Indigoids

There are three color additives of the indigoid type, including D C Blue No. 6 (35) (an insoluble pigment), FD C Blue No. 2 (2) (the water-soluble disodium sulfonate derivative of indigo), and D C Red No. 30 (23) (an insoluble thioindigoid). AH are related to indigo [482-89-3] which has stmcture (35) (Fig. 3). 

Fig. 3. Miscellaneous dyes used in cosmetics and medical devices. Dye classification (32), azo (33), anthraquinone (34), phthalocyanine (35), indigoid.

Indigoid Dyes. Like the anthraquinone, ben2odifuranone, and polycycHc aromatic carbonyl dyes, the indigoid dyes also contain carbonyl groups. They are also vat dyes. 

Indigoid dyes represent one of the oldest known classes of dyes. For example, 6,6 -dibromoindigo [19201 -53-7] (44) is Tyrian Purple, the dye made famous by the Romans. Tyrian Purple was so expensive that only the very wealthy were able to afford garments dyed with it. Indeed, the phrase "bom to the purple" is still used today to denote wealth. 

Hsynthesis from, 3, 767 Indenobenzazepines pharmacological properties, 7, 546 Indenone oxide, 2,3-diphenyl-photochromic compound, 1, 385 In deno[ 1,2-c][ 1,2,4]triazines synthesis, 3, 434 Indicated hydrogen nomenclature, 1, 33 Indigo, I, 317, 318-319, 4, 370 Baeyer synthesis, 1, 319 colour and constitution, 1, 344-345 molecular structure, 4, 162 photochromic compound, 1, 386 synthesis, 4, 247 Indigoid dyes... 

Selenobiotin synthesis, 4, 968 Seleno indigo synthesis, 4, 959 Seleno indigoid dyes applications, 4, 971 Selenolane, octafiuoro-synthesis, 4, 967 Selenolane, tetrafiuoromethyl-synthesis, 4, 967 Selenolo[3,4-b]benzofuran, aryl-synthesis, 4, 1076... 

Tlie desulfurization of thiono compounds is another frequently used synthetic approach for the formation of double bonds via carbenoid intermediates. By this methodology, some indigoid 1,3,5,7-tetraazafulvalenes 88 and 90 were synthesized (83BSB781 90JPR949).Tliis dimerization starting from 2,4,5-tris(dimethylamino)imidazolium chloride via the appropriate thione 87 has been realized in the presence of phosphanes or phosphites to... 

In context with the formation of peraminosubstituted 1,4,5,8-tetraazaful-valenes of type 85 it must be mentioned that the bis-vinylogous compounds 94 can be easily prepared by reaction of acetamidine with bisimidoylchlo-rides derived from oxalic acid (96S1302). In the course of a complex reaction a cyclic ketene aminal was produced it immediately underwent an oxidative dimerization to yield deeply colored TAFs. Tlieir high chemical stability can be compared with that of indigoid dyes and manifests itself, for example, by the fact that they are soluble in hot concentrated sulfuric acid without decomposition. Tire same type of fulvalene is also available by cy-... 

Anthraquinone leuco dyes are widely known as vat dyes.10 Vat dyes possess extensively conjugated aromatic systems containing two or more carbonyl groups, e.g., anthraquinone, indigoid chromophores. The colored form of vat dyes are insoluble in water. The dyes are applied by a process whereby the dye is converted to the reduced form (leuco dye) which is soluble in water and can penetrate into a cellulosic fiber. On exposure to the atmosphere the leuco form is oxidized to the original quinoid form which then precipitates as an aggregate. Vat dyes generally have excellent chemical and photochemical stability. 

The chromophores contained in natural dyes are mainly flavonoids, antrachinoids, indigoids and gallotannins. Other molecular types include carotenoids, benzochinons and anthocyanidins. 

Debromination with ageing has been observed in the indigoid components of purple [171,172], and photochemical breakdown patterns of the three anthocyanidins contained in Arrabidaea chica red dye, produced by Andean Indian cultures in the tenth to fifteenth centuries, have been hypothesized [173]. Although identifying dye sources in ancient artefacts is quite difficult, it is helped considerably by understanding the fading and degradation mechanisms. 

HPLC-UV-Vis-ESI MS was used to identify indigoid dyes in blue fibre extracts taken from a Japanese tapestry (nineteenth century). Two main colourants were recognized as indigotin and Methylene Blue, [44] a thiazine cationic dye first synthesized at the end of the nineteenth century, commonly used for silk and cotton dying (Figure 13.9). 

Indigoid species are also present in another dyestuff, Tyrian Purple, extracted from molluscs from the Muricidae family. It owes its specific red shade to the presence of bromoindigoids. In the extract of the dyestuff, after chromatographic separation of its components,[44] in addition to indigotin, indirubin and isoindigo, 6,6 -dibromoindigotin is... 

I. Karapanagiotis, Identification of indigoid natural dyestuffs used in art objects by HPLC coupled to APCI MS, Am. Lab., 38, 36 40 (2006). 

M. Puchalska, K. Polec Pawlak, I. Zadrozna, H. Hryszko and M. Jarosz, Identification of indigoid dyes in natural organic pigments used in historical art objects by high performance liquid chromatography coupled to electrospray ionization mass spectrometry, J. Mass Spectrom., 39, 1441 1449 (2004). 

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