Arsenic trisulfide is the inorganic compound with the formula . It is a dark yellow solid that is insoluble in water. It also occurs as the mineral

orpiment Orpiment is a deep-colored, orange-yellow arsenic sulfide mineral with formula . It is found in volcanic fumaroles, low-temperature hydrothermal veins, and hot springs and is formed both by sublimation and as a byproduct of the decay of anothe ...

(Latin: auripigmentum), 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 In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...

p-type

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

and exhibits photo-induced phase-change properties.

Structure

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 force In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and th ...

s. The crystalline form is usually found in geological samples. Amorphous 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. is a good glass former and exhibits a wide glass-forming region in its phase diagram.

Properties

It is a

, with a direct

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference ( ...

of 2.7 eV. The wide band gap makes it transparent to

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

light between 620 nm and 11 µm.

Synthesis

From the elements

Amorphous 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: :

Aqueous precipitation

forms when aqueous solutions containing As(III) are treated with . Arsenic was in the past analyzed and assayed by this reaction, which results in the

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

of , which is then weighed. can even be precipitated in 6 M HCl. is so insoluble that it is not toxic.

Reactions

Upon heating in a vacuum, polymeric "cracks" to give a mixture of molecular species, including molecular . adopts the

adamantane Adamantane is an organic compound with a formula C10H16 or, more descriptively, (CH)4(CH2)6. Adamantane molecules can be described as the fusion of three cyclohexane rings. The molecule is both rigid and virtually stress-free. Adamantane is the ...

geometry, like that observed for and . 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: : characteristically dissolves upon treatment with aqueous solutions containing sulfide ions. The dissolved arsenic species is the pyramidal trithioarsenite

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

: : is the anhydride of the hypothetical trithioarsenous acid, . Upon treatment with

polysulfide Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. Among the inorganic polysulfides, there are ones which contain anions, which have the general formu ...

ions, dissolves to give a variety of species containing both S–S and As–S bonds. One derivative is , an eight-membered ring that contains 7 S atoms and 1 As atom, and an

exocyclic In organic chemistry, an alicyclic compound contains one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached. The ...

sulfido center attached to the As atom. also dissolves in strongly alkaline solutions to give a mixture of and . "Roasting" in air gives volatile, toxic derivatives, this conversion being one of the hazards associated with the refining of heavy metal

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...

s: :

Contemporary uses

As an inorganic photoresist

Due to its high

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

of 2.45 and its large Knoop hardness compared to organic

photoresist A photoresist (also known simply as a resist) is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronic industry. ...

s, has been investigated for the fabrication of

photonic crystal A photonic crystal is an optical nanostructure in which the refractive index changes periodically. This affects the propagation of light in the same way that the structure of natural crystals gives rise to X-ray diffraction and that the atomic ...

s with a full-photonic band-gap. Advances in laser patterning techniques such as three-dimensional direct laser writing (3-D DLW) and chemical wet- etching chemistry, has allowed this material to be used as a photoresist to fabricate 3-D nanostructures. has been investigated for use as a high resolution photoresist material since the early 1970s, using aqueous etchants. Although these aqueous etchants allowed for low-aspect ratio 2-D structures to be fabricated, they do not allow for the etching of high aspect ratio structures with 3-D periodicity. Certain organic reagents, used in organic solvents, permit the high-etch selectivity required to produce high-aspect ratio structures with 3-D periodicity.

Medical applications

and have been investigated as treatments for acute promyelocytic leukemia (APL).

For IR-transmitting glasses

Arsenic trisulfide manufactured into amorphous form is used as a

chalcogenide glass Chalcogenide glass (pronounced hard ''ch'' as in ''chemistry'') is a glass containing one or more chalcogens (sulfur, selenium and tellurium, but excluding oxygen). Such glasses are covalently bonded materials and may be classified as covalent netw ...

for

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

. It is transparent for light between wavelengths of 620 nm and 11 µm. The arsenic trisulfide glass is more resistant to oxidation than crystalline arsenic trisulfide, which minimizes toxicity concerns. It can be also used as an acousto-optic material. Arsenic trisulfide was used for the distinctive eight-sided conical nose over the infra-red seeker of the de Havilland Firestreak missile.

Role in ancient artistry

The ancient Egyptians reportedly used orpiment, natural or synthetic, as a pigment in artistry and cosmetics.

Miscellaneous

Arsenic trisulfide is also used as a

tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...

agent. It was formerly used with indigo dye for the production of pencil blue, which allowed dark blue hues to be added to fabric via pencil or brush. Precipitation of arsenic trisulfide is used as an analytical test for presence of dissimilatory arsenic-reducing bacteria (DARB).Linping Kuai, Arjun A. Nair, and Martin F. Polz "Rapid and Simple Method for the Most-Probable-Number Estimation of Arsenic-Reducing Bacteria" Appl Environ Microbiol. 2001, vol. 67, 3168–3173. .

Safety

is so insoluble that its toxicity is low. Aged samples can contain substantial amounts of arsenic oxides, which are soluble and therefore highly toxic.

Natural occurrence

Orpiment is found in volcanic environments, often together with other arsenic sulfides, mainly

realgar Realgar ( ), also known as "ruby sulphur" or "ruby of arsenic", is an arsenic sulfide mineral with the chemical formula α-. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in asso ...

. It is sometimes found in low-temperature hydrothermal veins, together with some other sulfide and sulfosalt minerals.

References

External links

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{{DEFAULTSORT:Arsenic Trisulfide Arsenic(III) compounds Sulfides Optical materials Non-oxide glasses