Isatin purification

Commercial isatin from Eastman Kodak or Matheson, Coleman and Bell has been used, but poorer yields are obtained (about 10% less) than when purified material is employed. Purification by reprecipitation or by recrystallization from glacial acetic acid is equally satisfactory. 

The experimental cell, the measurement technique, and the method used for purification of the solutions are the same as given in Section IV (l(i)). The organic substances studied are vanillin, isatin, and 5-nitrobenzimidazole. Each of them will be dealt with in detail. 

For purification, 200 g. of the crude product is suspended in 1 1. of hot water and treated with a solution of 88 g. of sodium hydroxide in 200 cc. of water. The solution is stirred mechanically and the isatin passes into solution. Dilute hydrochloric acid is then added, with stirring, until a slight precipitate appears. This requires about 290-300 cc. of an acid made by diluting one volume of concentrated hydrochloric acid (sp. gr. 1.19) with two volumes of water (Note 8). The mixture is then filtered at once, the precipitate is rejected, and the filtrate is made acid to Congo red paper with hydrochloric acid. The solution is then cooled rapidly and the isatin which separates is filtered with suction and dried in the air. The pure product thus obtained weighs 150-170 g. (Notes 9 and xo) and melts at 197-200° (corr.)... 

Dandia et al. [129] have developed an efficient and novel green catalytic protocol for the synthesis of biologically important spirooxindole derivatives (196) in a one-pot, three-component approach involving substituted isatin (193), activated methylene reagent (194), and 3-methyl-l-phenyl-2-pyrazolin-5-one (195) in water, xmder sonication. The report describes the use of sodium chloride as a nonacidic catalyst in aqueous media. The desired compoxmds were obtained in excellent yield (purity not less than 95%) without using complex catalysts and organic solvents, and without additional purification (Scheme 51). 

Hyperbranched poly(aryl ether oxindole)s (hb-PAE-Oxns) with a DB of 100% were prepared by Fu et al. [176] from an isatin-based AB2 monomer (1—36, Scheme 12) by one-pot polymerization without using toxic organometaUics nor chromatographic purification. The hb-PAE-Oxns soluble in apolar solvents were able to encapsulate a hydrophilic dye from the same polymer. 

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