Arsenic trichloride is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

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 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 fungic ...

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

AsCl₃ is a pyramidal molecule with C_3v

symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...

. The As-Cl bond is 2.161 Å and the angle Cl-As-Cl is 98° 25'±30. AsCl₃ has four normal modes of vibration: ν1(A₁) 416, ν2(A₁) 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: : 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. : 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 reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

gives

arsenous acid Arsenous acid (or arsenious acid) is the inorganic compound with the formula H3AsO3. It is known to occur in aqueous solutions, but it has not been isolated as a pure material, although this fact does not detract from the significance of As(OH)3. ...

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 Potassium bromide ( K Br) is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the US. Its action is due to the bromide ion (sodium bromide is equall ...

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 Arsenic triiodide is the inorganic compound with the formula As I3. 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 reacti ...

, respectively. AsCl₃ is useful in organoarsenic chemistry, for example

triphenylarsine Triphenylarsine is the chemical compound with the formula As(C6H5)3. This organoarsenic compound, often abbreviated As Ph3, is a colorless crystalline solid that is used as a ligand and a reagent in coordination chemistry and organic synthesis. T ...

is derived from AsCl₃:. Describes the preparation of As(C₆H₅)₃. :AsCl₃ + 6 Na + C₆H₅Cl → As(C₆H₅)₃ + 6 NaCl The poison gases called

Lewisite Lewisite (L) (A-243) is an organoarsenic compound. It was once manufactured in the U.S., Japan, Germany and the Soviet Union for use as a Chemical warfare, chemical weapon, acting as a vesicant (blister agent) and lung irritant. Although the substa ...

s 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