Indole

Indole is an organic compound with the formula C8H7N. It consists of a benzene ring fused to a five-membered nitrogen-containing ring (pyrrole), forming a bicyclic aromatic heterocycle. Indole is a colorless solid with a distinctive odor, sparingly soluble in water and soluble in most organic solvents. It is notable for its ultraviolet absorption near 280 nm.

Occurrence and synthesis

Indole occurs widely in nature. It is produced by bacteria through the enzyme tryptophanase, which degrades the essential amino acid tryptophan to indole, pyruvate, and ammonia. In plants, indole serves as a core scaffold for the biosynthesis of indole-3-acetic acid (IAA), a principal plant hormone, via several metabolic routes that convert tryptophan into IAA.

Chemistry and properties

As a fused-ring heteroaromatic compound, indole is highly planar and undergoes electrophilic substitution mainly at the C-3 position of the pyrrole ring. The nitrogen is of the pyrrolic type and is not easily protonated, rendering indole a weak base. Its chemistry makes it a versatile building block in organic synthesis and in the preparation of various indole derivatives.

Applications

Indole is a foundational scaffold in the synthesis of dyes, pharmaceuticals, and fragrance ingredients. Many indole derivatives exhibit significant biological activity. The indole nucleus is also present in essential biomolecules, such as the amino acid tryptophan and several plant metabolites.

Safety and handling

Indole is of low to moderate toxicity and can act as an irritant. It should be handled with standard laboratory safety practices, including appropriate ventilation and personal protective equipment.

See also

Tryptophan; indole-3-acetic acid; serotonin; skatole.