Compounds · Other compounds · Anthranilate pathway
Indole
Also known as 2,3-Benzopyrrole · 1-Benzazole — an analysis may use any of these names
Overripe white flowers, faecal at high concentration. The most off-putting and also the most indispensable compound in the floral family.
- CAS
- 120-72-9
- Formula
- C8H7N
- Molar mass
- 117.15
- Odour threshold
- 140 ppbin water
- Boiling point
- ≈ 253 °C at atmospheric pressure
For this compound the two axes sit close together. Volatility tells you whether it leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices.
Where it comes from
Biosynthetic pathway: Anthranilate pathway — the sister branch of the phenylpropanoids, and the one that carries nitrogen.
Indole comes from tryptophan, not from phenylalanine — so it belongs to the anthranilate branch rather than to the phenylpropanoids, where many sources lump it. The nitrogen atom in the molecule is the trace of that lineage.
About the threshold figure
Moderately high. Below the threshold it contributes to a warm white-flower impression; many times above it, it becomes faecal.
Published thresholds differ by several orders of magnitude, because of differences in measuring method, sample purity and panel. The figure here is an order of magnitude for relative comparison, not a measurement. We give it only for compounds where the literature broadly agrees — 52 of the 106 compounds in the library. The rest are left blank rather than guessed.
Why it sits where it does
A two-ring aromatic compound containing nitrogen, flat and stable, boiling at around 253 degrees. It stays a very long time and is one of the natural fixatives of the white-flower family.
Where else you meet it
Jasmine, white champaca, orange blossom, and also the animal gut — the source of its bad reputation.