Benzophenone (CAS: 119-61-9)

Basic Information

Benzophenone is the organic compound with the formula (C6H5)2CO, generally

abbreviated Ph2CO. Benzophenone is a widely used building block in organic

chemistry, being the parent diarylketone.

Uses

Benzophenone can be used as a photo initiator in UV-curing applications such as inks,

imaging, and clear coatings in the printing industry. Benzophenone prevents ultraviolet

(UV) light from damaging scents and colors in products such as perfumes and soaps. It

can also be added to the plastic packaging as a UV blocker. Its use allows manufacturers

to package the product in clear glass or plastic. Without it, opaque or dark packaging

would be required.

In biological applications, benzophenones have been used extensively as photophysical

probes to identify and map peptide–protein interactions.

Synthesis

Benzophenone can be prepared by the reaction of benzene with carbon tetrachloride followed

by hydrolysis of the resulting diphenyldichloromethane, or by Friedel-Crafts acylation of benzene

 with benzoyl chloride in the presence of a Lewis acid (e.g. aluminium chloride) catalyst. The

industrial synthesis relies on the copper-catalyzed oxidation of diphenylmethane with air.

Organic chemistry

Benzophenone is a common photosensitizer in photochemistry. It crosses from the S1 state into

the triplet state with nearly 100% yield. The resulting diradical will abstract a hydrogen atom

from a suitable hydrogen donor to form a ketyl radical.

Benzophenone radical anion

Main article: Air-free technique

Alkali metals reduce benzophenone to the deeply blue colored radical anion, diphenylketyl:

M + Ph2CO → M+Ph2CO·−

Generally sodium is used as the alkali metal. Although inferior in safety and effectiveness relative

to molecular sieves, this ketyl is used in the purification of organic solvents, particularly ethers,

because it reacts with water and oxygen to give non-volatile products. The ketyl is soluble in the

organic solvent being dried, so it accelerates the reaction of the sodium with water and oxygen. In

comparison, sodium is insoluble, and its heterogeneous reaction is much slower. When excess alkali

metal is present a second reduction may occur, resulting in a color transformation from deep blue to purple:

M + M+Ph2CO·− → (M+)2(Ph2CO)2-

Commercially significant derivatives

Substituted benzophenones such as oxybenzone and dioxybenzone are used in some sunscreens.

The use of benzophenone-derivatives which structurally resemble a strong photosensitizer has

been strongly criticized (see sunscreen controversy).

Michler’s ketone has dimethylamino substituents at each para position.

The high-strength polymer PEEK is prepared from derivatives of benzophenone.

Pharmacological activity of Benzophenone analogs

Benzophenone derivatives are known to be pharmacologically active molecules against various

pathological conditions, like anti-tumor, anti-inflammatory and anti-angiogenic activity. One of

the benzophenone analogs, was found to inhibit angiogenesis, thereby preventing

angiogenesis-dependent disorders, such as mammary carcinoma and rheumatoid arthritis,

where it down-regulated the Vascular endothelial growth factor (VEGF) gene expression

responsible for angiogenesis.

Benzophenone tagged with coumarin have showed significant reduction in tumour – growth in

both Dalton’s Lymphoma, and murine ascites carcinoma, by inducing DNA degradation, leading

to apoptosis, and by inhibiting angiogenesis. Recent study reports that, benzophenone tagged with

 benzimidazolehave showed an, enormous tumor inhibiting activity with more than 90% inhibition

in murine carcinoma which is due to the down regulation of neo-vessel formation. Moreover this

activity was found to increase with methoxy and number of methyl groups which played an

important role in the biological activity of the compound.