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a heterocyclic compound; yellowish red crystals. Melting point 203.5°C. Characterized by tautomerism, isatin exists both in the lactam (I) and lactim (II) forms:
Isatin is soluble in acetone, benzene, methanol, and hot water. It exhibits mild acidic and basic properties, correspondingly forming salts with acids and bases. It is readily acylated, alkylated, nitrated, halogenated, sulfonated, and so forth.
Isatin can be obtained from aniline, by oxidation of indigo, and by other methods.
Isatin and some of its derivatives are valuable intermediates in the manufacture of indigoid vat dyes; it is also used for the detection and photometric determination of thiophene in benzene (so-called indophenine reaction), pyrrole, and mercaptans in air and for the detection of Cu and Ag. Isatin-β3-oxime, a product of the interaction of isatin with hydroxylamine, is used for the detection and determination of U and for the detection of Ag, Co, and many other elements.