Benzil (i.e. Bz
2, systematically known as 1,2-diphenylethane-1,2-dione) is the
organic compound with the formula (
C6H5 CO)
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.
[Hardo Siegel, Manfred Eggersdorfer "Ketones" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, 2002 by Wiley-VCH, Weinheim. ]
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
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
analogues (
glyoxal,
biacetyl,
oxalic acid
Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...
derivatives), the (RCO)
2 group adopts a planar, anti-conformation.
Applications
Most benzil can be used as a photoinitiator in the free-radical
curing of
polymer networks. It absorbs
ultraviolet radiation at a wavelength of 260 nm, leading to decomposition with formation of free-radical species and formation of
cross-links within the material. However, it is a relatively poor photoinitiator, and is seldom used. It undergoes
photobleaching, which allows the curing light to reach deeper layers of the material on longer exposure.
derivatives, such as
2,2-dimethoxy-2-phenylacetophenone, have better properties for this application.
Benzil is a potent
inhibitor
Inhibitor or inhibition may refer to:
In biology
* Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity
* Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotra ...
of human
carboxylesterases,
enzymes involved in the hydrolysis of carboxylesters and many clinically used drugs.
Reactions
Benzil is a standard building block in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
. It condenses with amines to give
diketimine
Diimines are organic compounds containing two imine (RCH=NR') groups. Common derivatives are 1,2-diketones and 1,3-diimines. These compounds are used as ligands and as precursors to heterocycles. Diimines are prepared by condensation reactions ...
ligands. A classic
organic reaction
Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, Mechanistic Organ ...
of benzil is the
benzilic acid rearrangement The benzilic acid rearrangement is formally the 1,2-rearrangement of 1,2-diketones to form α- hydroxy–carboxylic acids using a base. This reaction receives its name from the reaction of benzil with potassium hydroxide to form benzilic acid. Firs ...
, in which base catalyses the conversion of benzil to
benzilic acid
Benzilic acid is an organic compound with formula or ()2(HO)C(COOH). It is a white crystalline aromatic acid, soluble in many primary alcohols.
Preparation
Benzilic acid can be prepared by a heating mixture of benzil, ethanol, and potassium hy ...
. 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
Tetraphenylcyclopentadienone is an organic compound with the formula (C6H5)4C4CO. It is a dark purple to black crystalline solid that is soluble in organic solvents. It is an easily made building block for many organic and organometallic compounds ...
.
Preparation
Benzil is prepared from
benzoin, for example with
copper(II) acetate:
:PhC(O)CH(OH)Ph + 2 Cu
2+ → PhC(O)C(O)Ph + 2 H
+ + 2 Cu
+
Other suitable oxidizing agents such as
nitric acid (HNO
3) are used routinely.
Iron(III) chloride
Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The col ...
(FeCl
3) can be used as an inexpensive catalyst for this chemical conversion.
[{{cite journal, doi=10.4067/S0717-97072011000200008, title=One-Pot Synthesis Benzils from Aldehydes Via Nhc-Catalyzed Benzoin Dimerization Under Metal-Free Conditions in Water, journal=Journal of the Chilean Chemical Society, volume=56, issue=2, pages=663, year=2011, last1=Bi, first1=Xiaoxin, last2=Wu, first2=Lintao, last3=Yan, first3=Chaoguo, last4=Jing, first4=Xiaobi, last5=Zhu, first5=Hongxiang, doi-access=free]
References
Aromatic ketones
Diketones