The Collaborative International Dictionary of English v.0.48:

Isatin \I"sa*tin\, n. [See Isatis.] (Chem.)
   An orange-red crystalline substance, C8H5NO2, obtained by
   the oxidation of indigo blue. It is also produced from
   certain derivatives of benzoic acid, and is one important
   source of artificial indigo. [Written also, less properly,
   isatine.]
   [1913 Webster]