Arsenic pentasulfide

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Arsenic pentasulfide
Arsenic pentasulfide.svg
IUPAC name
Arsenic pentasulfide
Other names
Arsenic(V) sulfide
Diarsenic pentasulfide
3D model (Jmol)
ECHA InfoCard 100.154.195
UN number 1557
Molar mass 310.14 g·mol−1
Appearance Vivid, dark orange, opaque crystals
Melting point 300 °C (572 °F; 573 K)(minimum)
Boiling point 500 °C (932 °F; 773 K)(decomposes)
0.014 g dm−3 (at 0 °C)
Toxic T Dangerous for the Environment (Nature) N
R-phrases R23/25, R50/53
S-phrases S20/21, S28, S45, S60, S61
Related compounds
Related compounds
Arsenic pentoxide

Arsenic trisulfide
Phosphorus pentasulfide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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]


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.


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(V) centres.


  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9. 
  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, doi:10.1134/S002016850702001X
  3. ^ ed. by N. C. Norman. (1998). Chemistry of arsenic, antimony and bismuth. London: Blackie Acad. & Professional. pp. 114–115. ISBN 978-0-7514-0389-3.