Mercury(I) iodide

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Mercury(I) iodide
Spacefil model of crystalline mercury(I) iodide
IUPAC name
Mercury(I) iodide[citation needed]
Other names
Mercurous iodide[citation needed]
Red mercury
3D model (Jmol)
ECHA InfoCard 100.035.811
EC Number 239-409-6
UN number 1638
Molar mass 654.99 g mol−1
Appearance Dark yellow, opaque crystals
Odor Odourless
Density 7.7 g mL−1
−41.5·10−6 cm3/mol
241.47 J K−1 mol−1
−119.09 kJ mol−1
GHS pictograms The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
H300, H310, H330, H373, H410
P260, P273, P280, P284, P301+310
Very Toxic T+ Dangerous for the Environment (Nature) N
R-phrases R26/27/28, R33, R50/53
S-phrases (S1/2), S13, S28, S45
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Mercury(I) iodide is a chemical compound of mercury and iodine. The chemical formula is Hg2I2. It is photosensitive and decomposes easily to mercury and HgI2.


Mercury(I) iodide can be prepared by direct combination of mercury and iodine:

2 Hg + I2 → Hg2I2


In common with other Hg(I) (mercurous) compounds which contain linear X-Hg-Hg-X units, Hg2I2 contains linear IHg2I units with an Hg-Hg bond length of 272 pm (Hg-Hg in the metal is 300 pm) and an Hg-I bond length of 268 pm.[1] The overall coordination of each Hg atom is octahedral as it has in addition to the two nearest neighbours there are four other I atoms at 351 pm. [1]The compound is often formulated as Hg22+ 2I.[2]

Historical Uses[edit]

Mercury(I) iodide, called Protiodide, was a very commonly used drug in the 19th century, prescribed for everything from acne to kidney disease. It was also the treatment of choice for syphilis. It was available over the counter at any drugstore in the world, the most common form being a concoction of protiodide, licorice, glycerin and marshmallow.

Taken orally, and in low doses, protiodide causes excessive salivation, fetid breath, spongy and bleeding gums and sore teeth. Excessive use or an overdose causes physical weakness, loss of teeth, hemolysing (destruction of the red blood cells) of the blood and necrosis of the bones and tissues of the body. Early signs of an overdose or excessive use are muscular tremors, chorea, and locomotor ataxia. Violent bloody vomiting and voiding also occur.

Protiodide is banned as a medication, even though it persisted in use as a quack remedy until the early 20th century.

See also[edit]


  1. ^ a b Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  2. ^ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5