Hydrogen selenide
IUPAC name Hydrogen selenide
Other names Hydroselenic acid selane selenium hydride
Identifiers
CAS number	7783-07-5 Y
PubChem	533
ChemSpider	518 Y
UN number	2202
KEGG	C01528 Y
ChEBI	CHEBI:16503 Y
RTECS number	X1050000
Jmol-3D images	Image 1
SMILES [SeH2]
InChI InChI=1S/H2Se/h1H2 Y Key: SPVXKVOXSXTJOY-UHFFFAOYSA-N Y InChI=1/H2Se/h1H2 Key: SPVXKVOXSXTJOY-UHFFFAOYAF
Properties
Molecular formula	H2Se
Molar mass	80.98 g/mol
Appearance	Colorless gas
Odor	horseradish
Density	3.553 g/cm3
Melting point	-65.73 °C, 207 K, -86 °F
Boiling point	-41.25 °C, 232 K, -42 °F
Solubility in water	0.70 g/100 mL
Solubility	soluble in CS2, phosgene
Acidity (pKa)	3.89
Structure
Molecular shape	Bent
Hazards
MSDS	ICSC 0284
EU Index	034-002-00-8
EU classification	Highly Flammable (F+) Toxic (T) Dangerous for the environment (N)
R-phrases	R23/25, R33, R50/53
S-phrases	(S1/2), S20/21, S28, S45, S60, S61
NFPA 704	4 4 0
Flash point	flammable gas
Related compounds
Other anions	H2O H2S H2Te H2Po
Other cations	Na2Se Ag2Se
Related compounds	Arsine
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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.

  Structure and properties

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 pK_a = 3.89, and the second pK_a = 11.0 at 25 °C. Reflecting its acidity, H₂Se is soluble in water.

  Preparation

Industrially, it is produced by treating elemental selenium at T > 300 °C with hydrogen gas.^[1] 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.^[2]

Al₂Se₃ + 6 H₂O ⇌ 2 Al(OH)₃ + 3 H₂Se

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.^[3] H₂Se can be purchased in cylinders.

  Reactions

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

2 H₂Se + SO₂ ⇌ 2 H₂O + Se + S

Its decomposition is used to prepare highly pure Se metal.

  Applications

H₂Se is commonly used in the synthesis of Se-containing compounds. It adds across alkenes. Illustrative is the synthesis of selenoureas from nitriles.^[4] H₂Se gas is used to dope semiconductors with selenium.

  Safety

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.^[1][5]

  References

1. ^ ^{a b} Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a23_525.
2. ^ Féher, F. In "Handbook of Preparative Inorganic Chemistry"; Brauer, E., Ed.; Academic: New York, 1963; 1, p 418.
3. ^ Sonoda, N.; Kondo K.; Nagano, K.; Kambe, N.; Morimoto, F. Angewandte Chemie, International Edition English 1980, vol. 19, page 308
4. ^ V.I. Cohen "A Convenient Synthesis of Mono-, N,N′-Di-, and Trisubstituted Selenoureas from Methyl Carbamimidothioates (S-Methylpseudothioureas)" Synthesis, 1980, 60-3 (1980).
5. ^ http://www.osha.gov/dts/chemicalsampling/data/CH_246700.html, OSHA GENERAL INDUSTRY PEL: 0.05 ppm, 0.2 mg/m3 ,OSHA CONSTRUCTION INDUSTRY PEL: 0.05 ppm, 0.2 mg/m3 TWA

  External links

• WebElements page on compound's properties