Benzil

Benzil

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
CAS Number	134-81-6 Y
3D model (JSmol)	Interactive image Interactive image
Beilstein Reference	608047
ChEBI	CHEBI:51507 Y
ChEMBL	ChEMBL189886 Y
ChemSpider	8329 Y
ECHA InfoCard	100.004.689
EC Number	205-157-0
PubChem CID	8651
RTECS number	DD1925000
UNII	S85X61172J Y
CompTox Dashboard (EPA)	DTXSID3044380
InChI InChI=1S/C14H10O2/c15-13(11-7-3-1-4-8-11)14(16)12-9-5-2-6-10-12/h1-10H Y Key: WURBFLDFSFBTLW-UHFFFAOYSA-N Y InChI=1/C14H10O2/c15-13(11-7-3-1-4-8-11)14(16)12-9-5-2-6-10-12/h1-10H Key: WURBFLDFSFBTLW-UHFFFAOYAZ
SMILES O=C(C(=O)c1ccccc1)c2ccccc2 c1ccccc1C(=O)C(=O)c2ccccc2
Properties
Chemical formula	C14H10O2
Molar mass	210.232 g·mol−1
Appearance	yellow crystalline powder
Density	1.521 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 water	insoluble
Solubility in ethanol	soluble
Solubility in diethyl ether	soluble
Solubility in benzene	soluble
Magnetic susceptibility (χ)	−118.6·10−6 cm3/mol
Structure
Crystal structure	P31,221
Dipole moment	3.8 D
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Irritant
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335
Precautionary statements	P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
NFPA 704 (fire diamond)	2 1 0
Lethal dose or concentration (LD, LC):
LD50 (median dose)	>3 g/kg (mouse, oral)
Related compounds
Related diketones	diacetyl
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). Y verify (what is YN ?) Infobox references

Benzil (i.e. Bz₂, 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.

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

Benzil can function as a photoinitiator in the free-radical curing of polymers. Upon exposure to ultraviolet (UV) radiation, it may initiate polymerisation through two distinct photochemical pathways. Irradiation at wavelengths below 330 nm causes a Type I Norrish reaction that produces benzoyl radicals capable of initiating free-radical polymerisation. At wavelengths above 330 nm, benzil is promoted to an excited triplet state, from which it can initiate polymerisation through hydrogen atom abstraction. 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. Acetal derivatives, such as 2,2-dimethoxy-2-phenylacetophenone, have better properties for this application.

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

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.

References