2-Octen-4-one (CAS 4643-27-0) — Green Middle Note Fragrance Ingredient
2-Octen-4-one
CAS 4643-27-0
What Is 2-Octen-4-one?
2-Octen-4-one is a synthetic fragrance molecule used to add mushroom-like, earthy nuances to perfumes. You’ll encounter it in fragrances aiming for damp forest or truffle-like sophistication. This ketone matters because it creates a bridge between natural-smelling wood notes and more abstract modern accords, giving perfumers precise control over earthy effects.
Safety Profile
USE WITH AWARENESSWhat Does 2-Octen-4-one Smell Like?
2-Octen-4-one delivers an intensely damp, fungal character reminiscent of wild mushrooms and wet humus. The initial burst evokes sliced Portobello caps with a metallic edge, softening into a dry hay-like nuance. Unlike simpler mushroom materials, it carries an almost fatty depth that mimics truffle’s luxurious decay. In dry-down, it leaves a phantom trace of rusted iron and dried leaves—perfect for creating haunted forest effects. When dosed carefully, it adds dimension to woody bases without overwhelming the composition.
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
Used here to amplify the ink-like vetiver with subterranean mushroom notes, creating a chillingly damp forest floor effect that contrasts with the fragrance’s mineral dryness.
2-Octen-4-one forms the core of this gourmand-woody scent, replicating the umami richness of black truffles while avoiding literal foodiness through its dry, woody undertones.
2D Molecular Structure
SMILES: CCCCC(=O)C=CC
Chemistry, Properties & Perfumer Guide
The Chemistry
This unsaturated ketone belongs to the alkenone class, featuring a conjugated double bond system that contributes to its potent odor characteristics. While trace amounts occur naturally in certain fungi, commercial production typically involves oxidation of corresponding alcohols or controlled pyrolysis of fatty acids. The E-isomer dominates synthetic production due to greater olfactory potency. Its electrophilic α,β-unsaturated carbonyl structure requires careful handling to prevent polymerization.
Physical & Chemical Properties
| Boiling Point | ~175 °C (est.) |
|---|---|
| Vapor Pressure | 0.3 mmHg (25°C est.) |
| XLogP | 2.1 (est.) |
| Appearance | Pale yellow liquid |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 0.01-0.1% | Up to 0.3% | Used sparingly for earthy effects |
| Functional Fragrance | 0.001-0.01% | Up to 0.05% | Masking agent for damp odors |
Classic Accords
Tip: Stabilize in ethanol before adding to oil phase to prevent uneven distribution in the concentrate.
Alternatives & Comparisons
The alcohol analog offers similar mushroom character but with greener, more metallic top notes—better for fresh-cut mushroom effects rather than decayed richness.
Safety, Regulatory & Sustainability
⚠ Regulatory Disclaimer
General reference only. Consult current IFRA Standards Library before formulating.
IFRA Status
Not currently restricted under IFRA standards. Recommended maximum 0.3% in finished products based on RIFM sensitization data.
GHS Classification
RIFM Assessment
RIFM evaluation ongoing. Preliminary data suggests moderate skin sensitization potential at concentrations above 0.5%.
Sustainability
As a purely synthetic material, 2-octen-4-one avoids ecological impacts associated with mushroom harvesting. Production typically uses petrochemical feedstocks, though some manufacturers are exploring bio-based routes via fermentation-derived intermediates. Its high potency means minimal quantities are required per formulation, reducing overall environmental load compared to less powerful naturals.
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References
- Burdock, G.A. (2010). Fenaroli’s Handbook of Flavor Ingredients. CRC Press. ISBN 9781439852270
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.
Report a data errorIngredient Data Sheet
CAS 4643-27-0Physical Properties
| Molecular Weight | 126.2 g/mol🔬 PubChem |
| LogP (Octanol-Water) | 2.1🔬 PubChem |
| Boiling Point | 179.5 °C🔬 EPA CompTox |
| Vapor Pressure | 1.0965 mmHg @ 25°C📊 OPERA |
| Flash Point | 51.3 °C🔬 EPA CompTox |
| Involatility Index | 0.1052💻 Calculated |
| log Kp (skin permeability) | -1.979💻 Calculated |
| SMILES | CCCCC(=O)C=CC🔬 PubChem |
Volatility & Performance
| Fragrance Note | Top💻 Calculated |
| Volatility Class | Moderate💻 Calculated |
| Persistence Score | 0.5 / 5💻 Calculated |
Odor & Flavor
| Functional Groups | ketonealkene💻 RDKit |
Sensory Thresholds
| Odor Detection Threshold | 0.2 ppm📖 van Gemert |
Regulatory Status
| IFRA Listed | Yes — see IFRA Standards for category limits⚖️ IFRA 51 |
Physical data: PubChem (NIH/NLM), U.S. EPA CompTox Dashboard, EPA OPERA models, RDKit. Odor & flavor: Arctander (Perfume & Flavor Chemicals), Fenaroli's Handbook of Flavor Ingredients, Leffingwell. Thresholds: van Gemert (Compilations of Odour Threshold Values). Regulatory: IFRA Standards 51st, FEMA GRAS. Trade names: Surburg (Common Fragrance & Flavor Materials). All data compiled and cross-referenced for perfumertools.com.
Physicochemical Properties
DTXSID: DTXSID3047134
Physical Properties
| Molecular Weight | 126.199 g/mol🔬 EPA CompTox |
| Density | 0.839 g/cm^3🔬 EPA CTX |
| Boiling Point | 179.5 °C🔬 EPA CTX |
| Melting Point | -30.18 °C📊 OPERA |
| Flash Point | 59.171 °C📊 OPERA |
| Refractive Index | 1.431 Dimensionless📊 OPERA |
| Molar Volume | 151.324 cm^3/mol📊 OPERA |
Partition & Solubility
| LogP (Octanol-Water) | 2.183 Log10 unitless📊 OPERA |
| LogD (pH 5.5) | 2.183 Log10 unitless📊 OPERA |
| LogD (pH 7.4) | 2.183 Log10 unitless📊 OPERA |
| LogKoa (Octanol-Air) | 4.52 Log10 unitless📊 OPERA |
| Water Solubility | 0.046 mol/L📊 OPERA |
| Henry's Law Constant | 0 atm-m3/mole📊 OPERA |
Transport Properties
| Vapor Pressure | 1.073 mmHg📊 OPERA |
| Surface Tension | 26.962 dyn/cm📊 OPERA |
Molecular Descriptors
| Topological Polar Surface Area | 17.07 Ų💻 Computed |
| H-Bond Donors | 0 count💻 Computed |
| H-Bond Acceptors | 1 count💻 Computed |
| Rotatable Bonds | 4 count💻 Computed |
| Aromatic Rings | 0 count💻 Computed |
| Molar Refractivity | 39.199 cm^3/mol📊 OPERA |
| Polarizability | 15.54 Å^3📊 OPERA |
Data Sources:
🔬 EPA Experimental data from U.S. EPA CompTox Chemicals Dashboard & CTX APIs. 📊 OPERA Predicted using EPA's OPERA QSAR models. 💻 Computed Calculated from SMILES using RDKit.
