Arsenic pentasulfide is an inorganic compound contains arsenic and sulfur with the formula. The identity of this reddish solid remains uncertain.^[1] Solids of the approximate formula As₂S₅ have been used as pigments and chemical intermediates but are generally only of interest in academic laboratories.^[2]

Preparation

Arsenic pentasulfide is prepared by precipitation from an acidic solution of soluble As(V) salts by treatment with hydrogen sulfide.^[3] It may be also prepared by heating a mixture of arsenic and sulfur, extracting the fused mass with an ammonia solution and reprecipitating arsenic pentasulfide at low temperature by addition of hydrochloric acid.

Phosphorus pentasulfide with the formula P₄S₁₀, is a molecular compound featuring tetrahedral phosphorus(V) centres. Trends in arsenic redox potentials suggest that As₂S₅ adopts a similar structure, a plausible alternative being an arsenic polysulfide.

Reactions

Arsenic pentasulfide hydrolyzes in boiling water, giving arsenous acid and sulfur:

As₂S₅ + 6 H₂O 2 H₃AsO₃ + 2 S + 3 H₂S

It oxidizes in air at elevated temperatures producing arsenic oxides, the products and yields of which are variable. In alkali metal sulfide solutions arsenic pentasulfide forms a thioarsenate anion, [AsS₄]³ , which contain As(III) centres.

References

1. ↑
2. ↑ A. L. Emelina, A. S. Alikhanian, A. V. Steblevskii and E. N. Kolosov "Phase diagram of the As-S system" Inorganic Materials, 2007, Volume 43, pages95-104,
3. ↑