1911 Encyclopædia Britannica/Indole
INDOLE, or Benźopyrrol, C8H7N, a substance first prepared by A. Baeyer in 1868. It may be synthetically obtained by distilling oxindole (C8H8NO) with zinc dust; by heating orthonitrocinnamic acid with potash and iron filings; by the reduction of indigo blue; by the action of sodium ethylate on orthoaminochlorstyrene; by boiling aniline with dichloracetaldehyde; by the dry distillation of ortho-tolyloxamic acid; by heating aniline with dichloracetal; by distilling a mixture of calcium formate and calcium anilidoacetate; and by heating pyruvic acid phenyl hydrazone with anhydrous zinc chloride. It is also formed in the pancreatic fermentation of albumen, and, in small quantities, by passing the vapours of mono- and dialkylanilines through a red-hot tube. It crystallizes in shining leaflets, which melt at 52° C. and boil at 245° C. (with decomposition), and is volatile in a current of steam. It is a feeble base, and gives a cherry-red coloration with a pine shaving. Many derivatives of indole are known. B-methylindol or skatole occurs in human faeces.