Indigo

Phenylglycine-o-carboxylic acid. In a 750 ml. round-bottomed flask, fitted with a reflux condenser, place 14 g. of anthranilic acid (Section IV,170), 10 g. of chloroacetic acid, 20 g. of anhydrous sodium carbonate and 200 ml. of water. Reflux the mixture for. 3 hours, then pour into a beaker, cool, render shghtly acid with concentrated hy dro-chloric acid, and allow to stand overnight. Filter off the crude acid and wash it with water. Recrystalhse from hot water with the aid of a little decolourising carbon, and dry the acid at 100°. The yield of phenyl-glycine-o-carboxyhc acid, m.p. 208°, is 12 g. 

AnthTanilic acid ChlOFoacettc acid Phenylglycine-o-carboxylic acid 

4 Cave painting from Lascaux and a rose chafer. 

Apart from ultramarine (see marginal note on next page) [2], indigo was one of the few colourants to close this blue gap in the colour palette. In ancient times, it was reckoned as valuable on accoimt of its beauty and lightfastness, which lent itself to wider applications, not only for the colouring of precious textiles but also for artwork. 

All the Britains, indeed, dye themselves with woad, which occasions a bluish colour, and thereby have a more horrible appearance in fight. 

In De Bello GaUico, Julius Caesar (100-44 BC) describes another interesting use of indigo by the British Celts. Indigo serves as a component of make-up for 

In the High Gothic period, there developed a diverse colour symbolism. By virtue of the price of clear deep blue shades, artists confined themselves to use blue only to depict the saints. In this way, blue emerged as the symbolic colour for the Virgin Mary (Fig. 2.6). 

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It is an important dyestuffs intermediate. It condenses with chloroethanoic acid to give phenylglycine-o-carboxylic acid for the synthesis of indigo. It can be diazotized and used as a first component in azo-dyes it condenses also with chloroanthraquinones to give intermediates for anthraquinone dyes. 

It is an important intermediate in the indigo industry. When phenylglycine is fused with sodamide a good yield of indoxyl is obtained. The indoxyl is easily oxidized to indigo. 

It is used for the preparation of indigo into which it is readily converted on alkaline fusion. 

When treated with alkaline hypochlorite solution anthranilic acid is obtained. This reaction, the first stage in the indigo synthesis, is the most important commercial outlet for phthalimide. 

The reducing action of sulphurous acid and sulphites in solution leads to their use as mild bleaching agents (for example magenta and some natural dyes, such as indigo, and the yellow dye in wool and straw are bleached). They are also used as a preservative for fruit and other foodstuffs for this reason. Other uses are to remove chlorine from fabrics after bleaching and in photography. 

The way a synthesis is planned has changed substantially over time. Until the beginning of the 20th century many noteworthy syntheses had been developed, c.g., of alizarin (C. Gracbc, C, Licbermann, 1869) and indigo (A, Bacycr, 1878). 

Supplement (combined with Volumes XXIV and 1936 3458-3793 methane, 25. Pyrimidine, 89. Pyrazine, 91. Nicotine, 110. Dipyridyl, 199. Phenanthroline, 227. Hydroxy compounds, 348 Cinchonine, 424. Quinine, 511. Indigo white, i... 

Supplement 1936 3458-3793 Picrolonic acid, 51. Hydantoin, 242. Uracil, 312. Indigo, 416. Barbituric j acid, 467. Alloxan, 500. ... 

Supplement 1955 3634-3793 Sulphonic acids Indigo-disulphonic acid (indigocarmine), 304. Amines, 308. Keto-ammes Pyramidone, 452. Allan-toin, 474. Murexide, 499. Amino-carboxylic acids Histidine, 513. j Hydrazines, 531. Azo compounds, 535. 1... 

Thio-2-oxoselenazolidine can be obtained in 89% yield by treating the 2,4-dione with P4SJ0 in boiling dioxane (81). This structure is found in heterocyclic indigo-type dyes (Scheme 78). 

For more on Tyrian purple see the article Indigo and Tyrian Purple—In Nature and in the Lab in the November 2001 issue of the Journal of Chemical Educa tion pp 1442-1443... 

As early as 2500 bce m India indigo was used to dye cloth a deep blue The early Phoenicians discovered that a purple dye of great value Tyrian purple could be extracted from a Mediterranean sea snail The beauty of the color and its scarcity made purple the color of royalty The availability of dyestuffs underwent an abrupt change m 1856 when William Henry Perkin an 18 year old student accidentally discovered a simple way to prepare a deep purple dye which he called mauveme from extracts of coal tar This led to a search for other synthetic dyes and forged a permanent link between industry and chemical research... 

Although better known now for his incorrect theory that cycloalkanes were planar Baeyer was responsible for notable advances in the chemistry of organic dyes such as indigo and was awarded the 1905 Nobel Prize in chemistry for his work in that area... 

Aniline was first isolated in 1826 as a degradation prod uct of indigo a dark blue dye obtained from the West Indian plant Indigofera anil from which the name aniline IS derived... 

Indigo-5,5, 7-trisulfonic acid (Na salt) 0.332 -0.081 <9 Colorless to blue... 

Titrate with KBr03—KBr until color of indigo changes to yellow. 

Indigo carmine, sodium indigodisulfonate (indicator) dissolve 0.25 g in 100 mL 50% alcohol pH range blue 11.6-14.0 yellow. 

Indigo Disulfo Acid, Sodium Salt pD C Blue No. 2)... 

Chloroacetic acid can be esterified and aminated to provide useful chemical intermediates. Amphoteric agents suitable as shampoos have been synthesized by reaction of sodium chloroacetate with fatty amines (4,5). Reactions with amines (6) such as ammonia, methylamine, and trimethylamine yield glycine [66-40-6J, sarcosine [107-97-17, and carhoxymethyltrimethylammonium chloride, respectively. Reaction with aniline forms /V-phenylglycine [103-01 -5] a starting point for the synthesis of indigo (7). 

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). 

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