C8H5NO2

ISATIN  , in chemistry, a derivative of indol, interesting on account of its relation to indigo; it may be regarded as the anhydride of ortho-aminobenzoylformic or isatinic acid . It crystallizes in orange red prisms which melt at 200-201° C . It may be prepared by oxidizing indigo with nitric or chromic acid (0 . L . Erdmann, Jour. prak . Chem., 1841, 24, p . 11); by boiling ortho-nitrophenylpropiolic acid with alkalis (A . Baeyer, Ber., 188o, 13, p . 2259), or by oxidizing carbostyril with alkaline potassium permanganate (P . Friedlander and H . Qstermaier, Ber., 1881, 14, p . 1921) .

P . J .

Meyer (German Patent 26736 (1883)) obtains substituted isatins by condensing para-toluidine with dichloracetic acid, oxidizing the product with air and then hydrolysing the oxidized product with hydrochloric acid . T . Sandmeyer (German Patents 113981 and 119831 (1899)) obtained isatin-a-anilide by condensing aniline with chloral hydrate and hydroxylamine, an intermediate product isonitrosodiphenylacetamidine being obtained, which is converted into isatin-aanilide by sulphuric acid . This can be converted into indigo II by reduction with ammonium sulphide . Isatin dissolved in concentrated sulphuric acid gives a blue coloration with thiophene, due to the formation of indophenin (see Abst . J.C.S., 1907) . Concentrated nitric acid oxidizes it to oxalic acid, and alkali fusion yields aniline . It dissolves in soda forming a violet solution, which soon becomes yellow, a change due to the transformation of sodium N-isatin into sodium isatate, the aciisatin salt being probably formed intermediately (Heller, Abst . J.C.S., 1907, i. p . 442) .

Most metallic salts are N-derivatives yielding N-methyl

ethers; the silver salt is, however, an 0-derivative, yielding an 0-methyl ether (A. v . Baeyer, 1883; W . Peters, Abst . J.C.S., 1907, i. p . 239) .