Indigo from indoxyl

Indigo (62) is made from indoxyl (60) upon treatment with O2 in base, via the captodative radical 61 [40]. 

In the present case, this was accomplished with isatin-5-sulfonate instead of isatin, using the urea-Unked cyclodextrin dimer to alter the ratio of formation of indigo, through oxidative dimerisation of indoxyl, to indirubin-5 -sulfonate, from indoxyl and the isatin-sulfonate (Figure 3.5). The isatinsulfonate exists in solution in equilibrium with its hydrate, which deprotonates with a pA a of 9.55 to give the corresponding anion... 

Oxygen sodium carbonate Indigo compds. from indoxyls... 

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-... 

Indigo, indirubin, indoxyl and indican which have all been found in mammalian urine are probably formed from indole, itself produced by the action of intestinal bacteria on L-tryptophan. 

Oxygen sodium carbonate Indigo compounds from indoxyls s. 11,806... 

Hydroxyindole (181) represents a well known example of a compound in which the hydroxyl group is to the ring heteroatom. The equilibrium mixture again contains mainly the carbonyl form (182), indoxyl. Deprotonation gives a reactive ambident anion which can be methylated either on oxygen or C-2 (Scheme 73). Indoxyl is easily oxidized to indigo (184), which may be formed by dimerization of the radical (183) produced by electron loss from the anion. 

From its alkali salt, which is partially hydrolysed, the large indigo white molecule is adsorbed by the fibre and then, in this finely divided condition, dehydrogenated by the oxygen of the air, so that the dye now remains as a fast blue pigment. The oxidation is analogous to that of indoxyl. 

Important indole derivatives (see Scheme 2) include (i) indigo, a vat dye known and widely used since antiquity, and originally obtained from indican, a (3-glucoside of indoxyl which occurs in some plants. Indigo is now prepared synthetically. Tyrian purple, a natural dye used since classical times, is 6,6 -dibromoindigo (ii) the numerous indole alkaloids, with complex derivatives such as yohimbine and strychnine (iii) tryptophan, an essential amino acid found in most proteins. Its metabolites include skatole and tryptamine and (iv) 3-indoleacetic acid, which is important as a plant growth hormone. 

Incubate the filters with 5-bromo-4-chloro-3-indolylphosphate (BCIP) and nitroblue tetrazolium (NBT). Indoxyl generated from BCIP by the action of alkaline phosphatase condenses to form indigo (blue). Indigo then reacts with NBT to form insoluble diformazan (purple). 

Voltammetric detection of indigo carmine formed by ALP from 3-indoxyl phosphate... 

The enzyme responsible for cleaving indican is indoxyl- 3-D-glucosidase, which is formed on the plant by microorganisms. The resulting indoxyl (16), which under alkaline conditions is soluble in water, is discharged from the fermentation vat and oxidized to indigo (1) by aeration. The insoluble dye is isolated by precipitation and air drying. 

Nearly all indigo is produced from N-phenylglycine (see Fig. 8.18) via fusion with potassium and sodium hydroxide, followed by treatment with sodamide [103]. The melt containing the dialkalimetal salt of indoxyl is subsequently dissolved in water, and indigo is formed by aerobic oxidation. Filtration and wash-... 

A problem connected with the microbial production of indigo is the formation of a small amount of isatin, which could be partly suppressed by adjusting the 02 concentration [108]. Isatin reacts with indoxyl to give indirubin, which gives the finished denim an undesirable red cast. The introduction of an isatin-de-grading enzyme (isatin hydrolase from P. putida) satisfactorily reduced the level of indirubin [107]. 

Indigo (178a) was originally prepared from an indoxyl glucoside occurring in various species of Indigofera (Leguminosae), until the industrial synthesis was developed. 

Indoxyl.—One more derivative of indole must be mentioned connected with the synthetic production of indigo. Isomeric with oxindole is another mono-hydroxy indole known as indoxyl. It is prepared from phenyl glycine or//fo-carboxylic acid, anthranil acetic acid. 

Heumann s Synthesis, Phenyl Glycine Ortho-carboxylic Acid.—The synthesis that has resulted in placing synthetic indigo on the market is that of Heumann by the fusion of phenyl glycine ortho-carboxylic acid with caustic potash. The product of this fusion is indoxyl which by atmospheric oxygen is oxidized to indigo. The industrial success of this synthesis was achieved only when the preparation of the-phenyl glycine ortho-carboxylic acid from a cheap source was accomplished. 

From the researches of Baeyer [51] and Bloem it is shown that on brominating acetylortho-amidoacetophenone, the bromine atom enters in the methyl group. If the benzene chain is substituted brominated indigos are formed but if only the benzene chain contains bromine, indigo cannot be produced. In these reactions indoxyl appears to be formed as an intermediate product in the reaction. 

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