Quinone
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.
| File:Orthobenzoquinone.png orthobenzoquinone |
File:Parabenzoquinone.png parabenzoquinone |
The word quinone refers to the entire class of cyclohexadienediones.
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 deterent in the animal world.
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].
See also
External links
- Redox system Benzoquinone / Hydroquinone Website