Other Indigo Derivatives

Indigo-5,5 -disulfonic acid, disodium salt, C.I. Acid Blue 74, 73015 [860-22-0, Indigotin I, indigo carmine, is approved almost worldwide as a food colorant, and has gained some significance as a dye for foodstuffs, cosmetics, and pharmaceuticals. 

With a few exceptions, sulfur dyes [1] are employed to dye cellulosic fibers. The main applications are the dyeing of corduroy, velveteen, denim articles, twill work clothes, tarpaulins, and backpack fabrics. The dyeing of the cellulosic fiber component of blended fabrics (polyester/cotton blends above all) is increasingly important. 

Sulfur dyes of the Indocarbon type (C.I. Sulphur Black 6, 53295 [1327-16-8], C.I. Sulphur Black 7, 53300 [1327-17-9] and C.I. Sulphur Black 11, 53290 [1327-14-6]) are also used for printing on these fibers. Sulfur dyes find limited use with polyamide fibers, silk, leather, paper, and wood. 

Sulfur dyes with a constitution number are defined in the Colour Index by the starting materials, the type of sulfurization, and in some cases the type of workup. These definitions naturally cannot be precise and were therefore only chosen because little is known about the structures of sulfur dyes. 

The intermediates for sulfur-bake dyes are heated to between 200 and 350° C with sulfur alone, and those for polysulfide bake dyes, with sodium polysulfide. The process is carried out primarily in gas-fired rotating steel drums. 

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Redox indicators include indophenols for example, 2,6-dichlorophenolindophenol azine dyes such as the well-known thiazine dye methylene blue indigo carmine and other indigo derivatives derivatives of diphenylamine including diphenylamine-4-sulfonic acid and variamine blue and the 1,10-phenanthro-line-ferrous complex. 

At the present time we have not attempted to isolate a-thioisatin, the presumed intermediate in the synthesis of indigo. However, it is immediately apparent that if this intermediate could be isolated or intercepted in situ, then many possibilities would open up for the conversion of this compound directly into other indole derivatives. It is also apparent that it should be possible to carry out the reaction with substituted thioureas. We shall be exploring these possibilities. 

Dyes are intensely colored compounds used in fabrics, plastics, inks, and other products. Dyes were originally extracted from plants or animals and used to color cloth. For example, red carmine (page 2) was extracted from cochineal insects, and blue indigo (the dye used in blue jeans) was extracted from plant material. Both of these dyes are now synthesized in large quantities. The Romans extracted the indigo derivative Tyrian purple (imperial purple) from a sea snail and used the dye to color the robes of emperors and high-ranking senators. 

Among many other experiments that Hofmann undertook with aniline was treatment of the indigo-derived base with chlorine. He identified the products. They were used to demonstrate that the two main rival theories of chemical combination were entirely compatible. These were the electrochemical theory of attraction of Jons Jacob Berzelius and the substitution theory of Jean Baptiste Andr6 Dumas. This work was published in 1845 when Hofmann was at Bonn4. Hofmann then moved on to synthesis of aniline in... 

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). 

Vat Dyes. Vat dyes are insoluble in water. Indigo, for example, an ancient blue dye, is probably the best-known example of an ancient vat dye others include woad and Tyrian purple. Since the process of dyeing requires that the dye be in solution, dyeing with a vat dye (or vat dyeing, as the process is known) is possible only after the vat dye has been made soluble by a relatively long and somewhat complicated chemical procedure. The terms vat dye and vat dyeing are probably derived from the large tanks or "vats", in which the process was carried out in ancient times. 

Besides indigo, many other natural products have been produced in the laboratory. One of these is quinine, a compound used for hundreds of years to treat malaria. Quinine is naturally derived from the bark of the tropical Cinchona trees found in Amazonia. Chemists had been trying to synthesize this important drug since the mid-1800s, and finally succeeded in the 1940s. The availability of synthetic quinine helped the Allied troops combat malaria in the Pacific during World War II, and thus it may indirectly be partly responsible forthe outcome of the war. 

Tryptophan malabsorption (blue diaper syndrome) Indigo blue and other indoles (amino acid excretion is normal) Tryptophan Hypercalcemia, retarded growth, febrile episodes, and irritability Chromatographic separation and detection of indole derivatives (H21, S36) (D16, R9, T3a)... 

Other industrial applications of cw-dihydrodiols have also been pursued. Merck has considered using the diol derived fi om indene in the production of the HIV-protease inhibitor indinavir (9). A bioprocess for indigo production was developed by Genencor where the keystep involved the dioxygenation of indole using toluene dioxygenase, summarized in Scheme 3 (10). 

A great variety of dyes have been prepared by fusing with an alkali derivatives of anthraquinone which contain chlorine, alkyl, and other radicals. Condensation in other ways than those illustrated above take place and compounds with very complex structures are obtained. Indigo is the most important vat dye its structure and synthesis are described later (667). 

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