A Indigo

Fig. 3.26 SQWVsofPlGEs modified with (a) indigo and (b) pristine palygorskite from Sak lu um, and MB samples from (c) Chakmultun, and (d) El Tabasqueno, immersed in 0.50 M HAc +0.50M NaAc buffer at pH 4.85. Potential scan initiated at —750 mV in the positive direction. Potential step increment 4 mV square-wave amplitude 25 mV frequency 5 Hz [223]...

Diphenyl blue 2B Direct blue A Indigo blue 2B Phenamine blue 2B Sodium diphenyl-4,4 -bis-azo-2"-8"-amino-1 "-naphthol-3",6"-disulfonate... 

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. 

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). 

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... 

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... 

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). 

Many sodium compounds are made from sodium. Sodium is employed as a reducing agent in numerous preparations, including the manufacture of dyes (see Dyes and dye intermediates), eg, indigo herbicides (qv) (128) pharmaceuticals (qv) high molecular weight alcohols (129) perfume materials (130) (see Perfumes) and isosebacic acid (131,132). 

Addition of sodium dithionite to formaldehyde yields the sodium salt of hydroxymethanesulfinic acid [79-25-4] H0CH2S02Na, which retains the useful reducing character of the sodium dithionite although somewhat attenuated in reactivity. The most important organic chemistry of sodium dithionite involves its use in reducing dyes, eg, anthraquinone vat dyes, sulfur dyes, and indigo, to their soluble leuco forms (see Dyes, anthraquinone). Dithionite can reduce various chromophores that are not reduced by sulfite. Dithionite can be used for the reduction of aldehydes and ketones to alcohols (348). Quantitative studies have been made of the reduction potential of dithionite as a function of pH and the concentration of other salts (349,350). 

Piesendy, all ceitified colois aie factory-piepaied materials belonging to one of several different chemical classes. Although a few such as D C Blue No. 6 (indigo) are known to exist in nature, certified colors owe their commercial importance to their synthetic production. Because of the starting materials used in their manufacture in the past, certified colors were once known as coal-tar dyes. Today, since most of the raw materials used in their preparation are obtained from petroleum, this term no longer appHes. 

Cha.in Wa.rp Dyeing. This procedure is widely used in the dyeing of indigo on warp yams which are in the form of ropes or chains. In this procedure, several warp ropes are pulled through a series of tubs containing the dye Hquor and gradually are dyed to the desired shade. 

The leaves of the indigo plant do not contain the dye as such, but in the form of its precursor, a glycoside known as indican (109). Indican [487-60-5] is the dextrose derivative (35) of indoxyl [480-93-3] (110). Indoxyl occurs also in the urine of humans as the potassium salt of indoxyl sulfonic acid (111). 

Enzymatic stone-washing is performed either entirely without stones or sometimes by a combination of stones and enzymes. CeUulases are used to attack the surface of the cellulose fiber, but leave the interior intact. Denim garments are dyed with indigo blue, which stays on the surface of the yam. The ceUulase partiy hydrolyzes the surface of the fiber, and the indigo blue is partiy removed. Either neutral-type ceUulases acting at pH 6—8 or acid-type ceUulases acting at pH 4—5 are used for these processes. 

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