{{Short description|Class of chemical compounds}} [[File:Anthraquinone Numeration.svg|thumb|200px|Anthraquinone]] '''Anthraquinone dyes''' are an abundant group of dyes comprising a anthraquinone unit as the shared structural element. Anthraquinone itself is colourless, but red to blue dyes are obtained by introducing electron donor groups such as hydroxy or amino groups in the 1-, 4-, 5- or 8-position.<ref name="Hunger">{{citation |editor-first=Klaus |editor-last=Hunger |publisher=WILEY-VCH Verlag|publication-place=Weinheim|pages=35 ff.|isbn=978-3-662-01950-4|date=2003 |title=Industrial Dyes: Chemistry, Properties, Applications |url={{Google books|uAzS4Hk2TgwC|plainurl=yes}}}}</ref> Anthraquinone dyestuffs are structurally related to indigo dyestuffs and are classified together with these in the group of carbonyl dyes.<ref name="Zollinger">{{citation|first=Heinrich |last=Zollinger|edition=3rd|publisher=WILEY-VCH Verlag|publication-place=Weinheim|pages=255 ff.|isbn=3-906390-23-3|date=2003 |title=Color Chemistry: Syntheses, Properties, and Applications of Organic Dyes and Pigments}}</ref>
Members of this dye group can be found in natural dyes as well as in synthetic dyes. Anthraquinone dyestuffs are represented in mordant and vat, but also in reactive and disperse dyes. They are characterized by very good light fastness.<ref>{{RömppOnline|Name=Anthrachinon-Farbstoffe|Datum=14. Dezember 2018 |ID=RD-01-02681}}</ref>
== Natural anthraquinone dyes == [[File:Alizarin.svg|thumb|200px|Alizarin]] One of the most important anthraquinone dyes of herbal origin is alizarin, which is extracted from the dyer's madder (Rubia tinctorum). Alizarin is the eponym for a number of structurally related dyes that use alizarin dyes (sometimes synonymous with anthraquinone dyes). It was the first natural dye for which an industrial synthesis was developed as early as 1869.
Anthraquinone dyes include red insect dyes derived from scale insects such as carminic acid, kermesic acid, and laccaic acids. The colorant carmine, with the main component carminic acid, is used, for example, as an approved food colorant E 120.<ref name="Cooksey">{{cite journal |last1=Cooksey |first1=C. J. |title=The red insect dyes: carminic, kermesic and laccaic acids and their derivatives |journal=Biotechnic & Histochemistry |date=17 February 2019 |volume=94 |issue=2 |pages=100–107 |doi=10.1080/10520295.2018.1511065 |url=https://doi.org/10.1080/10520295.2018.1511065 |access-date=28 March 2022 |issn=1052-0295|url-access=subscription }}</ref> The traditional methods for carmine production are labour-, land-, and insect-intensive. Because demand for red dyes is predicted to increase, researchers are exploring metabolic engineering approaches for the production of synthetic carminic acid.<ref name="Miller">{{cite journal |last1=Miller |first1=Brittney J. |title=Cochineal, a red dye from bugs, moves to the lab |journal=Knowable Magazine |date=25 March 2022 |doi=10.1146/knowable-032522-1 |doi-access=free |url=https://knowablemagazine.org/article/technology/2022/cochineal-red-dye-bugs-moves-lab |access-date=28 March 2022|url-access=subscription }}</ref><ref name="Seo">{{cite journal |last1=Seo |first1=Seung-Oh |last2=Jin |first2=Yong-Su |title=Next-Generation Genetic and Fermentation Technologies for Safe and Sustainable Production of Food Ingredients: Colors and Flavorings |journal=Annual Review of Food Science and Technology |date=25 March 2022 |volume=13 |issue=1 |pages=463–488 |doi=10.1146/annurev-food-052720-012228 |url=https://doi.org/10.1146/annurev-food-052720-012228 |access-date=28 March 2022 |issn=1941-1413|url-access=subscription }}</ref>
== Synthetic anthraquinone dyes == The synthesis of most anthraquinone dyes is based on anthraquinone sulfonic acid ('''2''') or nitroanthraquinone ('''3'''), which is obtained by sulfonation or nitration of anthraquinone ('''1''').
:frameless|upright=2.2|Synthese von 1-Aminoanthrachinon :<small>Synthesis of 1-aminoanthraquinone</small>
Sulfonation in α position is reversible and both the sulfonic acid groups and the nitro groups can be relatively easily replaced by amino, alkylamino, hydroxy and alkoxy groups. Aminoanthraquinone ('''4''') is thus accessible by reaction of anthraquinone sulfonic acid with ammonia or by reduction of nitroanthraquinone.<ref>{{citation |editor-first=Klaus |editor-last=Hunger |publisher=WILEY-VCH Verlag|publication-place=Weinheim|pages=200 ff.|isbn=978-3-662-01950-4|date=2003 |title=Industrial Dyes: Chemistry, Properties, Applications |url={{Google books|uAzS4Hk2TgwC|plainurl=yes}} }}</ref>
An important intermediate product for many acid anthraquinone dyes is bromamic acid (1-amino-4-bromoanthraquinone-2-sulfonic acid) ('''6'''), which can be obtained from 1-aminoanthraquinone ('''4''') by sulfonation with chlorosulfonic acid and subsequent bromination.
:frameless|upright=2.7|Synthese von Bromaminsäure :<small>Synthesis of bromamic acid</small>
By replacing the bromine substituent with an aliphatic or aromatic amine, vibrant blue dyes are obtained.<ref>{{citation|surname1=Heinz-Gerhard Franck, Jürgen W. Stadelhofer|publisher=Springer Verlag|publication-place=Berlin, Heidelberg|pages=365 ff.|isbn=978-3-662-07876-1|date=1978 |language=de |title=Industrielle Aromatenchemie: Rohstoffe · Verfahren · Produkte |url={{Google books|sAuzBgAAQBAJ|plainurl=yes}} }}</ref> For example, bromamic acid can be condensed with 3-(2-hydroxyethylsulfonyl)-aniline ('''7''') to form the vibrant blue dye ('''8''') (oxysulfone blue), from which the reactive dye C.I. Reactive Blue 19 is obtained after esterification with sulfuric acid.
:frameless|upright=3.0|Synthese von C.I. Reactive Blue 19 :<small>Synthesis of C.I. Reactive Blue 19</small>
Reactive Blue 19 is one of the oldest and still the most important reactive dyes,<ref>{{Cite patent | country =DE| number =4422160 | title = Verfahren zur Herstellung von C.I. Reactive Blue 19 | fdate = 1994-06-24 | gdate =1996-04-01 | invent1 =Andreas Von Der Eltz | assign1 = Hoechst AG}}</ref> patented in 1949.<ref>{{Cite patent | country =DE| number = 965902 | title = Verfahren zum Fixieren wasserloeslicher organischer Verbindungen auf Unterlagen faseriger Struktur | fdate =1949-07-19 | gdate =1957-09-19 | invent1 =Johannes Heyna, Willy Schumacher | assign1 = Hoechst AG}}</ref>
The first anthraquinone-based synthetic vat dye was indanthrone (C.I. Vat Blue 4) - the synthesis of which was developed by René Bohn in 1901:
:frameless|upright=3.2|Synthese von Indanthron :<small>Synthesis of indanthrone</small>
By dimerization of 2-aminoanthraquinone ('''1''') under strongly alkaline conditions at 220-235 °C, intermediate stage '''3''' is obtained in two steps, which is cyclized intramolecularly and oxidized to indanthrone 5.<ref>{{citation |first=Heinrich |last=Zollinger |edition=3rd |publisher=WILEY-VCH Verlag|publication-place=Weinheim|page=289|isbn=3-906390-23-3|date=2003 |title=Color Chemistry: Syntheses, Properties, and Applications of Organic Dyes and Pigments}}</ref>
== References == <references />
Category:Anthraquinone dyes