803. Arsenic Triiodide

Nomenclature

CAS number: 7784-45-4
Arsenous triiodide.
AsI3; mol wt 455.64.
As 16.44%, I 83.56%.

Description and references

Prepd from the elements or from AsCl3 and KI: Bailar, Inorg. Synth. I, 103 (1939).

Properties

Orange-red, trigonal rhombohedra from acetone. Reacts slowly with O2 from air, liberating iodine. d425 4.688. Some tendency to sublime below 100°. mp 140.9° forming a red liquid. bp760 ≈400°. One gram dissolves in 12 ml water forming a yellow soln. Does not hydrolyze rapidly and may be recovered from the water soln unchanged within 5 hrs. Aqueous solns are strongly acid (pH of 0.1N soln about 1.1) and ultimately form HI and As2O3, although an equilibrium AsI3 + 3H2O = H3AsO3 + 3HI has been observed. Freely sol in carbon disulfide, chloroform, benzene, toluene, xylene. Less sol in alc, ether.