Arsenic triiodide
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 457814846
| ImageFile = Arsenic-triiodide-from-xtal-unit-cell-3D-bs-17.png
| ImageName = Unit cell ball and stick model of arsenic triiodide
| PIN = Arsenic triiodide
| SystematicName = Triiodoarsane
| OtherNames = Arsenic(III) iodide
Arsenous iodide
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 7784-45-4
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 3029988O2T
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/AsI3/c2-1(3)4
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = IKIBSPLDJGAHPX-UHFFFAOYSA-N
| PubChem = 24575
| ChemSpiderID = 22979
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| EINECS = 232-068-4
| RTECS = CG1950000
| SMILES = I[As](I)I
| InChI = 1S/AsI3/c2-1(3)4
| InChIKey = IKIBSPLDJGAHPX-UHFFFAOYSA-N}}
|Section2={{Chembox Properties
| Formula = AsI3
| MolarMass = 455.635 g/mol
| Appearance = orange-red crystalline solid
| Density = 4.69 g/cm3
| Solubility = 6 g/100 mL
| SolubleOther = soluble in alcohol, ether, CS2
dissolves in chloroform, benzene, toluene
| MeltingPtC = 146
| MeltingPt_notes =
| BoilingPtC = 403
| BoilingPt_notes =
| RefractIndex = 2.23
| MagSus = −142.0·10−6 cm3/mol
}}
|Section3={{Chembox Structure
| CrystalStruct = Rhombohedral, hR24, SpaceGroup = R-3, No. 148
}}
|Section7={{Chembox Hazards
| NFPA-H =
| NFPA-R =
| NFPA-F =
| IDLH = Ca [5 mg/m3 (as As)]{{PGCH|0038}}
| REL = Ca C 0.002 mg/m3 [15-minute]
| PEL = [1910.1018] TWA 0.010 mg/m3
}}
}}
Arsenic triiodide is the inorganic compound with the formula AsI3.{{Cite web |title=Arsenic triiodide - Hazardous Agents {{!}} Haz-Map |url=https://haz-map.com/Agents/3750 |access-date=2023-01-20 |website=haz-map.com}}{{Cite web |title=T3DB: Arsenic triiodide |url=http://www.t3db.ca/toxins/T3D1300 |access-date=2023-01-20 |website=www.t3db.ca}}{{Cite web |title=arsenic triiodide |url=https://webbook.nist.gov/cgi/inchi/InChI=1S/AsI3/c2-1(3)4 |access-date=2023-01-20 |website=webbook.nist.gov |language=en}}{{Cite web |last=PubChem |title=Arsenic triiodide |url=https://pubchem.ncbi.nlm.nih.gov/compound/24575 |access-date=2023-01-20 |website=pubchem.ncbi.nlm.nih.gov |language=en}} It is an orange to dark red solid that readily sublimes. It is a pyramidal molecule that is useful for preparing organoarsenic compounds.
Preparation
It is prepared by a reaction of arsenic trichloride and potassium iodide:John C. Bailar, Jr. "Arsenic Triiodide" Inorganic Syntheses 1939, volume 1, pp. 103–104, 2007. {{doi|10.1002/9780470132326.ch36}}
: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.Shakhashiri BZ, [http://scifun.chem.wisc.edu/chemweek/Arsenic/Arsenic.html "Chemical of the Week: Arsenic"] {{Webarchive|url=https://web.archive.org/web/20080802165618/http://scifun.chem.wisc.edu/chemweek/Arsenic/Arsenic.html |date=2008-08-02 }}, University of Wisconsin–Madison Chemistry Dept. Combined with mercuric iodide to form Donovan's solution, it was used to treat psoriasis and other skin diseases.{{cite journal|journal=The Lancet|date=August 1857|volume=70|issue=1770|page=116|doi=10.1016/S0140-6736(02)38789-0|url=https://books.google.com/books?id=NbI1AQAAMAAJ&q=%22Donovan%27s+solution%22&pg=PA116|title=Good Results of Donovan's Solution in Psoriasis}}