Arsenic triiodide

Arsenic triiodide
Preferred IUPAC name Arsenic triiodide
Systematic name Triiodoarsane
Other names Arsenic(III) iodide Arsenous iodide Donovan's solution[1]
Identifiers
CAS number	7784-45-4 N
PubChem	24575 Y
ChemSpider	22979 Y
EC number	232-068-4
RTECS number	CG1950000
Jmol-3D images	Image 1
SMILES I[As](I)I
InChI InChI=1S/AsI3/c2-1(3)4 Y Key: IKIBSPLDJGAHPX-UHFFFAOYSA-N Y InChI=1S/AsI3/c2-1(3)4 Key: IKIBSPLDJGAHPX-UHFFFAOYSA-N
Properties
Molecular formula	AsI3
Molar mass	455.635 g/mol
Appearance	orange-red crystalline solid
Density	4.69 g/cm3
Melting point	146 °C
Boiling point	403 °C
Solubility in water	6 g/100 mL
Solubility	soluble in alcohol, ether, CS2
Refractive index (nD)	2.23
Structure
Crystal structure	Rhombohedral, hR24, SpaceGroup = R-3, No. 148
N triiodide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Arsenic triiodide is the inorganic compound with the formula AsI₃. It is a dark red solid that readily sublimes. It is a pyramidial molecule that is useful for preparing organoarsenic compounds.

Preparation

It is prepared by a reaction of arsenic trichloride and potassium iodide:^[2]

AsCl₃ + 3KI → AsI₃ + 3 KCl

Reactions

Hydrolysis occurs only slowly in water forming arsenic trioxide and hydroiodic acid. The reaction proceeds via formation of arsenous acid which exists in equilibrium with hydroiodic acid. The aqueous solution is highly acidic, pH of 0.1N solution is 1.1. It decomposes to arsenic trioxide, elemental arsenic and iodine when heated in air at 200 °C. The decomposition, however, commences at 100 °C and occurs with the liberation of iodine.

Former uses

Under the name of Donovan's solution, it was once recommended to treat rheumatism, arthritis, malaria, trypanosome infections, tuberculosis, and diabetes.^[1]

References

1. ^ ^{a b} Shakhashiri BZ, "Chemical of the Week: Arsenic", University of Wisconsin–Madison Chemistry Dept.
2. ^ John C. Bailar, Jr. "Arsenic Triiodide" Inorganic Syntheses 1939, volume 1, pp. 103–104, 2007. doi:10.1002/9780470132326.ch36