Unit - Chemistry of Fibres, Textiles and Garments
Dyeing of fabrics.

The following links are to wikipedia for information on traditional textile dyes.
Black walnut Bloodroot Brazilin Cochineal (Polish cochineal) Cudbear Cutch Dyewoods Fustic Henna Indigo Kermes Logwood Madder Saffron Turmeric Tyrian purple Weld Woad

Dyers at work
Medieval dyers use long poles to stir cloth in the dye bath to produce red cloth.
From the British Library, Royal Ms 15 E. III f.269 (1482) via Wikipedia

This lecture will attempt to summarise some of the topics covered in a "Tutorial Review" of historical dyes published by Hamish McNab (University of Edinburgh) in Chem. Soc. Rev., 2004, 33, 329-336.

Throughout the world, natural dyes have been used since the most ancient times until the end of 19th century when they were largely replaced by cheaper synthetic dyes. The ancient dyestuffs were generally organic materials obtained from plants, insects, shellfish and lichens, whereas many of the earliest pigments were inorganic materials obtained from natural ores.

Where did the earliest dyes come from? See the "Worst jobs in history" Tudor era video clips that feature 4- indigo and 5- indigo continued from woad (Isatis tinctoria) and Royal age 6- Tyrian purple from (Murex brandaris).

Initially the method we will use for classifying the dyes will be based on their colour; blue, purple, red, yellow as well as by a description of the chemical structure and identifying the chromophore responsible.

Most blue and purple colours were derivatives of indigo, obtained either from woad or from the indigo plant, though some other sources (e.g. shellfish and lichens) were used. Reds were often anthraquinone derivatives obtained from plants or insects. Yellows were almost always flavonoid derivatives obtained from a variety of plant species. Most other colours were produced by over-dyeing, e.g. greens were obtained by over-dyeing a blue with a yellow dye.

Blue dyes

Most of the naturally occurring indigo derivatives are insoluble in water but may become soluble in the presence of reducing agents. The fibres are therefore treated using a technique called vat dyeing such that whilst the dye is in solution the fibre is added to the dye bath and following its removal and exposure to air the insoluble dye is trapped inside the fibre.

The natural products from which indigo is obtained include indican (2a), which occurs in Indigofera species, e.g. the indigo plant itself Indigofera tinctoria L., as well as woad (Isatis tinctoria L. which contains both indican (2a) and isatan (2b).

Irrespective of the starting plant source the dye extraction follows the same process. The fermentation stage degrades the glycosides by enzymatic hydrolysis to indoxyl (3) (a mixture of keto-enol tautomers) which is then oxidised to 'leuco-indigo' (6) and eventually to indigotin (1). A side reaction can occur if indoxyl is converted by oxidation to the diketone, isatin (4) that can then further react with another molecule of indoxyl (3) to produce indirubin (5).

preparation of indigo UV/Vis spectrum of indigo
Preparation and UV/Vis spectrum of Indigotin (wavelength /nm)

The primary use for indigo today (several thousand tons each year) is as a dye for cotton yarn, which is mainly for the production of denim cloth for blue jeans. On average, a pair of blue jeans requires 3 - 12 g of indigo. Small amounts are used for dyeing wool and silk. All of the dye used is synthetically produced.

Indigo carmine, or indigotine, is an indigo derivative (sodium salt of 5,5'-indigodisulfonic acid) that is also used as a colorant. Approximately 20M kilograms are annually produced, again mainly for blue jeans. In addition it is used as a food colorant, and is listed in the USA as FD&C Blue No. 2, and in the European Union as E132.

Assignment
Describe the processes that have been used for the commercial synthesis of indigotin and indigo carmine.

Shellfish purple

The purple dyes obtained from shellfish are bromo-derivatives of indigotin (1). Arguably, 6,6'-dibromoindigotin is the oldest known pigment, the longest lasting, the subject of the first chemical industry, the most expensive and the best known. See the Review by Chris Cooksey in Molecules 6 (9),736-769 (2001). and a bibliographic list of references related to Tyrian purple.

The three main species of molluscs used in the Mediterranean region were spiny dye-murex (Bolinus brandaris L. or Murex brandaris), rock-shell (Thais haemastoma L. or Purpura haemastoma), and banded dye-murex (Hexaplus trunculus L. or Murex trunculus). As in the case of indigo plant sources, the dye is not present in the live mollusc. It is generated by enzymatic hydrolysis of precursors found in the animals' hypobranchial glands, to provide derivatives of indoxyl (3) followed by photochemical conversion to the purple pigment. Only very small amounts of dye (often < 1 mg) can be obtained from each mollusc (enough to dye only ca. 1 g of wool) making these dyes very expensive commodities.


indigo chromophore
possible chromophore and crystal structure of 6,6'-dibromoindigotin

A comparison between the use of indigo or dibromoindigo as dyes can be seen from the reflectance spectra of wool samples. The absorption maximum of indigo shifts from 605 nm in solution to over 650 nm as a dye, whereas that of dibromoindigo shifts from 590 nm to 520 nm.

reflectance spectra of wool dyed with dibromoindigo and indigo
Reflectance spectra of wool samples dyed with dibromoindigo (purple) and indigo (blue).

Red dyes

Insect dyes
The main red insect dyes are from plant parasites belonging to the Coccidea family and are extracted from American cochineal (Dactylopius coccus Costa), kermes (Kermes vermilio Planchon), Polish cochineal (Porphyrophora polonica L.), Armenian cochineal (Porphyrophora hamelii Brandt) and lac (Kerria lacca Kerr). The chromophores in all of these scale insect dyes are derivatives of anthraquinone.

In the case of cochineal the colourant (carminic acid) is extracted from the bodies of female insects just prior to egg-laying time and as such, may contain from 10 to 20% of their dry weight of the dye. The collected insects are dried and extracted with hot aqueous basic solution that may contain a samll amount of ethanol. It has estimated that about 25 million insects are required to make 14.5 kg of water-soluble extract.

kermes and lac dyes
Red dyes and the structure of carminic acid

Plant anthraquinone reds

Redwoods

Logwood and Brazilwood and Logwood in Jamaica

Haematoxylum campechianum (Logwood) was used for a long time as a natural source of dye, and still remains an importance source of haematoxylin, which is used in histology for staining. The bark and leaves have found use in various medical applications. In its time, logwood was considered a versatile dye, and was widely used on textiles and for paper. The dye's colour depends on the mordant used as well as the pH. Like litmus, it is red in acidic environments and blue in alkaline ones.

Caesalpinia echinata (Brazilwood) is a species of Brazilian timber tree in the pea family, Fabaceae. Common names include Brazilwood, Pau-Brasil, Pau de Pernambuco and Ibirapitanga (Tupi). This plant has a dense, orange-red heartwood that takes a high shine, and it is the premier wood used for making bows for stringed instruments. The wood yields a red dye called brazilin, which oxidizes to brazilein.

redwood dyes
A=haematoxylin, B=haematein, C=brazilin and D=brazilein.

ACD/Labs simulation of C NMR of haematein
Simulation of C-NMR of B=Haematein

Yellow dyes

Flavonoids and flavones

Flavonoids are the most important plant pigments for flower colouration producing yellow or red/blue pigmentation in petals designed to attract pollinator animals.

flavonoids

R'= H, R"=H apigenin; R'= H, R"=OH luteolin; R'= OH, R"=H kaempferol

MS of flavonoids
MS of luteolin and kaempferol

Although both luteolin and kaemferol have the same RMM and show a peak at 287 they can be readily distinguished by the intense peak at 165 for kaempferol that comes about by the cleavage shown by the red dotted line above. This leaves the left hand benzene ring intact and is stabilised by the R' hydroxy group (not present in luteolin).

The plant species Reseda luteola was the most widely used source of the natural dye known as weld. The plant is rich in luteolin, a flavonoid which produces a bright yellow dye. The yellow could be mixed with the indigo blue from woad (Isatis tinctoria) to produce greens, such as Lincoln green. The dye was in use by the first millennium BC, and perhaps earlier than either woad or madder. Use of this dye came to an end at the beginning of the twentieth century, when cheaper synthetic yellow dyes came into use.

Saffron, turmeric and other yellows

Saffron is obtained from the stigmatas of the flowers of Crocus sativus L. and has a long history of use as a direct dye dating back to Egyptian times. It was very popular in Persia in Classical times. It was later replaced by cheaper dyes, like weld, with better fastness properties. When used as a direct dye, it gives a beautiful orange yellow colour and it can also be used with alum mordant.

Saffron contains more than 150 volatile and aroma-yielding compounds. In addition it has many nonvolatile active components, many of which are carotenoids, including zeaxanthin, lycopene, and various α- and β-carotenes. However, saffron's golden yellow-orange colour is primarily the result of α-crocin, a glucoside of crocetin, a polyunsaturated diacid.

crocin
Yellow dyes and the structure of crocin

Turmeric (Curcuma longa) is a rhizomatous herbaceous perennial plant of the ginger family, Zingiberaceae.

If the rhizomes are boiled for several hours and then dried in hot ovens, They can then be ground into a deep orange-yellow powder commonly used as a spice in curries and other South Asian and Middle Eastern cuisine, for dyeing, and to impart color to mustard condiments. Its active ingredient is curcumin and it has a distinctly earthy, slightly bitter, slightly hot peppery flavor and a mustardy smell.

In medieval Europe, turmeric became known as Indian saffron, since it was widely used as an alternative to the far more expensive saffron spice.

See Wikipedia for a description of traditional dyes of the Scottish Highlands to see what colours were available for Scottish kilts?

Synthetic Dyes

In 1853, when William Henry Perkins (1838-1907) was only 15, he entered the Royal College of Chemistry in London (now part of Imperial College London), and began his studies under August Wilhelm von Hofmann.
For an introduction see the TED lecture by Susan Clark on synthetic dyes.

Hofmann had published a hypothesis on how it might be possible to synthesise quinine, an expensive natural substance much in demand for the treatment of malaria. Perkin, who had by then become one of Hofmann's assistants, embarked on a series of experiments to try to achieve this end. During the Easter vacation in 1856, while Hofmann was away visiting his native Germany, Perkin performed some further experiments and made his great discovery: that aniline could be partly transformed into a crude mixture which when extracted with alcohol produced a substance with an intense purple colour.

William Perkins
William Perkins, who in 1856 (aged 18) discovered the first aniline dye, mauveine.

The brilliant violet hue quickly attracted much attention, especially following an appearance at the Royal Exhibition of 1862, by Queen Victoria wearing a silk gown dyed with mauveine and this stimulated other chemists to carry out similar experiments. In 1859, François-Emmanuel Verguin in Lyon, France discovered fuchsine, (see the visible spectum of fuchsine) whilst the discovery of diazo compounds by Peter Griess at the Royal College of Chemistry in London laid the foundation for the development of the currently largest class of synthetic dyes, namely the azo compounds. The first true azo dye, Bismarck Brown, (see the visible spectum of Bismarck Brown Y and Bismarck Brown R) was developed by Carl Alexander Martius in 1863. Martius was another chemist who worked for Hofmann and apparently kept secret from him his discovery. He later moved to Manchester and with Heinrich Caro produced a range of dyestuffs for Roberts, Dale and Co.

This was clearly a vibrant era for chemistry entrepreneurs covering a quite short 1856 - 1864 time frame as shown by the Table below of the leading coal tar dyes from that era.

Year and product Invented by
(date of discovery shown if different from year of first production)
Synonyms Procedure
1858
Tyrian purple
Perkin (1856) aniline purple, mauve (1859) commercial aniline/ potassium dichromate
1859
Fuchsine/aniline red
Verguin roseine, rosaniline commercial aniline/stannic chloride
1860
magenta/aniline red
Nicholson, Medlock commercial aniline/arsenic acid
1861
aniline blue
Girard and de Laire aniline red + aniline
1861
mauve
Caro (1860) commercial aniline/copper salts
1862
aniline black
Caro residue of Caro's mauve process
1862
aniline green
Usèbe aldehyde green aniline red + aldehyde
1862
rosolic acid
Caro, (Mùller Kolbe and Schmitt; Persoz 1859) aurin(e), yellow coralline phenol + oxalic acid + sulfuric acid
1862
cyan brown
Caro picric acid + potassium cyanide
1863
aniline black
Lightfoot (1859) direct application of aniline to cotton during printing
1863
phosphine
Nicholson chrysaniline by-product of magenta manufacture (Nicholson's process)
1863
Hofmann's violets
Hofmann trimethylrosaniline and triethylrosaniline aniline red + alkyl halides
1863/64
induline
Martius and Caro azobenzene + aniline
1863/64
aniline yellow
Martius and Caro nitrous acid on aniline
1863/64
phenylene brown
Martius and Caro Bismarck brown (c.1870), Manchester Brown, Vesuvin (BASF) nitrous acid on m-diaminobenzene
1864
Martius yellow
Martius and Caro Manchester yellow, jaune d'or (France), chrysonaphthalic acid, dinitronaphthylalcohol, dinitronaphthalinic acid, binitrohydroxynaphthalene, naphthalene yellow naphthylamine > diazotise > naphthol + dinitronaphthol


Perkin's new colour fell out of fashion by the late 1860s, but he soon discovered two new dyes, Britannia Violet and Perkin's Green (the water in the nearby Grand Union Canal was said to have turned a different colour every week- depending on what dyes were being made at the time). In 1869, Perkin synthesised the vivid natural red dye called Alizarin (see the visible spectum of alizarin) .

The German company BASF beat him to the patenting process by one day! Perkin and BASF came to an agreement over the manufacturing processes (Perkin would sell Alizarin in Britain, some 400 tons a year and BASF to the rest of the world) but the heyday of synthetic dye manufacturing at Perkin's plant was now waning (allegedly because British universities were not producing a sufficient supply of chemists for the constant innovation now required in the dye industry) and in 1874, Perkin sold his dyeworks to Brooke, Simpson and Spiller. It continued operation under its new owners only until 1876, when it was sold to the tar makers Burt, Boulton and Haywood, the dye operations of which joined the British Alizarine Company. This in turn became part of ICI in 1931, and in more modern times became known as Zeneca, a company which can claim to be the successor of Perkin.

Not long after that Chrysoidine was discovered by O. N. Witt in 1876, and Congo Red, by P.Böttiger in 1883, the first dyestuff capable of direct application to cotton.
At the same time came the first determinations of the structures of natural dyes and the artificial production of them. The first of these can be considered as alizarin, then indigo (1870-1890). In 1901 the first anthraquinone vat dye, indanthrone was discovered by R. Bohn.

The possible relationship between composition and colour on the one hand, and fastness on the other, were the subject of several attempts at theoretical explanations. One in particular was the theory of O. N. Witt on chromophores and auxochromes, and the theory - valid only in special cases - of E. Schirm, J. Prakt. Chem., 144 (1936) 69, concerning the connexion between composition and affinity to cellulose fibre.

Tuning Azo dyes for different colours
See for example Tuning Azo dyes.
Modifying the substituents on a ring can influence solubility as well as changing the colour. This can be seen from the Table below where the following effects of substituents are shown:


1 λ=320 nm

2 λ=375 nm

3 λ=470 nm

4 λ=520 nm

5 λ=578 nm

Another paper on tuning of azo-dyes is at J. Biomed. Opt. 20(9), 095003 (Sep 03, 2015). doi:10.1117/1.JBO.20.9.095003

The dye process

Apart from the colour they produce, dyes may be characterised by the method of their application to the fabric. For example:

The 5 most widely used dyes (1996).
Dye t/year
Indigo 15,000
Disperse blue 79 15,000
Sulphur black 1 10,000
Reactive dye black 5 8,000
Acid black 194 7,000

A dye with one of the largest molar absorbances (ε).

octaethyl-[22]porphyrin
ε= 112000 m2 mol-1 with λmax =460 nm

References
JAIC 1992, Volume 31, Number 2, Article 7 (pp. 237 to 255)
World Records in Chemistry, H-J. Quadbeck-Seeger (ed), Wiley-VCH, 1999, Weinheim, Germany

Acknowledgements.
Much of the information in these course notes has been sourced from Wikipedia under the Creative Commons License. Students taking this course will be encouraged to contribute to Wikipedia as a part of their course assignments.

On to Textile Treatments or return to CHEM2402 course outline.

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