Hydrogen selenide

Hydrogen selenide

Structural diagram of the hydrogen selenide molecule Space-filling model of the hydrogen selenide molecule
Names
IUPAC name Hydrogen selenide
Other names Hydroselenic acid selane selenium hydride
Identifiers
CAS Number	7783-07-5 N
ChemSpider	518
ECHA InfoCard	100.029.071
RTECS number	X1050000
UN number	2202
CompTox Dashboard (EPA)	DTXSID20872822
Properties
Chemical formula	H2Se
Molar mass	80.98 g/mol
Appearance	Colorless gas
Density	3.553 g/cm3
Melting point	-65.73°C (207.42 K)
Boiling point	-41.25°C (231.9 K)
Solubility in water	0.70 g/100 mL
Solubility	soluble in CS2, phosgene
Acidity (pKa)	3.89
Structure
Molecular shape	Bent
Hazards
NFPA 704 (fire diamond)	4 4 0
Flash point	flammable gas
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox 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: 0.05 ppm over an 8 hour period. This compound has a very irritating smell of decayed horseradish.

Structure

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.

Properties

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

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 T > 300 °C.

• H₂Se can also be prepared by means of different methods based on the in situ generation in aqueous solution of nascent hydrogen used as reducing agent, a.o., boron hydride, Marsh test and Devarda's alloy.

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

2 H₂Se + SO₂ ⇌ 2 H₂O + Se + S

Elemental selenium can also be directly obtained by reduction of selenite by strong reducing agent such as, e.g., ascorbic acid, hydrazine hydrochloride, or hydroxylamine hydrochloride.

Applications

• H₂Se is commonly used in the synthesis of Se-containing compounds; it adds across alkenes. Illustrative is the synthesis of selenoureas from nitriles.

Selenourea reaction

• H₂Se gas is used to dope semiconductors with selenium.

References

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).
5. Féher, F. In "Handbook of Preparative Inorganic Chemistry"; Brauer, E., Ed.; Academic: New York, 1963; 1, p 418.
6. Sonoda, N.; Kondo K.; Nagano, K.; Kambe, N.; Morimoto, F. Angewandte Chemie, International Edition English 1980, vol. 19, page 308
7. 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