Compounds · Other compounds · Phenylpropanoid pathway
trans-Anethole
Also known as Anethole · p-Propenylanisole — an analysis may use any of these names
Star anise, round sweetness, slightly cool at the end. One of the few molecules almost nobody describes wrongly.
- CAS
- 4180-23-8
- Formula
- C10H12O
- Molar mass
- 148.20
- Odour threshold
- —
- Boiling point
- ≈ 234 °C at atmospheric pressure
Must be declared on the label
This compound was added by Regulation (EU) 2023/1545 to the list of allergens that must be declared individually on cosmetic labels in the European Union. Name to use on the label: ANETHOLE.
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 ring carrying a methoxy group and a propenyl chain. The conjugated system between ring and chain makes the molecule very stable, and it boils high, at around 234 degrees.
A note on classification. Anethole is often wrongly classed as a phenol because it has an aromatic ring and because it accompanies eugenol in many spices. But a phenol requires a hydroxyl group attached directly to the ring, while anethole has only a methoxy group — formula C10H12O, with exactly one oxygen atom. Eugenol is C10H12O2: two oxygens, one in a methoxy group and one in a free hydroxyl. That second oxygen atom makes the difference, and it is also why eugenol is slightly acidic and anethole is not.
Where else you meet it
Star anise, fennel, Japanese star anise, and most aniseed sweets.