Arsenic pentasulfide

Uses

has been used as a pigment and chemical intermediate but is generally only of interest in academic laboratories.

Preparation

Arsenic pentasulfide is prepared by precipitation from an acidic solution of soluble As(V) salts by treatment with hydrogen sulfide ().

A similar preparation is by treatment of an ice-cooled aqueous solution of orthoarsenic acid () with twice its volume of concentrated hydrochloric acid, rapid bubbling of into the solution for an hour, followed by washing of the precipitate with water and alcohol: :

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.

Reactions

Arsenic pentasulfide decomposes to arsenic trioxide (), sulfur, and arsenic trisulfide () when boiled in water.

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, , which contain As(V) centers.

References

References

1. (2012). "Handbook of Preparative Inorganic Chemistry". Academic Press.
2. (February 2007). "Phase diagram of the As-S system". Inorganic Materials.
3. (1998). "Chemistry of arsenic, antimony and bismuth". Blackie Acad. & Professional.