Indoxylic acid

This hydroxy-indol occurs in the urine of herbivorous animals as indoxylsulphuric acid. Indol is converted into indoxyl-sulphuric acid in the animal organism. From this compound indoxyl is formed by warming with concentrated hydrochloric acid. It may also be obtained by heating indoxylic acid, according to the equation ... 

The constitution or indoxyl may be deduced by its formation from indoxylic acid ... 

From certain reactions it appears probable that isatin, indoxylic acid, and indoxyl are capable of existing in two isomeric forms. One of these exists only in the form of derivatives (for example, ethers). Baeyer terms these labile or pseudo forms, and gives the following formulae to them —... 

Among later syntheses of indigo was that from phenylglycine carboxylic acid by Heumann. This was first made from aniline, but its preparation from naphthalene made the process technically workable. The research was carried out for the Badische Co. by their chemist E. Sapper (1891-7) and depended on the oxidation of naphthalene to phthalic acid by heating with concentrated sulphuric acid in presence of mercury as a catalyst (said to have been discovered accidentally by the breaking of a thermometer bulb). Phthalic acid was converted into phthalic anhydride, phthalimide, and anthranilic acid, and phenylglycine carboxylic acid by condensation of this with chloracetic acid. On fusion with caustic potash, or better sodamide, this formed indoxylic acid, and indoxyl, which was easily oxidised to indigo. 

Indoxylic Acid (i-Hydroxyindole-2-carboxylic acid, indogenic acid)... 

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). 

The quindoline 224 may be prepared by the condensation of indoxyl-2-carboxylic acid with 6-aminopiperonaldehyde in the presence of hydrochloric acid, when decarboxylation and cyclization take place. Nitric acid oxidation of 224 gave an unstable nitrodicarboxylic acid which decarboxylated readily to a nitromonocarboxylic acid formulated as 8-nitro-8-carboline-3-carboxylic acid (225). ... 

Isatin is the inner anhydride (lactam) of a y-amino-a-ketocarboxylic acid, isatinic acid (A), and is converted into a salt of this acid by the action of alkali. The keto-group in position 3 can condense with many other substances, and for this reason isatin is manufactured on a technical scale and converted into valuable indigoid vat dyes. The magnificent thioindigo scarlet, which is obtained from isatin and a sulphur analogue of indoxyl (the so-called hydroxythionaphthene), may be taken as example qq... 

Fig. 2.40. Plausible sequence of formation of indigotin from indican (I), of indirubin from indoxyl and isatin (II), and of tryptanthrin from anthranillic acid and isatin (III). Reprinted with permission from A. V. Muruganandam et al. [118].

Once the structure of indigo was established in 1870, it was quite logical to attempt its synthesis, not only as an intellectual challenge, but also as a profitable source of cheaper indigo that could advantageously compete with the natural dyestuff. The first industrial synthesis used by "Badische Anilin und Soda Fabrik" (BASF) was the procedure developed by Karl Neumann, which utilised the reaction of aniline with chloroacetic acid and then cyclisation of the resulting product to indoxyl promoted by NaNHj at high temperatures (over 200 °C). However, the... 

Indolebutyric acid org chem C12H13O2N A crystalline acid similar to indoleacetic acid in auxin activity. Abbreviated IBA. in,dol-byu tir-ik as-od indoxyl orgchem (C8H6N)0H A yellow crystalline glycoside, used as an intermediate in the manufacture of indigo. in dak-sol ... 

Fig. 29.9 Inlet and time-dependent outlet concentrations of uremic toxins CMPF ( ), indoxyl sulfate ( ) and hippuric acid (/////) during 4 h perfusion of HSA-containing mixture of these metabolites through HSGD mierocolumn...

Bilirubin A false negative may occur when the sample contains ascorbic acid concentrations of 25 mg/dl or more. The yellow/orange-to-red color produced by the presence of indican (indoxyl sulfate) is also problematic. 

In 1906 Angeli and Angelico53 treated 78a with amyl nitrite under alkaline conditions. They isolated the oxime (84), which on treatment with chromic acid gave 79a. They claimed to have identified the isatogen by its reduction to the unstable indoxyl 82 (R = Ph), which has subsequently been shown to give dimeric compounds (Section III,B). 

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. 

Indoxyls and their oxygen and sulfur analogues are prepared by the cyclization of anilino-, phenoxy-and phenylthio-acetic acids, respectively (64 — 65), with NaNH2 (for Z = NH), P205 (for Z = O) and H2S04 (for Z = S). 

S-Arylthioglycolic acids possessing an ortho carboxyl group (77 R = R = H) are cyclized by acetic anhydride or base to the corresponding thioindoxyl-2-carboxylic acids (78 R = H) (method c), which often lose carbon dioxide spontaneously to give the thio-indoxyls (Table V).315 S>-(o-Cyanophenyl)thioglycolic acids give similar products on treatment with alkali (method d) (Table V).315... 

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