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, malodorous compound is a 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
  • InChI=1S/C6H6Se/c7-6-4-2-1-3-5-6/h1-5,7H Y
    Key: WDODWFPDZYSKIA-UHFFFAOYSA-N Y
  • InChI=1/C6H6Se/c7-6-4-2-1-3-5-6/h1-5,7H
    Key: WDODWFPDZYSKIA-UHFFFAOYAD
  • [SeH]c1ccccc1
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
Occupational safety and health (OHS/OSH):
Main hazards
 toxic
GHS labelling:
Danger
H301, H331, H373, 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).
Y verify (what is YN ?)
Infobox references

Synthesis

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

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

Since benzeneselenol does not have a long shelflife, it is often generated in situ. A common method is by reduction of diphenyldiselenide. A further reason for this conversion is that often, it is the anion that is sought.[1]

Reactions

More so than thiophenol, benzeneselenol is easily oxidized by air. The facility of this reaction reflects the weakness of the Se-H bond, bond dissociation energy of which is estimated to be between 67 and 74 kcal/mol.[1] In contrast, the S-H BDE for thiophenol is near 80 kcal/mol.[3] 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).[4][5]

Safety

The compound is intensely malodorous[6] 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. Chandra, Asit K.; Nam, Pham-Cam; Nguyen, Minh Tho (2003). "The S−H Bond Dissociation Enthalpies and Acidities of Para and Meta Substituted Thiophenols: A Quantum Chemical Study". The Journal of Physical Chemistry A. 107 (43): 9182–9188. Bibcode:2003JPCA..107.9182C. doi:10.1021/jp035622w.
  4. 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.
  5. 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.
  6. Lowe, D. (2012-05-15). "Things I wont work with: Selenophenol". In the Pipeline.
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