INDOLE (BENZOPYRROLE), first prepared by A. Baeyer in 1866 and regarded by him as the parent substance of indigo. It crystallizes in colourless lustrous leaflets, melts at 5 2 ° C, boils at 2 54 ° C, is readily volatile in steam and easily soluble in water, alcohol, ether or benzene. Its odour is generally faecal, but after careful purification and in sufficient dilution indole possesses a not unpleasant odour of flowers. Accordingly it finds a limited application in perfumery. Indole occurs in the coal-tar fraction (see COAL TAR), boiling at 22o-26o° C; after removal of phenols and strong bases the oil is treated with sodium or sodamide to form sodium indole, which is separated mechani cally and decomposed by water. It is synthesized by boiling dichloroether, C1.0C2H5, with aniline and water, or by heating ethylaniline to redness. These reactions indicate its con stitution (I.).
Scatole (3-methylindole; II.) occurs in human faeces, of which it is the chief volatile constituent; it melts at 95° C and boils at 265-6° C.