Isatins indigos

Our measurements [1, 2] of the integral intensities of valence vibration bands of the 0—H, X—H groups (isatin, indigo, phenol, methyl alcohol, ethyl alcohol, and 2-oxyanthraquinone) reveal their sharp rise (by a factor of 5-10) while changing from vapour into liquid or solid state. 

Isatin. -The formation of isatin fiom indigo may be represented as follows —... 

Gopala Rao and Venkateswara Rao found that the oxidation of indigo to isatin by chromic acid is accelerated by the presence of oxalic acid, and at the same time the extent of the oxidation of oxalic acid by chromic acid is increased. This observation is an example of mutual induction. 

The synthesis of indigo was much more difficult than that of alizarin (6.2) [43]. In 1865 von Baeyer first attempted to obtain indigo by reductive dimerisation of isatin (6.116) he finally achieved a seven-step synthesis from phenylglycine via isatin in 1878. Many syntheses have been developed subsequently for indigo, but very few of these have achieved industrial importance. 

The best known oxidative transformation of indigo is that into isatin. This is a normal oxidation at a double bond ... 

It may be recalled that the first synthesis of indigo, by Baeyer, started from isatin chloride. (Formulate it.)... 

Attempts to prepare 2-diazo-3-oxindole failed. In fact, base decomposition of the isatin-2-tosylhydrazone under conventional conditions with potassium hydroxide at room temperature led to the potassium salt (64JOC3577). When an aqueous solution of the potassium salt was heated at 70°C, indigo blue was obtained in 62% yield. 

Lithium aluminum hydride reduction of isatin gave mixtures of 3-hydroxyindolinc, indole, indigo, and indirubin with compositions depending upon the experimental conditions.246 The latter three products... 

There are only two practical laboratory methods lor the production of isatin, viz. the oxidation of indigo,1 and the condensation of aniline, chloral hydrate, and hydroxylamine salts, followed by the action of sulfuric acid.2... 

Adolf von Baeyer reported the chemical structure of indigo in 1883, having already prepared the first synthetic indigo from isatin (2) in 1870. Until then, isa-tin had only been obtainable by oxidation of indigo. It was not until 1878 that von Baeyer first synthesized it from phenylacetic acid, making a complete synthesis of indigo possible [1],... 

Oxidation of indigo results in dehydroindigo (4). Oxidation with permanganate or chromate splits the molecule, forming isatin (5). Oxidation and reduction of the indigo system are accompanied by corresponding changes in the spectroscopic properties (see Section 2.4). 

Synthetic indigo was made by A. von Baeyer in 1870 by treating isatin (5) with phosphorus trichloride and phosphorus in acetyl chloride [9], He obtained isatin by oxidizing indigo. The first complete synthesis of indigo (Scheme 1) was achieved in 1878, when von Baeyer succeeded in deriving isatin from phenylace-tic acid (6) [10],... 

Towards organic substances ozone is strikingly active. Organic colouring matters are bleached for example, indigo is oxidised to isatin.8 Turpentine rapidly absorbs the gas, and if the hquid is exposed on filter paper in an atmosphere of ozone, inflammation may occur.9 India-rubber is rapidly attacked and so is of little value for connections... 

Isatin (lH-indole-2,3-dione, Figure 1) was first obtained by Erdman and Laurent in 1841 as a product from the oxidation of indigo by nitric and chromic acids. 

Isatins are also formed during the photo-oxidation of 5,6-dihydroindoles68, from the oxidation of indoles with thallium (m) trinitrate69 and by electrochemical oxidation of indigo... 

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]. 

Isatin.— Another compound is also obtained on the oxidation of indigo, viz., isatin. That isatin is related to anthranilic acid and is probably another intermediate product of the breaking down of indigo, lying between indigo and anthranilic acid, may be seen by the following synthesis of isatin from ortho-nitro benzoic acid. 

All of these compounds which we have given as related to anthranilic acid and to indigo are plainly derivatives of ortho-amino aromatic acids, either benzoic acid itself, as in anthranilic acid and anthranil, or side-chain-carboxy acids, as in isatin and oxindole. 

Isatin, Indole, etc.—By oxidation indigo yields isatin which by successive reductions as recently explained yields di-oxindole, oxindole and finally indole. Also indoxyl, the isomer of oxindole, yields indigo by oxidation. The composition formulas of indigo and these last compounds are as follows ... 

On treatment of isatin chloride with zinc dust and acetic acid the chlorine is eliminated and two hydrogens added with the formation of indigo. The reaction, with the formula for indigo which is supported, as we shall find, by other syntheses, is as follows ... 

From Di-phenyl Di-acetylene.—The proof that the two isatin or indole residues are linked together by the carbons is in the synthesis of indigo from di-phenyl di-acetylene, CeHs—C = C—C = C—CeHs. This compound by conversion into the di- (ortho-nitro) product, and treatment with sulphuric acid and reduction with ammonium sulphide, yields indigo. This indicates that the chain of carbon linkings remains as in the above compound. 

The presence of thiophene is made known through a color reaction with isatin, a compmmd related to indigo. The isatin reagent is prepared by dissolving 1 g of isatin in 100 ml of concentrated sulfuric acid. It is best to prepare a smaller amount of solution as needed. Add to 3 ml of commercial benzene 1 ml of isatin reagent. 

Isatin is formed by oxidation of indigo with nitric acid or chromic acid [16]. It may also he obtained by oxidation of amido-oxindol, and of carbostyril [18], and by boiling ortho-nitrophenylpropiolic acid with caustic-potash solution. Furtlier methods of formation are given under the synthesis of indigo-blue. 

Dinitro- and diamido-indigotin have been prepared from dinitro-isatin [33]. (Compare the Synthesis of Indigo Blue, p. 231.)i... 

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