Mercury(II) chloride

Mercury(II) chloride or mercuric chloride (historically "corrosive sublimate")[2] is the chemical compound of mercury and chlorine with the formula HgCl₂. It is white crystalline solid and is a laboratory reagent and a molecular compound that is very toxic to humans. Once used as a treatment for syphilis, it is no longer used for medicinal purposes because of mercury toxicity and the availability of superior treatments.

Mercury(II) chloride

Names
IUPAC names Mercury(II) chloride Mercury dichloride
Other names Mercuric chloride Corrosive sublimate
Identifiers
CAS Number	7487-94-7^Y
3D model (JSmol)	Interactive image
ChemSpider	22517^N
ECHA InfoCard	100.028.454
EC Number	231-299-8
KEGG	C13377^N
PubChem CID	24085
RTECS number	OV9100000
UNII	53GH7MZT1R^Y
UN number	1624
CompTox Dashboard (EPA)	DTXSID5020811
InChI InChI=1S/2ClH.Hg/h2*1H;/q;;+2/p-2^N
SMILES Cl[Hg]Cl
Properties
Chemical formula	HgCl2
Molar mass	271.52 g/mol
Appearance	colorless or white solid
Odor	odorless
Density	5.43 g/cm^3
Melting point	276 °C (529 °F; 549 K)
Boiling point	304 °C (579 °F; 577 K)
Solubility in water	3.6 g/100 mL (0 °C) 7.4 g/100 mL (20 °C) 48 g/100 mL (100 °C)
Solubility	4 g/100 mL (ether) soluble in alcohol, acetone, ethyl acetate slightly soluble in benzene, CS2, pyridine
Acidity (pKa)	3.2 (0.2M solution)
Magnetic susceptibility (χ)	−82.0·10^−6 cm^3/mol
Refractive index (nD)	1.859
Structure
Crystal structure	orthogonal
Coordination geometry	linear
Molecular shape	linear
Dipole moment	zero
Thermochemistry
Std molar entropy (S^o298)	144 J·mol^−1·K^−1[1]
Std enthalpy of formation (ΔfH^⦵298)	−230 kJ·mol^−1[1]
Pharmacology
ATC code	D08AK03 (WHO)
Hazards
Safety data sheet	ICSC 0979
EU classification (DSD) (outdated)	T+ (T+) C (C) N (N)
R-phrases (outdated)	R28, R34, R48/24/25, R50/53
S-phrases (outdated)	(S1/2), S36/37/39, S45, S60, S61
NFPA 704 (fire diamond)	0 4 1
Flash point	Non-flammable
Related compounds
Other anions	Mercury(II) fluoride Mercury(II) bromide Mercury(II) iodide
Other cations	Zinc chloride Cadmium chloride Mercury(I) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is ^YN ?)
Infobox references

Synthesis

Mercuric chloride is obtained by the action of chlorine on mercury or on mercury(I) chloride. It can also be produced by the addition of hydrochloric acid to a hot, concentrated solution of mercury(I) compounds such as the nitrate:[2]

Hg₂(NO₃)₂ + 4 HCl → 2 HgCl₂ + 2 H₂O + 2 NO₂

Heating a mixture of solid mercury(II) sulfate and sodium chloride also affords volatile HgCl₂, which can be separated by sublimation.[2]

Properties

Mercuric chloride exists not as a salt composed of discrete ions, but rather is composed of linear triatomic molecules, hence its tendency to sublime. In the crystal, each mercury atom is bonded to two chloride ligands with Hg—Cl distance of 2.38 Å; six more chlorides are more distant at 3.38 Å.[3]

Its solubility increases from 6% at 20 °C (68 °F) to 36% in 100 °C (212 °F). In the presence of chloride ions, it dissolves to give the tetrahedral coordination complex [HgCl₄]²⁻.

Applications

The main application of mercuric chloride is as a catalyst for the conversion of acetylene to vinyl chloride, the precursor to polyvinylchloride:

C₂H₂ + HCl → CH₂=CHCl

For this application, the mercuric chloride is supported on carbon in concentrations of about 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).[4] It is being used in plant tissue culture for surface sterilisation of explants such as leaf or stem nodes.

As a chemical reagent

Mercuric chloride is occasionally used to form an amalgam with metals, such as aluminium.[5] Upon treatment with an aqueous solution of mercuric chloride, aluminium strips quickly become covered by a thin layer of the amalgam. Normally, aluminium is protected by a thin layer of oxide, thus making it inert. Once amalgamated, aluminium can undergo a variety of reactions. For example, upon removal of the oxide layer, the exposed aluminium will immediately react with water generating Al(OH)₃ and hydrogen gas. Halocarbons 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 aluminium is also used as a reducing agent in organic synthesis. Zinc is also commonly amalgamated using mercuric chloride.

Mercuric chloride is used to remove dithiane groups attached to a carbonyl in an umpolung reaction. This reaction exploits the high affinity of Hg²⁺ for anionic sulfur ligands.

Mercuric chloride may be used as a stabilising agent for chemicals and analytical samples. Care must be taken to ensure that detected mercuric chloride does not eclipse the signals of other components in the sample, such as is possible in gas chromatography.[6]

Historical 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.[7]

Historical 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". This was done to prevent the specimens' destruction by moths, mites and mold. Objects in drawers were protected by scattering crystalline mercuric chloride over them.[8] It finds minor use in tanning, and wood was preserved by kyanizing (soaking in mercuric chloride).[9] Mercuric chloride was one of the three chemicals used for railroad tie wood treatment between 1830 and 1856 in Europe and the United States. Limited railroad ties were treated in the United States until there were concerns over lumber shortages in the 1890s.[10] The process was generally abandoned because mercuric chloride was water-soluble and not effective for the long term, as well as being highly poisonous. Furthermore, alternative treatment processes, such as copper sulfate, zinc chloride, and ultimately creosote; were found to be less toxic. Limited kyanizing was used for some railroad ties in the 1890s and early 1900s.[11]

Historic use in medicine

Mercuric chloride was used to disinfect wounds by Arab physicians in the Middle Ages.[12] It continued to be used by Arab doctors into the twentieth century, until modern medicine deemed it unsafe for use.

Syphilis was frequently treated with mercuric chloride before the advent of antibiotics. It was inhaled, ingested, injected, and applied topically. Both mercuric-chloride treatment for syphilis and poisoning during the course of treatment were so common that the latter's symptoms were often confused with those of syphilis. This use of "salts of white mercury" is referred to in the English-language folk song "The Unfortunate Rake".[13]

Yaws was treated with mercuric chloride (labeled as Corrosive Sublimate) before the advent of antibiotics. It was applied topically to alleviate ulcerative symptoms. Evidence of this is found in Jack London's book "The Cruise of the Snark" in the chapter entitled The Amateur M.D.

Historic use in crime and accidental poisonings

• In volume V of Alexandre Dumas' Celebrated Crimes, he recounts the history of Antoine François Desrues, who killed a noblewoman, Madame de Lamotte, with "corrosive sublimate".[14]
• In 1906, in New York, Richard Tilghman died after mistaking bichloride of mercury tablets for lithium citrate tablets.[15]
• In one highly publicized case in 1920, "mercury bichloride" was reported to have caused the death of 25-year-old American silent-film star Olive Thomas. While vacationing in France and staying at the Hôtel Ritz in Paris, she accidentally (or perhaps intentionally) ingested the compound, which had been prescribed to her husband Jack Pickford in liquid topical form to treat his "chronic syphilis". Thomas died five days later.[16][17]
• Mercuric chloride was used by Madge Oberholtzer to commit suicide after she was kidnapped, raped, and tortured by Ku Klux Klan leader D.C. Stephenson. Oberholtzer died from a combination of mercury poisoning and staph infection, the latter caused by Stephenson biting her during the assault.[18]

Toxicity

Main article: Mercury poisoning

Mercuric chloride is extremely toxic, both acutely and as a cumulative poison. Its toxicity is due not just to its mercury content but also to its corrosive properties, which can cause serious internal damage, including ulcers to the stomach, mouth, and throat, and corrosive damage to the intestines. Mercuric chloride also tends to accumulate in the kidneys, causing severe corrosive damage which can lead to acute kidney failure. However, mercuric chloride, like all inorganic mercury salts, does not cross the blood-brain barrier as readily as organic mercury, although it is known to be a cumulative poison.

Common side effects of acute mercuric chloride poisoning include burning sensations in the mouth and throat, stomach pain, abdominal discomfort, lethargy, vomiting of blood, corrosive bronchitis, severe irritation to the gastrointestinal tract, and kidney failure. Chronic exposure can lead to symptoms more common with mercury poisoning, such as insomnia, delayed reflexes, excessive salivation, bleeding gums, fatigue, tremors, and dental problems.

Acute exposure to large amounts of mercuric chloride can cause death in as little as 24 hours, usually due to acute kidney failure or damage to the gastrointestinal tract. In other cases, victims of acute exposure have taken up to two weeks to die.[19][20]

References

1. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 978-0-618-94690-7.
2. Chisholm, Hugh, ed. (1911). "Corrosive Sublimate" . Encyclopædia Britannica. 7 (11th ed.). Cambridge University Press. p. 197.
3. Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
4. Matthias Simon, Peter Jönk, Gabriele Wühl-Couturier, Stefan Halbach "Mercury, Mercury Alloys, and Mercury Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2006: Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_269.pub2
5. Deng, James; Wang, Yu-Pu; Danheiser, Rick L. (2015). "Synthesis of 4,4-Dimethoxybut-1-yne". Organic Syntheses. 92: 13–25. doi:10.15227/orgsyn.092.0013.
6. Foreman, W. T.; Zaugg, S. D.; Faires, L. M.; Werner, M. G.; Leiker, T. J.; Rogerson, P. F. (1992). "Analytical interferences of mercuric chloride preservative in environmental water samples: Determination of organic compounds isolated by continuous liquid-liquid extraction or closed-loop stripping". Environmental Science & Technology. 26 (7): 1307. Bibcode:1992EnST...26.1307F. doi:10.1021/es00031a004.
7. Towler, J. (1864). 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.
8. Goldberg, Lisa (1996). "A History of Pest Control Measures in the Anthropology Collections, National Museum of Natural History, Smithsonian Institution". JAIC. 35 (1): 23–43. Retrieved April 17, 2005.
9. Freeman, M.H. Shupe, T.F. Vlosky, R.P. Barnes, H.M. (2003). Past, present and future of the wood preservation industry Archived 2005-05-03 at the Wayback Machine. Forest Products Journal. 53(10) 8–15. Retrieved on April 17, 2005.
10. Pg. 19-75 "Date Nails and Railroad Tie Preservation" (3 vol.; 560 p.), published in 1999 by the Archeology and Forensics Laboratory, University of Indianapolis; Jeffrey A. Oaks
11. Oaks, Jeffrey A. "History of Railroad Tie Preservation" (PDF). p. 20-30; p. 64, Table I. Archived from the original (PDF) on 2011-07-18. Retrieved 2009-01-14.
12. Maillard, Adam P. Fraise, Peter A. Lambert, Jean-Yves (2007). Principles and Practice of Disinfection, Preservation and Sterilization. Oxford: John Wiley & Sons. p. 4. ISBN 978-0470755068.
13. Pimple, K.D. Pedroni, J.A. Berdon, V. (2002, July 09). Syphilis in history Archived 2008-04-30 at the Wayback Machine. Poynter Center for the Study of Ethics and American Institutions at Indiana University-Bloomington. Retrieved on April 20, 2008.
14. Dumas, Alexandre (1895). Celebrated Crimes Volume V: The Cenci. Murat. Derues. G. Barrie & sons. p. 250. Retrieved 30 June 2015 – via Google Books.
15. https://chroniclingamerica.loc.gov/lccn/sn86063756/1906-06-28/ed-1/seq-1/
16. "Bichloride of Mercury Killed Olive Thomas". The Toronto World. September 15, 1920. p. 6. Retrieved August 27, 2018.
17. Foster, Charles (2000). Stardust and Shadows: Canadians in Early Hollywood, page 257. Toronto, Canada: Dundurn Press, 2000. ISBN 978-1550023480.
18. http://murderpedia.org/male.S/s/stephenson-david.htm
19. https://www.chemeurope.com/en/encyclopedia/Mercury(II)_chloride.html
20. https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+33

External links

• Agency for toxic substances and disease registry. (2001, May 25). Toxicological profile for Mercury. Retrieved on April 17, 2005.
• National institutes of health. (2002, October 31). Hazardous substances data bank: Mercuric chloride. Retrieved on April 17, 2005.
• Young, R.(2004, October 6). Toxicity summary for mercury. The risk assessment information system. Retrieved on April 17, 2005.
• ATSDR - ToxFAQs: Mercury
• ATSDR - Public Health Statement: Mercury
• ATSDR - Medical Management Guidelines (MMGs) for Mercury (Hg)
• ATSDR - Toxicological Profile: Mercury
• International Chemical Safety Card 0979
• National Pollutant Inventory - Mercury and compounds Fact Sheet
• NIOSH Pocket Guide to Chemical Hazards
• Mercury chloride toxicity - includes excerpts from research reports.