Benzeneselenol

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

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Synthesis and basic properties

PhSeH is prepared via a Grignard reagent:^[1]

PhMgBr + Se → PhSeMgBr

PhSeMgBr + HCl → 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 → 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.^[2]

History

Benzeneselenol was first prepared by the reaction of benzene with SeCl₄ in the presence of AlCl₃.^[3]

References

1. ^ Foster, D. G. (1955). "Selenophenol". Org. Synth.; Coll. Vol. 3: 771. 
2. ^ Sonoda, N.; Ogawa, A.; Recupero, F. "Benzeneselenol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
3. ^ Chabrié, M. Camille “Premiers essays de synthèse de composés organiques séléniés dans la série aromatique” Bull. soc. chim. France, 50, 133 (1888); Ann. chim. phys., (6) 20, 229 (1890)