mercuric cyanide
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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° (AylettAylett, 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 + H2O 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: : K4Fe(CN)6 + 3 HgSO4 → 3 Hg(CN)2 + 2 K2SO4 + FeSO4 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: : Hg2(NO3)2 + 2 KCN → Hg + Hg(CN)2 + 2 KNO3


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>2HgCl4] form upon treating copper(II) chloride, CuCl2, 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