Selenous acid

Selenous acid

Selenous acid (also known as selenious acid) is the chemical compound with the formula H2SeO3, perhaps more descriptively written as (HO)2SeO. Selenous acid is the principal oxoacid of selenium.

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: [Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.] :H2SeO3 unicode| H+ + HSeO3- pKa = 2.62:HSeO3- unicode| H+ + SeO32- pKa = 8.32

It is moderately oxidizing in nature, but kinetically slow. In 1 M H+::H2SeO3 + 4H+ + 4e− unicode| Se + 3H2O "E"o = +0.74 VIn 1 M OH−::SeO32− + 4e− + 3H2O unicode| Se + 6OH− "E"o = −0.37 VIt is used in organic synthesis for the synthesis of 1,2-diketones (e.g. glyoxal). [ [http://www.orgsyn.org/orgsyn/pdfs/CV3P0438.pdf “Glyoxal Bisulfite”] , Organic Syntheses, Collected Volume 3, p.438 (1955).]

Health effects

Like many compounds of selenium, selenous acid is highly toxic, and ingestion of any significant quantity of selenous acid is usually fatal. Symptoms of selenium poisoning can occur several hours after exposure, and may include stupor, nausea, severe hypotension and death. [ [http://www.sirchie.com/msds/NARK20010.pdf MSDS for "Reagent for Special Opiates (Codeine, Heroin, & Morphine)"] , Sirchie Finger Print Laboratories, Inc. May 12, 2006.]

Congeners

*S Sulfurous acid
*Se Selenous acid
*Te Tellurious acid
*Po Polonous acid

References


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  • selenous — variant of selenious * * * /seuh lee neuhs, sel euh /, adj. Chem. selenious. * * * selēˈnious or selēˈnous adjective Of selenium in lower valency (selenious acid H2SeO3) • • • Main Entry: ↑selenic …   Useful english dictionary

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