What Is Anthraquinone?
Anthraquinones are organic compounds belonging to the aromatic family that are also found in natural plants such as aloe. They have the IUPAC systematic name of anthracene-9,10-dione. They are also known as 9,10-anthracenedione, anthracene-9,10-quinone, and anthradione.
Anthraquinones are the source of pigments in fruit peels and leaves.
Uses of Anthraquinones
Anthraquinones are mainly used in industrial applications.
As an example, they can be used as a starting material for the production of anthraquinone-based dyes. Anthraquinone-based dyes are characterized by their resistance to sunlight and washing and rich and vivid colors, and are positioned as high-grade dyes.
Other applications include intermediates in the manufacture of laxatives, additives in pulp evaporation, and hydrogen carriers in the production of hydrogen peroxide.
In the agricultural field, they can also be used as a bird repellent.
Properties of Anthraquinone
Anthraquinone has a melting point of 286°C and a boiling point of 379.8°C. At room temperature, it exists in the form of yellow crystals.
Anthraquinone is soluble in nitrobenzene and aniline. It dissolves in benzene and toluene when heated, but not in water or alcohol. Under normal conditions, anthraquinone is chemically very stable.
Structure of Anthraquinone
Anthraquinone is a derivative of anthracene. The chemical formula of anthracene is C14H10, and that of anthraquinone is C14H8O2. The molar mass is 208.21 g/mol and the density is 1.308 g/cm3.
Three isomers exist: 1,2-Anthraquinone, 1,4-Anthraquinone, and 9,10-Anthraquinone. However, 9,10-Anthraquinone is usually referred to as specifically 9,10-Anthraquinone.
Other Information on Anthraquinone
1. Synthesis of Anthraquinone
Anthraquinone is obtained by oxidizing anthracene.
They can also be synthesized using the Friedel-Crafts reaction. Anthraquinone is produced by the condensation of phthalic anhydride with benzene using aluminum chloride. In this reaction, o-benzoylbenzoic acid is produced, which spontaneously cyclizes to yield anthraquinone.
Anthraquinone can also be synthesized by the Diels-Alder reaction of 1,3-diene and naphthoquinone (1,4-naphthoquinone).
2. Reaction of Anthraquinone
The Bally-Scholl synthesis is an example of a classical reaction using anthraquinone. Anthraquinones react with glycerol to form benzanthrone. In the Barry-Scholl synthesis, one carbonyl group of the quinone is reduced to methylene in the presence of copper and sulfuric acid, and glycerol is added.
3. Application of Anthraquinone
Many natural dyes have an anthraquinone skeleton. For example, anthraquinone is used as a raw material for the dye alizarin. In addition, the industrial derivative 2-ethylanthraquinone is used for the production of hydrogen peroxide.