ISATIN

isatin, c8h5no2, 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 deg. c. it may be prepared by oxidizing indigo with nitric or chromic acid (o. l. erdmann, _jour. prak. chem._, 1841, 24, p. 11); by boiling ortho-nitrophenylpropiolic acid with alkalis (a. baeyer, _ber._, 1880, 13, p. 2259), or by oxidizing carbostyril with alkaline potassium permanganate (p. friedlander and h. ostermaier, _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-[alpha]-anilide by condensing aniline with chloral hydrate and hydroxylamine, an intermediate product isonitrosodiphenylacetamidine being obtained, which is converted into isatin-[alpha]-anilide by sulphuric acid. this can be converted into indigo 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 _aci_-isatin 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 o-derivative, yielding an o-methyl ether (a. v. baeyer, 1883; w. peters, _abst. j.c.s._, 1907, i. p. 239). /\ /co /\ /co /\ /co /\ /co / \ / \ / \ / \ / \ / \ / \ / \ | | \co | | \co | | \ | | \ | | / | | / | | //c(oh) | | //coag. \ / \ / \ / \ / \ / \ // \ / \ // \/ \nh \/ \n(na) \/ \n \/ \n isatin([psi]) sodium salt isatin silver salt