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Sodium selenite (Na2SeO3) is a toxic inorganic salt that is highly soluble in water and insoluble in organic solvents. The crystal structure of the anhydrous salt has been variously reported as tetragonal or monoclinic.
In 1889, Irish chemists Sir Charles A. Cameron* and John Macallan and the previously unknown selenium oxychloride1 (SeOCl2) by heating selenium oxide (SeO2) with sodium chloride. This finding was reported in a pioneering series of articles on selenium chemistry.
In an improved 1929 synthesis, J. B. Krak at the Roessler and Hasslacher Chemical Co. (Perth Amboy, NJ) by evaporating a solution of sodium hydroxide and selenious acid (H2SeO3) at 60鈥�100 掳C. Commercial Na2SeO3 is now made by heating an aqueous solution of SeO2 and NaOH to form its pentahydrate2, which is crystallized and then warmed to 40 掳C to liberate the anhydrous salt.
Na2SeO3 and other selenite salts are used to 鈥渘eutralize鈥� green impurities during the manufacture of colorless glass. Iron-containing impurities in the natural silicas (e.g., sand) used to make glass absorb red and blue wavelengths of light, giving it a green appearance. Selenites have no color; but when they are dissolved in the glass mixture, they appear pinkish, counteracting the green hue and making the glass colorless.
Sodium selenite hazard information
| Hazard class* | GHS code and hazard statement | |
|---|---|---|
| Acute toxicity, oral, category 2 | H300鈥擣atal if swallowed |  |
| Skin corrosion/irritation, category 2 | H315鈥擟auses skin irritation听 |  |
| Skin sensitization, category 1 | H317鈥擬ay cause an allergic skin reaction | |
| Serious eye damage/eye irritation, category 2A | H319鈥擟auses serious eye irritation | |
| Acute toxicity, inhalation, category 2 | H330鈥擣atal if inhaled | |
| Short-term (acute) aquatic hazard, category 2 | H401鈥擳oxic to aquatic life |  |
| Long-term (chronic) aquatic hazard, category 2 | H411鈥擳oxic to aquatic life with long-lasting effects | |
MOTW update
Tetrodotoxin听was the Molecule of the Week for听April 5, 2010. It is an extremely toxic natural substance鈥攖he poisonous principle in pufferfish and other marine animals. Tetrodotoxin, a nerve blocker, has been tested as a local anesthetic, but its concentration range must be limited to prevent it from becoming systemically toxic. It is not used currently for clinical purposes.
Anesthesiologist Daniel S. Kohane and his team at Boston Children鈥檚 Hospital and Harvard Medical School developed a self-assembling drug delivery system that听听than direct injection. In experiments with rats, they used modified versions of peptides from the same voltage-gated sodium channels that tetrodotoxin targets to deliver the drug. The slower release allowed the toxin to block the rats鈥� sciatic nerves >3 times as long as free tetrodotoxin, without harmful effects.
See this week's MOTW update below.
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Sodium selenite听fast facts
| CAS Reg. No. | 10102-18-8 |
nomenclature | Selenious acid, sodium salt (1:2) |
| Empirical formula | Na2O3Se |
| Molar mass | 172.94 g/mol |
| Appearance | Colorless crystals or white powder |
| Melting point | 720掳 C (dec.)a |
| Water solubility | 900 g/L |
a. Decomposition temperatures as low as
320 掳C are reported.
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