Dimethylmercury

Dimethylmercury ((CH3)2Hg) is an 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.[2] It has a slightly sweet odor,[3] although inhaling enough of the chemical to notice this would be hazardous.

Dimethylmercury
Names
IUPAC name
Dimethylmercury[1]
Identifiers
3D model (JSmol)
3600205
ChEBI
ChemSpider
ECHA InfoCard 100.008.916
EC Number
  • 209-805-3
25889
MeSH dimethyl+mercury
RTECS number
  • OW3010000
UNII
UN number 2929
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)
1.543
Thermochemistry
57.9–65.7 kJ mol−1
Hazards
GHS pictograms
GHS Signal word Danger
H300, H310, H330, H373, H410
P260, P264, P273, P280, P284, P301+310
NFPA 704 (fire diamond)
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneHealth code 4: Very short exposure could cause death or major residual injury. E.g. VX gasReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazards (white): no code
4
4
3
Flash point 5 °C (41 °F; 278 K)
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

The acute toxicity of the compound was demonstrated by the 1997 death of heavy metal chemist Karen Wetterhahn, who died 10 months after a single exposure on August 14th, 1996 of only a few drops permeated through her disposable latex gloves which were at the time mistakenly believed to offer adequate protection.

Synthesis, structure, and reactions

The compound was one of the earliest organometallics reported, reflecting its considerable stability. It is formed 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.[4]

Reactions

A novel feature of this compound is its unreactivity towards water and the fact that it reacts with mineral acids at a significant rate only at elevated temperatures,[5][6] 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, methylmercury chloride is a crystalline solid.[7]

Use

Dimethylmercury currently has few 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 less toxic diethylmercury and ethylmercury compounds, 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 diethylmercury and less toxic mercury salts are now preferred.[8][9][10]

Safety

Dimethylmercury is extremely toxic and dangerous to handle. Absorption of doses as low as 0.1 mL can result in severe mercury poisoning.[3] The risks are enhanced because of the high vapor pressure of the liquid.[3]

Permeation tests showed that several types of disposable latex or polyvinyl chloride gloves (typically, about 0.1 mm thick), commonly used in most laboratories and clinical settings, had high and maximal rates of permeation by dimethylmercury within 15 seconds.[11] The American Occupational Safety and Health Administration advises handling dimethylmercury with highly resistant laminated gloves with an additional pair of abrasion-resistant gloves worn over the laminate pair, and also recommends using a face shield and working in a fume hood.[3][12]

Dimethylmercury is metabolized after several days to methylmercury.[11] Methylmercury crosses the blood–brain barrier easily, probably owing to formation of a complex with cysteine.[12] 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 cases in which a diagnosis is ultimately discovered, but only at the point in which it is too late for an effective treatment regimen to be successful.[12]

The toxicity of dimethylmercury was highlighted with the death of Karen Wetterhahn, a professor of chemistry at Dartmouth College, in 1997. Professor Wetterhahn specialized in heavy metal poisoning. After she spilled a few drops of this compound on her latex glove, the barrier was compromised, and within seconds it had permeated her gloves and was absorbed into her skin. It circulated through her body and accumulated in her brain, resulting in her death ten months later.[3] This accident is a common toxicology case-study and directly resulted in improved safety procedures for chemical-protection clothing and fume hood use,[13] which are now called for when any exposure to such severely toxic and/or highly penetrative substances is possible (e.g., in chemical munitions stockpiles and decontamination facilities).

See also

References
  1. "dimethyl mercury - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 29 January 2021.
  2. "Toxicological Profile for Mercury". Agency for Toxic Substances and Disease Registry. March 1999. Retrieved 29 January 2021.
  3. "OSHA Hazard Information Bulletins - Dimethylmercury". OSHA.gov. Retrieved 29 January 2021.
  4. Holleman, A. F.; Wiberg, Egon; Wiberg, Nils (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
  5. Crabtree, Robert H. (2005). The Organometallic Chemistry of the Transition Metals (4th ed.). Hoboken, N.J.: John Wiley. p. 424. ISBN 0471662569. OCLC 61520528.
  6. Baughman, George L.; Gordon, John A.; Wolfe, N. Lee; Zepp, Richard G. (September 1973). Chemistry of Organomercurials in Aquatic Systems. United States Environmental Protection Agency Ecological Research Series. U.S. Govt. Print. Off. pp. 34–40. Retrieved 29 January 2021.
  7. "Methylmercury chloride". PubChem. National Center for Biotechnology Information, United States National Institutes of Health. Retrieved 29 January 2021.
  8. O'Halloran, T. V.; Singer, C. P. (10 March 1998). "199Hg Standards". Northwestern University. Archived from the original on 14 May 2005. Retrieved 20 January 2021.
  9. Hoffman, R. (1 August 2011). "(Hg) Mercury NMR". Jerusalem: The Hebrew University. Retrieved 29 January 2021.
  10. "Delayed Toxic Syndromes" (PDF). Terrorism by Fear and Uncertainty. ORAU. Archived from the original (PDF) on 23 April 2012. Retrieved 29 January 2021.
  11. Nierenberg, David W.; Nordgren, Richard E.; Chang, Morris B.; Siegler, Richard W.; Blayney, Michael B.; Hochberg, Fred; Toribara, Taft Y.; Cernichiari, Elsa; Clarkson, Thomas (1998). "Delayed Cerebellar Disease and Death after Accidental Exposure to Dimethylmercury". New England Journal of Medicine. 338 (23): 1672–1676. doi:10.1056/NEJM199806043382305. PMID 9614258.
  12. Cotton, Simon (October 2003). "Dimethylmercury and Mercury Poisoning: The Karen Wetterhahn story". Molecule of the Month. Bristol University School of Chemistry. doi:10.6084/m9.figshare.5245807. Retrieved 29 January 2021.
  13. Cavanaugh, Ray (19 February 2019). "The dangers of dimethylmercury". Chemistry World. Royal Society of Chemistry. Retrieved 29 January 2021.

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