Benzil (i.e. Bz₂, systematically known as 1,2-diphenylethane-1,2-dione) is the

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the formula ( C₆H₅ CO)₂, generally abbreviated ( PhCO)₂. This yellow solid is one of the most common

diketone In organic chemistry, a dicarbonyl is a molecule containing two carbonyl () groups. Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls ...

s. Its main use is as a

photoinitiator In chemistry, a photoinitiator is a molecule that creates reactive species (free radicals, cations or anions) when exposed to radiation (Ultraviolet, UV or Visible spectrum, visible). Synthetic photoinitiators are key components in photopolymers ...

polymer chemistry Polymer chemistry is a sub-discipline of chemistry that focuses on the structures, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are also applic ...

.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 generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivi ...

analogues (

glyoxal Glyoxal is an organic compound with the chemical formula OCHCHO. It is the smallest dialdehyde (a compound with two aldehyde groups). It is a crystalline solid, white at low temperatures and yellow near the melting point (15 °C). The liquid ...

, biacetyl,

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...

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 A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

networks. It absorbs

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

radiation at a wavelength of 260 nm, leading to decomposition with formation of free-radical species and formation of

cross-link In chemistry and biology, a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...

s within the material. However, it is a relatively poor photoinitiator, and is seldom used. It undergoes

photobleaching In optics, photobleaching (sometimes termed fading) is the photochemical alteration of a dye or a fluorophore molecule such that it is permanently unable to fluoresce. This is caused by cleaving of covalent bonds or non-specific reactions between ...

, which allows the curing light to reach deeper layers of the material on longer exposure.

Acetal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments n ...

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: 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 neurotransmi ...

of human

carboxylesterase The enzyme carboxylesterase (or carboxylic-ester hydrolase, EC 3.1.1.1; systematic name carboxylic-ester hydrolase) catalysis, catalyzes reactions of the following form: :a Ester, carboxylic ester + H2O \rightleftharpoons an Alcohol (chemistry), ...

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s 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 branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

. It condenses with amines to give diketimine 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, in which base catalyses the conversion of benzil to benzilic acid. This reactivity is exploited in the preparation of the drug

phenytoin Phenytoin (PHT), sold under the brand name Dilantin among others, is an anticonvulsant, anti-seizure medication. It is useful for the prevention of tonic-clonic seizures (also known as grand mal seizures) and focal seizures, but not absence se ...

. Benzil also reacts with 1,3-diphenylacetone in an

aldol condensation An aldol condensation is a condensation reaction in organic chemistry in which two carbonyl moieties (of aldehydes or ketones) react to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), and this is then followed by dehydration t ...

to give

tetraphenylcyclopentadienone Tetraphenylcyclopentadienone is an organic compound with the formula . It is classified as a cyclic dienone. 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 a ...

Preparation

Benzil is prepared from benzoin, for example with

copper(II) acetate Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula where is acetate (). The hydrated derivative, , which contains one molecule of water for each copper atom, is available commercially. Anhydrous co ...

: :PhC(O)CH(OH)Ph + 2 Cu²⁺ → PhC(O)C(O)Ph + 2 H⁺ + 2 Cu⁺ Other suitable oxidizing agents such as

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

(HNO₃) are used routinely.

Iron(III) chloride Iron(III) chloride describes the inorganic compounds with the formula (H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated f ...

(FeCl₃) 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