Benzeneselenol

Benzeneselenol, also known as selenophenol, is the organoselenium compound with the formula C6H5SeH, often abbreviated PhSeH. It is the selenium analog of phenol. This colourless, intensely malodorous compound is a useful reagent in organic synthesis.[1]

Benzeneselenol
Names
IUPAC name
benzeneselenol
Other names
Selenaphenol,
selenophenol,
phenylselenol
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.010.417
EC Number
  • 211-457-2
Properties
C6H6Se
Molar mass 157.07 g/mol
Appearance colorless liquid
Odor extremely foul yet characteristic
Density 1.479 g/cm3
Boiling point 71 to 72 °C (160 to 162 °F; 344 to 345 K) (18 mm Hg)
slightly
Solubility in other solvents most organic solvents
1.616
Structure
1.1 D
Hazards
Main hazards toxic
GHS pictograms
GHS Signal word Danger
H301, H331, H373, H400, H410
Related compounds
Related compounds
 Thiophenol,
Hydrogen selenide,
Diphenyl diselenide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

Benzeneselenol is prepared by the reaction of phenylmagnesium bromide and selenium:[2]

PhMgBr + Se → PhSeMgBr
PhSeMgBr + HCl → PhSeH + MgBrCl

Reactions

More so than thiophenol, benzeneselenol is easily oxidized by air. The facility of this reaction reflects the weakness of the Se-H bond. The product is diphenyl diselenide as shown in this idealized equation:

4 PhSeH + O2 → 2 PhSeSePh + 2 H2O

The presence of the diselenide in benzeneselenol is indicated by a yellow coloration. The diselenide can be converted back to the selenol by reduction followed by acidification of the resulting PhSe−.

PhSeH is acidic with a pKa of 5.9. Thus at neutral pH, it is mostly ionized:

PhSeH → PhSe− + H+

It is approximately seven times more acidic than the related thiophenol. Both compounds dissolve in water upon the addition of base. The conjugate base is PhSe−, a potent nucleophile.[1]

History

Benzeneselenol was first reported in 1888 by the reaction of benzene with selenium tetrachloride (SeCl4) in the presence of aluminium trichloride (AlCl3).[3][4]

Safety

The compound is intensely malodorous[5] and, like other organoselenium compounds, toxic.

References
  1. Sonoda, Noboru; Ogawa, Akiya; Recupero, Francesco (2005). "Benzeneselenol". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rb018.pub2. ISBN 0471936235.
  2. Foster, D. G. (1944). "Selenophenol". Organic Syntheses. 24: 89. doi:10.15227/orgsyn.024.0089.
  3. Chabrié, M. C. (1888). "Premiers essais de synthèse de composés organiques séléniés dans la série aromatique". Bulletin de la Société Chimique de Paris. 50: 133–137.
  4. Chabrié, M. C. (1890). "Sur la synthèse de quelques composés séléniés dans la série aromatique". Annales de Chimie et de Physique. 6 (20): 202–286.
  5. Lowe, D. (2012-05-15). "Things I wont work with: Selenophenol". In the Pipeline.
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