|Jmol-3D images||Image 1|
|Molar mass||80.98 g/mol|
-65.73 °C, 207 K, -86 °F
-41.25 °C, 232 K, -42 °F
|Solubility in water||0.70 g/100 mL|
|Solubility||soluble in CS2, phosgene|
|EU classification||Highly Flammable (F+)
Dangerous for the environment (N)
|S-phrases||, , , , ,|
|Flash point||flammable gas|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Hydrogen selenide is the inorganic compound with the formula H2Se. It is the simplest and virtually the only hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound with an exposure limit: 0.05 ppm over an 8 hour period. This compound has a very irritating smell resembling that of decayed horseradish but smells of rotten eggs at higher concentrations.
H2Se adopts a "bent" structure with a H-Se-H bond angle of 91°. Consistent with this structure, three IR-active vibrational bands are observed: 2358, 2345, and 1034 cm−1.
The properties of H2S and H2Se are similar, although the selenide is more acidic with pKa = 3.89, and the second pKa = 11.0 at 25 °C. Reflecting its acidity, H2Se is soluble in water.
Industrially, it is produced by treating elemental selenium at T > 300 °C with hydrogen gas. A number of routes to H2Se have been reported, which are suitable for both large and small scale preparations. In the laboratory, H2Se is usually prepared by the action of water on Al2Se3, concomitant with formation of hydrated alumina. A related reaction involves the acid hydrolysis of FeSe.
H2Se can also be prepared by means of different methods based on the in situ generation in aqueous solution using boron hydride, Marsh test and Devarda's alloy. According to the Sonoda method, H2Se is generated from the reaction of H2O and CO on Se in the presence of Et3N. H2Se can be purchased in cylinders.
Elemental selenium can be recovered from H2Se through a reaction with aqueous sulfur dioxide (SO2).
Its decomposition is used to prepare highly pure Se metal.
H2Se is commonly used in the synthesis of Se-containing compounds. It adds across alkenes. Illustrative is the synthesis of selenoureas from nitriles. H2Se gas is used to dope semiconductors with selenium.
The gas is hazardous, being one of the most toxic compound of selenium and far more toxic than its congener hydrogen sulfide. The threshold limit value is 0.05 ppm. At high concentrations even exposure for less than a minute causes the gas to attack the eyes and mucous membranes causing cold-like symptoms for at least a few days afterwards. In Germany, the limit in drinking water is 0.008 mg/L, and the US EPA recommends a maximum contamination of 0.01 mg/L.
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