Organomercury refers to the group of organometallic compounds that contain mercury. Typically the Hg–C bond is stable toward air and moisture but sensitive to light. Important organomercury compounds are the methylmercury(II) cation, CH₃Hg⁺; ethylmercury(II) cation, C₂H₅Hg⁺;

dimethylmercury Dimethylmercury (( C H3)2 Hg) is an extremely toxic 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 in ...

, (CH₃)₂Hg,

diethylmercury Diethylmercury is a flammable, colorless liquid, and one of the strongest known neurotoxins. This organomercury compound is described as having a slightly sweet smell, though inhaling enough fumes to notice this would be hazardous. This chemical c ...

and

merbromin Merbromin (marketed as Mercurochrome, Merbromine, Mercurocol, Sodium mercurescein, Asceptichrome, Supercrome, Brocasept and Cinfacromin) is an organomercuric disodium salt compound used as a topical antiseptic for minor cuts and scrapes and a ...

("Mercurochrome"). Thiomersal is used as a preservative for vaccines and intravenous drugs. The toxicity of organomercury compounds presents both dangers and benefits. Dimethylmercury in particular, is notoriously toxic, but found use as an antifungal agent and insecticide. Merbromin and

phenylmercuric borate Phenylmercuric borate is a topical antiseptic and disinfectant that is soluble in water, ethanol and glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorle ...

are used as topical antiseptics, while

nitromersol Nitromersol (metaphen) is a mercury-containing organic compound that is primarily used as an antiseptic and disinfectant. It is a brown-yellow solid that has no odor or taste, does not irritate the skin or mucous membranes, and has no impact on ...

is used as a preservative for vaccines and antitoxins.

Synthesis

Organomercury compounds are generated by many methods, including the direct reaction of hydrocarbons and mercury(II) salts. In this regard, organomercury chemistry more closely resembles organopalladium chemistry and contrasts with organocadmium compounds.

Mercuration of aromatic rings

Electron-rich

arene Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...

s undergo mercuration upon treatment with Hg(O₂CCH₃)₂. The one acetate group that remains on mercury can be displaced by chloride: :C₆H₅OH + Hg(O₂CCH₃)₂ → C₆H₄(OH)–2-HgO₂CCH₃ + CH₃CO₂H :C₆H₄(OH)–2–HgO₂CCH₃ + NaCl → C₆H₄(OH)–2-HgCl + NaO₂CCH₃ The first such reaction, including a mercuration of

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...

itself, was reported by Otto Dimroth between 1898 and 1902.

Addition to alkenes

The Hg²⁺ center binds to alkenes, inducing the addition of

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

and alkoxide. For example, treatment of

methyl acrylate Methyl acrylate is an organic compound, more accurately the methyl ester of acrylic acid. It is a colourless liquid with a characteristic acrid odor. It is mainly produced to make acrylate fiber, which is used to weave synthetic carpets. It is al ...

with mercuric acetate in methanol gives an α--mercuri ester: :Hg(O₂CCH₃)₂ + CH₂=CHCO₂CH₃ → CH₃OCH₂CH(HgO₂CCH₃)CO₂CH₃ The resulting Hg-C bond can be cleaved with

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...

to give the corresponding

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...

bromide: :CH₃OCH₂CH(HgO₂CCH₃)CO₂CH₃ + Br₂ → CH₃OCH₂CHBrCO₂CH₃ + BrHgO₂CCH₃ This reaction is called the Hofmann-Sand Reaction.

Reaction of Hg(II) compounds with carbanion equivalents

A general synthetic route to organomercury compounds entails alkylation with Grignard reagents and organolithium compounds. Diethylmercury results from the reaction of mercury chloride with two equivalents of ethylmagnesium bromide, a conversion that would typically be conducted in

diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...

solution. The resulting (CH₃CH₂)₂Hg is a

dense Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematically ...

liquid (2.466 g/cm³) that

boils A boil, also called a furuncle, is a deep folliculitis, which is an infection of the hair follicle. It is most commonly caused by infection by the bacterium '' Staphylococcus aureus'', resulting in a painful swollen area on the skin caused by ...

at 57 °C at 16

torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one " millimeter of merc ...

. The compound is slightly soluble in ethanol and soluble in ether. Similarly, diphenylmercury (m.p. 121–123 °C) can be prepared by reaction of mercury chloride and phenylmagnesium bromide. A related preparation entails formation of

phenylsodium Phenylsodium C6H5Na is an organosodium compound. Solid phenylsodium was first isolated by Nef in 1903. Although the behavior of phenylsodium and phenyl magnesium bromide are similar, the organosodium compound is very rarely used. Synthesis The ...

in the presence of mercury(II) salts.

Other methods

Hg(II) can be alkylated by treatment with

diazonium salt Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide. General properti ...

s in the presence of copper metal. In this way 2-chloromercuri-naphthalene has been prepared.

Phenyl(trichloromethyl)mercury Phenyl(trichloromethyl)mercury is an organomercury compound with the formula C6H5HgCCl3. It is a white solid that is soluble in organic solvents. The compound is used as a source of dichlorocarbene, e.g. in cyclopropanation reactions, illustr ...

can be prepared by generating dichlorocarbene in the presence of phenylmercuric chloride. A convenient carbene source is

sodium trichloroacetate Sodium trichloroacetate is a chemical compound with a formula of CCl3CO2Na. It is used to increase sensitivity and precision during transcript mapping. It was previously used as an herbicide starting in the 1950s but regulators removed it from t ...

. This compound on heating releases

dichlorocarbene Dichlorocarbene is the reactive intermediate with chemical formula CCl2. Although this chemical species has not been isolated, it is a common intermediate in organic chemistry, being generated from chloroform. This bent diamagnetic molecule rapidly ...

: :C₆H₅HgCCl₃ → C₆H₅HgCl + CCl₂

Reactions

Organomercury compounds are versatile synthetic intermediates due to the well controlled conditions under which they undergo cleavage of the Hg-C bonds.

Diphenylmercury Diphenylmercury is the organomercury compound with the formula Hg(C6H5)2. It is a white solid. The compound is of historic interest as a particularly stable organometallic compound but it finds few uses because of its high toxicity. Preparation ...

is a source of the phenyl radical in certain syntheses. Treatment with aluminium gives triphenyl aluminium: :3 Ph₂Hg + 2 Al → (AlPh₃)₂ + 3 Hg As indicated above, organomercury compounds react with halogens to give the corresponding organic halide. Organomercurials are commonly used in transmetalation reactions with lanthanides and alkaline-earth metals. Cross coupling of organomercurials with organic halides is catalyzed by palladium, which provides a method for C-C bond formation. Usually of low selectivity, but if done in the presence of halides, selectivity increases. Carbonylation of lactones has been shown to employ Hg(II) reagents under palladium catalyzed conditions. (C-C bond formation and Cis ester formation).

Applications

Due to their toxicity and low

nucleophilicity In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

, organomercury compounds find limited use. The

oxymercuration reaction The oxymercuration reaction is an electrophilic addition organic reaction that transforms an alkene into a neutral alcohol. In oxymercuration, the alkene reacts with mercuric acetate (AcO–Hg–OAc) in aqueous solution to yield the addition of an ...

of alkenes to alcohols using mercuric acetate proceeds via organomercury intermediates. A related reaction forming phenols is the Wolffenstein–Böters reaction. The toxicity is useful in antiseptics such as thiomersal and merbromin, and fungicides such as ethylmercury chloride and

phenylmercury acetate Phenylmercuric acetate is an organomercury compound used as a preservative, disinfectant, and antitranspirant. Properties Phenylmercuric acetate forms colorless, lustrous crystals, and is soluble in ethanol, benzene, acetic acid, and sparingly ...

. 220px, Thiomersal (Merthiolate) is a well-established antifungal_agent..html" ;"title="antiseptic and antifungal agent.">antiseptic and antifungal agent. Mercurial diuretics such as mersalyl acid were once in common use, but have been superseded by the

thiazide Thiazide () refers to both a class of sulfur-containing organic molecules and a class of diuretics based on the chemical structure of benzothiadiazine. The thiazide drug class was discovered and developed at Merck and Co. in the 1950s. The firs ...

s and

loop diuretic Loop diuretics are diuretics that act on the Na-K-Cl cotransporter along the thick ascending limb of the loop of Henle in the kidney. They are primarily used in medicine to treat hypertension and edema often due to congestive heart failure ...

s, which are safer and longer-acting, as well as being orally active.

Thiol affinity chromatography

Thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...

s are also known as mercaptans due to their propensity for ''mer''cury ''capt''ure. Thiolates (R-S⁻) and

thioketone In organic chemistry, thioketones (; also known as thiones or thiocarbonyls) are organosulfur compounds related to conventional ketones in which the oxygen has been replaced by a sulfur. Instead of a structure of , thioketones have the structure ...

s (R₂C=S), being soft nucleophiles, form strong coordination complexes with mercury(II), a soft electrophile. This mode of action makes them useful for

affinity chromatography Affinity chromatography is a method of separating a biomolecule from a mixture, based on a highly specific macromolecular binding interaction between the biomolecule and another substance. The specific type of binding interaction depends on the ...

to separate thiol-containing compounds from complex mixtures. For example, organomercurial agarose gel or gel beads are used to isolate thiolated compounds (such as thiouridine) in a biological sample.

References

External links

* * * Safety data for a typical organomercury compound: {{Authority control Obsolete pesticides