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Concept
Diméthylmercure
Résumé
Dimethylmercury ((CH3)2Hg), also known as mercury dimethanide, is an extremely toxic organomercury compound. A highly volatile, reactive, flammable, and colorless liquid, dimethylmercury is one of the strongest known neurotoxins, with a quantity of less than 0.1 mL capable of inducing severe mercury poisoning resulting in death, and is easily absorbed through the skin. Dimethylmercury is capable of permeating many materials, including plastic and rubber compounds. It has been described as having a slightly sweet odor, although those who have reported its smell were exposed to harmful amounts.
The compound was one of the earliest organometallics reported, reflecting its considerable stability. The compound was first prepared by George Buckton in 1857 by a reaction of methylmercury iodide with potassium cyanide:
2 CH3HgI + 2 KCN → Hg(CH3)2 + 2 KI + (CN)2 + Hg
Later, Frankland discovered that it could be synthesized by treating sodium amalgam with methyl halides:
Hg + 2 Na + 2 CH3I → Hg(CH3)2 + 2 NaI
It can also be obtained by alkylation of mercuric chloride with methyllithium:
HgCl2 + 2 LiCH3 → Hg(CH3)2 + 2 LiCl
The molecule adopts a linear structure with Hg–C bond lengths of 2.083 Å.
An unusual feature of this compound is its low reactivity towards proton sources, being stable in water and reacting with mineral acids at a significant rate only at elevated temperatures, whereas the corresponding organocadmium and organozinc compounds (and most metal alkyls in general) hydrolyze rapidly. The difference reflects the high electronegativity of Hg (Pauling EN = 2.00) and the low affinity of Hg(II) for oxygen ligands. The compound undergoes a redistribution reaction with mercuric chloride to give methylmercury chloride:
(CH3)2Hg + HgCl2 → 2 CH3HgCl
Whereas dimethylmercury is a volatile liquid, methylmercury chloride is a crystalline solid.
Dimethylmercury currently has few applications because of the risks involved.
Source officielle
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