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Not to be confused with benzyl.
IUPAC name
Other names
134-81-6 YesY
ChEBI CHEBI:51507 YesY
ChEMBL ChEMBL189886 YesY
ChemSpider 8329 YesY
Jmol-3D images Image
PubChem 8651
Molar mass 210.23 g·mol−1
Appearance yellow crystals or powder
Density 1.23 g/cm3, solid (1.255 g/cm3, x-ray)
Melting point 94.0 to 96.0 °C; 201.2 to 204.8 °F; 367.1 to 369.2 K
Boiling point 346.0 to 348.0 °C; 654.8 to 658.4 °F; 619.1 to 621.1 K
Solubility in ethanol soluble
Solubility in diethyl ether soluble
Solubility in benzene soluble
Crystal structure P31,221[1]
Dipole moment 3.8 D[2]
Main hazards Irritant
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Related compounds
Related diketones
Related compounds
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Benzil (systematically known as 1,2-diphenylethane-1,2-dione) is the organic compound with the formula (C6H5CO)2, generally abbreviated (PhCO)2. This yellow solid is one of the most common diketones. Its main use is as a photoinitiator in polymer chemistry.[3]


The compound's most noteworthy structural feature is the long carbon-carbon bond of 1.54 Å, which indicates the absence of pi-bonding between the two carbonyl centers. The PhCO centers are planar, but the pair of benzoyl groups are twisted with respect to the other with a dihedral angle of 117°.[4] In less hindered analogues (glyoxal, biacetyl, oxalic acid derivatives), the (RCO)2 group adopts a planar, anti-conformation.


Most benzil is used in the free-radical curing of polymer networks. Ultraviolet radiation decomposes benzil, generating free-radical species within the material, promoting the formation of cross-links. Recently, benzil has been demonstrated to be a potent inhibitor of human carboxylesterases, enzymes involved in the hydrolysis of carboxylesters and many clinically used drugs.[5]


Benzil is a standard building block in organic synthesis. It condenses with amines to give diketimines ligands. A classic organic reaction of benzil is the benzilic acid rearrangement, in which base catalyses the conversion of benzil to benzilic acid. This reactivity is exploited in the preparation of the drug phenytoin. Benzil also reacts with 1,3-diphenylacetone in an aldol condensation to give tetraphenylcyclopentadienone.


Benzil is prepared from benzoin, which in turn is easily obtained via the benzoin condensation from benzaldehyde.[6]

PhC(O)CH(OH)Ph + 2 Cu2+ → PhC(O)C(O)Ph + 2 H+ + 2 Cu+


  1. ^ Acta Cryst. B43 398 (1987)
  2. ^ Spectrochim. Acta A60 (8-9) 1805 (2004)
  3. ^ Hardo Siegel, Manfred Eggersdorfer "Ketones" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, 2002 by Wiley-VCH, Weinheim. doi:10.1002/14356007.a15_077
  4. ^ Quang. Shen, Kolbjoern. Hagen "Gas-phase molecular structure and conformation of benzil as determined by electron diffraction" J. Phys. Chem., 1987, 91 (6), pp 1357–1360. doi:10.1021/j100290a017.
  5. ^ Wadkins. R. M. et al "Identification and characterization of novel benzil (diphenylethane-1,2-dione) analogues as inhibitors of mammalian carboxylesterases. J. Med. Chem., 2005 48 pp 2906-15.
  6. ^ Clarke, H. T.; Dreger.E. E. (1941). "Benzil". Org. Synth. ; Coll. Vol. 1, p. 87