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 white powder. It is highly
soluble in
polar solvents such as
water,
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; slightly soluble in
ether; and insoluble in
benzene and other
hydrophobic solvents.
[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 and
ambient pressure, Hg(CN)
2 takes the form of
tetragonal crystals.
These crystals are composed of nearly linear Hg(CN)
2 molecules 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 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
ligands, 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 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 of mercury(I) derivatives. In these reactions, metallic mercury
precipitates, 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
glycosides.
, (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
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.
["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