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Anthraquinone, also called anthracenedione or dioxoanthracene, is an
aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
with formula .
Isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...
s include various
quinone The quinones are a class of organic compounds that are formally "derived from aromatic compounds
uch as benzene or naphthalene Uch ( pa, ; ur, ), frequently referred to as Uch Sharīf ( pa, ; ur, ; ''"Noble Uch"''), is a historic city in the southern part of Pakistan's Punjab province. Uch may have been founded as Alexandria on the Indus, a town founded by Alexand ...
by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double ...
derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinone (
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
: 9,10-dioxoanthracene) wherein the keto groups are located on the central ring. It is a building block of many
dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...
s and is used in bleaching pulp for papermaking. It is a yellow, highly crystalline solid, poorly
soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...
in
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
but soluble in hot organic solvents. It is almost completely insoluble in
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
near room temperature but 2.25 g will dissolve in 100 g of boiling ethanol. It is found in nature as the rare mineral
hoelite Hoelite is a mineral, discovered in 1922 at Mt. Pyramide, Spitsbergen, Norway and named after Norwegian geologist Adolf Hoel (1879–1964). Its chemical formula is C14H8O2 (9,10-anthraquinone). It is a very rare organic mineral which occurs in ...
.


Synthesis

There are several current industrial methods to produce 9,10-anthraquinone: # The oxidation of
anthracene Anthracene is a solid polycyclic aromatic hydrocarbon (PAH) of formula C14H10, consisting of three fused benzene rings. It is a component of coal tar. Anthracene is used in the Economic production, production of the red dye alizarin and other dyes ...
. Chromium(VI) is the typical oxidant. # The Friedel-Crafts reaction of
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
and
phthalic anhydride Phthalic anhydride is the organic compound with the formula C6H4(CO)2O. It is the anhydride of phthalic acid. Phthalic anhydride is a principal commercial form of phthalic acid. It was the first anhydride of a dicarboxylic acid to be used commer ...
in presence of AlCl3. o-Benzoylbenzoic acid is an intermediate. This reaction is useful for producing substituted anthraquinones. # The Diels-Alder reaction of
naphthoquinone Naphthoquinones constitute a class of organic compounds structurally related to naphthalene. Two isomers are common for the parent naphthoquinones: * 1,2-Naphthoquinone * 1,4-Naphthoquinone Natural products * Alkannin * Hexahydroxy-1,4-napht ...
and
butadiene 1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two viny ...
followed by oxidative dehydrogenation. # The acid-catalyzed dimerization of
styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
to give a 1,3-diphenylbutene, which then can be transformed to the anthraquinone. This process was pioneered by
BASF BASF Societas Europaea, SE () is a German multinational corporation, multinational chemical company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters is located in Ludwigshafen, Germany. The ...
. It also arises via the Rickert-Alder reaction, a retro-Diels-Alder reaction.


Reactions

Hydrogenation gives dihydroanthraquinone (anthrahydroquinone). Reduction with copper gives
anthrone Anthrone is a tricyclic aromatic ketone. It is used for a common cellulose assay and in the colorimetric determination of carbohydrates. Derivatives of anthrone are used in pharmacy as laxative. They stimulate the motion of the colon and reduce w ...
. Sulfonation with sulfuric acid gives anthroquinone-1-sulfonic acid, which reacts with sodium chlorate to give 1-chloroanthaquinone.


Applications


Digester additive in papermaking

9,10-Anthraquinone is used as a digester additive in production of
paper pulp Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, waste paper, or rags. Mixed with water and other chemical or plant-based additives, pulp is the major raw mate ...
by
alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...
ne processes, like the kraft, the alkaline
sulfite Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid ( sulfurous acid) is elusive, its salts are wide ...
or the Soda-AQ processes. The anthraquinone is a
redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
. The reaction mechanism may involve
single electron transfer In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spon ...
(SET). The anthraquinone oxidizes the reducing end of polysaccharides in the pulp, i.e.,
cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
and
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov H ...
, and thereby protecting it from alkaline degradation (peeling). The anthraquinone is reduced to
9,10-dihydroxyanthracene 9,10-Dihydroxyanthracene is an organic compound with the formula (C6H4CHOH)2. It is the hydroquinone form of 9,10-anthraquinone (AQ). It formed when AQ is hydrogenated. It is easily dissolved in alkaline solutions and is often called ''soluble ...
which then can react with
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
. The lignin is degraded and becomes more watersoluble and thereby more easy to wash away from the pulp, while the anthraquinone is regenerated. This process gives an increase in yield of pulp, typically 1-3% and a reduction in
kappa number The Kappa number is an indication of the residual lignin content or bleachability of wood pulp by a standardized analysis method. Measuring method The Kappa number is determined by ISO 302:2004. ISO 302 is applicable to all kinds of chemical an ...
.


Use in flow batteries

9,10-Anthraquinone is used as an electrolyte in
flow battery A flow battery, or redox flow battery (after reduction–oxidation), is a type of electrochemical cell where chemical energy is provided by two chemical components dissolved in liquids that are pumped through the system on separate sides of a ...
which can provide long term electrical storage.


Niche uses

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 The kea (; ; ''Nestor notabilis'') is a species of large parrot in the family Nestoridae found in the forested and alpine regions of the South Island of New Zealand. About long, it is mostly olive-green with a brilliant orange under its wing ...
attacks in New Zealand.


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 Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
atoms replaced by other atoms or
functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
s. 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 Self-healing refers to the process of recovery (generally from psychological disturbances, trauma, etc.), motivated by and directed by the patient, guided often only by instinct. Such a process encounters mixed fortunes due to its amateur nature, ...
properties when doped in
PMMA PMMA may refer to: * para-Methoxymethamphetamine, a stimulant drug * Philippine Merchant Marine Academy The Philippine Merchant Marine Academy ( fil, Akademiya sa Bapor Pangkalakalan ng Pilipinas) also referred to by its acronym PMMA) is a ma ...
matrix.


Safety

Anthraquinone has no recorded , probably because it is so insoluble in water. In terms of metabolism of substituted anthraquinones, the enzyme encoded by the gene UGT1A8 has glucuronidase activity with many substrates including anthraquinones.


See also

*
Benzoquinone Benzoquinone (C6H4O2) is a quinone with a single benzene ring. There are 2 (out of 3 hypothetical) benzoquinones: * 1,4-Benzoquinone, most commonly, right image (also ''para''-benzoquinone, ''p''-benzoquinone, ''para''-quinone, or just quinone) * 1 ...
*
Naphthoquinone Naphthoquinones constitute a class of organic compounds structurally related to naphthalene. Two isomers are common for the parent naphthoquinones: * 1,2-Naphthoquinone * 1,4-Naphthoquinone Natural products * Alkannin * Hexahydroxy-1,4-napht ...
*
Parietin Parietin is the predominant cortical pigment of lichens in the genus ''Caloplaca'', a secondary product of the lichen ''Xanthoria parietina'', and a pigment found in the roots of Curled Dock (''Rumex crispus''). It has an orangy-yellow color and ...


References


External links


National Pollutant Inventory — Polycyclic Aromatic Hydrocarbon Fact Sheet
{{Organic reactions