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Selenous acid

Names
IUPAC names Selenous acid Selenic(IV) acid
Other names Selenious acid
Identifiers
CAS Number	7783-00-8
3D model (JSmol)	Interactive image
ChEBI	CHEBI:26642
ChEMBL	ChEMBL2009089
ChemSpider	1060
DrugBank	DB11127
ECHA InfoCard	100.029.067
EC Number	231-974-7
KEGG	D05814
PubChem CID	1091
RTECS number	VS7175000
UNII	F6A27P4Q4R
UN number	3283 2630
CompTox Dashboard (EPA)	DTXSID9024300
InChI InChI=1S/H2O3Se/c1-4(2)3/h(H2,1,2,3)Key: MCAHWIHFGHIESP-UHFFFAOYSA-N InChI=1/H2O3Se/c1-4(2)3/h(H2,1,2,3)Key: MCAHWIHFGHIESP-UHFFFAOYAW
SMILES O()O
Properties
Chemical formula	H2SeO3
Molar mass	128.984 g·mol
Appearance	white hygroscopic crystals
Density	3.0 g/cm
Melting point	decomposes at 70 °C
Solubility in water	very soluble
Solubility	soluble in ethanol
Acidity (pKa)	pKa1 = 2.46 pKa2 = 7.3
Conjugate base	Hydrogenselenite
Magnetic susceptibility (χ)	−45.4·10 cm/mol
Pharmacology
Routes of administration	Intravenous infusion
Legal status	US: ℞-only
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H331, H373, H410
Precautionary statements	P260, P261, P264, P270, P271, P273, P301+P310, P304+P340, P311, P314, P321, P330, P391, P403+P233, P405, P501
Related compounds
Other anions	Selenic acid Hydrogen selenide
Other cations	Sodium selenite
Related compounds	Sulfurous acid Tellurous acid Polonous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Selenious Acid

Clinical data
AHFS/Drugs.com	Monograph
License data	US DailyMed: Selenious_acid
Identifiers
DrugBank	DB11127
CompTox Dashboard (EPA)	DTXSID9024300
ECHA InfoCard	100.029.067

Selenous acid (or selenious acid) is the chemical compound with the formula H₂SeO₃. Structurally, it is more accurately described by O=Se(OH)₂. It is the principal oxoacid of selenium; the other being selenic acid.

Formation and properties

Selenous acid is analogous to sulfurous acid, but it is more readily isolated. Selenous acid is easily formed upon the addition of selenium dioxide to water. As a crystalline solid, the compound can be seen as pyramidal molecules that are interconnected with hydrogen bonds. In solution it is a diprotic acid:

H₂SeO₃ ⇌ H + HSeO−3  (pK_a = 2.62)

HSeO−3 ⇌ H + SeO2−3  (pK_a = 8.32)

It is moderately oxidizing in nature, but kinetically slow. In 1 M H:

H₂SeO₃ + 4 H + 4 e ⇌ Se + 3 H₂O  (E = +0.74 V)

In 1 M OH:

SeO2−3 + 4 e + 3 H₂O ⇌ Se + 6 OH  (E = −0.37 V)

Selenous acid is hygroscopic.

Uses

The major use is in protecting and changing the color of steel, especially steel parts on firearms. The so-called cold-bluing process uses selenous acid, copper(II) nitrate, and nitric acid to change the color of the steel from silver-grey to blue-grey or black. Alternative procedures use copper sulfate and phosphoric acid instead. This process deposits a coating of copper selenide and is fundamentally different from other bluing processes which generate black iron oxide. Some older razor blades were also made of blued steel.

Another use for selenious acid is the chemical darkening and patination of copper, brass and bronze, producing a rich dark brown color that can be further enhanced with mechanical abrasion.

It is used in organic synthesis as an oxidizing agent for the synthesis of 1,2-dicarbonyl compounds, e.g. in laboratory preparation of glyoxal (oxaldehyde) from acetaldehyde.

Selenious acid is a key component of the Mecke reagent used for drug checking.

Medical

Selenous acid can supply the trace element indicated in people as a source of selenium.

Health effects

Like many selenium compounds, selenous acid is highly toxic in excessive quantities, and ingestion of any significant quantity of selenous acid is usually fatal, however it is an approved dietary source in proper amounts. Symptoms of selenium poisoning can occur several hours after exposure, and may include stupor, nausea, severe hypotension and death.

References

1. Lide DR (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 4–81. ISBN 0-8493-0594-2.
2. K_a and pK_a for Polyprotic Acids. ucdsb.on.ca
3. Holleman AF, Wiberg E (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
4. Lide DR, ed. (1995). CRC Handbook of Chemistry and Physics (76th ed.). Boca Raton, FL: CRC Press Inc. pp. 4–82.
5. "Selenious acid". PubChem. Retrieved 2020-01-17.
6. ^ Scarlato EA, Higa J (28 June 1990). "SELENIUM (PIM483)". Retrieved 29 December 2010.
7. "Glyoxal Bisulfite", Organic Syntheses, Collected Volume 3, p.438 (1955).
8. "Colour Test Reagents-Kits for Preliminary Identification of Drugs of Abuse" (PDF). National Institute of Justice. 2000-07-01. Retrieved 2012-01-26.
9. "Material Safety Data Sheet - Product Name: Reagent for Special Opiates" (PDF). Sirchie Finger Print Laboratories, Inc. May 12, 2006. Archived from the original (PDF) on October 18, 2006.
10. "Selenious acid injection, solution". DailyMed. 1 May 2020. Retrieved 22 October 2020.
11. "Drug Approval Package: Selenious Acid Injection". U.S. Food and Drug Administration (FDA). Retrieved 22 October 2020.

External links

• "Selenious acid". Drug Information Portal. U.S. National Library of Medicine.

• Medicine

• Oxoacids
• Selenites
• Oxidizing acids
• Chalcogen oxoacids
• Selenium(IV) compounds