Indigo natural sources

Other well-known indoles that have various natural sources are skatole (3-methylindole) (2), serotonin (3), L-tryptophan (4), tryptamine (5), the plant growth hormones 3-indoleacetic acid (6) and 4-chloro-3-indoleacetic acid (7) [19], the mushroom hallucinogen psilocin (8), and the indole-derived ancient dyes indigo (9) [20] and Tyrian Purple (10) [19] (Scheme 1). 

The chemistry of colorants, particularly in the dyeing of textiles, has a long and rich history. There are indications that the art of dyeing was practiced as early as 3000 B.C.E. in China and Egypt [21]. The colorants used were obtained from natural sources. Examples include blue indigo from the indigo plant, reds fi om the root of madder, yellows and reds from saffiower, and lyrian Purple produced by the Phoenicians from shellfish [22]. 

Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

Once the structure of indigo was established in 1870, it was quite logical to attempt its synthesis, not only as an intellectual challenge, but also as a profitable source of cheaper indigo that could advantageously compete with the natural dyestuff. The first industrial synthesis used by "Badische Anilin und Soda Fabrik" (BASF) was the procedure developed by Karl Neumann, which utilised the reaction of aniline with chloroacetic acid and then cyclisation of the resulting product to indoxyl promoted by NaNHj at high temperatures (over 200 °C). However, the... 

There are over 8000 chemicals that exhibit commercially significant optical properties. Some of these are natural products such as indigo, chlorophyll, and cochineal, but the majority are synthesized in a series of steps involving dye intermediates (any of the 3000 or more organic and inorganic chemicals used as raw material precursors to manufactured dyes, the most important of which are benzene and naphthalene). Coal tar dyes refers to the dyestuffs originating from the complex mix of hydrocarbons (benzene, toluene, xylene, pyrene, naphthalene, anthracene, etc.) present in coal tar (8007-45-2). Petroleum has succeeded coal as the dominant source of dye intermediates. Dyes, pigments, and dye intermediates include... 

In addition to the anthocyanins, another important source of dyes is the naturally occurring indican which on hydrolysis yields indoxyl and glucose. The indoxyl upon oxidation is converted to the dye indigo. The preparation of indigo from plants involves the extraction of the glucoside, its enzymic hydrolysis by microorganisms, and the oxidation of the indoxyl to indigo by air. The synthesis by Robertson (Iof indican, illustrated below, fur-... 

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