Arsenic triiodide

Arsenic triiodide is the inorganic compound with the formula AsI₃.^[2][3][4] It is an orange to dark red solid^[5] that readily sublimes. It is a pyramidal molecule that is useful for preparing organoarsenic compounds.

Arsenic triiodide

Unit cell ball and stick model of arsenic triiodide
Names
Preferred IUPAC name Arsenic triiodide
Systematic IUPAC name Triiodoarsane
Other names Arsenic(III) iodide Arsenous iodide
Identifiers
CAS Number	7784-45-4 Y
3D model (JSmol)	Interactive image
ChemSpider	22979 Y
ECHA InfoCard	100.029.153
EC Number	232-068-4
PubChem CID	24575
RTECS number	CG1950000
UNII	3029988O2T Y
CompTox Dashboard (EPA)	DTXSID9064843
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
SMILES I[As](I)I
Properties
Chemical formula	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)
Solubility in water	6 g/100 mL
Solubility	soluble in alcohol, ether, CS2 dissolves in chloroform, benzene, toluene
Magnetic susceptibility (χ)	−142.0·10−6 cm3/mol
Refractive index (nD)	2.23
Structure
Crystal 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

The triiodide is made by treating arsenic(III) oxide with concentrated hydroiodic acid:^[5]

As₂O₃ + 6 HI → 2 AsI₃ + 3 H₂O

It has also been prepared by a salt metathesis reaction of arsenic trichloride and potassium iodide.^[6]

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.^[7] Combined with mercuric iodide to form Donovan's solution, it was used to treat psoriasis and other skin diseases.^[8]