Selenious acid

• CAT Number: M017494
• CAS Number: 7783-00-8
• Molecular Formula: H2SeO3
• Molecular Weight: 128.984
• Purity: ≥95%
• Storage: 2-8°C
• IUPAC Name: selenous acid
• InChI: InChI=1S/H2O3Se/c1-4(2)3/h(H2,1,2,3)
• InChIKey: MCAHWIHFGHIESP-UHFFFAOYSA-N
• SMILES: O[Se](=O)O

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.

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.[citation needed]

It can be use used as an oxidizing agent e.g. in laboratory preparation of glyoxal (ethane-1,2-dione) from glycol.

Reference

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7: Ganther HE, Kraus RJ. Chemical stability of selenious acid in total parenteral
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