Benzeneselenol

Benzeneselenol is the chemical compound with the formula C6H5SeH, often abbreviated PhSeH. This intensely malodorous liquid is a useful reagent in organic synthesis.

Synthesis and basic properties
PhSeH is prepared via a Grignard reagent:
 * PhMgBr +  Se  &rarr;  PhSeMgBr
 * PhSeMgBr +  HCl  &rarr;  PhSeH  +  MgBrCl

More so that thiophenol, benzeneselenol is easily oxidized by air to give diphenyl diselenide. An idealized equation for this reaction is:
 * 2 PhSeH +  O  &rarr;  PhSeSePh  +  H2O

The presence of the diselenide is signaled by a yellow coloration in most samples of PhSeH. The diselenide can be converted back to the selenol by reduction followed by acidification of the resulting PhSe-.

PhSeH is ca 7x stronger acid than the related thiophenol. Both compounds dissolve in water upon the addition of base.

PhSeH is renowned in organic synthesis as the precursor to its conjugate base PhSe-, a potent nucleophile.

History
Benzeneselenol was first prepared by the reaction of benzene with SeCl4 in the presence of AlCl3.

Safety
Organoselenium compounds are toxic.