The selenious acid is an inorganic compound of formula H 2 SO 3 stands out as the main Oxoacid selenium (the other is selenic acid). Its structure is similar to that of sulfurous acid.
It is prepared by dissolving selenium oxide in hot water and then allowing it to cool. It is more stable than sulfurous acid (H 2 SO 3), despite being a weaker acid, its pKa values at 25 ° C equal to 2.62 and 8.32, which corresponds to the two protons it releases.
Figure 1: Structure of selenious acid.
Its conjugated base is selenites, it has the ability to form salts called selenites and acid selenites of formula M 2 SeO 3 and MHSeO 3 respectively (Egon Wiberg, 2001).
Physical and chemical properties
Selenious acid is a white hygroscopic solid with a hexagonal crystalline structure. When dissolved in water it forms a colorless solution. Its appearance is shown in figure 2.
Figure 2: appearance of selenium acid.
It has a molecular weight of 128.97 g / mol, a density of 3 g / ml and a melting point of 70 ° C where it begins to decompose (National Center for Biotechnology Information, nd).
The compound is very soluble in water, being able to dissolve 167 grams per 100 ml. It is also soluble in ethanol and insoluble in ammonia (Royal Society of Chemistry, 2015).
Selenious acid decomposes to volatile, toxic selenium dioxide when heated, serving as an oxidizing agent.
It reacts exothermically with many reducing agents including hydroiodic acid, sulfurous acid, sodium hyposulfite, hydroxylamine salts, hydrazine salts, hypophosphorous acid or phosphorous acid (SELENIOUS ACID, 2016).
Reactivity and hazards
Selenious acid is a stable compound that is classified as poisonous. It is very dangerous in case of contact with the skin and eyes, where it can be irritating, and in case of ingestion and inhalation. Severe overexposure can cause death.
Repeated exposure to this type of highly toxic material can produce effects of deterioration of health by accumulation in one or many human organs (Material Safety Data Sheet Selenious acid, 2013).
Severely toxic effects can result from accidental ingestion of the material; Animal experiments indicate that ingestion of less than 5 grams can be fatal or can cause serious damage to the health of the individual.
Selenious acid can be fatal if ingested, unless immediate treatment is applied.
The acute effects of selenium poisoning include nervousness, seizures, drowsiness, frontal headaches, and, in extreme cases, death from respiratory depression.
There may also be skin rashes, tiredness, an upset stomach, tooth discoloration, garlic odorous breath, and loss of hair and nails. Selenium is rapidly absorbed from the intestine and accumulates in the liver and kidneys in the form of selenates and selenites.
It can cause kidney, heart, spleen, stomach, and intestinal damage. Selenites may increase the rate of miscarriage.
Although the material is not believed to be an irritant, direct contact with the eye may cause transient discomfort characterized by tearing or conjunctival redness. It can also cause slight abrasive damage.
The material is not believed to be a skin irritant (as classified using animal models). However, abrasive damage can result from prolonged exposure.
Good hygiene practice requires that exposure is minimized and that suitable gloves are used in an occupational setting (New jersey department of health and senior services, 1999).
Skin contact with the material can harm the health of the individual, producing systemic effects after absorption. Open cuts, worn or irritated skin should not be exposed to this material.
Entry into the bloodstream, through cuts, abrasions, or injuries, can cause systemic injury with deleterious effects. Examine the skin before using the material and make sure any external damage is adequately protected.
Inhalation of dust from this type of material during the course of normal handling can produce toxic effects.
The material is not believed to cause respiratory irritation (as classified using animal models). However, inhaling dust, or smoke, especially for prolonged periods, can cause respiratory discomfort.
People with impaired respiratory function, respiratory diseases, and conditions such as emphysema or chronic bronchitis may be more disabled if excessive concentrations of particles are inhaled (Selenous acid, 2010).
Applications
Selenious acid has many uses. The main use is to protect and change the color of steel, especially in parts such as weapons (fire. The so-called cold bleaching process, uses selenious acid, copper nitrate II) and nitric acid to change the color of steel from gray silver to blue-gray or black.
Another use for selenious acid is the chemical darkening of copper, brass and bronze, producing a rich dark brown color that can be further enhanced by mechanical abrasion.
It can be used as an oxidizing agent. In synthesis of glyoxal (ethane-1,2-dione) from glycol. Selenious acid is a key component of the Mecke reagent used for drug control.
The isotope is used in the labeling of radiopharmaceuticals. Selenious acid is also used as a dietary supplement for the intake of selenium, being supplied to the patient through an intravenous injection.
Selenium is an essential micronutrient for the body, being an antioxidant agent similar to vitamin E.
It is necessary for the enzyme glutathione peroxidase, which facilitates the decrease of peroxide levels in tissue in the body by destroying hydrogen peroxide, which attacks the cell membrane.
Selenium is also needed to maintain the integrity and function of the pancreas. Its deficiency can lead to atrophy of this organ, as well as muscular dystrophy, general symptoms of slow growth in animals and infertility (selenious acid drug supplement, 1995).
References
- Egon Wiberg, NW (2001). Inorganic Chemistry. academic press.
- Material Safety Data Sheet Selenious acid. (2013, May 21). Recovered from sciencelab.com.
- National Center for Biotechnology Information. (sf). PubChem Compound Database; CID = 1091. Recovered from PubChemm.
- New jersey department of health and senior services. (1999, September). selenious acid. Recovered from nj.gov.
- Royal Society of Chemistry. (2015). Selenious acid. Recovered from ChemSpider.
- SELENIOUS ACID. (2016). Recovered from cameochemicals.
- selenious acid drug supplement. (1995, January 5). Recovered from drugs.com.
- Selenous acid. (2010, September 8). Recovered from datasheets.scbt.