Arsenic trichloride is an

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

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 Chemical compound, compounds containing a chemical bond between arsenic and carbon. A few organoarsenic compounds, also called "organoarsenicals," are produced industrially with uses as insecticides, herb ...

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 () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is Invariant (mathematics), invariant und ...

. 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 Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

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 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 Volatility (chemistry), volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a Halogenation, chlorinating reagen ...

: : 2 As₂O₃ + 3 SOCl₂ → 2 AsCl₃ + 3 SO₂ Arsenic trichloride can also be prepared by the reaction of hydrochloric acid and arsenic(III) sulfide. :As₂S₃ + 6 HCl → 2 AsCl₃ + 3 H₂S

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 and

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

: : AsCl₃ + 3 H₂O → As(OH)₃ + 3 HCl Although AsCl₃ is less moisture sensitive than PCl₃, it still fumes in moist air.Holleman, A. F.; Wiberg, E. ''Inorganic Chemistry'' Academic Press: San Diego, 2001. . AsCl₃ undergoes redistribution upon treatment with As₂O₃ to give the

inorganic polymer In polymer chemistry, an inorganic polymer is a polymer with a skeletal structure that does not include carbon atoms in the Polymer backbone, backbone. Polymers containing Inorganic compound, inorganic and Organic compound, organic components are ...

AsOCl. With chloride sources, AsCl₃ also 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 equa ...

and potassium iodide give arsenic tribromide 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 chemical weapons called

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

s are prepared by the addition of arsenic trichloride to acetylene: :

Safety

Inorganic arsenic compounds are highly toxic, 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 Octobe ...

(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 Highly-toxic chemical substances