Dimethylmercury
Organomercury chemical compound
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Synthesis, structure, and reactions
The compound was one of the earliest organometallics reported, reflecting its considerable stability. The compound was first prepared by George Buckton in 1857 by a reaction of methylmercury iodide with potassium cyanide:
- 2 CH3HgI + 2 KCN → Hg(CH3)2 + 2 KI + (CN)2 + Hg
Later, Edward Frankland discovered that it could be synthesized 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.
Reactivity and physical properties
Dimethylmercury is stable in water and reacts with mineral acids at a significant rate only at elevated temperatures, whereas the corresponding organocadmium and organozinc compounds (and most metal alkyls in general) hydrolyze rapidly. The difference reflects the high electronegativity of Hg (Pauling EN = 2.00) and the low affinity of Hg(II) for oxygen ligands. The compound undergoes a redistribution reaction with mercuric chloride to give methylmercury chloride:
- (CH3)2Hg + HgCl2 ⇌ 2 CH3HgCl
Whereas dimethylmercury is a volatile liquid, methylmercury chloride is a crystalline solid.
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Use
Dimethylmercury has few practical applications because of its danger to human life. It has been studied for reactions involving bonding methylmercury cations to target molecules, forming potent bactericides, but methylmercury's bioaccumulation and ultimate toxicity has led to it being largely abandoned in favor of the less toxic ethylmercury and diethylmercury compounds, which perform a similar function without the bioaccumulation hazard.
In toxicology, it still finds limited use as a reference toxin. It is also used to calibrate NMR instruments for detection of mercury (δ 0 ppm for 199Hg NMR), although diethylmercury and less toxic mercury salts are now preferred.
Around 1960, Phil Pomerantz, a worker at the Bureau of Naval Weapons, suggested that dimethylmercury be used as a fuel mix with red fuming nitric acid. This was never done, although it did lead to testing a red fuming nitric acid-unsymmetrical dimethylhydrazine rocket with elemental mercury being injected into the combustion chamber at the Naval Ordnance Test Station.
Safety
Dimethylmercury is extremely toxic and dangerous to handle. Absorption of doses as low as 0.1 mL can result in severe mercury poisoning. The risks are enhanced because of the compound's high vapor pressure. Since it is highly lipophilic, it is very easily absorbed through the skin and into body fat.
Dimethylmercury can rapidly permeate many materials, including latex, PVC and neoprene. 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. The American Occupational Safety and Health Administration (OSHA) 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.
Dimethylmercury is metabolized after several days to methylmercury. Methylmercury crosses the blood–brain barrier easily, probably owing to formation of a complex with cysteine. It easily absorbs into the body and has a tendency to bioaccumulate in adipose tissue, plasma proteins and the brain. The symptoms of mercury poisoning may be delayed by months, resulting in cases in which a diagnosis is ultimately discovered, but only at a point in which it is too late or almost too late for an effective treatment regimen to be successful. Symptoms include tingling, nausea and deterioration of balance, speech, hearing and vision. Organomercury poisoning is also known as Minamata disease.
Incidents
- As early as 1865, two workers in the laboratory of Edward Frankland died after exhibiting progressive neurological symptoms following accidental exposure to the compound.
- In 1971, a chemist died in Czechoslovakia after preparing 6000g of dimethylmercury over a three month period.
- Karen Wetterhahn, a professor of chemistry at Dartmouth College, died in 1997, ten months after spilling only a few drops of dimethylmercury onto her latex gloves. This incident resulted in improved awareness of the substance's extreme toxicity and its ability to easily penetrate latex. New material-handling guidelines were published, many institutions purged their supplies of the compound, and it became almost impossible to buy.
- The 2012 death of Christoph Bulwin, a 40-year-old database administrator for IG Bergbau, Chemie, Energie, may have been caused by an attack involving dimethylmercury.
- On August 26, 2026, a graduate student at the Massachusetts Institute of Technology visited a local emergency room after self-reporting an exposure to synthesized dimethylmercury. The student showed “no sign of exposure to mercury" in initial blood tests, per a statement from MIT officials. The incident prompted a several day closure of the Camille Edouard Dreyfus Chemistry Building, more commonly known as Building 18, amid "specialized decontamination efforts." Subsequent investigation questioned whether the student had synthesized the compound.