mercuric chloride

 

or mercury (II) chloride, chemical compound, HgCl₂, a white powder of colorless rhombohedral crystals, somewhat soluble in water. It is also called bichloride of mercury or corrosive sublimate. It is extremely poisonous. Raw egg white may be given as an antidote, since mercuric chloride reacts with egg albumin to form a nearly insoluble precipitate; medical treatment should be sought immediately. Mercuric chloride is sometimes used in dilute solution as an antiseptic for inanimate objects and as a fungicide. It is also used in preparing other mercury compounds; it reacts with mercury metal to form mercurous chloride. Mercuric chloride is prepared by reacting mercury with chlorine gas or by subliming a mixture of mercuric sulfate and sodium chloride (common salt).

Mercury(II) chloride
IUPAC name	Mercury(II) chloride Mercury dichloride
Other names	Mercuric chloride Corrosive sublimate
Identifiers
CAS number	7487-94-7
Properties
Molecular formula	HgCl2
Molar mass	271.52 g/mol
Appearance	white solid
Density	6.5 g/cm³, solid
Melting point	277 °C
Boiling point	302 °C
Solubility in water	7.4 g/100 ml (20 °C)
Solubility in other solvents	33 g/100 ml (25 °C)
Structure
Coordination geometry	linear
Molecular shape	linear
Dipole moment	zero
Hazards
EU classification	Very toxic (T+) Dangerous for the environment (N)
R-phrases	R28, R34, R48/24/25, R50/53
S-phrases	(S1/2), S36/37/39, S45, S60, S61
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 noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Mercury(II) chloride (also called mercuric chloride and corrosive sublimate) is a poisonous white soluble crystalline salt of mercury. It was formerly used in insecticides, batteries; as an antiseptic, disinfectant, preservative, in metallurgy and as a photographic fixitive. Mercuric chloride is one of the most toxic forms of mercury because it easily forms organomercury complexes with proteins. Unlike other mercury halogenides it is soluble in water (~6%).

Production

Mercury(II) 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) nitrate,

HgNO₃ + 2HCl → HgCl₂ + H₂O + NO₂,

or by heating a mixture of mercury(II) sulfate and sodium chloride. The mercuric chloride then sublimes and condenses in the form of small rhombic crystals.

Applications

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.^[1]

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.^[2]

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.^[3]

Mercury(II) chloride is used in the manufacture of calomel, chemical reagents, metallurgy, tanning, as a catalyst for vinyl chloride and in electroplating. Wood was preserved by kyanizing (soaking in mercuric chloride) beginning in 1848.^[4]

Mercuric chloride is often used to form an amalgam with mercury soluble metals, such as aluminum. When aluminum strips are soaked in mercuric chloride solution, they quickly become covered by a thin layer of mercury. Normally, aluminum is protected by a thin layer of oxide making it inert, but amalgamated aluminum can undergo a variety of reactions - it will dissolve in water (this can be dangerous, as hydrogen gas and heat are generated.) When added to a halocarbon, amalgamated aluminum can insert in the carbon-halogen bond (the Barbier reaction). These alkylaluminum compounds are nucleophilic and can be used in a similar fashion to the Grignard reagent. Amalgamated aluminum is also used to reduce carbonyls.

Mercuric chloride is used to remove dithiane groups attached to a carbonyl in an umpolung reaction.

Toxicity

Mercury(II) chloride is highly toxic and corrosive. Once absorbed into the bloodstream, inorganic mercury 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. 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 accumlates 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 Nabakov'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^{[citation needed]} 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.

See also

• corrosive
• mercury(I) chloride

References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
• 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.

1. ^ 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.
2. ^ Goldberg, L. (1996). 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.
3. ^ Pimple, K.D. Pedroni, J.A. Berdon, V. (2002, July 09). Syphilis in history. Poynter Center for the Study of Ethics and American Institutions at Indiana University-Bloomington. Retrieved on April 17, 2005.
4. ^ Freeman, M.H. Shupe, T.F. Vlosky, R.P. Barnes, H.M. (2003). Past, present and future of the wood preservation industry. Forest Products Journal. 53(10) 8–15. Retrieved on April 17, 2005.

External links

• 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.

Antiseptics and disinfectants (D08)
Acridine derivatives	Ethacridine lactate - Aminoacridine - Euflavine
Biguanides and amidines	Dibrompropamidine - Chlorhexidine - Propamidine - Hexamidine - Polihexanide
Phenol and derivatives	Hexachlorophene - Policresulen - Phenol - Triclosan - Chloroxylenol - Biphenylol
Nitrofuran derivatives	Nitrofurazone
Iodine products	Iodine/octylphenoxypolyglycolether - Povidone-iodine - Diiodohydroxypropane
Quinoline derivatives	Dequalinium - Chlorquinaldol - Oxyquinoline - Clioquinol
Quaternary ammonium compounds	Benzalkonium - Cetrimonium - Cetylpyridinium - Cetrimide - Benzoxonium chloride - Didecyldimethylammonium chloride
Mercurial products	Mercuric amidochloride - Phenylmercuric borate - Mercuric chloride - Mercurochrome - Thiomersal - Mercuric iodide
Silver compounds	Silver nitrate
Others	Hydrogen peroxide - Eosin - Propanol - Tosylchloramide sodium - Isopropanol - Potassium permanganate - Sodium hypochlorite - Ethanol

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