. This substance, on boiling with alkali and then with dilute acid yields thioindoxyl,
, which is converted by alkaline oxidation into thioindigotin, having the constitution
. The new dyestuff is therefore analogous to indigotine, from which it differs by having the imino groups replaced by sulphur atoms. Thioindigo red can be readily crystallized from boiling benzene, and forms reddish brown crystals possessing a metallic reflex. Thioindigo scarlet,
, is also obtained synthetically. Both products come into the market in the form of pastes and are used in dyeing like indigo (see [Dyeing]).
(E. K.)