Indole, benzopyrrole, is a yellow crystalline powder with unpleasant aroma. It
has the pyrrole ring (five-membered unsaturated ring structure composed of four
carbon atoms and one nitrogen atom) which is fused to benzene ring. There are
tautomerer called indolenine (unsubstituted 3H-indole) and structural isomer,
isoindole. But they are unstable. Indole occurs in some plants or in coal tar,
and is formed in the intestine during putrefaction and by certain cultures of
bacteria. it is commercially synthesized from phenylhydrazine and pyruvic acid. Indole structure is a
motif in nature. Prominent examples include tryptophan (aromatic side chain amino acid), serotonin
(neurotransmitter), auxin (plant growth hormone), and indigo (plant colorant).
One more interesting point is all these compounds have functional branches at
Indole is used in perfumery and in preparing tryptophan, one of the 20 amino acids
commonly found in animal proteins. It has important application in the industry
of plant growth. It is used to prepare indoleacetic acid (auxin) and other
plant growth substances which help the development of roots in plant. It is used
to make selective herbicides. Indole and its derivatives are widely used in
making perfumes, dyes, agrochemicals and medicines.