Quinone

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A quinone (or benzoquinone) is either one of the two isomers of cyclohexadienedione or a derivative thereof. Quinones are not aromatic, but are dienes. The carbonyl groups are ketone-like. Benzoquinone exists in either of two isomers with the chemical formula C₆H₄O₂. Ortho-Benzoquinone is the 1,2-dione, whereas para-quinone, or parabenzoquinone, is the 1,4-dione. Parabenzoquinone is the oxidized form of hydroquinone, and ortho-benzoquinone is the oxidized form of catechol (1,2-dihydroxybenzene). For example, an acidic Potassium iodide solution reduces a solution of benzoquinone to hydroquinone, which is oxidized back with a solution of silver nitrate.

orthobenzoquinone

parabenzoquinone

The word quinone refers to the entire class of cyclohexadienediones.

1 Biochemistry
2 Organic chemistry
3 See also
4 External links

[edit] 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 quinones as oxidizing agents 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.

[edit] Organic chemistry

Benzoquinone is used in organic chemistry as an oxidizing agent. Even stronger agents exist such as 2,3,5,6-tetrachloro-parabenzoquinone or p-chloranil and 2,3-dicyano-5,6-dichloro-parabenzoquinone or DDQ for short [1].