceeds via organomercury intermediates. A related reaction forming phenols is the Wolfenstein-Boters reaction. The toxicity is useful in antiseptics such as thiomersal and merbromin, and fungicides such as ethylmercury chloride and phenylmercury acetate.
Thiols are also known as mercaptans due to their propensity for mercury capture. Thiolates (R-S-) and thioketones (R2-C=S) being soft nucleophiles form a strong coordination complex with mercury(II), a soft electrophile.14 As a result, organomercurial agarose gel or gel beads are used to isolate thiolated compounds (such as thiouridine) in a biological sample.15
- Heavy metal poisoning
- Mercury poisoning
- Minamata disease
- Compounds of carbon with other elements in the periodic table:
|Core organic chemistry||Many uses in chemistry|
|Academic research, but no widespread use||Bond unknown|
- Hintermann, H. (2010). Organomercurials. Their Formation and Pathways in the Environment. Metal Ions in Life Sciences 7. Cambridge: RSC publishing. pp. 365–401. ISBN 978-1-84755-177-1.
- Aschner, M.; Onishchenko, N.; Ceccatelli, S. (2010). Toxicology of Alkylmercury Compounds. Metal Ions in Life Sciences 7. Cambridge: RSC publishing. pp. 403–434. ISBN 978-1-84755-177-1.
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- Otto Dimroth (1898). "Directe Einführung von Quecksilber in aromatische Verbindungen". Berichte der deutschen chemischen Gesellschaft 31 (2): 2154–2156. doi:10.1002/cber.189803102162.
- Otto Dimroth (1899). "Ueber die Einwirkung von Quecksilberoxydsalzen auf aromatische Verbindungen". Berichte der deutschen chemischen Gesellschaft 32 (1): 758–765. doi:10.1002/cber.189903201116.
- Otto Dimroth (1902). "Ueber die Mercurirung aromatischer Verbindungen". Berichte der deutschen chemischen Gesellschaft 35 (2): 2032–2045. doi:10.1002/cber.190203502154.
- Carter, H. E.; West, H. D. (1955), "dl-Serine", Org. Synth.; Coll. Vol. 3: 774
- K. A. Hofmann, J. Sand (1900). "Ueber das Verhalten von Mercurisalzen gegen Olefine". Berichte der deutschen chemischen Gesellschaft 33 (1): 1340–1353. doi:10.1002/cber.190003301231.
- W.A. Herrmann (ed.). Synthetic Methods of Organometallic and Inorganic Chemistry Volume 5, Copper, Silver, Gold, Zinc, Cadmium, and Mercury. ISBN 3-13-103061-5.
- Calvery, H. O. (1941), "Diphenylmercury", Org. Synth.; Coll. Vol. 1: 228
- Nesmajanow, A. N. (1943), "β-Naphthylmercuric Chloride", Org. Synth.; Coll. Vol. 2: 432
- Logan, T. J. (1973), "Phenyl(trichloromethyl)mercury", Org. Synth.; Coll. Vol. 5: 969
- "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
- . ISBN 0-19-850346-6. Missing or empty
- Masao Ono and Masaya Kawakami (1977). "Separation of Newly-Synthesized RNA by Organomercurial Agarose Affinity Chromatography". J. Biochem 81 (5): 1247–1252. PMID 19428.
- "1967 Evaluations of some Pesticide Residues in Food: Organomercury compounds". International Programme on Chemical Safety.
- "Organomercury Compounds". Comparative Toxicogenomics Database. Mount Desert Island Biological Laboratory.
- Safety data for a typical organomercury compound: phenylmercuric hydroxide