Isatin sulphonic acid

Isatin chloride and 3-hydroxyselenonaphthene are. mixed in benzene and the solution boiled, when the required compound separates as a violet precipitate. It dissolves sparingly in xylene with a red-violet fluorescence and deposition of violet-black needles, M.pt. 335° C. In concentrated or fuming sulphuric acid and chlorosulphonic acid it gives intense blue solutions, forming a water-soluble red-violet fluorescent sulphonic acid, which yields pale yellow alkali salts. 

Isatin forms orange prisms, ] I.P. 200°. It is sparingly soluble in water, easily in alcohol and ether. It possesses the properties of a weak monobasic acid, but also reacts like the aldehydes and ketones for example, it combines with bisulphites of the alkalies, and with phenylhydrazine and its sulphonic acids [65]. 

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. 

Chlorophenylmagnesium bromide attacked only the ketonic carbonyl group of isatin (426) to give the oxindole (427). Michael addition to acrylonitrile followed by reduction gave the saturated primary amine (428) which in refluxing xylene containing 4-toluene sulphonic acid cyclized to ciclazindol (429) Scheme 5.101.). The intermediate (428) can also be... 

In related work, the same researchers described a four-component domino reaction that allows the one-pot synthesis of highly complex spiro systems, i.e. spiro[indoline/acenaphthylene-3,4-pyrazolo[3,4-6]pyridine derivatives 59 and 60 from phertylhydrazine, 3-aminocrotononitrile, isatin or acenaphthylene-1,2-dione and cyclic 1,3-dicarbonyl compoimds, including cyclohexane-l,3-diones and barbituric or thiobaibituric acid, in the presence of ( )-camphor-10-sulphonic acid (CSA) as catalyst (Scheme 1.30). 

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