He Arsenic acid , Which is also known as orthoarsenic acid, is a chemical compound whose formula is H3AsO4.
An arsenic oxacid comprises an oxo group and three hydroxyl groups attached to a central arsenic atom. Its structure is presented in figure 1 (CHEBI: 18231 - arsenic acid, S.F.).
Figure 1: structure of arsenic acid.
Its structure is analogous to phosphoric acid (Royal Society of Chemistry, 2015) and can be rewritten as AsO (OH) 3. This compound is prepared by treating arsenic trioxide with nitric oxide according to the reaction:
As 2 O 3 + 2HNO 3 + 2H 2 O → 2H 3 AsO 4 + N 2 O 3
The resulting solution is cooled to give colorless crystals of the hemihydrate H 3 AsO 4 · ½H 2 O, although the H 3 AsO 4 · 2H 2 O dihydrate occurs when crystallization takes place at lower temperatures (Budavari, 1996).
Arsenic acid is an extremely toxic compound. Many safety data sheets advise against contact if possible.
Physical and chemical properties of arsenic acid
Arsenic acid is a white hygroscopic solid. Their appearance is shown in figure 2.
Figure 2: appearance of arsenic acid.
In aqueous solution, it is a viscous and transparent hygroscopic liquid (National Center for Biotechnology Information., 2017). Its molecular weight is 141.94 g / mol and its density is 2.5 g / ml. Its melting point is 35.5 ° C and its boiling point is 120 ° C where it decomposes.
Arsenic acid is very soluble in water and can dissolve 16.7 g per 100 ml, it is also soluble in alcohol. The compound has a pKa of 2.19 for the first deprotonation and 6.94 and 11.5 for the second and third deprotonation (Royal Society of Chemistry, 2015).
Arsenic acid is an oxidizing agent. It can corrode steel and reacts with galvanized metals and brass.
Arsenic acid solutions can develop very toxic arsine gas (AsH3) on contact with active metals, such as zinc and aluminum. When heated to decomposition, it produces toxic vapors of metallic arsenic.
The solution is slightly acidic and a weak oxidizing agent. Reacts with alkalis to generate some heat and precipitate arsenates (ARSENIC ACID, LIQUID, 2016).
Reactivity and hazards
Arsenic acid is a stable, non-combustible compound that can be corrosive to metals. The compound is highly toxic and a carcinogen confirmed for humans.
Inhalation, ingestion or skin contact with the material can cause serious injury or death. Contact with molten substance may cause severe burns to the skin and eyes.
Avoid contact with skin. The effects of contact or inhalation may be delayed. Fire may produce irritating, corrosive and / or toxic gases. Wastewater control product or fire dilution can be corrosive and / or toxic and cause pollution.
The symptoms of poisoning with arsenic acid are coughing and shortness of breath in case of inhalation. Redness in the skin, pain and burning sensation may also occur if it comes in contact with it. Finally, the symptoms on ingestion are redness and pain in the eyes, sore throat, nausea, vomiting, diarrhea and seizures.
In case of contact with eyes
They should be washed with plenty of water for at least 15 minutes, lifting the upper and lower eyelids sporadically until there is no evidence of chemical debris.
In case of contact with skin
Wash immediately with plenty of soap and water for at least 15 minutes while removing contaminated clothing and shoes. Cover the burns with a dry sterile dressing (secure, not tight).
In case of ingestion
Rinse the mouth and give the conscious victim large amounts of water to dilute the acid. In this case, gastric lavage should be used and do not induce vomiting.
In case of inhalation:
Artificial respiration should be provided if necessary. The mouth-to-mouth method should not be used if the victim has ingested or inhaled the substance.
Artificial respiration should be performed with the aid of a pocket mask fitted with a one-way valve or other suitable respiratory medical device. The victim should be moved to a cool place and kept warm and at rest.
In all cases, seek immediate medical attention (National Institute for Occupational Safety and Health, 2015).
Arsenic acid is harmful to the environment. The substance is very toxic for aquatic organisms. Measures should be taken to limit the release of this chemical.
Applications
Arsenic acid, given its high toxicity, has limited uses. However this compound was used as a pesticide and soil sterilant, although it is currently obsolete (University of Hertfordshire, 2016).
It is also used in wood processing and as a desiccant in cotton production since 1995. Spraying in the plants causes the leaves to dry quickly without falling. The plant needs to be dry enough so that the cotton capsules can easily come out.
Arsenic acid is used in the production of glass. Although in the records the substance is considered as an intermediate, this use of arsenic acid seems more like a"processing agent", similar to the use of diarsene trioxide (As2O3) as the finishing agent.
This compound breaks the oxygen bonds between other elements through the redox reaction and produces oxygen gas that helps to eliminate the bubbles in the glass (Position Paper of the European Glass Industries on the, 2012).
Arsanilic acid or 4-aminophenylarsonic acid is a derivative of ortho-sarsic acid. It is used as an arsenical antibacterial veterinary medicine used in the prevention and treatment of swine dysentery (ARSENIC ACID, S.F.).
Arsenate is arsenic acid salt or ester having a negative ion of AsO43-. Arsenate resembles phosphate in many respects, since arsenic and phosphorus occur in the same group (column) of the periodic table.
Arsenate can replace inorganic phosphate in the glycolysis step which produces 1,3-bisphosphoglycerate, producing 1-arene-3-phosphoglycerate instead. This molecule is unstable and rapidly hydrolyzes, forming the next intermediate in the path, 3-phosphoglycerate.
Therefore, glycolysis continues, but the ATP molecule that would be generated from 1,3-bisphosphoglycerate is lost. Arsenate is a glycolysis decoupler, which explains its toxicity.
Some species of bacteria get their energy by oxidizing different fuels while reducing the arsenates to form arsenites. The enzymes involved are known as arsenate reductases.
In 2008, bacteria were discovered using a version of photosynthesis with arsenites as electron donors, producing arsenates (just as ordinary photosynthesis uses water as an electron donor, producing molecular oxygen).
The researchers conjectured that historically these photosynthetic organisms produced the arsenates that allowed the arsenic-reducing bacteria to thrive (Human Metabolome Database, 2017).
References
- ARSENIC ACID. (S.F.). Recovered from chemicalland21.com.
- ARSENIC ACID, LIQUID. (2016). Recovered from cameochemicals.noaa.gov.
- Budavari, S. (1996) Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals, Whitehouse Station, NJ: Merck and Co.
- CHEBI: 18231 - arsenic acid. (S.F.). Retrieved from ebi.ac.uk.
- Human Metabolome Database. (2017, March 2). Showing metabocard for Arsenate. Retrieved from hmdb.ca.
- National Center for Biotechnology Information. . (2017, March 4). PubChem Compound Database; CID = 234. Recovered from PubChem.
- National Institute for Occupational Safety and Health. (2015, July 22). ARSENIC ACID. Retrieved from cdc.gov.
- Position Paper of the European Glass Industries on the. (2012, September 18). Retrieved from glassallianceeurope.
- Royal Society of Chemistry. (2015). Arsenic acid. Recovered from chemspider.
- Royal Society of Chemistry. (2015). Phosphoric acid. Recovered from chemspider.
- University of Hertfordshire. (2016, January 13). Arsenic acid. Recovered from PPDB.