Quinone

The quinones are a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double bonds", resulting in "a fully conjugated cyclic dione structure".

[4] Quinic acid, like quinine is obtained from cinchona bark, called quinaquina in the indigenous languages of Peruvian tribes.

In alkaline conditions, quinones undergo a reversible single-step, two-electron reduction.

9,10-Anthraquinone-2,7-disulphonic acid (AQDS) a quinone similar to one found naturally in rhubarb has been used as a charge carrier in metal-free flow batteries.

[10] The quinone acts as the dienophile and reacts with a diene at a carbon-carbon double bond.

[11] A large scale industrial application of quinones is for the production of hydrogen peroxide.

2-Alkylanthraquinones are hydrogenated to the corresponding hydroquinones (quinizarins), which then transfer H2 to oxygen: in this way, several million metric tons of H2O2 are produced annually.

Phylloquinone is also known as vitamin K1 as it is used by animals to carboxylate certain proteins, which are involved in blood coagulation, bone formation, and other processes.

In the spray of bombardier beetles, hydroquinone reacts with hydrogen peroxide to produce a fiery blast of steam, a deterrent in the animal world.

These applications include purgative (sennosides), antimicrobial and antiparasitic (rhein and saprorthoquinone, atovaquone), anti-tumor (emodin and juglone), inhibition of PGE2 biosynthesis (arnebinone and arnebifuranone) and anti-cardiovascular disease (tanshinone).

Another quinone-containing drug is Mecarbinate (dimecarbine), made by the reaction of ethyl N-methyl-β-aminocrotonate with para-benzoquinone.

Alizarin (1,2-dihydroxy-9,10-anthraquinone), extracted from the madder plant, was the first natural dye to be synthesized from coal tar.

[18] Quinones are commonly named with a prefix that indicates the parent aromatic hydrocarbon ("benzo-" for benzene, "naphtho-" for naphthalene, "anthra-" for anthracene, etc.)