Mercury(II) cyanide, also known as mercuric cyanide, is a
compound of
mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
. It is an odorless,
toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
white powder. It is highly
soluble in
polar
Polar may refer to:
Geography
Polar may refer to:
* Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates
* Polar climate, the c ...
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s such as
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
,
alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
, and
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
; slightly soluble in
ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...
; and insoluble in
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, ...
and other
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s.
[Kocovsky, P., G. Wang, and V. Sharma. "Mercury(II) Cyanide." ''e-EROS Encyclopedia of Reagents for Organic Synthesis.'' Chichester, UK: John Wiley & Sons, Ltd., 2001. http://www.mrw.interscience.wiley.com/eros/articles/rm034/sect0-fs.html]
Molecular and crystal structure
At
ambient temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
and
ambient pressure
Ambient or Ambiance or Ambience may refer to:
Music and sound
* Ambience (sound recording), also known as atmospheres or backgrounds
* Ambient music, a genre of music that puts an emphasis on tone and atmosphere
* ''Ambient'' (album), by Moby
* ...
, Hg(CN)
2 takes the form of
tetragonal crystals.
These crystals are composed of nearly linear Hg(CN)
2 molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
s with a C-Hg-C
bond angle of 175.0° and an Hg-C-N bond angle of 177.0° (Aylett
[Aylett, B.J. "Mercury (II) Pseudohalides: Cyanide, Thiocyanate, Selenocyanate, Azide, Fulminate." ''Comprehensive Inorganic Chemistry'' 3:304-306. J.C. Bailar, Harry Julius Emeléus, Sir Ronald Nyholm, and A.F. Trotman-Dickenson, ed. Oxford: Pergamon Press, 1973; distributed by Compendium Publishers (Elmsford, NY), p. 304.] gives slightly different values of 189° and 175°, respectively).
Raman spectra show that the molecules distort at higher pressures. Between 16-20
kbar
The bar is a metric unit of pressure, but not part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa (100 kPa), or slightly less than the current average atmospheric pressure on Earth at sea lev ...
, the structure undergoes a phase transition as the Hg(II) center changes from 2- to 4-
coordinate as the C''N'' groups bind to neighboring Hg centers forming via Hg-N bonds. The coordination geometry thus changes from tetragonal to
tetrahedral, forming a
cubic crystal structure
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
There are three main varieties of ...
, analogous to the structure of Cd(CN)
2. Due to the
ambidentate nature of the CN
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s, this tetrahedral structure is distorted, but the distortion lessens with increasing pressure until the structure becomes nearly perfectly tetrahedral at >40 kbar.
[Wong, P.T.T. ''J. Chem. Phys.'' 1984, 80(12), 5937-41.]
As in the solid state, in
aqueous solution
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
, Hg(CN)
2 molecules are linear.
Synthesis
Mercuric cyanide can be prepared by mixing yellow
mercury oxide Mercury oxide can refer to:
* Mercury(I) oxide (mercurous oxide), Hg2O
* Mercury(II) oxide
Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, is the inorganic compound with the formula Hg O. It has a red or orange color. Mer ...
with
hydrocyanic acid in the following chemical reaction
which is generally carried out by passing HCN gas into HgO in water. When soluble Hg(CN)
2 is formed, the solution is evaporated to
crystallize the product.
: HgO + 2 HCN → Hg(CN)
2 + H
2O
Hg(CN)
2 can also be prepared by mixing HgO with finely powdered
Prussian blue
Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
.
[Miller, W.L. ''Elements of Chemistry: Organic chemistry, 5th ed.'' New York: John Wiley & Sons, 1880, p. 100.] In addition, it can be produced by reacting
mercuric sulfate with
potassium ferrocyanide
Potassium ferrocyanide is the inorganic compound with formula K4 e(CN)63H2O. It is the potassium salt of the coordination complex e(CN)6sup>4−. This salt forms lemon-yellow monoclinic crystals.
Synthesis
In 1752, the French chemist Pierr ...
in water:
: K
4Fe(CN)
6 + 3 HgSO
4 → 3 Hg(CN)
2 + 2 K
2SO
4 + FeSO
4
Another method to generate mercuric cyanide is through the
disproportionation
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can b ...
of mercury(I) derivatives. In these reactions, metallic mercury
precipitates
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
, and Hg(CN)
2 remains in solution:
: Hg
2(NO
3)
2 + 2 KCN → Hg + Hg(CN)
2 + 2 KNO
3
Reactions
It rapidly decomposes in
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
to give off
hydrogen cyanide
Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on an ...
. It is photosensitive, becoming darker in color.
[Brunton, L.T. ''A Text-Book Of Pharmacology, Therapeutics And Materia Medica.'' London: MacMillan & Co., 1885.]
Mercury cyanide
catalyzes
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
the
Koenigs–Knorr reaction The Koenigs–Knorr reaction in organic chemistry is the substitution reaction of a glycosyl halide with an alcohol to give a glycoside. It is one of the oldest glycosylation reactions. It is named after Wilhelm Koenigs (1851–1906), a student o ...
for the synthesis of
glycoside
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...
s.
Cyanogen
Cyanogen is the chemical compound with the formula ( C N)2. It is a colorless and highly toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecule ...
, (CN)
2, forms upon heating dry mercury cyanide, but the method is inferior to other routes:
[Brotherton, T.K.; Lynn, J.W. ''Chemical Reviews'' 1959, 59(5), 841-883, 844-846.]
: Hg(CN)
2 → (CN)
2 + Hg
Coordination polymer
A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands. More formally a coordination polymer is a coordination compound with repeating coordination entities extending in 1, 2, o ...
s can be synthesized from Hg(CN)
2 building blocks. Large single crystals of
2">tmeda)Cu-[Hg(CN)2sub>2">g(CN)<sub>2<_sub>.html" ;"title="tmeda)Cu-[Hg(CN)
2">tmeda)Cu-[Hg(CN)
2sub>2HgCl
4] form upon treating copper(II) chloride, CuCl
2, the HSAB theory, soft Lewis acids and bases, Lewis acid Hg(CN)
2, and Tetramethylethylenediamine, N,N,N',N'-tetramethylethylenediamine (TMEDA). The migration of two labile chloride ligands from
HSAB theory, harder Cu(II) to
softer Hg(II) drives the formation of the crystal.
Past applications
The use of mercuric cyanide as an
antiseptic was discontinued due to its toxicity.
[Benaissa, M.L.; Hantson, P.; Bismuth, C.; Baud, F.J. ''Intensive Care Med.'' 1995, 21(12), 1051-1053.] Hg(CN)
2 is also used in
photography
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed ...
.
["Cyanides, Cyanide Oxides and Complex Cyanides." http://www.dncustoms.gov.vn/web_eglish/bieu_thue/E_HTM/E2837.HTM (accessed April 30, 2009).] It is still used in
homeopathy
Homeopathy or homoeopathy is a pseudoscientific system of alternative medicine. It was conceived in 1796 by the German physician Samuel Hahnemann. Its practitioners, called homeopaths, believe that a substance that causes symptoms of a dis ...
under the Latin name ''Hydrargyrum bicyanatum''.
Toxicology
Mercury(II) cyanide is
poison
Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...
with health hazard classification 3, having an oral
LD50 of 33 milligrams per kilogram in mice and a subcutaneous LD50 of 2.7 milligrams per kilogram in dogs.
References
External links
National Pollutant Inventory: Cyanide compounds fact sheet
{{Cyanides
Mercury(II) compounds
Cyanides