- Organomercury
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Organomercury compounds
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 IV drugs.
The toxicity of organomercury compounds[1][2] 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 a topical antiseptic, while Nitromersol is used as a preservative for vaccines and antitoxins.
Contents
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 direct mercuration upon treatment with Hg(O2CCH3)2. The one acetate group that remains on mercury can be displaced by chloride:[3]
- C6H5OH + Hg(O2CCH3)2 → C6H4(OH)-2-HgO2CCH3 + CH3CO2H
- C6H4(OH)-2-HgO2CCH3 + NaCl → C6H4(OH)-2-HgCl + NaO2CCH3
The first such reaction, including a mercuration of benzene itself was reported by Otto Dimroth between 1898 and 1902.[4][5][6]
Addition to alkenes
The Hg2+ center binds to alkenes, inducing the addition of hydroxide and alkoxide. For example, treatment of methyl acrylate with mercuric acetate in methanol gives an α--mercuri ester:[7]
- Hg(O2CCH3)2 + CH2=CHCO2CH3 → CH3OCH2CH(HgO2CCH3)CO2CH3
The resulting Hg-C bond can be cleaved with bromine to give the corresponding alkyl bromide:
- CH3OCH2CH(HgO2CCH3)CO2CH3 + Br2 → CH3OCH2CHBrCO2CH3 + BrHgO2CCH3
This reaction is called the Hofmann-Sand Reaction.[8]
Reaction of Hg(II) compounds with carbanion equivalents
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]
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.[11]
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
Reactions
Organomercury compounds are versatile synthetic intermediates due to the well controlled conditions that 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.
Applications
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.
Mercurial diuretics such as mersalyl acid were once in common use, but have been superseded by the thiazides and loop diuretics, which are safer and longer-acting, as well as being orally active.
Thiol affinity chromatography
Thiols are also known as mercaptans due to their propensity for mercury capture. Thiolates (R-S-) and thioketones (R2-S=O) being soft nucleophiles form a strong coordination complex with mercury(II), a soft electrophile.[13] As a result, organomercurial agarose gel or gel beads are used to isolate thiolated compounds (such as thiouridine) in a biological sample.[14]
See also
- Heavy metal poisoning
- Mercury poisoning
- Minamata disease
- Compounds of carbon with other elements in the periodic table:
CH He CLi CBe CB CC CN CO CF Ne CNa CMg CAl CSi CP CS CCl CAr CK CCa CSc CTi CV CCr CMn CFe CCo CNi CCu CZn CGa CGe CAs CSe CBr CKr CRb CSr CY CZr CNb CMo CTc CRu CRh CPd CAg CCd CIn CSn CSb CTe CI CXe CCs CBa CHf CTa CW CRe COs CIr CPt CAu CHg CTl CPb CBi CPo CAt Rn Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Uuq Uup Uuh Uus Uuo ↓ CLa CCe CPr CNd CPm CSm CEu CGd CTb CDy CHo CEr CTm CYb CLu Ac Th Pa CU Np Pu Am Cm Bk Cf Es Fm Md No Lr Chemical bonds to carbon Core organic chemistry Many uses in chemistry Academic research, but no widespread use Bond unknown / not assessed References
- ^ 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.
- ^ Whitmore, F. C.; Hanson, E. R. (1941), "o-Chloromercuriphenol", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0161; Coll. Vol. 1: 161
- ^ 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., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0774; 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., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0228; Coll. Vol. 1: 228
- ^ Nesmajanow, A. N. (1943), "β-Naphthylmercuric Chloride", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV2P0432; Coll. Vol. 2: 432
- ^ Logan, T. J. (1973), "Phenyl(trichloromethyl)mercury", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p0969; Coll. Vol. 5: 969
- ^ . ISBN 0-19-850346-6.
- ^ Masao Ono and Masaya Kawakami (1977). "Separation of Newly-Synthesized RNA by Organomercurial Agarose Affinity Chromatography". J. Biochem 81 (5): 1247–1252. PMID 19428.
External links
- "1967 Evaluations of some Pesticide Residues in Food: Organomercury compounds". International Programme on Chemical Safety. http://www.inchem.org/documents/jmpr/jmpmono/v067pr27.htm.
- "Organomercury Compounds". Comparative Toxicogenomics Database. Mount Desert Island Biological Laboratory. http://ctdbase.org/detail.go?type=chem&acc=D009941.
- Safety data for a typical organomercury compound: phenylmercuric hydroxide
Categories:- Organomercury compounds
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