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Arsenic trichloride

Arsenic trichloride
Ball-and-stick model of arsenic trichloride
Names
Other names
Arsenic(III) chloride, Arsenous trichloride, Butter of arsenic, de Valagin's solution
Identifiers
7784-34-1 YesY
3D model (Jmol) Interactive image
ChemSpider 22974 YesY
ECHA InfoCard 100.029.144
PubChem 24570
RTECS number CG1750000
UN number 1560
Properties
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)
decomposes
Solubility soluble in alcohol, ether, HCl, HBr
-79.9·10−6 cm3/mol
1.6006
Viscosity 9.77 x 10−6 Pa s
Hazards
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 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Lethal dose or concentration (LD, LC):
LD50 (median dose)
 48 mg/kg
100 mg/m3 (cat, 1 hr)
200 mg/m3 (cat, 20 min)
338 ppm (rat, 10 min)
US health exposure limits (NIOSH):
PEL (Permissible)
 [1910.1018] TWA 0.010 mg/m3
REL (Recommended)
 Ca C 0.002 mg/m3 [15-minute]
IDLH (Immediate danger)
 Ca [5 mg/m3 (as As)]
Related compounds
Other anions
Arsenic trioxide, Arsenic trifluoride
Other cations
Antimony trichloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
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.

AsCl3 is a pyramidal molecule with C3vsymmetry. 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. Arsenic trichloride contains predominantly covalent bonds, which explains its low melting point.

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

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

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

Hydrolysis with water gives arsenous acid and hydrochloric acid:

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 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:

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


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