English

Noun

1. In the context of "organic chemistry|countable": Any of a class of aromatic ketones based on the parent compound diphenylketone (C6H5)2CO; used, amongst other things, as ingredients in sunblock.
2. In the context of "organic compound|uncountable": The compound diphenylketone.

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.

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

Sodium reduces benzophenone to the deeply colored radical anion, diphenylketyl:

Na + Ph2CO → Na+Ph2CO−

This ketyl is used in the purification of hydrocarbon solvents, because it reacts with water and oxygen to give colorless non-volatile products:

Na + H2O → NaOH + ½H2

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 critisized. (see sunscreen controversy)

p,p-bis(N,N-dimethylamino)benzophenone or Michler's ketone has dimethylamino substituents at each para position.

The high-strength polymers PEEK, polyetherether ketones, are prepared from derivatives of benzophenone.

References

• Merck Index, 11th Edition, 1108.

Gallery