DIMETHYLMERCURY

General Description

Mercury dimethyl is a toxic environmental pollutant. It is found in polluted bottom sediments and in the bodies of fishes and birds. In the bodies of fishes and birds it occurs along with monomethyl mercury. The latter, as CH3Hg+ ion, is formed by microorganism-induced biological methylation of elemental mercury or agricultural fungicide mercury compounds that are discharged into the environment.
Mercury dimethyl is used in inorganic synthesis; and as a reference standard for Hg-NMR.

Reaction

Mercury dimethyl, unlike zinc dimethyl, is fairly stable at ordinary temperatures, and is not attacked by air or water.
Mercury dimethyl undergoes single replacement reactions with several metals such as alkali and alkaline earth metals, zinc, aluminum, tin, lead and bismuth forming their corresponding dialkyls.
Such reaction is a synthetic route to prepare many organometallic compounds. Thus, reaction with metallic zinc yields zinc dimethyl:
(CH3)2Hg + Zn → (CH3)2Zn + Hg

Toxicity

Mercury dimethyl is a highly toxic substance by all routes of exposure. Several cases of human poisoning are well documented. (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, 2nd ed. p. 574, New York: John Wiley & Sons.) The compound can accumulate in the brain and blood of humans. Intake of small quantities can cause death.

Description

The first indication of the extreme toxicity of dimethylmercury (DMM) was documented in 1863 when two laboratory assistants died of DMM poisoning while synthesizing DMM in the laboratory of Frankland and Duppa. There are numerous reports of people dying from alkyl mercury compounds including a chemist who was preparing several thousand grams ofDMMin his laboratory in 1974. The extreme toxicity was revisited in 1997, when Karen Wetterhahn, an internationally renowned researcher of the carcinogenic effects of heavy metals on DNA repair proteins, died within a few months after a single exposure of less than a milliliter of DMM on her latex-covered hand. DMM is extremely toxic and lethal at a dose of approximately 400 mg of mercury (equivalent to a few drops) or about 5mgkg-1 of body weight or as little as 0.1 ml

Chemical Properties

Dimethyl mercury is a volatile colorless liquid with faint sweet odor.

Chemical Properties

colourless liquid

Uses

DMM has limited use because of its toxicity but can be used to calibrate research equipment, as in its application as a standard reference material for 199Hg NMR measurements.

Uses

Dimethylmercury is used as a reagent ininorganic synthesis, and as a reference standardfor mercury nuclear magnetic resonance(Hg NMR). It is an environmental pollutantfound in bottom sediments and also inthe bodies of birds and marine mammalssuch as whales and fishes. It occurs in fishesand birds along with monomethylmercury. Inhumans, its presence is attributed to the consumptionof pilot whale meat, cod fish, andother sea food.

Uses

As inorganic reagent.

Definition

ChEBI: Dimethylmercury is a methylmercury compound.

Health Hazard

All alkylmercury compounds are highly toxicby all routes of exposure. There are manyserious cases of human poisoning frommethylmercury (Lu 2003). Outbreaks ofmass poisoning from consumption of contaminatedfish occurred in Japan during the1950s, causing a severe neurological disease,so-called “Minamata disease,” whichresulted in hundreds of deaths. A similaroutbreak of food poisoning from contaminatedwheat caused several hundred deathsin Iraq in 1972. A tragic death from a singleacute transdermal exposure to dimethylmercury(estimated between 0.1 to 0.5 mL) thatpenetrated into the skin through disposablelatex gloves has occurred (Blayney et al.1997; The New York Times, June 11, 1997).The symptoms reported were episodes ofnausea and vomiting occurring three monthsafter the exposure followed by onset ofataxia, slurred speech (dysarthia), and loss ofvision and hearing 2 months after that. Thedeath occurred in about six months after theaccident.
Methylmercury can concentrate in certainfetal organs, such as the brain. Thetarget organs are the brain and the centralnervous system. It can cause death, miscarriage,and deformed fetuses. Unlike inorganicmercury compounds, it can penetrate throughthe membrane barrier of the erythrocyte,accumulating at about 10 times greater concentrationthan that in the plasma (WHO1976). Its rate of excretion on the bloodlevel is very slow. It gradually accumulatesin the blood. Such accumulation was found toreach 60% equilibrium at about 90 days, culminatedafter 270 days (Munro and Willes,1978). Skin absorption exhibits the symptomsof mercury poisoning. The toxic thresholdconcentration of mercury in the wholeblood is usually in the range 40 to 50 μg/L,while the normal range should be below10 μg/L.

Fire Hazard

It is a flammable liquid; flash point 38°C (101°F). The flammability of this compound, its ease of oxidation and the energy of decomposition is relatively lower than the alkyls of lighter metals. It is mildly endothermic. The heat of formation, △H°f is ＋75.3 kJ/mol (Bretherick 1995). Unlike most other metal alkyls formed by elements of lower atomic numbers, dimethylmercury does not pose any serious fire or explosion hazard. Although it does not ignite in air, the compound is easily inflammable. It dissolves in lower alcohols without any violent decomposition. Heating with oxidizing substances can cause explosion. Violent explosion is reported with diboron tetrachloride at －63°C (－81°F) under vacuum (Wartik et al. 1971).

Safety Profile

Suspected carcinogen. Highly toxic. Mutation data reported. Easily flammable. When heated to decomposition it emits toxic fumes of Hg.

Potential Exposure

Dimethyl mercury has been used as seed disinfectants and for fungicides. It has also been used in organic synthesis.

Environmental Fate

DMM is a colorless liquid that is volatile at room temperature (vapor pressure 62.3 mmHg) and is slightly soluble in water (water solubility 8860 mg l^-1). There are no reports on the partition behavior of DMM but it is known to readily evaporate and is thus rarely found in sediment or soil. No reports were found on the environmental persistence of DMM. While DMM vaporizes, no studies were found on long range transport. The lipophilicity ofDMMresults in its accumulation inadipose tissue, plasma proteins, and brain. DMM has not been found in fish.

Shipping

UN2025 Mercury compounds, solid, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required.

Toxicity evaluation

In contrast to the white crystalline solids of the pure forms of methylmercury (MMM) and phenylmercury, DMM exists as a colorless liquid at room temperature with high volatility. These physical qualities enable high concentrations of the substance to be absorbed by exposure pathways of the skin and lungs that circumvent first-pass elimination. Effectively, this prolongs the systemic circulation of DMM, and extends its residence time in the body.
The additional alkyl group flanking the mercury imparts DMM with lipophilicity that exceeds its monoalkylated counterpart, and allows DMM to be sequestered in lipid-rich depots. The metabolic delay allows the neurotoxicity of DMM to remain latent for months.
The gradual conversion into MMM results in the release of DMM from depots such as lipid-rich tissues and plasma proteins, and permits its movement through barriers such as the blood–brain and placenta. A cysteine complex of the monomethylated metabolite penetrates the endothelial cells of the blood–brain barrier by mimicking methionine and using the large neutral amino acid transporter.
Thus, the toxicity of DMM is mediated by its dealkylation. Cleavage of the carbon–mercury bond generates MMM metabolites, which can form covalent bonds with cellular ligands with amphiphilic properties. The mercury center reacts with sulfur and sulfur-containing thiol groups of enzymes and thereby inhibits them, resulting in cellular dysfunction.
The metal center of DMM acts as a soft acid, and binds tightly to polarizable donor atoms in soft bases. An additional mechanism of adverse effect is the disruption of the prooxidant– antioxidant balance, causing oxidative damage to biomolecules resulting cellular damage. Within cells, mercury may interact with a variety of proteins, particularly microsomal and mitochondrial enzymes. Recent studies demonstrated that the combined administration of the antioxidants N-acetyl cysteine, zinc, and selenium mitigated DMM acute and chronic toxicity by reducing enzymatic and cellular dysfunction.

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. May be sensitive to light.

Raw materials

Preparation Products