Mercury(II) chloride
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{{Chembox new
| Name = Mercury(II) chloride
| ImageFile = Mercury(II) chloride.jpg
| ImageSize = 200px
| ImageName = Mercury(II) chloride
| IUPACName = Mercury(II) chloride<br />Mercury dichloride
| OtherNames = Mercuric chloride<br/>Corrosive sublimate
| Section1 = {{Chembox Identifiers
| CASNo = 7487-94-7
}}
| Section2 = {{Chembox Properties
| Formula = HgCl<sub>2</sub>
| MolarMass = 271.52 g/mol
| Appearance = white solid
| Density = 5.43 g/cm³, solid
| Solubility = 7.4 g/100 ml (20 °C)
| Solvent = other solvents
| SolubleOther = 33 g/100 ml (25 °C)
| MeltingPt = 277 °C
| BoilingPt = 302 °C
}}
| Section3 = {{Chembox Structure
| MolShape = linear
| Coordination = linear
| CrystalStruct =
| Dipole = zero
}}
| Section7 = {{Chembox Hazards
| EUClass = Very toxic ('''T+''')<br />Dangerous for<br /> the environment ('''N''')
| RPhrases = {{R28}}, {{R34}}, {{R48/24/25}}, {{R50/53}}
| SPhrases = {{S1/2}}, {{S36/37/39}}, {{S45}}, {{S60}}, {{S61}}
| FlashPt = non-flammable
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Mercury(II) fluoride]]<br />[[Mercury(II) bromide]]<br />[[Mercury(II) iodide]]
| OtherCations = [[Zinc chloride]]<br />[[Cadmium chloride]]<br />[[Mercury(I) chloride]]
}}
}}
'''Mercury(II) chloride''' or '''mercuric chloride''' (formerly ''corrosive sublimate''), is the [[chemical compound]] with the [[chemical formula|formula]] [[mercury (element)|Hg]]Cl<sub>2</sub>. This white crystalline [[solid]] is a laboratory reagent. It was formerly used more widely, however it is one of the most toxic forms of mercury because it is more soluble than most other forms in water.
==Production and basic properties==
Mercuric chloride is not a salt but a linear triatomic molecule, hence its tendency to sublime. In the crystal, each mercury atom is bonded to two close chloride [[ligand]]s with Hg---Cl distance of 2.38 Å; four more chlorides are more distant at 3.38 Å.<ref>Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.</ref>
Mercuric chloride is obtained by the action of [[chlorine]] on mercury or [[mercury(I) chloride]], by the addition of [[hydrochloric acid]] to a hot, concentrated solution of mercury(I) compounds such as the nitrate:
:HgNO<sub>3</sub> + 2 HCl → HgCl<sub>2</sub> + H<sub>2</sub>O + NO<sub>2</sub>,
Heating a mixture of solid [[mercury(II) sulfate]] and [[sodium chloride]] also affords volatile HgCl<sub>2</sub>, which [[Sublimation (physics)|sublimes]] and condenses in the form of small rhombic crystals.
Its solubility increases from 6% at 20 °C to 36% in boiling water. In the presence of chloride ions, it dissolves to give the tetrahedral complex [HgCl<sub>4</sub>]<sup>2-</sup>.
==Applications==
The main application of mercuric chloride is as a [[catalyst]] for the conversion of [[acetylene]] to [[vinyl chloride]], the precursor to [[polyvinylchloride]] :
:C<sub>2</sub>H<sub>2</sub> + HCl → CH<sub>2</sub>=CHCl
For this application, the mercuric chloride is supported on carbon in concentrations of ca 5 weight percent. This technology has been eclipsed by the thermal cracking of [[1,2-dichloroethane]]. Other significant applications of mercuric chloride include its use as a depolarizer in batteries and as a reagent in [[organic synthesis]] and [[analytical chemistry]] (see below).<ref>Matthias Simon, Peter Jönk, Gabriele Wühl-Couturier, Stefan Halbach "Mercury, Mercury Alloys, and Mercury Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2006: Wiley-Interscience. DOI: 10.1002/14356007.a16_269.pub2</ref>
===As a chemical reagent===
Mercuric chloride is often used to form an [[amalgam]] with metals, such as [[aluminium]]. When aluminium strips are soaked in mercuric chloride solution, they quickly become covered by a thin layer of mercury. Normally, aluminium is protected by a thin layer of oxide making it inert. Once amalgamated, aluminium can undergo a variety of reactions. For example, it will dissolve in water (this can be dangerous, as hydrogen gas and heat are generated). [[Halocarbon]] react with amalgamated aluminium in the [[Barbier reaction]]). These alkylaluminium compounds are [[nucleophilic]] and can be used in a similar fashion to the Grignard reagent. Amalgamated aluminum is also used as a [[Redox|reducing agent]] in organic synthesis. Another metal commonly amalgamated using mercuric chloride include zinc.
Mercuric chloride is used to remove [[dithiane]] groups attached to a carbonyl in an [[umpolung]] reaction.
===Historic use in photography===
Mercury(II) chloride was used as a photographic intensifier to produce positive pictures in the [[collodion process]] of the 1800s. When applied to a negative, the mercury(II) chloride whitens and thickens the image, thereby increasing the opacity of the shadows and creating the illusion of a positive image.<ref>Towler, J. (1864). [http://albumen.stanford.edu/library/monographs/sunbeam/toc.html Stereographic negatives and landscape photography]. Chapter 28. In: The silver sunbeam: a practical and theoretical textbook of sun drawing and photographic printing. Retrieved on April 13, 2005.</ref>
===Historic use in preservation===
For the preservation of anthropological and biological specimens during the late 19th and early 20th centuries, objects were dipped in or were painted with a mercuric solution. Objects in drawers were protected by scattering crystalline mercuric chloride over them.<ref> Goldberg, L. (1996). [http://aic.stanford.edu/jaic/articles/jaic35-01-003.html A history of pest control measures in the anthropology collections, national museum of natural history, Smithsonian Institution].JAIC 35(1) 23–43. Retrieved on April 17, 2005.</ref> It finds minor use in tanning, and wood was preserved by [[Wood preservation#Kyanizing|kyanizing]] (soaking in mercuric chloride) beginning in 1848.<ref>Freeman, M.H. Shupe, T.F. Vlosky, R.P. Barnes, H.M. (2003). [http://www.cfr.msstate.edu/forestp/preservation.pdf#search='wood%20preservative%20mercuric%20chloride' Past, present and future of the wood preservation industry]. Forest Products Journal. 53(10) 8–15. Retrieved on April 17, 2005.</ref>
===Historic use in medicine===
[[Syphilis]] was frequently treated with mercuric chloride before the advent of [[antibiotics]]. It was inhaled, ingested, injected, and applied topically. Poisoning was so common that its symptoms were confused with those of syphilis.<ref>Pimple, K.D. Pedroni, J.A. Berdon, V. (2002, July 09). [http://wisdomtools.com/poynter/syphilis.html Syphilis in history]. Poynter Center for the Study of Ethics and American Institutions at Indiana University-Bloomington. Retrieved on April 20, 2008.</ref>
==Toxicity==
Mercury(II) chloride is highly toxic and corrosive. Once absorbed into the bloodstream, Hg<sup>2+</sup> combines with proteins in the plasma or enters the red blood cells. It does not readily pass into the brain or fetus but may enter into other body organs.{{Fact|date=November 2007}} The liver is a major site of metabolism for mercury, and all mercury absorbed from the stomach and intestine is carried in blood directly to the liver. It accumulates in the kidneys, and may cause severe damage. Poisoning can result from inhalation, ingestion, or absorption through the skin.
Inhalation may result in corrosive [[bronchitis]], interstitial [[pneumonitis]], and death. Systemic effects following inhalation exposure may include shock, renal disorders, and central nervous system effects characterized by lethargy and neurobehavioral effects (insomnia, loss of memory, excitability, etc). Chronic exposure to low levels of vapor may result in central nervous system effects including fatigue, tremors, and gingivitis. As exposure increases, the frequency and magnitude of muscle tremors increase and are accompanied by personality and behavioral changes (memory loss, excitability, depression, and hallucinations).
Ingestion may cause severe gastrointestinal irritation, renal failure, and death with acute lethal doses in humans ranging from 1 to 4 g. The toxic effects are usually evident within 10–15 minutes of ingestion. Death can occur within 24 hours, resulting from shock, renal damage, severe gastrointestinal damage or kidney failure. Chronic symptoms include increased salivation, bleeding gums and loosening of the teeth.
Dermal contact with mercuric chloride may cause dermatitis and neurological effects. [[Acrodynia]] occurs in children and is characterised by a generalised body rash. Other symptoms include swelling and irritation of the hands, feet, cheeks and nose, hair loss, irritability, insomnia, and profuse perspiration which may lead to dehydration. Chronic exposure through absorption is usually the result of regular applications of topical ointments containing mercuric chloride.
==In popular culture==
[[Humbert Humbert]], the protagonist in [[Vladimir Nabokov's]] novel ''[[Lolita]]'', contemplates killing his child lover's mother with "five bichloride-of-mercury tablets in her preprandial sherry.", and newspaper headlines in the early part of the 20th century suggest that this compound was popular method of suicide and attempted suicide. Perhaps the most famous{{Fact|date=September 2007}} person to succumb to what the papers called "mercury bichloride" or "bi-chloride of mercury" was silent film star [[Olive Thomas]] whose 1920 death in Paris was ruled accidental.
In [[Patrick O'Brian]]'s novel [[The Wine-Dark Sea]], set in the early 19th century, the character [[Nathaniel Martin]] is a physician's assistant. He nearly poisons himself with "The Vienna Treatment", a preparation of the "corrosive sublimate" which is considered extremely dangerous in the wrong hands.
==References==
{{reflist}}
==External links==
*{{1911}}
* Agency for toxic substances and disease registry. (2001, May 25). [http://www.atsdr.cdc.gov/toxprofiles/tp46.html Toxicological profile for Mercury]. Retrieved on April 17, 2005.
* National institutes of health. (2002, October 31). [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@rn+@rel+7487-94-7 Hazardous substances data bank: Mercuric chloride]. Retrieved on April 17, 2005.
* Young, R.(2004, October 6). [http://risk.lsd.ornl.gov/tox/profiles/mercury_f_V1.shtml Toxicity summary for mercury]. The risk assessment information system. Retrieved on April 17, 2005.
*[http://www.atsdr.cdc.gov/tfacts46.html ATSDR - ToxFAQs: Mercury]
*[http://www.atsdr.cdc.gov/toxprofiles/phs46.html ATSDR - Public Health Statement: Mercury]
*[http://www.atsdr.cdc.gov/MHMI/mmg46.html ATSDR - Medical Management Guidelines (MMGs) for Mercury (Hg)]
*[http://www.atsdr.cdc.gov/toxprofiles/tp46.html ATSDR - Toxicological Profile: Mercury]
*{{ICSC|0979|09}}
* [http://www.npi.gov.au/database/substance-info/profiles/53.html National Pollutant Inventory - Mercury and compounds Fact Sheet]
*[http://www.cdc.gov/niosh/npg/npgd0383.html NIOSH Pocket Guide to Chemical Hazards]
*[http://www.altcorp.com/DentalInformation/mercuric.htm Mercury chloride toxicity] - includes excerpts from research reports.
{{Antiseptics and disinfectants}}
[[Category:Mercury compounds]]
[[Category:Chlorides]]
[[Category:Metal halides]]
[[Category:Alchemical substances]]
[[cs:Chlorid rtuťnatý]]
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[[ja:塩化水銀(II)]]
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[[ru:Хлорид ртути(II)]]
[[zh:氯化汞]]