Arsenic trisulphide

Arsenic trisulfide

Names
Preferred IUPAC name Arsenic trisulfide
Other names Arsenic(III) sulfide Orpiment Sulphuret of arsenic
Identifiers
CAS Number	1303-33-9 Y
3D model (Jmol)	Interactive image
ChemSpider	21241348 Y
ECHA InfoCard	100.013.744
EC Number	215-117-4
PubChem	4093503
RTECS number	CG2638000
UNII	44SIJ800OX Y
InChI InChI=1S/As4S6/c5-1-6-3-8-2(5)9-4(7-1)10-3 Y Key: OUFDYFBZNDIAPD-UHFFFAOYSA-N Y InChI=1/As4S6/c5-1-6-3-8-2(5)9-4(7-1)10-3 Key: OUFDYFBZNDIAPD-UHFFFAOYAM
SMILES S1[As]3S[As]2S[As](S[As]1S2)S3
Properties
Chemical formula	As2S3
Molar mass	246.02 g·mol−1
Appearance	Orange crystals
Density	3.43 g cm−3
Melting point	310 °C (590 °F; 583 K)
Boiling point	707 °C (1,305 °F; 980 K)
Magnetic susceptibility (χ)	-70.0·10−6 cm3/mol
Structure
Space group	P21/n (No. 11)
Lattice constant	a = 1147.5(5) pm, b = 957.7(4) pm, c = 425.6(2) pm α = 90°, β = 90.68(8)°, γ = 90°
Coordination geometry	pyramidal (As)
Hazards
GHS pictograms
GHS signal word	DANGER
GHS hazard statements	H300, H331, H400, H411
NFPA 704	0 3 0
US health exposure limits (NIOSH):
PEL (Permissible)	[1910.1018] TWA 0.010 mg/m3
REL (Recommended)	Ca C 0.002 mg/m3 [15-minute]
IDLH (Immediate danger)	Ca [5 mg/m3 (as As)]
Related compounds
Other anions	Arsenic trioxide Arsenic triselenide
Other cations	Phosphorus trisulfide Antimony trisulfide Bismuth sulfide
Related compounds	Tetraarsenic tetrasulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Orpiment

Arsenic trisulfide is the inorganic compound with the formula As₂S₃. It is a bright yellow solid that is insoluble in water. It also occurs as the mineral orpiment (Latin: auripigment), which has been used as a pigment called King's yellow. It is produced in the analysis of arsenic compounds. It is a group V/VI, intrinsic p-type semiconductor and exhibits photo-induced phase-change properties. The other principal arsenic sulfide is As₄S₄, a red-orange solid known as the mineral realgar.

As₂S₃ occurs both in crystalline and amorphous forms. Both forms feature polymeric structures consisting of trigonal pyramidal As(III) centres linked by sulfide centres. The sulfide centres are two-fold coordinated to two arsenic atoms. In the crystalline form, the compound adopts a ruffled sheet structure. The bonding between the sheets consists of van der Waals forces. The crystalline form is usually found in geological samples. Amorphous As₂S₃ does not possess a layered structure but is more highly cross-linked. Like other glasses, there is no medium or long-range order, but the first co-ordination sphere is well defined. As₂S₃ is a good glass former and exhibits a wide glass-forming region in its phase diagram.

Amorphous As₂S₃ is obtained via the fusion of the elements at 390 °C. Rapid cooling of the reaction melt gives a glass. The reaction can be represented with the chemical equation:

As₂S₃ forms when aqueous solutions containing As(III) are treated with H₂S. Arsenic was in the past analyzed and assayed by this reaction, which results in the precipitation of As₂S₃, which is then weighed. As₂S₃ can even be precipitated in 6M HCl. As₂S₃ is so insoluble that it is not toxic.

Upon heating in a vacuum, polymeric As₂S₃ "cracks" to give a mixture of molecular species, including molecular As₄S₆. As₄S₆ adopts the adamantane geometry, like that observed for P₄O₆ and As₄O₆. When a film of this material is exposed to an external energy source such as thermal energy (via thermal annealing ), electromagnetic radiation (i.e. UV lamps, lasers, electron beams)), As₄S₆ polymerizes: