Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula C14H8O2. Isomers include various quinone derivatives. The term anthraquinone, however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxoanthracene) where in 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.
Appearance: Yellow solid
Moleular weight: 208.216 g·mol−1
Melting point: 286 °C
Boiling point: 379.8 °C
Density: 1.308 g/cm3
Hydrogenation gives dihydroanthraquinone (anthrahydroquinone). Reduction with copper gives anthrone. Sulfonation with sulfuric acid gives anthroquinone-1-sulfonic acid, which reacts with sodium chlorate to give 1-chloroanthaquinone.
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 redox catalyst. 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