Arsenic trichloride

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Arsenic trichloride
Ball-and-stick model of arsenic trichloride
Identifiers
CAS number 7784-34-1 YesY
PubChem 24570
ChemSpider 22974 YesY
RTECS number CG1750000
Jmol-3D images Image 1
Properties
Molecular formula AsCl3
Molar mass 181.28 g/mol
Appearance colourless liquid
Density 2.163 g/cm3, liquid
Melting point −16.2 °C (2.8 °F; 256.9 K)
Boiling point 130.2 °C (266.4 °F; 403.3 K)
Solubility in water decomposes
Solubility soluble in alcohol, ether, HCl, HBr
Refractive index (nD) 1.6006
Viscosity 9.77 x 10−6 Pa s
Hazards
EU classification Very Toxic (T+)
Dangerous for the environment (N)
R-phrases R23/25, R50/53
S-phrases (S1/2), S20/21, S28, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
LD50 48 mg/kg
Related compounds
Other anions Arsenic trioxide
Other cations Antimony trichloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Arsenic trichloride is an inorganic compound with the formula AsCl3, also known as arsenous chloride or butter of arsenic. This poisonous oil is colourless, although impure samples may appear yellow. It is an intermediate in the manufacture of organoarsenic compounds.[1]

Structure[edit]

AsCl3 is a pyramidal molecule with C3v symmetry. The As-Cl bond is 2.161 Å and the angle Cl-As-Cl is 98° 25'±30.[2][3] AsCl3 has four normal modes of vibration: ν1(A1) 416, ν2(A1) 192, ν3 393, and ν4(E) 152 cm−1.[4] Arsenic trichloride contains predominantly covalent bonds, which explains its low melting point.

Synthesis[edit]

This colourless liquid is prepared by treatment of arsenic(III) oxide with hydrogen chloride followed by distillation:

As2O3 + 6 HCl → 2 AsCl3 + 3 H2O

It can also be prepared by chlorination of arsenic at 80–85 °C, but this method requires elemental arsenic.[1]

2 As + 3 Cl2 → 2 AsCl3

Arsenic trichloride can also be prepared by the reaction of arsenic oxide and sulfur monochloride. This method requires simple apparatus and proceeds efficiently:[5]

2 As2O3 + 6 S2Cl2 → 4 AsCl3 + 3 SO2 + 9 S

Reactions[edit]

Hydrolysis with water gives arsenous acid and hydrochloric acid:

AsCl3 + 3 H2O → As(OH)3 + 3 HCl

Although AsCl3 is less moisture sensitive than PCl3, it still fumes in moist air.[6]

AsCl3 undergoes redistribution upon treatment with As2O3 to give the inorganic polymer AsOCl. With chloride sources, AsCl3, forms salts containing the anion [AsCl4]. Reaction with potassium bromide and potassium iodide give arsenic tribromide and arsenic triiodide, respectively.

AsCl3 is useful in organoarsenic chemistry, for example triphenylarsine is derived from AsCl3:[7]

AsCl3 + 6 Na + 3 C6H5Cl → As(C6H5)3 + 6 NaCl

Safety[edit]

Arsenic compounds are highly toxic, and AsCl3 especially so because of its volatility and solubility.

References[edit]

  1. ^ a b Sabina C. Grund, Kunibert Hanusch, Hans Uwe Wolf "Arsenic and Arsenic Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, VCH-Wiley, 2008, Weinheim.doi:10.1002/14356007.a03_113.pub2
  2. ^ P. Kisliuk; C. H. Townes. "The Microwave Spectra and Molecular Structure of Phosphorus and Arsenic Trichloride". J. Chem. Physics 1950, 18.
  3. ^ Jean Galy; Renee Enjalbertl Pierre Lecante; Andrzej Burian "AsCl3: From the crystalline to the liquid state. XRD (176< T (K) < 250) and WAXS (295K) studies" Inorg. Chem 2002, volume 41, pp. 693–698.doi:10.1021/ic0102788
  4. ^ Klapoetke, Thomas M. "The vibrational spectrum of arsenic trichloride" Main Group Metal Chemistry 1997, volume 20, pp. 81–83.
  5. ^ R. C. Smith, "Manufacture of Arsenic trichloride" The Journal of Industrial and Engineering Chemistry 1919, volume 11, pp. 109–110. doi:10.1021/ie50110a009
  6. ^ Holleman, A. F.; Wiberg, E. Inorganic Chemistry Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  7. ^ Shriner, R. L.; Wolf, C. N. (1963), "Tetraphenylarsonium Chloride Hydrochloride", Org. Synth. ; Coll. Vol. 4: 910 . Describes the preparation of As(C6H5)3.