Benzeneselenol, also known as selenophenol, is the

organoselenium compound Organoselenium chemistry is the science exploring the properties and reactivity of organoselenium compounds, chemical compounds containing carbon-to-selenium chemical bonds. Selenium belongs with oxygen and sulfur to the group 16 elements or chalco ...

with the

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

, often abbreviated PhSeH. It is the

selenium Selenium is a chemical element; it has symbol (chemistry), symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elem ...

analog of

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

. This colourless, malodorous compound is a

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

Synthesis

Benzeneselenol is prepared by the reaction of

phenylmagnesium bromide Phenylmagnesium bromide, with the simplified formula , is a magnesium-containing organometallic compound. It forms colorless crystals. It is commercially available as a solution in diethyl ether or tetrahydrofuran (THF). Phenylmagnesium bromide i ...

and

: :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 Diphenyl diselenide is the chemical compound with the formula (C6H5)2Se2, abbreviated Ph2Se2. This yellow-coloured solid is the oxidized derivative of benzeneselenol. It is used as a source of the PhSe unit in organic synthesis. Preparation a ...

. 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 The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical ...

of which is estimated to be between 67 and 74 kcal/mol. In contrast, the S-H BDE for thiophenol is near 80 kcal/mol. The product is diphenyl diselenide as shown in this idealized equation: : The presence of the

diselenide Diselenide may refer to: * Diselane, H-Se-Se-H * Carbon diselenide, CSe2, a yellow-orange oily liquid with pungent odor * Any organic chemical compound with a selenium-selenium bond, R-Se-Se-R (see Organoselenium chemistry) ** Diphenyl 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 p''K''_a of 5.9. Thus at neutral pH, it is mostly ionized: : It is approximately seven times more acidic than the related

thiophenol Thiophenol is an organosulfur compound with the formula C6H5SH, sometimes abbreviated as PhSH. This foul-smelling colorless liquid is the simplest aromatic thiol. The chemical structures of thiophenol and its derivatives are analogous to phen ...

. Both compounds dissolve in water upon the addition of base. The conjugate base is , a potent

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

History

Benzeneselenol was first reported in 1888 by the reaction of

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

with

selenium tetrachloride Selenium tetrachloride is the inorganic compound composed with the formula SeCl4. This compound exists as yellow to white volatile solid. It is one of two commonly available selenium chlorides, the other example being selenium monochloride, Se2 ...

() in the presence of

aluminium trichloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms a hexahydrate with the formula , containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are col ...

().

Safety

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

References

{{reflist Selenols Phenyl compounds Foul-smelling chemicals Reagents for organic chemistry