Benzeneselenol, also known as selenophenol, is the organoselenium compound with the chemical formula C6H5SeH, often abbreviated PhSeH. It is the selenium analog of phenol. This colourless, malodorous compound is a reagent in organic synthesis.[1]
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| Names | |||
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| IUPAC name Benzeneselenol | |||
Other names
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| Identifiers | |||
3D model (JSmol) | |||
| ChemSpider | |||
| ECHA InfoCard | 100.010.417 | ||
| EC Number |
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PubChem CID | |||
CompTox Dashboard (EPA) | |||
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| Properties | |||
| C6H5SeH | |||
| Molar mass | 157.085 g·mol−1 | ||
| Appearance | colorless liquid | ||
| Odor | extremely foul yet characteristic | ||
| Density | 1.479 g/cm3 | ||
| Boiling point | 71 to 72 °C (160 to 162 °F; 344 to 345 K) (18 mmHg) | ||
| slightly | |||
| Solubility in other solvents | most organic solvents | ||
Refractive index (nD) | 1.616 | ||
| Structure | |||
| 1.1 D | |||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards | toxic | ||
| GHS labelling: | |||
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| Danger | |||
| H301, H331, H373, H410 | |||
| Related compounds | |||
Related compounds | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |||
Synthesis
Benzeneselenol is prepared by the reaction of phenylmagnesium bromide and selenium:[2]
- 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. 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]
History
Benzeneselenol was first reported in 1888 by the reaction of benzene with selenium tetrachloride (SeCl4) in the presence of aluminium trichloride (AlCl3).[4][5]
Safety
The compound is intensely malodorous[6] and, like other organoselenium compounds, toxic.