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Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromaticorganic compound with formula . Isomers include various quinone derivatives. The term anthraquinone, however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxoanthracene) wherein the keto groups are located on the central ring. It is a building block of many dyes and is used in bleaching pulp for papermaking. It is a yellow, highly crystalline solid, poorly soluble in water but soluble in hot organic solvents. It is almost completely insoluble in ethanol near room temperature but 2.25 g will dissolve in 100 g of boiling ethanol.
There are several current industrial methods to produce 9,10-Anthraquinone:
The oxidation of anthracene, a reaction that is localized at the central ring. Chromium(VI) is the typical oxidant.
The yellow color of certain lichens (here Caloplaca thallincola) is due to the présence of anthraquinones.
Synthetic dyes are often derived from 9,10-anthraquinone, such as alizarin. Important derivatives are 1-nitroanthraquinone, anthraquinone-1-sulfonic acid, and the dinitroanthraquinone. Natural pigments that are derivatives of anthraquinone are found, inter alia, in aloe latex, senna, rhubarb, and cascara buckthorn, fungi, lichens, and some insects.
Selection of anthraquinone dyes. From the left: C.I.Acid Blue 43 an "acid dye" for wool (also called "Acilan Saphirol SE"), C.I. Vat Violet 1, which is applied by transfer printing using sublimation, a blue colorant commonly used in gasoline, and C.I. Disperse Red 60, a so-called vat dye.
Digester additive in papermaking
9,10-Anthraquinone is used as a digester additive in production of paper pulp by alkaline processes, like the Kraft, the alkaline sulfite or the Soda-AQ processes. The anthraquinone is a redoxcatalyst. The reaction mechanism may involve single electron transfer (SET). The anthraquinone is oxidizing the reducing end of polysaccharides in the pulp, i.e., cellulose and hemicellulose, and thereby protecting it from alkaline degradation (peeling). The anthraquinone is reduced to 9,10-dihydroxyanthracene which then can react with lignin. The lignin is degraded and becomes more watersoluble and thereby more easy to wash away from the pulp, while the antraquinone is regenerated. This process gives an increase in yield of pulp, typically 1-3% and a reduction in kappa number.
Sodium 2-anthraquinonesulfonate (AMS) is a watersoluble anthraquinone derivative that was the first anthraquinone derivative discovered to have a catalytic effect in the alkaline pulping processes.
9,10-Anthraquinone is used as a bird repellant on seeds, and as a gas generator in satellite balloons. It has also been mixed with lanolin and used as a wool spray to protect sheep flocks against kea attacks in New Zealand.
Natural anthraquinone derivatives tend to have laxative effects. Prolonged use and abuse leads to melanosis coli. 5 anthraquinones have been shown to inhibit the formation of Tau aggregates and dissolve paired helical filaments thought to be critical to Alzheimer's disease progression in both mouse models and in vitro testing but have not been investigated as a therapeutic agent.
Several other isomers of anthraquinone are possible, including the 1,2-, 1,4-, and 2,6-anthraquinones. They are of comparatively minor importance. The term is also used in the more general sense of any compound that can be viewed as an anthraquinone with some hydrogen atoms replaced by other atoms or functional groups. These derivatives include substances that are technically useful or play important roles in living beings.
Recently, a class of anthraquinone derivates were shown to have self-healing properties when doped in PMMA matrix.
Metabolism in humans
The enzyme encoded by the gene UGT1A8 has glucuronidase activity with many substrates including anthraquinones.
Honeycomb structure on Cu(111)
Anthraquinone molecules adsorbed onto a Cu(111) surface assemble into a highly ordered honeycomb structure. The self-assembly of organic molecules onto metal surfaces is a frequently occurring phenomenon. However, the honeycomb structure formed by anthraquinone is unique in its unusually large pore diameter (?5 nm). Additionally, the patterned structure of anthraquinone is supported theoretically using both classical Monte Carlo and quantum mechanical DFT approaches.
^Goor, G.; Glenneberg, J.; Jacobi, S. (2007). "Hydrogen Peroxide". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_443.pub2.
^Panigrahi, G.K.; Suthar, M.K.; Verma, N.; Asthana, S.; Tripathi, A.; Gupta, S.K.; Saxena, J. K.; Raisuddin, S.; Das, M. (2015). "Investigation of the interaction of anthraquinones of Cassia occidentalis seeds with bovine serum albumin by molecular docking and spectroscopic analysis: Correlation to their in vitro cytotoxic potential". Food Research International. doi:10.1016/j.foodres.2015.08.022.