Arsenic pentasulfide

Arsenic pentasulfide
IUPAC name Arsenic pentasulfide
Other names Arsenic(V) sulfide Diarsenic pentasulfide
Identifiers
CAS number	1303-34-0 N
PubChem	3371533
ChemSpider	2617071 Y
UN number	1557
Jmol-3D images	Image 1 Image 2
SMILES S=[As](=S)S[As](=S)=S S=[As]12S[As]3(=S)S[As](=S)(S1)S[As](=S)(S2)S3
InChI InChI=1S/As2S5/c3-1(4)7-2(5)6 Y Key: AYRZLUSHOXJGKY-UHFFFAOYSA-N Y InChI=1S/As4S10/c5-1-9-2(6)12-3(7,10-1)14-4(8,11-1)13-2 Key: CHQYGMAMCBQSIU-UHFFFAOYSA-N
Properties
Molecular formula	As2S5
Molar mass	310.17 g mol−1
Exact mass	309.703546284 g mol-1
Appearance	Vivid, dark orange, opaque crystals
Melting point	300 °C, 573 K, 572 °F (minimum)
Boiling point	500 °C, 773 K, 932 °F (decomposes)
Solubility in water	0.014 g dm-3 (at 0 °C)
Hazards
EU classification	T 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
N pentasulfide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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]

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. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
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 9780751403893. http://books.google.com/?id=vVhpurkfeN4C&pg=PA114.