Selenol
Selenols are
.Structure, bonding, properties
Selenols are structurally similar to
Selenols are about 1000 times stronger
The boiling points of selenols tend to be slightly greater than for thiols. This difference can be attributed to the increased importance of stronger
Applications and occurrence
Selenols have few commercial applications, being limited by the toxicity of selenium as well as the sensitivity of the Se−H bond. Their
Biochemical role
Selenols are important in certain biological processes. Three enzymes found in mammals contain selenols at their active sites: glutathione peroxidase, iodothyronine deiodinase, and thioredoxin reductase. The selenols in these proteins are part of the essential amino acid selenocysteine.[3] The selenols function as reducing agents to give selenenic acid derivative (RSe−OH), which in turn are re-reduced by thiol-containing enzymes. Methaneselenol (commonly named "methylselenol") (CH3SeH), which can be produced in vitro by incubating selenomethionine with a bacterial methionine gamma-lyase (METase) enzyme, by biological methylation of selenide ion or in vivo by reduction of methaneseleninic acid (CH3−Se(=O)−OH), has been invoked to explain the anticancer activity of certain organoselenium compounds.[4][5][6] Precursors of methaneselenol are under active investigation in cancer prevention and therapy. In these studies, methaneselenol is found to be more biologically active than ethaneselenol (CH3CH2SeH) or 2-propaneselenol ((CH3)2CH(SeH)).[7]
Preparation
Selenols are usually prepared by the reaction of organolithium reagents or Grignard reagents with elemental Se. For example, benzeneselenol is generated by the reaction of phenylmagnesium bromide with selenium followed by acidification:[8]
Another preparative route to selenols involves the alkylation of selenourea, followed by hydrolysis. Selenols are often generated by reduction of diselenides followed by protonation of the resulting selenolate:
- 2 RSe−SeR + 2 Li+[HB(CH2CH3)3]− → 2 RSe−Li+ + 2 B(CH2CH3)3 + H2
- RSe−Li+ + HCl → RSeH + LiCl
Dimethyl diselenide can be easily reduced to methaneselenol within cells.[9]
Reactions
Selenols are easily oxidized to diselenides, compounds containing an Se−Se bond. For example, treatment of benzeneselenol with bromine gives diphenyl diselenide.
- 2 C6H5SeH + Br2 → (C6H5Se)2 + 2 HBr
In the presence of base, selenols are readily alkylated to give selenides. This relationship is illustrated by the