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. Th ...
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.
Is ...
s include various
quinone
The quinones are a class of organic compounds that are formally "derived from aromatic compounds uch as benzene or naphthalene">benzene.html" ;"title="uch as benzene">uch as benzene or naphthalene] by conversion of an even number of –CH= group ...
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 and ...
s and is used in bleaching pulp for papermaking. It is a yellow, highly crystalline solid, poorly
soluble 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 ...
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 with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
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.
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 production of the red dye alizarin and other dyes. Anthracene is co ...
.
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 in presence of
AlCl3. o-Benzoylbenzoic acid is an intermediate. This reaction is useful for producing substituted anthraquinones.
# The
Diels-Alder reaction of
naphthoquinone 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 v ...
followed by oxidative dehydrogenation.
# The acid-catalyzed dimerization of
styrene to give a 1,3-diphenylbutene, which then can be transformed to the anthraquinone.
This process was pioneered by
BASF
BASF SE () is a German multinational chemical company and the largest chemical producer in the world. Its headquarters is located in Ludwigshafen, Germany.
The BASF Group comprises subsidiaries and joint ventures in more than 80 countries ...
.
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 ...
. 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 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 second incarnation of Kraft Foods is an American food manufacturing and processing conglomerate, split from Kraft Foods Inc. in 2012 and headquartered in Chicago, Illinois. It became part of Kraft Heinz in 2015.
A merger with Heinz, arran ...
, 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 w ...
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 change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
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 (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 wa ...
and
hemicellulose, 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 an ...
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 a ...
. 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.
Use in flow batteries
9,10-Anthraquinone is used as an electrolyte in
flow battery 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 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-to ...
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 r ...
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 properties when doped in
PMMA PMMA may refer to:
* para-Methoxymethamphetamine, a stimulant drug
* Philippine Merchant Marine Academy
* Poly(methyl methacrylate), a transparent thermoplastic often used as a glass substitute
{{disambig ...
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
*
Naphthoquinone
*
Parietin
References
External links
National Pollutant Inventory — Polycyclic Aromatic Hydrocarbon Fact Sheet
{{Organic reactions