Isatin

Isatin or 1H-indole-2,3-dione is an indole derivative. The compound was first obtained by Erdman and Laurent in 1841 as a product from the oxidation of indigo dye by nitric acid and chromic acids. The compound is found in many plants.

Schiff bases of isatin are investigated for their pharmaceutical properties.

Isatin forms a blue dye if it is mixed with sulfuric acid and crude benzene. The formation of the blue indophenin was long believed to be a reaction with benzene. Victor Meyer was able to isolate the substance responsible for this reaction from benzene. This new heterocyclic compound was thiophene.

Preparation
Isatin is commercially available. It may be prepared from cyclicizing the condensation product of chloral hydrate, aniline and hydroxylamine in sulfuric acid:. This reaction is called the Sandmeyer isonitrosoacetanilide Isatin Synthesis and discovered by Traugott Sandmeyer in 1919.


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Another classic reaction, the Sandmeyer diphenylurea isatin synthesis (Sandmeyer 1903), starts from diphenylthiourea, potassium cyanide, and lead carbonate

Isatins can be made from the corresponding indole in good yield by a mix of InCl3 and IBX in a acetonitrile-water solution at 80°C.