Dimethylmercury
Encyclopedia
Dimethylmercury is an organomercury compound. This colorless liquid is one of the strongest known neurotoxin
s. It is described as having a slightly sweet smell, although inhaling enough vapor to detect its odor would be hazardous.
with methyl halide
s:
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 Å.
Whereas dimethylmercury is a volatile liquid, CH3HgCl is a crystalline solid.
, it is 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. U.S. Department of Energy institute ORISE
reported the price of dimethylmercury as being $18.38 per gram.
of the liquid.
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.
Dimethylmercury crosses the blood–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.
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
s. 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 amalgamSodium amalgam
Sodium amalgam, commonly denoted Na, is an alloy of mercury and sodium. The term amalgam is used for alloys, intermetallic compounds, and solutions involving mercury as a major component. Sodium amalgam is often used in reactions as strong reducing agents with better handling properties compared...
with methyl halide
Halide
A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides...
s:
- Hg + 2 Na + 2 CH3I → (CH3)2Hg + 2 NaISodium iodideSodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.-Uses:Sodium iodide is commonly used to treat and prevent iodine deficiency....
It can also be obtained by alkylation
Alkylation
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in...
of mercuric chloride with methyllithium. The molecule adopts a linear structure with Hg-C bond lengths of 2.083 Å.
Reactions
The most striking feature of the compound is its nonreactivity toward water. 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 has almost no applications because of the risks involved. In toxicologyToxicology
Toxicology is a branch of biology, chemistry, and medicine concerned with the study of the adverse effects of chemicals on living organisms...
, it is used as a reference toxin. It has also been used to calibrate NMR
NMR spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained...
instruments for detection of mercury, although less toxic mercury salts are preferred. U.S. Department of Energy institute ORISE
Oak Ridge Institute for Science and Education
The Oak Ridge Institute for Science and Education is a U.S. Department of Energy institute headquartered in Oak Ridge, Tennessee focusing on scientific initiatives to research health risks from occupational hazards, assess environmental cleanup, respond to radiation medical emergencies, support...
reported the price of dimethylmercury as being $18.38 per gram.
Safety
Dimethylmercury is extremely dangerous. Absorption of doses as low as 0.1 mL has proven fatal. The risks are enhanced because of the high vapor pressureVapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
of the liquid.
Dimethylmercury passes through latex
Latex
Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...
, PVC
Polyvinyl chloride
Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
, butyl
Butyl rubber
Butyl rubber is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for Isobutylene Isoprene Rubber. Polyisobutylene, also known as "PIB" or polyisobutene, n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based...
, and neoprene
Neoprene
Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene in general has good chemical stability, and maintains flexibility over a wide temperature range...
rapidly (within seconds) and is absorbed through the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
. 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 blood–brain barrier easily, probably owing to formation of a complex with cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
. It is eliminated from the organism slowly, and therefore has a tendency to bioaccumulate. The symptoms of poisoning
Mercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...
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
Karen Wetterhahn
Karen Wetterhahn was a well-known professor of chemistry at Dartmouth College, New Hampshire, who specialized in toxic metal exposure. She made national headlines when mercury poisoning claimed her life at the age of 48 due to accidental exposure to the organic mercury compound dimethylmercury...
of Dartmouth College in 1997, months after spilling no more than a few drops of this compound on her latex-gloved hand.