- Structure of arsenic trioxide
- Claudetita
- Liquid and gaseous
- Arsenolite
- Properties
- Tradenames
- Molecular weight
- Physical appearance
- Odor
- Taste
- Boiling point
- Melting point
- ignition point
- Water solubility
- Solubility
- Density
- Vapor pressure
- Decomposition
- Corrosiveness
- Heat of vaporization
- Dissociation constant (Ka)
- Refractive index
- Reactivity
- Nomenclature
- Applications
- Industrial
- Doctors
- References
The arsenic trioxide is an inorganic compound whose chemical formula is As 2 O 3. Arsenic in its metallic state is quickly transformed into this oxide, which is a very toxic poison that can have acute and chronic manifestations.
As arsenic and oxygen are elements of the p block, with a relatively low electronegativity difference, it is expected that As 2 O 3 is a covalent compound; that is to say, that the As-O bonds predominate in its solid, over the electrostatic interactions between the As 3+ and O 2- ions.
Solid arsenic trioxide. Source: Walkerma from Wikimedia Commons.
Acute intoxication with arsenic trioxide occurs by ingestion or inhalation, the most important manifestations of this being: severe gastrointestinal disorders, cramps, circulatory collapse, and pulmonary edema.
However, despite its toxicity, it has been used industrially; for example, in the conservation of wood, in the production of pigments, semiconductors, etc. Also, in the past it was used in the treatment of many diseases.
Arsenic trioxide is an amphoteric compound, soluble in dilute acids and alkalis, insoluble in organic solvents, and relatively soluble in water. It occurs as a solid (top image), with two crystalline forms: cubic and monoclinic.
Structure of arsenic trioxide
Claudetita
At room temperature, As 2 O 3 crystallizes into two monoclinic polymorphs, both found in the mineral claudetite. In them there are trigonal pyramid units AsO 3, which are joined by their oxygen atoms to compensate for the electronic deficiency of the unit by itself.
In one polymorph the AsO 3 units are linked forming rows (claudetite I), and in the other they are linked as if they were weaving a network (claudetite II):
Structure of the polymorph Claudetite I. Source: Ben Mills.
Structure of the polymorph claudetite II. Source: Ben Mills.
Liquid and gaseous
When all those structures that define monoclinic crystals are heated, the vibrations are such that several As-O bonds are broken, and a smaller molecule ends up prevailing: As 4 O 6. Its structure is shown in the image below.
As4O6 molecule. Source: Ben Mills
It could be said to consist of a dimer of As 2 O 3. Its stability is such that it supports 800 ° C in the gas phase; but, above this temperature it fragments into As 2 O 3 molecules.
Arsenolite
As 4 O 6 itself can interact with each other to crystallize into a cubic solid, the structure of which is found in the mineral arsenolite.
As4O6 molecules in the arsenolite solid. Source: Ben Mills
Note that the image is showing the structure from a higher plane. Comparing with claudetite, its structural difference with arsenolite is evident. Here, they are discrete As 4 O 6 molecules that are held together by Van der Waals forces.
Properties
Tradenames
-Arsenolite
-Arsodent
-Trisenox
-Claudetite
Molecular weight
197.84 g / mol.
Physical appearance
-White cubic crystals (arsenolite).
-Colorless monoclinic crystals (Claudetite).
-White or transparent solid, vitreous, amorphous lumps or crystalline powder.
Odor
Toilet.
Taste
Tasteless.
Boiling point
460 ° C.
Melting point
-313 ° C (Claudetite).
-274 ° C (Arsenolite).
ignition point
485ºC (sublimates).
Water solubility
17 g / L at 18 ° C (20 g / L at 25 ° C).
Solubility
Soluble in acids (especially hydrochloric acid) and alkalis. Practically insoluble in chloroform and ether.
Density
-3.85 g / cm 3 (cubic crystals);
-4.15 g / cm 3 (rhombic crystals).
Vapor pressure
2.47 · 10 -4 mmHg at 25 ° C.
Decomposition
It is not combustible, but on heating it can create toxic smoke that may include arsine.
Corrosiveness
In the presence of moisture it can be corrosive to metals.
Heat of vaporization
77 kJ / mol.
Dissociation constant (Ka)
1.1 · 10 -4 at 25 ° C.
Refractive index
-1,755 (Arsenolite)
-1.92-2.01 (Claudetite).
Reactivity
-Arsenic trioxide is an amphoteric compound, but it functions preferably as an acid.
-It can react with hydrochloric acid or hydrofluoric acid, forming arsenic trichloride or arsenic trifluoride.
-It also reacts with strong oxidants, such as nitric acid, causing arsenic acid and nitrous oxide.
-Arsenic trioxide can react with nitric acid, producing arsine or the element arsenic, depending on the reaction conditions.
As 2 O 3 + 6 Zn + 12 HNO 3 => 2 AsH 3 + 6 Zn (NO 3) 2 + 3 H 2 O.
This reaction served as the basis for the creation of the Marsh Test, used for the detection of arsenic poisoning.
Nomenclature
As 2 O 3 can be named according to the following nomenclatures, knowing that arsenic works with valence +3:
-Arsenous oxide (traditional nomenclature).
-Arsenic (III) oxide (stock nomenclature).
-Diarsenic trioxide (systematic nomenclature).
Applications
Industrial
-It is used in the manufacture of glass, specifically as a bleaching agent. It is also used in the manufacture of ceramics, electronic products, and fireworks.
-It is added as a minor component to copper-based alloys, to increase the corrosion resistance of the alloy metals.
-As 2 O 3 is the starting material for the preparation of elemental arsenic, to improve electrical connections, and for the production of arsenide semiconductors
-As 2 O 3, as well as copper arsenate, are used as wood preservatives. It was used in combination with copper acetate to make the Paris green pigment, used to make paints and rodenticides.
Doctors
-Arsenic trioxide is a compound that has been used for centuries in the treatment of many diseases. It was used as a tonic in the treatment of nutritional disorders, neuralgia, rheumatism, arthritis, asthma, chorea, malaria, syphilis and tuberculosis.
-It has also been used in the local treatment of skin diseases, being used to destroy some superficial epitheliomas.
-Fowler's solution was used in the treatment of skin diseases and leukemia. The use of this medicine is discontinued.
-In the 1970s, the Chinese researcher Zhang Tingdong developed an investigation on the use of arsenic trioxide in the treatment of acute promyelocytic leukemia (APL). Which led to the production of the drug Trisenox, which was approved by the US FDA.
-Trisenox has been used in APL patients who do not respond to "first line" treatment, consisting of all-trans retinoic acid (ATRA). Arsenic trioxide has been shown to induce cancer cells to undergo apoptosis.
-Trisenox is used as a cytostatic in the treatment of the refractory promyelocytic subtype (M 3) of APL.
References
- Shen et al. (2001). Studies on the clinical efficacy and pharmacokinetics of low-dose arsenic trioxide in the treatment of relapsed acute promyelocytic leukemia: a comparison with conventional dosage. Leukemia 15, 735–741.
- Science Direct. (2014). Arsenic Trioxide. The Sevier. Recovered from: sciencedirect.com
- Wikipedia. (2019). Arsenic trioxide. Recovered from: en.wikipedia.org
- PubChem. (2019). Arsenic (III) oxide. Recovered from: pubchem.ncbi.nlm.nih.gov
- Deborah M. Rusta and Steven L. Soignetb. (2001). Risk / Benefit Profile of Arsenic Trioxide. The Oncologist vol. 6 Supplement 2 29-32.
- The New England Journal of Medicine. (July 11, 2013). Retinoic Acid and Arsenic Trioxide for Acute Promyelocytic Leukemia. n engl j med 369; 2.