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Arsenic trisulfide
Orpiment mineral.jpg
Other names Arsenic(III) sulfide

Sulphuret of arsenic

CAS number 1303-33-9
PubChem 4093503
EC number 215-117-4
RTECS number CG2638000
SMILES S1[As]3S[As]2S[As](S[As]1S2)S3
Molecular formula As2S3
Molar mass 246.04 g mol-1
Appearance Orange crystals
Density 3.43 g cm−3
Melting point

310 °C, 583 K, 590 °F

Boiling point

707 °C, 980 K, 1305 °F

-70.0·10−6 cm3/mol
NFPA 704

NFPA 704.svg

U.S. Permissible
exposure limit (PEL)
[1910.1018] TWA 0.010 mg/m3
Related compounds
Other anions Arsenic trioxide
Arsenic triselenide
Other cations Phosphorus trisulfide
Antimony trisulfide
Bismuth sulfide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Arsenic trisulfide, also known as orpiment or arsenic(III) sulfide, is a chemical compound. Its chemical formula is As2S3. It has arsenic and sulfide ions in it. The arsenic is in its +3 oxidation state.


Arsenic trisulfide is a yellow solid. It is a semiconductor. It has a glass (amorphous) form and a crystalline form. It burns in air to make sulfur dioxide and arsenic trioxide, which makes a highly toxic smoke. Arsenic trisulfide can oxidize on the surface to make a highly toxic layer of arsenic trioxide as well. Arsenic trisulfide is not toxic unless it oxidizes. It does not react with acids.


Arsenic trisulfide is found as the mineral orpiment.


Arsenic trisulfide is made when an arsenic compound like arsenic trichloride reacts with hydrogen sulfide. It is also made when arsenic and sulfur are heated together.


It was looked at for treating cancer. It was used by the Egyptians as a pigment and cosmetic. It is used in glass.

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