Arsenic trichloride is an
inorganic compound with the formula AsCl
3, 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 compound
Organoarsenic chemistry is the chemistry of compounds containing a chemical bond between arsenic and carbon. A few organoarsenic compounds, also called "organoarsenicals," are produced industrially with uses as insecticides, herbicides, and fu ...
s.
[Sabina C. Grund, Kunibert Hanusch, Hans Uwe Wolf "Arsenic and Arsenic Compounds" in ''Ullmann's Encyclopedia of Industrial Chemistry'', VCH-Wiley, 2008, Weinheim.]
Structure
AsCl
3 is a pyramidal molecule with C
3v symmetry. The As-Cl bond is 2.161 Å and the angle Cl-As-Cl is 98° 25'±30. AsCl
3 has four normal modes of vibration: ν1(A
1) 416, ν2(A
1) 192, ν3 393, and ν4(E) 152 cm
−1.
Synthesis
This colourless liquid is prepared by treatment of
arsenic(III) oxide with
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
followed by distillation:
: As
2O
3 + 6 HCl → 2 AsCl
3 + 3 H
2O
It can also be prepared by chlorination of arsenic at 80–85 °C, but this method requires elemental arsenic.
[
: 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:
: 2 As2O3 + 6 S2Cl2 → 4 AsCl3 + 3 SO2 + 9 S
A convenient laboratory method is refluxing arsenic(III) oxide with ]thionyl chloride
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...
:
: 2 As2O3 + 3 SOCl2 → 2 AsCl3 + 3 SO2
Reactions
Hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolys ...
gives arsenous acid and hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
:
: AsCl3 + 3 H2O → As(OH)3 + 3 HCl
Although AsCl3 is less moisture sensitive than PCl3, it still fumes in moist air.
AsCl3 undergoes redistribution upon treatment with As2O3 to give the inorganic polymer
An inorganic polymer is a polymer with a skeletal structure that does not include carbon atoms in the backbone. Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are ...
AsOCl. With chloride sources, AsCl3, forms salts containing the anion sCl4sup>−. Reaction with potassium bromide and potassium iodide give arsenic tribromide
Arsenic tribromide is the inorganic compound with the formula As Br3. This pyramidal molecule is the only known binary arsenic bromide. AsBr3 is noteworthy for its very high refractive index of approximately 2.3. It also has a very high diama ...
and arsenic triiodide, respectively.
AsCl3 is useful in organoarsenic chemistry, for example triphenylarsine is derived from AsCl3:[. Describes the preparation of As(C6H5)3.]
:AsCl3 + 6 Na + C6H5Cl → As(C6H5)3 + 6 NaCl
The poison gases called Lewisites are prepared by the addition of arsenic trichloride to acetylene:
:
Safety
Inorganic arsenic compounds are highly toxic,[Toxicity of inorganic compounds of arsenic] and AsCl3 especially so because of its volatility and solubility (in water).
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
The Emergency Planning and Community Right-to-Know Act of 1986 is a United States federal law passed by the 99th United States Congress located at Title 42, Chapter 116 of the U.S. Code, concerned with emergency response preparedness.
On October ...
(42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
References
{{Chlorides
Arsenic(III) compounds
Arsenic halides
Chlorides