Dye

==== Azo dyes ====

==== Azo dyes ====

{{Main|Azo dyes}}

{{Main|Azo dye}}

[[File:Azo Group Formula V1.svg|thumb|180px|Azo group, R^1,2=aryl / alkenyl]]

[[File:Azo Group Formula V1.svg|thumb|180px|Azo group, R^1,2=aryl / alkenyl]]

==== Dioxazine dyes ====

==== Dioxazine dyes ====

{{Main|Dioxazine dyes}}

[[File:Triphenodioxazine.svg|thumb|[[Triphendioxazine]]]]

[[File:Triphenodioxazine.svg|thumb|[[Triphendioxazine]]]]

Dioxazine dyes, also known as triphendioxazine dyes, contain [[triphendioxazine]] as their basic structure. These intensely colored, brilliant dyes exhibit good [[color fastness]] and thus combine advantages of both azo and anthraquinone dyes. Dioxazine dyes are commercially available as direct and reactive dyes.{{citation|date=2003 |editor=Klaus Hunger |isbn=978-3-662-01950-4 |location=Weinheim |publisher=WILEY-VCH Verlag |title=Industrial Dyes: Chemistry, Properties, Applications |url={{Google books|uAzS4Hk2TgwC|}}}}

Dioxazine dyes, also known as triphendioxazine dyes, contain [[triphendioxazine]] as their basic structure. These intensely colored, brilliant dyes exhibit good [[color fastness]] and thus combine advantages of both azo and anthraquinone dyes. Dioxazine dyes are commercially available as direct and reactive dyes.{{citation|date=2003 |editor=Klaus Hunger |isbn=978-3-662-01950-4 |location=Weinheim |publisher=WILEY-VCH Verlag |title=Industrial Dyes: Chemistry, Properties, Applications |url={{Google books|uAzS4Hk2TgwC|}}}}

==== Indigoid dyes ====

==== Indigoid dyes ====

{{Main|Indigo}}

{{Main|Indigo}}[[File:Indigo skeletal.svg|thumb|Chemical structure of [[indigo dye]], the blue coloration of blue jeans. Although once extracted from plants, indigo dye is now almost exclusively synthesized industrially.{{Ullmann|last=Steingruber|first=Elmar|title=Indigo and Indigo Colorants|doi=10.1002/14356007.a14_149.pub2}}]]

[[File:Indigo skeletal.svg|thumb|Chemical structure of [[indigo dye]], the blue coloration of blue jeans. Although once extracted from plants, indigo dye is now almost exclusively synthesized industrially.{{Ullmann|last=Steingruber|first=Elmar|title=Indigo and Indigo Colorants|doi=10.1002/14356007.a14_149.pub2}}]]

Indigoid dyes belong to the [[carbonyl dyes]] and are used as vat dyes. The most important representative is indigo, which was extracted from plants as a natural dye in ancient times and is still produced industrially in large quantities, particularly for dyeing [[jeans]]. Another natural dye is the ancient [[purple (dye)|purple]] (''C.I. Natural Violet 1'' / ''Dibromindigo'').

Indigoid dyes belong to the [[carbonyl dyes]] and are used as vat dyes. The most important representative is indigo, which was extracted from plants as a natural dye in ancient times and is still produced industrially in large quantities, particularly for dyeing [[jeans]]. Another natural dye is the ancient [[purple (dye)|purple]] (''C.I. Natural Violet 1'' / ''Dibromindigo'').

==== Metal complex dyes ====

==== Metal complex dyes ====

{{Main|Metal complex dyes}}

Metal complex dyes consist of [[Coordination complex|complex compounds]] formed from a [[metal]] and one or more dye [[ligands]] containing [[electron donors]]. Copper and chromium compounds predominate, although cobalt, nickel, and iron complexes are also used to a lesser extent. The ligands are often azo dyes, methine dyes, [[formazans]], or [[phthalocyanines]]. Metal complex dyes are characterized by excellent fastness properties.

Metal complex dyes consist of [[Coordination complex|complex compounds]] formed from a [[metal]] and one or more dye [[ligands]] containing [[electron donors]]. Copper and chromium compounds predominate, although cobalt, nickel, and iron complexes are also used to a lesser extent. The ligands are often azo dyes, methine dyes, [[formazans]], or [[phthalocyanines]]. Metal complex dyes are characterized by excellent fastness properties.

==== Methine dyes ====

==== Methine dyes ====

{{Main|Methine dyes}}

{{Main|Polymethine dyes}}

[[File:Methine Dyes.svg|thumb|360px|Structural principle of methine dyes]]

[[File:Methine Dyes.svg|thumb|360px|Structural principle of methine dyes]]

==== Direct dyes ====

==== Direct dyes ====

{{Main|Direct dyes}}

{{Main|Substantive dye}}

Direct dyes (or [[substantive dye]]s) are absorbed directly from aqueous solution onto the fiber due to their high [[substantivity (textile chemistry)|substantivity]]. They are particularly suitable for [[cellulose]] fibers. Binding to the fiber occurs through physical interactions, mainly [[Van der Waals forces]]. Most direct dyes belong to the azo dye group, especially polyazo dyes. In the Colour Index, they are designated as ''C.I. Direct Dyes''. Examples:

Direct dyes (or [[substantive dye]]s) are absorbed directly from aqueous solution onto the fiber due to their high [[substantivity (textile chemistry)|substantivity]]. They are particularly suitable for [[cellulose]] fibers. Binding to the fiber occurs through physical interactions, mainly [[Van der Waals forces]]. Most direct dyes belong to the azo dye group, especially polyazo dyes. In the Colour Index, they are designated as ''C.I. Direct Dyes''. Examples:

==== Disperse dyes ====

==== Disperse dyes ====

{{Main|Disperse dyes}}

Disperse dyes, which are almost insoluble in water, are primarily used for dyeing hydrophobic polyester and [[cellulose acetate]]. They are finely ground together with [[dispersing agents]], enabling the molecularly dissolved dye to diffuse into the fiber during dyeing, where it forms a solid solution. This results in dyes with good wash and light fastness.

Disperse dyes, which are almost insoluble in water, are primarily used for dyeing hydrophobic polyester and [[cellulose acetate]]. They are finely ground together with [[dispersing agents]], enabling the molecularly dissolved dye to diffuse into the fiber during dyeing, where it forms a solid solution. This results in dyes with good wash and light fastness.

==== Development or coupling dyes ====

==== Development or coupling dyes ====

{{Main|Developing dyes}}

In developing dyes, a practically water-insoluble dye is formed directly on the fiber by the reaction of a water-soluble coupling component (''C.I. Azoic Coupling Component'') with a water-soluble diazo component (''C.I. Azoic Diazo Component''). This dye class is mainly used for cellulose fibers and is characterized by very good wet fastness. The most important coupling component in developing dyes is [[Naphthol AS]].

In developing dyes, a practically water-insoluble dye is formed directly on the fiber by the reaction of a water-soluble coupling component (''C.I. Azoic Coupling Component'') with a water-soluble diazo component (''C.I. Azoic Diazo Component''). This dye class is mainly used for cellulose fibers and is characterized by very good wet fastness. The most important coupling component in developing dyes is [[Naphthol AS]].

==== Cationic dyes ====

==== Cationic dyes ====

{{Main|Cationic dyes}}

Cationic dyes are [[cation]]ic compounds that produce brilliant and lightfast colors, particularly on [[polyacrylonitrile]] (PAN) fibers and anionically modified [[polyester]] fibers. They form ionic bonds with negatively charged groups on the fiber. Various chromophores can be used in cationic dyes; in methine dyes, the positive charge is delocalized, in contrast to other chromophoric systems.

Cationic dyes are [[cation]]ic compounds that produce brilliant and lightfast colors, particularly on [[polyacrylonitrile]] (PAN) fibers and anionically modified [[polyester]] fibers. They form ionic bonds with negatively charged groups on the fiber. Various chromophores can be used in cationic dyes; in methine dyes, the positive charge is delocalized, in contrast to other chromophoric systems.

==== Vat dyes ====

==== Vat dyes ====

{{Main|Vat dyes}}

Vat dyes comprise water-insoluble pigments that are converted into their soluble dihydro or [[leuco base]] form for dyeing by [[reduction (chemistry)|reduction]] (''vatting'') in alkaline solution. The anion exhibits sufficient affinity for cotton or viscose fibers, allowing absorption. The dye is subsequently reconverted to its insoluble form by oxidation, either by atmospheric oxygen or by oxidizing agents. The dye is effectively fixed at the molecular level within the fiber; this "precipitation within the fiber" results in very high wash and light fastness.Wittko Francke, Wolfgang Walter: ''Lehrbuch der Organischen Chemie.'' S. Hirzel Verlag, Stuttgart 2004, ISBN 3-7776-1221-9, S. 684 f. Water-insoluble [[#sulfur dyes|sulfur dyes]] exhibit similar behavior.

Vat dyes comprise water-insoluble pigments that are converted into their soluble dihydro or [[leuco base]] form for dyeing by [[reduction (chemistry)|reduction]] (''vatting'') in alkaline solution. The anion exhibits sufficient affinity for cotton or viscose fibers, allowing absorption. The dye is subsequently reconverted to its insoluble form by oxidation, either by atmospheric oxygen or by oxidizing agents. The dye is effectively fixed at the molecular level within the fiber; this "precipitation within the fiber" results in very high wash and light fastness.Wittko Francke, Wolfgang Walter: ''Lehrbuch der Organischen Chemie.'' S. Hirzel Verlag, Stuttgart 2004, ISBN 3-7776-1221-9, S. 684 f. Water-insoluble [[#sulfur dyes|sulfur dyes]] exhibit similar behavior.

==== Food colorants / food dyes ====

==== Food colorants / food dyes ====

{{Main|Food colorant}}

{{Main|Food coloring}}

Food colorants are used as [[food additives]] to compensate for color changes caused by processing or to meet consumer expectations. Both naturally occurring and synthetically produced colorants are employed. The use of food colorants is strictly regulated by law—within the [[EU]] by Regulation (EC) No. 1333/2008 of December 16, 2008, on food additives.{{EUR-Lex link|uri=uriserv:OJ.L_.2008.354.01.0016.01.DEU|title=Verordnung (EG) Nr. 1333/2008 16 December 2008 über Lebensmittelzusatzstoffe|format=PDF}}, retrieved 5 August 2019. Only approved additives bearing an E number may be marketed, and these must be declared on the product.{{cite web|access-date=2019-08-05 |publisher=Bundesministerium für Ernährung und Landwirtschaft |title=Zulassung und Verwendung von Lebensmittelzusatzstoffen |url=https://www.bmel.de/DE/Ernaehrung/SichereLebensmittel/SpezielleLebensmittelUndZusaetze/Zusatzstoffe/_Texte/Lebensmittelzusatzstoffe.html}}

Food colorants are used as [[food additives]] to compensate for color changes caused by processing or to meet consumer expectations. Both naturally occurring and synthetically produced colorants are employed. The use of food colorants is strictly regulated by law—within the [[EU]] by Regulation (EC) No. 1333/2008 of December 16, 2008, on food additives.{{EUR-Lex link|uri=uriserv:OJ.L_.2008.354.01.0016.01.DEU|title=Verordnung (EG) Nr. 1333/2008 16 December 2008 über Lebensmittelzusatzstoffe|format=PDF}}, retrieved 5 August 2019. Only approved additives bearing an E number may be marketed, and these must be declared on the product.{{cite web|access-date=2019-08-05 |publisher=Bundesministerium für Ernährung und Landwirtschaft |title=Zulassung und Verwendung von Lebensmittelzusatzstoffen |url=https://www.bmel.de/DE/Ernaehrung/SichereLebensmittel/SpezielleLebensmittelUndZusaetze/Zusatzstoffe/_Texte/Lebensmittelzusatzstoffe.html}}

==== Reactive dyes ====

==== Reactive dyes ====

{{Main|Reactive dyes}}

{{Main|Reactive dye}}

During the dyeing process, reactive dyes form a [[covalent bond]] with functional groups of the fiber, resulting in dyes with high wet fastness. They constitute the largest group of dyes used for cellulose fibers, but are also employed for wool and polyamide in deep shades.H. Zollinger: ''Chemismus der Reaktivfarbstoffe''. In: ''[[Angewandte Chemie (Zeitschrift)|Angew. Chem.]]'' 73, Nr. 4, 1961, S. 125–136, [[doi:10.1002/ange.19610730402]].

During the dyeing process, reactive dyes form a [[covalent bond]] with functional groups of the fiber, resulting in dyes with high wet fastness. They constitute the largest group of dyes used for cellulose fibers, but are also employed for wool and polyamide in deep shades.H. Zollinger: ''Chemismus der Reaktivfarbstoffe''. In: ''[[Angewandte Chemie (Zeitschrift)|Angew. Chem.]]'' 73, Nr. 4, 1961, S. 125–136, [[doi:10.1002/ange.19610730402]].

==== Acid dyes ====

==== Acid dyes ====

{{Main|Acid dyes}}

{{Main|Acid dye}}

Acid dyes are [[Hydrophile|hydrophilic]] dyes containing [[anion]]ic substituents, usually sulfonic acid groups. Most acid dyes belong to the azo dye class, although other chromophores also occur. They are mainly used for dyeing wool, silk, and polyamide, with dyeing carried out in the pH range 2–6. When small dye molecules are used, uniform dyeing is achieved, with dye molecules forming primarily salt-like bonds with ammonium groups of the fiber. The wash fastness of such dyes is relatively moderate. With increasing molecular size, dye–fiber binding is enhanced through adsorption forces between the hydrophobic parts of the dye molecule and the fiber. This improves wet fastness, but often at the expense of dyeing uniformity.

Acid dyes are [[Hydrophile|hydrophilic]] dyes containing [[anion]]ic substituents, usually sulfonic acid groups. Most acid dyes belong to the azo dye class, although other chromophores also occur. They are mainly used for dyeing wool, silk, and polyamide, with dyeing carried out in the pH range 2–6. When small dye molecules are used, uniform dyeing is achieved, with dye molecules forming primarily salt-like bonds with ammonium groups of the fiber. The wash fastness of such dyes is relatively moderate. With increasing molecular size, dye–fiber binding is enhanced through adsorption forces between the hydrophobic parts of the dye molecule and the fiber. This improves wet fastness, but often at the expense of dyeing uniformity.