Mercury(II) cyanide: Difference between revisions

| verifiedrevid = 411349703

| ImageFile2 = Mercuric cyanide.png|Mercuric Cyanide

| OtherNames = mercuric cyanide; cyanomercury; mercury cyanide; mercury dicyanide; hydrargyri cyanidum<ref name="Hydrargyrum" />

| Section1 = {{Chembox Identifiers

| CASNo = 592-04-1

| PubChem = 11591

| SMILES = C(#N)[Hg]C#N

| Section2 = {{Chembox Properties

| Formula = Hg(CN)₂

| MolarMass = 252.63 g/mol

| Appearance = white powder

| Density = 3.996 g/cm³

| MeltingPt = 320°C<ref name="Kocovsky" />

| BoilingPt =

| Solubility = 9.3 g/100 mL (14 °C) <br> 53.9 g/100 mL (100 °C)<ref name="Aylett" />

| SolubleOther = soluble in [[ethanol]] <br> slightly soluble in [[ether]]

}}

| Section3 = {{Chembox Hazards

| MainHazards =

| NFPA-H = 3

| NFPA-F = 0

| NFPA-R = 0

| NFPA-O =

| FlashPt =

| Autoignition =

'''Mercury(II) cyanide''', also known as '''mercuric cyanide''', is a [[coordination compound]] of [[nitrogen]], [[carbon]] and [[mercury (element)|mercury]]. It is a colorless, odorless, [[toxicity|toxic]] white powder with a bitter metallic taste.<ref name="Hydrargyrum">"Hydrargyrum. Mercury. Part 5." http://chestofbooks.com/health/materia-medica-drugs/Manual-Pharmacology/Hydrargyrum-Mercury-Part-5.html (accessed April 1, 2009).</ref> It has a melting point of 320°C, at which it decomposes and releases toxic mercury fumes. It is highly [[solubility|soluble]] in [[chemical polarity|polar]] [[solvent]]s such as [[water]], [[alcohol]], and [[ammonia]]; slightly soluble in [[ether]]; and insoluble in [[benzene]] and other [[hydrophobe|hydrophobic]] solvents.<ref name="Kocovsky">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 (accessed April 1, 2009).</ref> It rapidly decomposes in [[acid]] to give off [[hydrogen cyanide]]. Samples also decompose when exposed to light, becoming darker in color.<ref name="Brunton">Brunton, L.T. ''A Text-Book Of Pharmacology, Therapeutics And Materia Medica.'' London: MacMillan & Co., '''1885'''.</ref> It reacts vigorously with [[oxidizing agent]]s; fusion with metal [[chlorate]]s, [[perchlorate]]s, [[nitrate]]s, or [[nitrite]]s can cause a violent explosion.<ref name="NOAA">NOAA, Office of Response and Restoration, CAMEO Chemicals. "Chemical Datasheet: Mercuric Cyanide." NOAA. http://cameochemicals.noaa.gov/chemical/3829 (accessed April 2, 2009).</ref>

At [[room temperature|ambient temperature]] and [[ambient pressure]], Hg(CN)₂ takes the form of [[tetragonal crystal system|tetragonal crystals]].<ref name="Kocovsky" /> These crystals are composed of nearly linear Hg(CN)₂ [[molecule]]s with a C-Hg-C [[molecular geometry|bond angle]] of 175.0° and an Hg-C-N bond angle of 177.0° (Aylett<ref name="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.</ref> gives slightly different values of 189° and 175°, respectively). [[Raman spectroscopy|Raman spectra]] show that the molecules distort at higher pressures. Between 16-20 [[bar (unit)|kbar]], the structure undergoes a phase transition as the Hg(II) center changes from 2- to 4-[[complex (chemistry)|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 symmetry|tetrahedral]], forming a [[cubic crystal system|cubic crystal structure]], analogous to the structure of Cd(CN)₂. Due to the [[ambidentate ligand|ambidentate]] nature of the CN [[ligand]]s, this tetrahedral structure is distorted, but the distortion lessens with increasing pressure until the structure becomes nearly perfectly tetrahedral at >40 kbar.<ref name="Wong">Wong, P.T.T. ''J. Chem. Phys''. '''1984''', 80(12), 5937-41.</ref>

As in the solid state, aqueous [[solution]], Hg(CN)₂ molecules are linear.<ref name="Aylett" />

Mercuric cyanide can be prepared by mixing yellow [[mercury(II) oxide|mercury oxide]] with [[hydrogen cyanide|hydrocyanic acid]] in the following [[chemical reaction]].<ref name="Aylett" /> This reaction is generally carried out by passing HCN gas into HgO in water. When soluble Hg(CN)₂ is formed, the solution is evaporated to [[crystallization|crystallize]] the product.<ref name="Hydrargyrum" />

: HgO + 2 HCN → Hg(CN)₂ + H₂O

Hg(CN)₂ can also be prepared by mixing HgO, finely powdered [[Prussian blue]]<ref name="Aylett" /><ref name="Miller">Miller, W.L. ''Elements of Chemistry: Organic chemistry, 5th ed.'' New York: John Wiley & Sons, '''1880''', p. 100.</ref> In addition, Hg(CN)2 can be produced by reacting [[mercury(II) sulfate|mercuric sulfate]] with [[potassium ferrocyanide]] in water:<ref name="Miller" />

: K₄Fe(CN)₆ + 3 HgSO₄ → 3 Hg(CN)₂ + 2 K₂SO₄ + FeSO₄

Another method to generate mercuric cyanide is through the disproportionation of mercury(I) derivatives. In these reactions, metallic mercury [[precipitation (chemistry)|precipitates]], and Hg(CN)₂ remains in solution:<ref name="Miller" />

: Hg₂(NO₃)₂ + 2 KCN → Hg + Hg(CN)₂ + 2 KNO₃

==Reactions==

Mercury cyanide can be used as a [[catalysis|promoter]] in the [[Koenigs–Knorr reaction]] for the synthesis of [[glycoside]]s.<ref name="Kocovsky" /> [[Cyanogen]], (CN)₂, forms upon heating dry mercury cyanide but the method is inferior to other routes:<ref name="Brotherton">Brotherton, T.K.; Lynn, J.W. ''Chemical Reviews'' '''1959''', 59(5), 841-883, 844-846.</ref>

: Hg(CN)₂ → (CN)₂ + Hg

[[Coordination polymer]]s can be synthesized from Hg(CN)₂ building blocks. Large single crystals of [(tmeda)Cu-[Hg(CN)₂]₂][HgCl₄] form upon reacting the [[lability|labile]] [[transition metal]] halide [[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 [[HSAB theory|softer]] Hg(II) drives the formation of the crystal.<ref name="Draper">Draper, N.D. ''Chemistry of Materials'' '''2003''', 15(8), 1612–1616.</ref><!--ultra-specialized report-->

Mercuric cyanide was once used as an [[antiseptic]], but this practice has been discontinued due to its toxicity.<ref name="Benaissa">Benaissa, M.L.; Hantson, P.; Bismuth, C.; Baud, F.J. ''Intensive Care Med.'' '''1995''', 21(12), 1051-1053.</ref> One example of this was the treatment of [[syphilis]]: a solution of 5-10 grains in an ounce of water, painted on with a [[camel]]-hair brush, was applied to syphilitic sores of the tongue or mouth.{{Citation needed|date=May 2009}} Hg(CN)₂ is also used in [[photography]].<ref name="Cyanides">"Cyanides, Cyanide Oxides and Complex Cyanides." http://www.dncustoms.gov.vn/web_eglish/bieu_thue/E_HTM/E2837.HTM (accessed April 30, 2009).</ref> It is still used in [[homeopathy]] under the Latin name ''Hydrargyrum bicyanatum''.

Mercury(II) cyanide is one of the most toxic [[poisons]]. Its high toxicity is due to [[mercury poisoning|mercury]] and its two [[cyanide poisoning|cyanide groups]].

{{Commons cat|Mercury(II) cyanide}}

* [http://www.npi.gov.au/database/substance-info/profiles/29.html National Pollutant Inventory: Cyanide compounds fact sheet]

* [http://www.npi.gov.au/database/substance-info/profiles/53.html National Pollutant Inventory: Mercury and compounds fact sheet]

[[Category:Mercury compounds]]

[[ar:سيانيد الزئبق الثنائي]]

[[de:Quecksilber(II)-cyanid]]

[[hu:Higany(II)-cianid]]

[[ja:シアン化水銀(II)]]

[[no:Kvikksølvcyanid]]

[[ru:Цианид ртути(II)]]

[[zh:氰化汞]]