This method requires simple apparatus and proceeds efficiently:[8] A convenient laboratory method is refluxing arsenic(III) oxide with thionyl chloride:[9] Arsenic trichloride can also be prepared by the reaction of hydrochloric acid and arsenic(III) sulfide.

[10] AsCl3 undergoes redistribution upon treatment with As2O3 to give the inorganic polymer AsOCl.

AsCl3 is useful in organoarsenic chemistry, for example triphenylarsine is derived from AsCl3:[11] The chemical weapons called Lewisites are prepared by the addition of arsenic trichloride to acetylene: Inorganic arsenic compounds are highly toxic,[4] 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.

11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.