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, CH
3Hg
+;
ethylmercury(II) cation, C
2H
5Hg
+;
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 ...
, (CH
3)
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
Thiomersal (INN), or thimerosal (USAN, JAN), is an organomercury compound. It is a well-established antiseptic and antifungal agent.
The pharmaceutical corporation Eli Lilly and Company gave thiomersal the trade name Merthiolate. It has been u ...
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:
:C
6H
5OH + Hg(O
2CCH
3)
2 → C
6H
4(OH)–2-HgO
2CCH
3 + CH
3CO
2H
:C
6H
4(OH)–2–HgO
2CCH
3 + NaCl → C
6H
4(OH)–2-HgCl + NaO
2CCH
3
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
Otto Dimroth (28 March 1872 – 16 May 1940) was a German chemist
A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the comp ...
between 1898 and 1902.
Addition to alkenes
The Hg
2+ 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(O
2CCH
3)
2 + CH
2=CHCO
2CH
3 → CH
3OCH
2CH(HgO
2CCH
3)CO
2CH
3
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:
:CH
3OCH
2CH(HgO
2CCH
3)CO
2CH
3 + Br
2 → CH
3OCH
2CHBrCO
2CH
3 + BrHgO
2CCH
3
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 Mercury chloride can refer to:
*Mercury(II) chloride or mercuric chloride (HgCl2)
*Mercury(I) chloride
Mercury(I) chloride is the chemical compound with the formula Hg2Cl2. Also known as the mineral calomel (a rare mineral) or mercurous 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 (CH
3CH
2)
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/cm
3) 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 ...
:
:C
6H
5HgCCl
3 → C
6H
5HgCl + CCl
2
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 Ph
2Hg + 2 Al → (AlPh
3)
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 diuretic
Mercurial diuretics are a form of renal diuretic containing mercury.
Although previously widely used, they have largely been superseded by safer diuretics such as thiazides, and are hardly used anymore.
History and mechanism
Inorganic mercury co ...
s 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 (R
2C=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.
See also
*
Heavy metal poisoning
A toxic heavy metal is any relatively dense metal or metalloid that is noted for its potential toxicity, especially in environmental contexts. The term has particular application to cadmium, mercury and lead, all of which appear in the World H ...
*
Mercury poisoning
*
Minamata disease
Minamata disease is a neurological disease caused by severe mercury poisoning. Signs and symptoms include ataxia, numbness in the hands and feet, general muscle weakness, loss of peripheral vision, and damage to hearing and speech. In extrem ...
References
External links
*
*
* Safety data for a typical organomercury compound:
{{Authority control
Obsolete pesticides