Isatins reaction with thiophene

Thienothiophenes undergo the indophenine reaction with isatin (see Section III,I). Oster reported that thieno[2,3-6]thiophene (1) gave a green product with a ratio of isatin to thienothiophene 1 1, and a blue substance with the ratio of the initial substances 2 1. Steinkopf and HempeP could not obtain this blue substance instead they isolated a brown material with the isatin to thienothiophene 1 ratio 2 3 at +50° they isolated a substance with the ratio 1 1 and at +70°, with ratio 1 2. Steinkopf and PetersdorP found that a reaction of 2-acetylthieno[2,3-6]thiophene with isatin produces 2- or 3-(2-thieno[2,3-6]thienyl) cinchoninic acid. The acid was decarboxylated to 2- or 3 2-thieno[2,3-6]thienyl)quinoline (the site of quinoline group in thienothiophene 1 molecule was not established). 

The reactive 3-carbonyl group in compounds of type (279) undergoes aldol condensation with active methylene compounds such reactions of isatin with indoxyl, oxindole (Section 3.3.2.5.4) and with thiophenes (Section 3.3.1.5.7.ii) have already been mentioned. These compounds also react with Grignard reagents and phosphorus halides as expected, e.g. isatin (279 Z = NH) with MeMgBr and PC13 yields (285) and (286), respectively. 

Biisatin, 5.5 -methylenebiisatin, 5,5 -diisatylether, and 5,5 -diisatylketones have proved to be useful compounds for the preparation of polymers. A series of polyindophenines (216-219) have been prepared by reaction of these isatins with thiophene under acidic condi-... 

The reaction of isatin with thiophene in the presence of sulfuric acid gave a blue color. This indophenine test was reported to be sensitive to 0.025% of thiophene in benzene. 

Tetrahydrobenzo[6]thiophene-2-carboxaldehyde condenses with compounds containing a CH2CN group.436 2-Acetyl- and 2-propionyl-4,5,6,7-tetrahydrobenzo[6]thiophene undergo the Pfitzinger reaction with isatins.436 Attempts to prepare 2-cyano-4,5,6,7-tetra-... 

The reaction of isatin with thiophene in an acidic medium, containing ferrous ion, gives rise to an intense violet color, due to the formation of indophenine dyes. Due to this phenomenon, it was proposed that isatin could be used as a revealing agent for the presence of thiophene in water-soluble organic solvents where it is used as a denaturating agent637. 

The acid and its derivatives do not give the usual colour reactions for thiophene with a sulphuric acid solution of isatin. Magnesium, barium and silver sdUs have been described. 

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. 

Poly(indophenine)s [17] are prepared by reaction of isatin with thiophene (Figure 14) and have conductivities up to 10 S/cm without additional dopant. The polymers are soluble in dimethyl sulfoxide and can be cast as films the material is thermostable up to 230 °C [129]. 

Pyrrole resembles thiophen in its ability to react with isatin and other compounds containing the grouping 00 00, in the presence of acids, to give deep blue products os Some authors have claimed that in the reaction with isatin two types of pyrrole blue are formed, and it is still not clear whether this is so or not. Pratesi s observed that blue products could be prepared from 2,3-dimethylpyrrole and cryptopyrrole, but not from phyllo-pyrrole, and favoured structures of type (29). However, Steinkopf and... 

Thiophene and its derivatives, unless substituted at both a-positions, give a positive reaction with isatin in cone, sulfuric acid. Where both positions are free a blue color is formed if one a-position is substituted, but the adjacent j -position is free, the color is green or violet. The structure of the colored substances formed is probably similar to that of the products described in the literature (67, 68). 

Properties.—Mobile, colourless liquid m. p. 5 4 b. p. So 4 sp. gr. o 874 at 20°. Coal-tar benzene usually contains a little thiophene, C4H4S, which may be detected by dissolving a few crystals of isatin (see p. 229) in concentrated sulphuiicacid and shaking up with the benzene. If thiophene is present, a blue colour is produced (indophenin reaction). 

Oximes and their derivatives are widely used in organic synthesis. A number of reviews are devoted to the chemistry and biological activity of oximes and their derivatives The synthesis, reactions and biological activity of oximes containing a heterocyclic substituent, e.g. furan and thiophene", indole and isatin, pyridine, pyrrole, quinoline and five-membered heterocycles with two heteroatoms have been reviewed. 

More rarely, ions of type (97) form dimeric products (possibly by initial loss of nuclear protons) thus, thiophenes with two free a-positions, or free adjacent a- and (3-positions, give indophenines (e.g. 103) with isatin (104). This reaction is used as a test for thiophene, the so-called indophenine test . 

In thiophen the oxygen of furfuran is replaced by sulphur. Its name indicates its occurrence in crude benzene as obtained from coal tar. Coal tar benzene gives a blue color with isatin known as the indo-phenin reaction. This reaction is not given by benzene made from benzoic acid and it was found, by Victor Meyer, to be due to the presence... 

A reaction of special historical interest, mentioned in the introduction to this chapter, is the condensation of thiophene with isatin in concentrated sulfuric acid, to give the deep blue indophenine as a mixture of geometrical isomers. ... 

When thiophene is treated with isatin (667) and sulphuric acid a blue coloration is formed. The production of color in this way, the so-called indophenin reaction, led to the discovery of thiophene by Victor Meyer. Before thiophene was discovered it was thought that the reaction was characteristic of benzene. A certain sample of the hydrocarbon failed to give the test. On investigation it was found that the benzene used had been prepared from benzoic acid. As benzene obtained from coal-tar gave the test, it was evident that the color-reaction was produced by a substance mixed with the hydrocarbon. When benzene containing thiophene is shaken with concentrated sulphuric acid, the thiophene is more rapidly converted into a sulphonic acid than is the benzene. Thiophene is obtained from the sulphonic acid prepared in this way by heating the latter with water under pressure. 

Thiophene, the foundation of this book, had a tricky birth. It masqueraded as benzene from 1879 to 1882, when Maeyer [1] uncovered the subterfuge. It turned out that coal tar-derived benzene, when treated with isatin and sulfuric acid, produced a beautifully deep-blue precipitate, named indophenine. This pigment was claimed by Baeyer in 1879 [2] to be a qualitative test for benzene and was the product of the indophenine reaction . The pigment s structure was eventually shown to consist of a quinoid form of bithiopene, shown below. 

The simple thiophenes are stable liquids that closely resemble the corresponding benzene compounds in boiling points and even in smell. The discovery of thiophene in coal tar benzene provides one of the classic anecdotes of organic chemistry, hi the days when colour reactions were essential for diagnosis, benzene was identified by the production of a blue colour on heating with a mixture of isatin (l//-indole-2,3-dione) and concentrated sulfuric acid. In 1882, during a lecture-demonstration... 

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