Quinone

"DDQ" redirects here. DDQ is also the former callsign of a TV station in Toowoomba, Queensland, Australia.

Benzoquinone, or quinone is one of the two isomers of cyclohexadienedione. These compounds have the molecular formula C₆H₄O₂. Orthobenzoquinone is the 1,2-dione, whereas parabenzoquinone is the 1,4-dione.

Orthobenzoquinone is the oxidized form of catechol (1,2-dihydroxybenzene), while parabenzoquinone is the oxidized form of hydroquinone. An acidic potassium iodide solution reduces a solution of benzoquinone to hydroquinone, which is oxidized back with a solution of silver nitrate.

Quinone is also the name for the class of compounds containing either benzoquinone isomers as part of their structure. Quinones are not aromatic, but are diketones.

• 
  1,2-Benzoquinone
• 
  1,4-Benzoquinone

Biochemistry

Quinone is a common constituent of biologically relevant molecules (e.g. Vitamin K1 is phylloquinone). Others serve as electron acceptors in electron transport chains such as those in Photosystems I & II of photosynthesis, and aerobic respiration. A natural example of the oxidization of hydroquinone to quinone is the spray of bombardier beetles. Hydroquinone is reacted with hydrogen peroxide to produce a fiery blast of steam, a strong deterrent in the animal world. Quinones can be partially reduced to quinols.

Oxidizing agents

Benzoquinone is used in organic chemistry as an oxidizing agent. Stronger quinone oxidising agents exist; for instance: 2,3,5,6-tetrachloro-parabenzoquinone (also known as p-chloranil) and 2,3-dicyano-5,6-dichloro-parabenzoquinone (also known as DDQ).

External Links

Special Issue: Quinones and Hydroxyquinones. Target Molecules and Building Blocks in Organic Synthesis