Benzil

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Benzil
Benzil
Benzil-from-LT-monoclinic-xtal-CM-3D-balls.png
Benzil-from-LT-monoclinic-xtal-CM-3D-SF.png
Names
Preferred IUPAC name
Diphenylethanedione
Systematic IUPAC name
1,2-Diphenylethane-1,2-dione
Other names
Diphenylethane-1,2-dione
Benzil
Dibenzoyl
Bibenzoyl
Diphenylglyoxal
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.004.689
Properties
C14H10O2
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
insoluble
Solubility in ethanol soluble
Solubility in diethyl ether soluble
Solubility in benzene soluble
-118.6·10−6 cm3/mol
Structure
P31,221[1]
3.8 D[2]
Hazards
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
biacetyl
Related compounds
benzophenone
glyoxal
bibenzil
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

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]

Structure[edit]

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.

Applications[edit]

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. Benzil is a potent inhibitor of human carboxylesterases, enzymes involved in the hydrolysis of carboxylesters and many clinically used drugs.[5]

Benzil is a relatively poor photoinitiator, and is seldom used. It absorbs at the 260 nm wavelength. It undergoes photobleaching, which allows the curing light to reach deeper layers of the material on longer exposure.[6]

Reactions[edit]

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.

Preparation[edit]

Benzil is prepared from benzoin, for example with copper(II) acetate:[7]

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

Other suitable oxidizing agents such as nitric acid (HNO3) are used routinely.

Iron(III) chloride (FeCl3) can be used as an inexpensive catalyst for this chemical conversion.[8]

References[edit]

  1. ^ Acta Crystallogr. 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. ^ https://books.google.cz/books?id=b1jRBQAAQBAJ&pg=PA78&dq=benzil+photoinitiator&hl=en&sa=X&redir_esc=y#v=onepage&q=benzil%20photoinitiator&f=false
  7. ^ Depreux, P.; Bethegnies, G.; Marcincal-Lefebvre, A. (1988). "Synthesis of benzil from benzoin with copper(II) acetate". Journal of Chemical Education. 65 (6): 553. doi:10.1021/ed065p553. 
  8. ^ Bi, Xiaoxin; Wu, Lintao; Yan, Chaoguo; Jing, Xiaobi; Zhu, Hongxiang (2011). "One-Pot Synthesis Benzils from Aldehydes Via Nhc-Catalyzed Benzoin Dimerization Under Metal-Free Conditions in Water". Journal of the Chilean Chemical Society. 56 (2): 663. doi:10.4067/S0717-97072011000200008.