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Hydrogen selenide

Hydrogen selenide
IUPAC name Hydrogen selenide
Other names Hydroselenic acid
selenium hydride
CAS number 7783-07-5
RTECS number X1050000
Molecular formula H2Se
Molar mass 80.9758 g/mol
Appearance Colorless gas.
Density 3.310 g/l, gas.
Melting point

-65.73°C (207.42 K)

Boiling point

-41.25°C (231.9 K)

Solubility in water 0.70 g/100 mL
Acidity (pKa) 3.89 (11.0 at 25C)
Molecular shape Bent
Main hazards Highly toxic, highly
flammable, corrosive
NFPA 704
R-phrases R11, R24, R26
Flash point  ?°C
Related Compounds
Other cations Ag2Se
Related compounds OSeCl2
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Hydrogen selenide is H2Se, the simplest hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound with an exposure limit: 0.3 ppm over an 8 hour period.



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.


H2Se can be purchased in cylinders. A number of routes to H2Se have been reported, which are suitable for both large and small scale preparations.

  • 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.
Al2Se3 + 6 H2O 2 Al(OH)3 + 3 H2Se
  • According to the Sonoda method, H2Se is generated from the reaction of H2O and CO on Se in the presence of Et3N.
  • H2Se can by synthesized by the direct reaction of H2 with elemental selenium at >350°C.

Selenium metal can be recovered from H2Se through a reaction with aqueous sulfur dioxide (SO2).

2 H2Se + SO2 2 H2O + Se + S


  • 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.


    1. Patnaik, Pradyot Handbook of Inorganic Chemicals. McGraw-Hill Handbooks New York (2003).
    2. V.I. Cohen, Synthesis 1:60-3 (1980).
    3. Greenwood, N. N., Earnshaw, A. Chemistry of the Elements Second Ed. Butterworth-Heinemann, Boston (1997).
    4. CRC Handbook of Chemistry and Physics Ed. 82. Chapman and Hall (2001-2002).
    • Feher, F. In "Handbook of Preparative Inorganic Chemistry"; Brauer, E., Ed.; Academic: New York, 1963; 1, p 418.
    • Sonoda, N.; Kondo K.; Nagano, K.; Kambe, N.; Morimoto, F. Angewandte Chemie, International Edition English 1980, vol. 19, page 308
    This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hydrogen_selenide". A list of authors is available in Wikipedia.
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