Compounds · Lactones · Phenylpropanoid pathway
Coumarin
Also known as 1,2-Benzopyrone · 2H-Chromen-2-one — an analysis may use any of these names
Hay, faint vanilla, baked goods. Sweet without sugar.
- CAS
- 91-64-5
- Formula
- C9H6O2
- Molar mass
- 146.14
- Odour threshold
- —
- Boiling point
- ≈ 301 °C at atmospheric pressure
This compound boils at 301 °C, so it is heavier than any ordinary essential-oil component. It lies outside the 150–290 °C band, so the marker stops at the right edge — not because that is where it sits, but because the axis does not reach that far.
Must be declared on the label
This compound is on the list of allergens that must be declared individually on cosmetic labels in the European Union, as one of the 24 substances listed before Regulation 2023/1545. Name to use on the label: COUMARIN.
The declaration threshold is 0.001% in leave-on products and 0.01% in rinse-off products. This is an EU requirement — see the regulations page for why it matters beyond the EU. This is not legal advice.
Where it comes from
Biosynthetic pathway: Phenylpropanoid pathway — plants build them around a six-carbon aromatic ring.
Why it sits where it does
An aromatic lactone, a flat and stable molecule boiling above three hundred degrees. It is one of the heaviest components the human nose still picks up at low concentration.
Where else you meet it
Hay, tonka bean, cassia, and some teas. Its concentration in food is restricted in many countries.