Benzeneselenol

Synthesis

Benzeneselenol is prepared by the reaction of phenylmagnesium bromide and selenium: :PhMgBr + Se → PhSeMgBr :PhSeMgBr + HCl → PhSeH + MgBrCl

Since benzeneselenol does not have a long shelf life, 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.

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. The product is diphenyl diselenide as shown in this idealized equation:

:

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 .

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

:

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 , a potent nucleophile.

History

Benzeneselenol was first reported in 1888 by the reaction of benzene with selenium tetrachloride () in the presence of aluminium trichloride ().

Safety

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

References

References

1. (1944). "Selenophenol". Organic Syntheses.
2. (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.
3. (2005). "Encyclopedia of Reagents for Organic Synthesis".
4. Chabrié, M. C.. (1888). "Premiers essais de synthèse de composés organiques séléniés dans la série aromatique". [[Bulletin de la Société Chimique de Paris]].
5. Chabrié, M. C.. (1890). "Sur la synthèse de quelques composés séléniés dans la série aromatique". [[Annales de Chimie et de Physique]].
6. Lowe, D.. (2012-05-15). "Things I wont work with: Selenophenol". In the Pipeline.