Arsenic trisulfide is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic che ...

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 another ...

(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, m ...

p-type semiconductor and exhibits photo-induced phase-change properties.

Structure

occurs both in crystalline and amorphous forms. Both forms feature polymeric structures consisting of

trigonal pyramidal In chemistry, a trigonal pyramid is a molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base, resembling a tetrahedron (not to be confused with the tetrahedral geometry). When all three atoms at the corn ...

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 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 semiconductor, with a direct band gap 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 electric charge, 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 po ...

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

Contemporary uses

As an inorganic photoresist

Due to its high refractive index 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 crystals 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 In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek ''a'' ("wit ...

form is used as a chalcogenide glass for

optics. 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 ...

agent. It was formerly used with

indigo dye Indigo dye is an organic compound with a distinctive blue color. Historically, indigo was a natural dye extracted from the leaves of some plants of the ''Indigofera'' genus, in particular '' Indigofera tinctoria''; dye-bearing ''Indigofera'' pl ...

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 as ...

. 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