Formula C14H10O2 Appearance yellow crystals or powder | Density 1.23 g/cm³ | |
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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.
Contents
Structure
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°. In less hindered analogues (glyoxal, biacetyl, oxalic acid derivatives), the (RCO)2 group adopts a planar, anti-conformation.
Applications
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.
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.
Reactions
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
Benzil is prepared from benzoin, for example with copper(II) acetate:
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.
