Dimethylmercury
| Skeletal formula of dimethylmercury with all hydrogens added | |
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| Names | |
|---|---|
| IUPAC name
Dimethylmercury[1]
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| Identifiers | |
3D model (JSmol)
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| 3600205 | |
| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.008.916 |
| EC Number |
|
| 25889 | |
| MeSH | dimethyl+mercury |
PubChem CID
|
|
| RTECS number |
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| UNII | |
| UN number | 3383 |
CompTox Dashboard (EPA)
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|
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| Properties | |
| HgC 2H 6 | |
| Molar mass | 230.66 g mol−1 |
| Appearance | Colorless liquid |
| Odor | Sweet |
| Density | 2.961 g mL−1 |
| Melting point | −43 °C (−45 °F; 230 K) |
| Boiling point | 93 to 94 °C (199 to 201 °F; 366 to 367 K) |
Refractive index (nD)
|
1.543 |
| Thermochemistry | |
Std enthalpy of
formation (ΔfH⦵298) |
57.9–65.7 kJ mol−1 |
| Hazards | |
| GHS labelling: | |
  
| |
| Danger | |
| H300, H310, H330, H373, H410 | |
| P260, P264, P273, P280, P284, P301+P310 | |
| NFPA 704 (fire diamond) | |
| Flash point | 5 °C (41 °F; 278 K) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
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.[2]
Synthesis, structure, reactions
The compound was one of the earliest organometallics reported, reflecting its considerable stability. It is formed by treating sodium amalgam with methyl halides:
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.[3]
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 → 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.[4][5][6]
Safety
Dimethylmercury is extremely toxic and dangerous to handle. Absorption of doses as low as 0.1 mL can result in severe mercury poisoning.[7] The risks are enhanced because of the high vapor pressure of the liquid.[7]
Dimethylmercury passes through latex, PVC, butyl, and neoprene within seconds, and is very quickly absorbed through the skin. Due to its chemical nature, it carries with it a high aptitude for its effortless ability to pass through the same safety equipment and barriers that prevent lab accidents such as direct bodily contact (skin; eyes; oral) that have proved to be adequate protection for a majority of laboratory chemical substances.
Therefore, due to its high efficiency in penetrating skin barriers, the most common gloves used in a majority of laboratories and/or clinical settings do not provide adequate protection from dimethylmercury. It's widely understood and accepted that the only safe precaution is to handle dimethylmercury while wearing highly resistant laminated gloves; adding long-cuffed neoprene or other heavy-duty gloves over the first pair. In addition, the consistent use of a long face shield and working under a fume hood should be observed.[7][8]
Dimethylmercury crosses the blood–brain barrier easily, probably owing to formation of a complex with cysteine.[9] It is eliminated from the organism slowly, and therefore has a tendency to bioaccumulate. The symptoms of poisoning may be delayed by months, resulting in many cases in which a diagnosis was ultimately discovered, but only at the point in which it is often too late for an effective treatment regimen to be successful.[9]
The toxicity of dimethylmercury was highlighted with the death of the inorganic chemist Karen Wetterhahn of Dartmouth College in 1997. After spilling no more than a few drops of this compound on her latex-glove, the barrier was immediately compromised and within seconds it was absorbed into the back of her hand, quickly circulating and resulting in her death ten months later.[7] This accident is a common toxicology case-study and spurred the development of modern advanced chemical-protection clothing which is now used when any exposure to severely toxic and/or highly penetrative substances is possible (ex. in chemical munitions stockpiles and decontamination facilities).[citation needed]
See also
References
- ^ "dimethyl mercury - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 10 March 2012.
- ^ Agency for Toxic Substances and Disease Registry (March 1999). "Toxological profile for mercury". United States Department of Health and Human Services, Public Health Service. Retrieved 16 August 2014.
- ^ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ O'Halloran, T. V.; Singer, C. P. (1998-03-10). "199Hg Standards". Northwestern University. Retrieved 2012-05-24.
{{cite web}}: CS1 maint: multiple names: authors list (link) - ^ Hoffman, R. (2011-08-01). "(Hg) Mercury NMR". Jerusalem: The Hebrew University. Retrieved 2012-05-24.
- ^ "Delayed Toxic Syndromes" (pdf). Terrorism by Fear and Uncertainty. ORAU.
- ^ a b c d "OSHA Safety Hazard Information Bulletin on Dimethylmercury". Safety and Health Information Bulletins (SHIBs), 1997-1998. OSHA. 1991-02-15.
- ^ Cotton, S. (October 2003). "Dimethylmercury and Mercury Poisoning. The Karen Wetterhahn story". Molecule of the Month. Bristol University.
- ^ a b "The Karen Wetterhahn story". Retrieved 1 September 2014.