Phenylacetylene

Phenylacetylene is an alkyne hydrocarbon containing a phenyl group. It exists as a colorless, viscous liquid. In research, it is sometimes used as an analog for acetylene; being a liquid, it is easier to handle than acetylene gas.

Phenylacetylene
Names
IUPAC name
Ethynylbenzene
Identifiers
CAS Number
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.007.861
PubChem CID
UNII
CompTox Dashboard (EPA)
Properties
Chemical formula
 C8H6
Molar mass 102.133 g/mol
Density 0.93 g/cm3
Melting point −45 °C (−49 °F; 228 K)
Boiling point 142 to 144 °C (288 to 291 °F; 415 to 417 K)
Acidity (pKa) 28.7 (DMSO)[1],
23.2 (aq, extrapolated)[2]
Magnetic susceptibility (χ)
 -72.01·10−6 cm3/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation

In the laboratory, phenylacetylene can be prepared by elimination of hydrogen bromide from styrene dibromide using sodium amide in ammonia:[3]

It can also be prepared by the elimination of hydrogen bromide from bromostyrene using molten potassium hydroxide.[4]

Reactions
  • Phenylacetylene can be reduced (hydrogenated) by hydrogen over Lindlar catalyst to give styrene.
  • It undergoes a metal catalyzed trimerization to give 1,2,4- (97%) and 1,3,5-triphenylbenzene:[5]
  • Choosing a rhodium catalyst leads to the cyclotrimerization producing both the 1,2,4- and 1,3,5- isomers along with substantial quantities of acyclic enyne dimer products:[6]
  • It undergoes a hydration reaction, catalyzed by gold(III) or mercury(II), to give acetophenone.

See also
  • Alkyne
  • Alkyne trimerisation

References
  1. Bordwell, F.G. Acc. Chem. Res. 1988, 21, 456-463.
  2. Streitwieser, A.,Jr.; Ruben, D.M.E; J. Am. Chem. Soc. 1971., 93, 1794-1795.
  3. Kenneth N. Campbell, Barbara K. Campbell (1950). "Phenylacetylene". Organic Syntheses. 30: 72. doi:10.15227/orgsyn.030.0072.
  4. John C. Hessler (1922). "Phenylacetylene". Organic Syntheses. 2: 67. doi:10.15227/orgsyn.002.0067.
  5. Gerhard Hilt; Thomas Vogler; Wilfried Hess; Fabrizio Galbiati (2005). "A simple cobalt catalyst system for the efficient and regioselective cyclotrimerisation of alkynes". Chemical Communications. 2005 (11): 1474–1475. doi:10.1039/b417832g. PMID 15756340.
  6. Ardizzoia, G. A.; Brenna, S.; Cenini, S.; LaMonica, G.; Masciocchi, N.; Maspero, A. (2003). "Oligomerization and Polymerization of Alkynes Catalyzed by Rhodium(I) Pyrazolate Complexes". Journal of Molecular Catalysis A: Chemical. 204–205: 333–340. doi:10.1016/S1381-1169(03)00315-7.