Description | 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.
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. |