View source for Arsenic trichloride

{{Chembox
| Name = Arsenic trichloride
| Reference =
| IUPACName = Arsenic(III) chloride
| PIN =
| SystematicName =
| OtherNames = Arsenic(III) chloride<br>Arsenous chloride<br>Butter of arsenic<br>de Valagin's solution<br>Trichloroarsine
<!-- Images -->
| ImageFile = 
| ImageSize = 
| ImageAlt = 
| ImageName = 
| ImageFile1 = 
| ImageSize1 = 
| ImageAlt1 = 
| ImageName1 = 
| ImageFile2 = 
| ImageSize2 = 
| ImageAlt2 = 
| ImageName2 = 
| ImageFile3 = 
| ImageSize3 = 
| ImageAlt3 = 
| ImageName3 = 
| ImageFileL1 = 
| ImageSizeL1 = 
| ImageAltL1 = 
| ImageNameL1 = 
| ImageFileR1 = 
| ImageSizeR1 = 
| ImageAltR1 = 
| ImageNameR1 = 
| ImageFileL2 = 
| ImageSizeL2 = 
| ImageAltL2 = 
| ImageNameL2 = 
| ImageFileR2 = 
| ImageSizeR2 = 
| ImageAltR2 = 
| ImageNameR2 = 
<!-- Sections -->
| Section1 = {{Chembox Identifiers
| 3DMet = 
| Abbreviations = 
| SMILES = 
  }}
| Section2 = {{Chembox Properties
| AtmosphericOHRateConstant = 
| Appearance = Colorless liquid
| BoilingPt = 
| BoilingPtC = 130.2
| BoilingPt_ref = 
| BoilingPt_notes = 
| Density = 2.163 g/cm<sup>3</sup> (20 °C)
| Formula = AsCl<sub>3</sub>
| HenryConstant = 
| LogP = 1.69
| MolarMass = 181.28 g/mol
| MeltingPt = 
| MeltingPtC = −16.2
| MeltingPt_ref = 
| MeltingPt_notes = 
| Odor = Acrid, acidic
| pKa = 
| pKb = 
| Solubility = Reacts
| SolubleOther = Reacts with alcohols<br>Miscible with [[carbon tetrachloride]], [[chloroform]], [[diethyl ether]], [[hydrochloric acid]], [[phosphorus trichloride]], [[Tetrahydrofuran|THF]], [[toluene]], [[xylene]]
| Solvent = 
| VaporPressure = 8.78 mmHg at 20 °C
  }}
| Section3 = {{Chembox Structure
| Coordination = 
| CrystalStruct = 
| MolShape = 
  }}
| Section4 = {{Chembox Thermochemistry
| DeltaGf = 
| DeltaHc = 
| DeltaHf = 
| Entropy = 
| HeatCapacity = 
  }}
| Section5 = {{Chembox Explosive
| ShockSens = 
| FrictionSens = 
| DetonationV = 
| REFactor = 
  }}
| Section6 = {{Chembox Hazards
| AutoignitionPt = Non-flammable
| ExploLimits = Non-flammable
| ExternalMSDS = [https://www.docdroid.net/24aCk66/arsenic-trichloride-sa-pdf Sigma-Aldrich]
| FlashPt = Non-flammable
| LD50 = 48 mg/kg (rat, oral)<br>80 mg/kg (rat, dermal)
| LC50 = 
| MainHazards = Corrosive<br>Extremely toxic
| NFPA-F = 
| NFPA-H = 
| NFPA-R = 
| NFPA-S = 
  }}
| Section7 = {{Chembox Related
| OtherAnions = 
| OtherCations = 
| OtherFunction = 
| OtherFunction_label = 
| OtherCompounds = [[Nitrogen trichloride]]<br>[[Phosphorus trichloride]]<br>[[Antimony(III) chloride]]<br>[[Bismuth chloride]]
  }}
}}
'''Arsenic(III) chloride''' or '''arsenic trichloride''' is an inorganic compound with the formula '''AsCl<sub>3</sub>'''. It is highly corrosive and poisonous.

As arsenic is in group 15, it can also form arsenic pentachloride (AsCl<sub>5</sub>). However, this compound is unstable at temperatures above −50 °C, meaning it has no uses in chemistry except for research.

==Properties==
===Chemical===
Arsenic trichloride will rapidly hydrolyze in contact with water, forming [[arsenous acid]] and [[hydrochloric acid]]:

: AsCl<sub>3</sub> + 3 H<sub>2</sub>O → As(OH)<sub>3</sub> + 3 HCl

Although AsCl<sub>3</sub> is less moisture sensitive than [[Phosphorus trichloride|PCl<sub>3</sub>]], it still fumes in moist air.

AsCl<sub>3</sub> undergoes redistribution upon treatment with As<sub>2</sub>O<sub>3</sub> to give arsenic oxychloride, AsOCl.

: AsCl<sub>3</sub> + As<sub>2</sub>O<sub>3</sub> → 3 AsOCl

With chloride sources, AsCl<sub>3</sub>, forms salts containing the anion [AsCl<sub>4</sub>]<sup>−</sup>. Reaction with [[potassium bromide]] and [[potassium iodide]] give [[arsenic tribromide]] and [[arsenic triiodide]], respectively.

: AsCl<sub>3</sub> + 3 KBr → AsBr<sub>3</sub> + 3 KCl

: AsCl<sub>3</sub> + 3 KI → AsI<sub>3</sub> + 3 KCl

===Physical===
Arsenic trichloride is a colorless liquid, that fumes in moist air. Impure samples may appear yellowish or cloudy. It reacts with water and alcohols, but it's miscible with ethers.

==Availability==
Arsenic(III) chloride is sold by chemical suppliers, however due to its hazards, and the fact that arsenic compounds are highly regulated in  most countries, it's practically impossible for the hobby chemist to acquire it.

It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.

==Preparation==
There are several preparation routes:

Reacting [[arsenic trioxide]] with an excess of [[hydrogen chloride]] will yield the compound, while the excess HCl will prevent hydrolysis:

: As<sub>2</sub>O<sub>3</sub> + 6 HCl → 2 AsCl<sub>3</sub> + 3 H<sub>2</sub>O

[[Disulfur dichloride]] can be used as substitute for HCl, and has the advantage of destroying any water produced by the reaction:<ref>[https://pubs.acs.org/doi/abs/10.1021/ie50110a009 R. C. Smith, "Manufacture of Arsenic trichloride" ''The Journal of Industrial and Engineering Chemistry'' 1919, volume 11, pp. 109–110]</ref>

: 2 As<sub>2</sub>O<sub>3</sub> + 6 S<sub>2</sub>Cl<sub>2</sub> → 4 AsCl<sub>3</sub> + 3 SO<sub>2</sub> + 9 S

[[Thionyl chloride]], while more expensive, can also be used:<ref>[https://onlinelibrary.wiley.com/doi/10.1002/9780470132623.ch24 S. K. Pandey, A. Steiner, H. W. Roesky, S. Kamepalli, A. H. Cowley, "Arsenic(III)chloride" ''Inorganic Synthesis'' 1997, volume 31, pp. 148-150]</ref>

: 2 As<sub>2</sub>O<sub>3</sub> + 3 SOCl<sub>2</sub> → 2 AsCl<sub>3</sub> + 3 SO<sub>2</sub>

In all these cases, the reaction takes place during reflux. The final product is distilled.

A water-free route, which gives a very pure product, involves direct chlorination of arsenic at 80–85 °C, but this method requires elemental [[arsenic]], which is volatile and more hazardous:

: 2 As + 3 Cl<sub>2</sub> → 2 AsCl<sub>3</sub>

==Projects==
*Make organoarsenic compounds (don't you have better things to do, though?)
*Make arsenic bromides and iodides
*Compound collecting

==Handling==
===Safety===
Arsenic and all of its compounds are highly toxic, and AsCl<sub>3</sub> more so, because of its volatility and solubility.

===Storage===
Arsenic trichloride must be kept away from moisture. Schlenck flasks or ampouling are recommended.

===Disposal===
The neutralization of arsenic halides is complicated not only by their volatility, but also by the high toxicity of arsenic compounds. Any neutralization must be done in a special installation, designed to scrub any traces of arsenic wastes.

==References==
<references/>
===Sciencemadness Library===
*[http://library.sciencemadness.org/library/books/ATBOIC/atboic_xi_ii_organoarsenic.pdf A TEXT-BOOK OF INORGANIC CHEMISTRY. VOLUME XI. ORGANOMETALLIC COMPOUNDS. PART II. DERIVATIVES OF ARSENIC.]

===Relevant Sciencemadness threads===
*[http://www.sciencemadness.org/talk/viewthread.php?tid=155002 Preparation of Arsenic trichloride]

[[Category:Chemical compounds]]
[[Category:Inorganic compounds]]
[[Category:Arsenic compounds]]
[[Category:Chlorine compounds]]
[[Category:Arsenic halides]]
[[Category:Choking agents]]
[[Category:Materials that react with water]]
[[Category:Materials unstable in basic solution]]
[[Category:Things that can kill you very quickly]]
[[Category:Things that should NOT be messed with except by professionals]]
[[Category:Corrosive chemicals]]
[[Category:Liquids]]