Organomercury
Encyclopedia
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
cation, CH3Hg+; ethylmercury
cation, C2H5Hg+; dimethylmercury
, (CH3)2Hg, diethylmercury and merbromin
("Mercurochrome"). Thiomersal
is used as a preservative for vaccines and IV drugs.
The toxicity of organomercury compounds presents both dangers and benefits. Dimethylmercury in particular, is notoriously toxic, but has found use as an antifungal agent and insecticide
. Merbromin
and phenylmercuric borate
are used as a topical
antiseptic
, while Nitromersol
is used as a preservative for vaccines and antitoxins.
s.
s undergo direct mercuration upon treatment with Hg(O2CCH3)2
. The one acetate group that remains on mercury can be displaced by chloride:
The first such reaction, including a mercuration of benzene
itself was reported by Otto Dimroth
between 1898 and 1902.
and alkoxide
. For example, treatment of methyl acrylate
with mercuric acetate in methanol
gives an α--mercuri ester:
The resulting Hg-C bond can be cleaved with bromine
to give the corresponding alkyl bromide:
This reaction is called the Hofmann-Sand Reaction.
with two equivalents of ethylmagnesium bromide, a conversion that would typically be conducted in diethyl ether
solution. The resulting (CH3CH2)2Hg is a dense
liquid (2.466 g/cm3) that boils
at 57 °C at 16 torr
. 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 in the presence of mercury(II) salts.
Phenyl(trichloromethyl)mercury compounds can be prepared by generating dichlorocarbene in the presence of phenylmercuric chloride. A convenient carbene source is sodium trichloroacetate. This compound on heating releases dichlorocarbene
:
is a source of the phenyl radical in certain syntheses. Treatment with aluminium gives triphenyl aluminium:
As indicated above, organomercury compounds react with halogens to give the corresponding organic halide.
of alkenes to alcohols using mercuric acetate proceeds via organomercury intermediates. A related reaction forming phenols is the Wolfenstein-Boters reaction. The toxicity is useful in antiseptics such as thiomersal
and merbromin
, and fungicides such as ethylmercury
chloride and phenylmercury acetate
.
Mercurial diuretic
s such as mersalyl acid
were once in common use, but have been superseded by the thiazide
s and loop diuretic
s, which are safer and longer-acting, as well as being orally active.
s are also known as mercaptans due to their propensity for mercury capture. Thiolates (R-S-) and thioketones (R2-C=S) being soft
nucleophile
s form a strong coordination complex with mercury(II), a soft electrophile. As a result, organomercurial agarose gel or gel beads are used to isolate thiolated compounds (such as thiouridine) in a biological sample.
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
compounds that contain mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. Typically the Hg-C bond is stable toward air and moisture but sensitive to light. Important organomercury compounds are the methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
cation, CH3Hg+; ethylmercury
Ethylmercury
Ethylmercury is a cation composed of an ethyl group bound to a mercury centre; its chemical formula is C2H5Hg+...
cation, C2H5Hg+; dimethylmercury
Dimethylmercury
Dimethylmercury is an organomercury compound. This colorless liquid is one of the strongest known neurotoxins. It is described as having a slightly sweet smell, although inhaling enough vapor to detect its odor would be hazardous....
, (CH3)2Hg, diethylmercury and merbromin
Merbromin
Merbromin is a topical antiseptic used for minor cuts and scrapes. Merbromin is an organomercuric disodium salt compound and a fluorescein...
("Mercurochrome"). Thiomersal
Thiomersal
Thiomersal , and commonly known in the US as thimerosal, is an organomercury compound. This compound is a well established antiseptic and antifungal agent....
is used as a preservative for vaccines and IV drugs.
The toxicity of organomercury compounds presents both dangers and benefits. Dimethylmercury in particular, is notoriously toxic, but has found use as an antifungal agent and insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
. Merbromin
Merbromin
Merbromin is a topical antiseptic used for minor cuts and scrapes. Merbromin is an organomercuric disodium salt compound and a fluorescein...
and phenylmercuric borate
Phenylmercuric borate
Phenylmercuric borate is a topical antiseptic and disinfectant that is soluble in water, ethanol and glycerol....
are used as a topical
Topical
In medicine, a topical medication is applied to body surfaces such as the skin or mucous membranes such as the vagina, anus, throat, eyes and ears.Many topical medications are epicutaneous, meaning that they are applied directly to the skin...
antiseptic
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...
, while Nitromersol
Nitromersol
Nitromersol is a mercury-containing organic compound containing that is primarily used as an antiseptic and disinfectant. It has no odor or taste and is stored as a brown-yellow granules or powder...
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 compoundOrganocadmium compound
An organocadmium compound is a organometallic compound containing a carbon to cadmium chemical bond. Organocadmium chemistry describes physical properties, synthesis, reactions and use of these compounds. Cadmium shares group 12 with zinc and mercury and their corresponding chemistries have much in...
s.
Mercuration of aromatic rings
Electron-rich areneArene
Arene or Arênê or Arène may refer to:*an aromatic hydrocarbon*Arene , a genus of marine snails in the family Areneidae*Arene , the wife of Aphareus and mother of Idas and Lynceus in Greek mythology...
s undergo direct mercuration upon treatment with Hg(O2CCH3)2
Mercury(II) acetate
Mercury acetate is the chemical compound with the formula Hg2. Commonly abbreviated Hg2, this compound is employed as a reagent to generate organomercury compounds from unsaturated organic precursors.-Structure:...
. 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
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
itself was reported by Otto Dimroth
Otto Dimroth
Otto Dimroth was a German chemist. He is known for the Dimroth rearrangement, as well as a type of condenser with an internal double spiral, the Dimroth condenser....
between 1898 and 1902.
Addition to alkenes
The Hg2+ center binds to alkenes, inducing the addition of hydroxideHydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
and alkoxide
Alkoxide
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands...
. For example, treatment of methyl acrylate
Methyl acrylate
Methyl acrylate is a volatile chemical compound classified as a methyl ester. It has a characteristic acrid odor used in the preparation of polyamidoamine dendrimers typically by Michael addition with a primary amine....
with mercuric acetate in methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
gives an α--mercuri ester:
- Hg(O2CCH3)2 + CH2=CHCO2CH3 → CH3OCH2CH(HgO2CCH3)CO2CH3
The resulting Hg-C bond can be cleaved with bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
to give the corresponding alkyl 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 chlorideMercury chloride
Mercury chloride can refer to:*Mercury chloride or mercuric chloride *Mercury chloride or mercurous chloride...
with two equivalents of ethylmagnesium bromide, a conversion that would typically be conducted in diethyl ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...
solution. The resulting (CH3CH2)2Hg is a dense
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
liquid (2.466 g/cm3) that boils
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
at 57 °C at 16 torr
Torr
The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...
. 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
Phenylmagnesium bromide
Phenylmagnesium bromide, with the simplified formula , is a magnesium-containing organometallic compound. It is so commonly used that it is commercially available as a solution in diethyl ether or tetrahydrofuran . Phenylmagnesium bromide is a Grignard reagent...
. A related preparation entails formation of phenylsodium in the presence of mercury(II) salts.
Other methods
Hg(II) can be alkylated by treatment with diazonium salts in the presence of copper metal. In this way 2-chloromercuri-naphthalene has been prepared.Phenyl(trichloromethyl)mercury compounds can be prepared by generating dichlorocarbene in the presence of phenylmercuric chloride. A convenient carbene source is sodium trichloroacetate. This compound on heating releases dichlorocarbene
Dichlorocarbene
Dichlorocarbene is a carbene commonly encountered in organic chemistry. This reactive intermediate with chemical formula CCl2 is easily available by reaction of chloroform and a base such as potassium t-butoxide or sodium hydroxide dissolved in water...
:
- C6H5HgCCl3 → C6H5HgCl + CCl2
Reactions
Organomercury compounds are versatile synthetic intermediates due to the well controlled conditions that they undergo cleavage of the Hg-C bonds. DiphenylmercuryDiphenylmercury
Diphenylmercury is a colourless, crystalline organomercury compound with the chemical formula C12H10Hg. It can be synthesised by the reaction of a 2:1 molar ratio of mercury chloride and methyltriphenyltin in ethanol...
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.
Applications
Due to their toxicity and low nucleophilicity, organomercury compounds find limited use. The oxymercuration reactionOxymercuration 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 in aqueous solution to yield the addition of an acetoxymercuri group and a hydroxy group across the double bond...
of alkenes to alcohols using mercuric acetate proceeds via organomercury intermediates. A related reaction forming phenols is the Wolfenstein-Boters reaction. The toxicity is useful in antiseptics such as thiomersal
Thiomersal
Thiomersal , and commonly known in the US as thimerosal, is an organomercury compound. This compound is a well established antiseptic and antifungal agent....
and merbromin
Merbromin
Merbromin is a topical antiseptic used for minor cuts and scrapes. Merbromin is an organomercuric disodium salt compound and a fluorescein...
, and fungicides such as ethylmercury
Ethylmercury
Ethylmercury is a cation composed of an ethyl group bound to a mercury centre; its chemical formula is C2H5Hg+...
chloride and phenylmercury acetate
Phenylmercury acetate
Phenylmercuric acetate is an organomercury compound used as a fungicide. When applied to the leaves of plants, it is an Antitranspirant....
.
Mercurial diuretic
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:...
s such as mersalyl acid
Mersalyl acid
Mersalyl acid is a mercurial diuretic. It is only rarely used, having been superseded by diuretic medications that do not contain mercury and are therefore less toxic....
were once in common use, but have been superseded by the thiazide
Thiazide
Thiazide is a term used to describe a type of molecule and a class of diuretics often used to treat hypertension and edema ....
s and loop diuretic
Loop diuretic
Loop diuretics are diuretics that act on the ascending loop of Henle in the kidney. They are primarily used in medicine to treat hypertension and edema often due to congestive heart failure or renal insufficiency...
s, which are safer and longer-acting, as well as being orally active.
Thiol affinity chromatography
ThiolThiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
s are also known as mercaptans due to their propensity for mercury capture. Thiolates (R-S-) and thioketones (R2-C=S) being soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....
nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
s form a strong coordination complex with mercury(II), a soft electrophile. As a result, organomercurial agarose gel or gel beads are used to isolate thiolated compounds (such as thiouridine) in a biological sample.
See also
- Heavy metal poisoningHeavy Metal PoisoningHeavy Metal Poisoning is a song by American rock band Styx. It was included as the fifth track on their 1983 studio album Kilroy Was Here.The song in the story of Kilroy Was Here has the character of Dr Righteous preaching the evils of rock and roll...
- Mercury poisoningMercury poisoningMercury 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...
- Minamata diseaseMinamata disease', sometimes referred to as , is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death...
- Compounds of carbon with other elements in the periodic table:
External links
- Safety data for a typical organomercury compound: phenylmercuric hydroxide