Dimethylmercury ((CH3)2Hg) is an organomercury compound. This colorless liquid is one of the strongest known neurotoxins. It is described as having a slightly sweet smell, although inhaling enough vapor to detect its odor would be hazardous.
Synthesis, structure, reactions
The compound was one of the earliest organometallic complexes reported, reflecting its considerable stability. It is formed by treating sodium amalgam with methyl halides:
- Hg + 2 Na + 2 CH3I â†' Hg(CH3)2 + 2 NaI
It can also be obtained by alkylation of mercuric chloride with methyllithium:
The molecule adopts a linear structure with Hg-C bond lengths of 2.083 Ã….
Reactions
The most striking feature of the compound is its nonreactivity toward water, whereas the corresponding organocadmium and organozinc compounds hydrolyze rapidly. The difference reflects the low affinity of Hg(II) for oxygen ligands. The compound reacts with mercuric chloride to give the mixed chloro-methyl compound:
- (CH3)2Hg + HgCl2 â†' 2 CH3HgCl
Whereas dimethylmercury is a volatile liquid, CH3HgCl is a crystalline solid.
Use
Dimethylmercury currently has almost no applications because of the risks involved. As with many methyl-organometallics, it is a methylating agent that can donate its methyl groups to an organic molecule; however, the development of less acutely toxic nucleophiles such as dimethylzinc and trimethylaluminium, and the subsequent introduction of Grignard reagents (organometallic halides), has essentially rendered this compound obsolete in organic chemistry. It was formerly studied for reactions in which the methylmercury cation was bonded to the target molecule, forming potent bactericides; however, the bioaccumulation and ultimate toxicity of methylmercury has largely led it to be abandoned for this purpose in favor of the related ethylmercury cation, which perform a similar function without the bioaccumulation hazard.
In toxicology, it was formerly used as a reference toxin. It has also been used to calibrate NMR instruments for detection of mercury, although less toxic mercury salts are preferred.
Safety
Dimethylmercury is extremely toxic and dangerous to handle. Absorption of doses as low as 0.1 mL has proven fatal. The risks are enhanced because of the high vapor pressure of the liquid.
Dimethylmercury passes through latex, PVC, butyl, and neoprene within seconds and is absorbed through the skin. Therefore, most laboratory gloves do not provide adequate protection from it, and the only safe precaution is to handle dimethylmercury while wearing highly resistant laminated gloves underneath long-cuffed neoprene or other heavy-duty gloves. A long face shield and work under a fume hood are also indicated.
Dimethylmercury crosses the bloodâ€"brain barrier easily, probably owing to formation of a complex with cysteine. It is eliminated from the organism slowly, and therefore has a tendency to bioaccumulate. The symptoms of poisoning may be delayed by months, possibly too late for effective treatment.
The toxicity of dimethylmercury was highlighted with the death of the inorganic chemist Karen Wetterhahn of Dartmouth College in 1997, months after spilling no more than a few drops of this compound on her latex-gloved hand.
See also
- Diethylmercury
- Mercury poisoning
- Karen Wetterhahn
- Minamata disease
- Methylmercury
- Cyclopentadienyl nickel nitrosyl
References
External links
- ATSDR - ToxFAQs: Mercury
- ATSDR - Public Health Statement: Mercury
- ATSDR - ALERT! Patterns of Metallic Mercury Exposure, 6/26/97
- ATSDR - MMG: Mercury
- ATSDR - Toxicological Profile: Mercury
- National Pollutant Inventory - Mercury and compounds Fact Sheet
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