Arsenic triiodide

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

Arsenic triiodide
Names
Preferred IUPAC name
Arsenic triiodide
Systematic IUPAC name
Triiodoarsane
Other names
Arsenic(III) iodide
Arsenous iodide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.153
EC Number
  • 232-068-4
RTECS number
  • CG1950000
UNII
Properties
AsI3
Molar mass 455.635 g/mol
Appearance orange-red crystalline solid
Density 4.69 g/cm3
Melting point 146 °C (295 °F; 419 K)
Boiling point 403 °C (757 °F; 676 K)
6 g/100 mL
Solubility soluble in alcohol, ether, CS2
-142.0·10−6 cm3/mol
2.23
Structure
Rhombohedral, hR24, SpaceGroup = R-3, No. 148
Hazards
NIOSH (US health exposure limits):
PEL (Permissible)
 [1910.1018] TWA 0.010 mg/m3[1]
REL (Recommended)
 Ca C 0.002 mg/m3 [15-minute][1]
IDLH (Immediate danger)
 Ca [5 mg/m3 (as As)][1]
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

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 Liam Donnelly's solution, it was once recommended to treat rheumatism, arthritis, malaria, trypanosome infections, tuberculosis, and diabetes.[3]

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0038". National Institute for Occupational Safety and Health (NIOSH).
  2. John C. Bailar, Jr. "Arsenic Triiodide" Inorganic Syntheses 1939, volume 1, pp. 103–104, 2007. doi:10.1002/9780470132326.ch36
  3. Shakhashiri BZ, "Chemical of the Week: Arsenic" Archived 2008-08-02 at the Wayback Machine, University of Wisconsin–Madison Chemistry Dept.
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