Dimethylmercury

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Dimethylmercury
Skeletal formula of dimethylmercury with all explicit hydrogen added
Dimethyl-mercury-3D-vdW.png
Identifiers
CAS number 593-74-8 N
PubChem 11645
ChemSpider 11155 YesY
UNII C60TQU15XY YesY
EC number 209-805-3
UN number 3383
MeSH dimethyl+mercury
ChEBI CHEBI:30786 YesY
RTECS number OW3010000
Beilstein Reference 3600205
Gmelin Reference 25889
Jmol-3D images Image 1
Properties
Molecular formula HgC
2
H
6
Molar mass 230.66 g mol−1
Appearance Colorless liquid
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
ΔfHo298
57.9–65.7 kJ mol−1
Hazards
GHS pictograms The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
GHS hazard statements H300, H310, H330, H373, H410
GHS precautionary statements P260, P264, P273, P280, P284, P301+310
EU Index 080-007-00-3
EU classification Very Toxic T+ Dangerous for the Environment (Nature) N
R-phrases R26/27/28, R33, R50/53
S-phrases (S1/2), S13, S28, S36, S45
NFPA 704
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., propane Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 5 °C (41 °F; 278 K)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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.[citation needed]

Synthesis, structure, reactions[edit]

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 → 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.[2]

Reactions[edit]

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[edit]

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 all but 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.[3][4][5]

Safety[edit]

Dimethylmercury is extremely toxic and dangerous to handle. Absorption of doses as low as 0.1 mL has proven fatal.[6] The risks are enhanced because of the high vapor pressure of the liquid.[citation needed]

Dimethylmercury passes through latex, PVC, butyl, and neoprene rapidly (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.[6][7]

Dimethylmercury crosses the blood–brain barrier easily, probably owing to formation of a complex with cysteine.[citation needed] 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.[citation needed]

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.[6]

See also[edit]

References[edit]

  1. ^ "dimethyl mercury - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 10 March 2012. 
  2. ^ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5. 
  3. ^ O'Halloran, T. V.; Singer, C. P. (1998-03-10). "199Hg Standards". Northwestern University. Retrieved 2012-05-24. 
  4. ^ Hoffman, R. (2011-08-01). "(Hg) Mercury NMR". Jerusalem: The Hebrew University. Retrieved 2012-05-24. 
  5. ^ "Delayed Toxic Syndromes" (pdf). Terrorism by Fear and Uncertainty. ORAU. 
  6. ^ a b c "OSHA Safety Hazard Information Bulletin on Dimethylmercury". Safety and Health Information Bulletins (SHIBs), 1997-1998. OSHA. 1991-02-15. 
  7. ^ Cotton, S. (October 2003). "Dimethylmercury and Mercury Poisoning. The Karen Wetterhahn story". Molecule of the Month. Bristol University. 

External links[edit]