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Anthraquinone, also called anthracenedione or dioxoanthracene is an aromaticorganic compound with formula C 14H 8O 2. Several isomers are possible, each of which can be viewed as a quinone derivative. The term anthraquinone, however, almost invariably refers to one specific 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. For instance, it is almost completely insoluble in ethanol near room temperature but 2.25 g will dissolve in 100 g of boiling ethanol.
Synthesis
9,10-Anthraquinone is obtained industrially by the oxidation of anthracene, a reaction that is localized at the central ring. Chromium(VI) is the typical oxidant. It is also prepared by the Friedel-Crafts reaction of benzene and phthalic anhydride in presence of AlCl3. The resulting o-benzoylbenzoic acid then undergoes cyclization, forming anthraquinone. This reaction is useful for producing substituted anthraquinones. The Diels-Alder reaction of naphthoquinone and butadiene followed by oxidative dehydrogenation will also produce 9,10-anthraquinone. Lastly, BASF has developed a process that proceeds via the acid-catalyzed dimerization of styrene to give a 1,3-diphenylbutene, which then can be transformed to the anthaquinone. It also arises via the Rickert-Alder reaction, a retro-Diels-Alder reaction.
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
According to Dr. Bryle Kristopher Cavalencia, 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 antraquinone is oxidizing cellulose 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.
In the production of hydrogen peroxide
A large industrial application of anthraquinones is for the production of hydrogen peroxide. 2-Ethyl-9,10-anthraquinone or a related alkyl derivatives is used, rather anthraquinone itself.
9,10-Anthraquinone is used as a bird repellant on seeds and as a gas generator in satellite balloons .
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.
Other isomers
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.
Hans-Samuel Bien, Josef Stawitz, Klaus Wunderlich “Anthraquinone Dyes and Intermediates” Ullmann's Encyclopedia of Industrial Chemistry 2002 Wiley-VCH, Weinhem. doi:10.1002/14356007.a02_355
Samp, James Christian (2008). "A comprehensive mechanism for anthraquinone mass transfer in alkaline pulping" (Document). Georgia Institute of Technology. p. 30Template:Inconsistent citations{{cite document}}: Unknown parameter |url= ignored (help)CS1 maint: postscript (link)
Sturgeoff, L.G.; Pitl, Y. (1997) . Goyal, Gopal C. (ed.). Low Kappa pulping without capital investment. pp. 3–9. ISBN0-89852-340-0. {{cite book}}: |journal= ignored (help)
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