Mercury(II) cyanide, also known as mercuric cyanide, is a
compound
Compound may refer to:
Architecture and built environments
* Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall
** Compound (fortification), a version of the above fortified with defensive struc ...
of
mercury. 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 subs ...
white powder. It is highly
soluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubi ...
in
polar 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 compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
,
alcohol, 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 wa ...
; 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 ...
; 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, t ...
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 bioche ...
s with a C-Hg-C
bond angle
Bond or bonds may refer to:
Common meanings
* Bond (finance), a type of debt security
* Bail bond, a commercial third-party guarantor of surety bonds in the United States
* Chemical bond, the attraction of atoms, ions or molecules to form chemical ...
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
Harry Julius Emeléus CBE, FRS (22 June 1903 – 2 December 1993) was a leading English inorganic chemist and a professor in the department of chemistry, Cambridge University.
Early life
Emeléus was born in Poplar, London on 22 June 1903, t ...
, 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 structure undergoes a phase transition as the Hg(II) center changes from 2- to 4-
coordinate
In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is sign ...
as the C''N'' groups bind to neighboring Hg centers forming via Hg-N bonds. The coordination geometry thus changes from tetragonal to
tetrahedral
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
, forming a
cubic crystal structure, 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 elec ...
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, Hg(CN)
2 molecules are linear.
Synthesis
Mercuric cyanide can be prepared by mixing yellow
mercury oxide with
hydrocyanic acid
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 in ...
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
Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...
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(Cyani ...
.
[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
Mercury(II) sulfate, commonly called mercuric sulfate, is the chemical compound Hg S O4. It is an odorless solid that forms white granules or crystalline powder. In water, it separates into an insoluble sulfate with a yellow color and sulfuric a ...
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 Pie ...
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 ...
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 to give off
hydrogen cyanide. 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 the
Koenigs–Knorr reaction 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 glycoside ...
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 molecu ...
, (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 polymers can be synthesized from Hg(CN)
2 building blocks. Large single crystals of
tmeda)Cu-[Hg(CN)2sub>2.html" ;"title="g(CN)
2.html" ;"title="tmeda)Cu-[Hg(CN)
2">tmeda)Cu-[Hg(CN)
2sub>2">g(CN)
2.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
An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...
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 employe ...
.
["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 under the Latin name ''Hydrargyrum bicyanatum''.
Toxicology
Mercury(II) cyanide is
poison with health hazard classification 3, having an oral
LD50
In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...
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