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.[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]
^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.
