2-Ethylbutyric acid (CAS 88-09-5) — Musky Middle Note Fragrance Ingredient
2-Ethylbutyric acid
CAS 88-09-5
What Is 2-Ethylbutyric acid?
2-Ethylbutyric acid is a synthetic fragrance ingredient used in perfumes and flavorings. It contributes a sharp, cheesy note that can enhance fruity or dairy accords. This molecule matters because it’s a building block for more complex aromas, adding depth and contrast in small doses.
Safety Profile
USE WITH AWARENESSWhat Does 2-Ethylbutyric acid Smell Like?
2-Ethylbutyric acid delivers an intensely sharp, pungent aroma reminiscent of aged cheese with sweaty undertones. The initial blast is aggressively sour, evoking parmesan rinds and unwashed gym clothes. As it settles, a fruity nuance emerges – like overripe pineapple mingling with yogurt. The dry-down reveals a lingering animalic warmth that adds raunchy depth to compositions. Used judiciously, it provides an edgy contrast to sweet florals.
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
This provocative fragrance uses 2-ethylbutyric acid to create its infamous metallic-bloody accord, amplifying the unsettling bodily realism with its sweaty, lactonic sharpness.
The cheesy tang of 2-ethylbutyric acid enhances the milky accord, adding barnyard authenticity to this pastoral composition.
2D Molecular Structure
SMILES: CCC(CC)C(O)=O
Chemistry, Properties & Perfumer Guide
The Chemistry
2-Ethylbutyric acid is a branched-chain carboxylic acid with the formula C6H12O2. As a synthetic material, it’s produced through oxidation of 2-ethylbutanol or hydrocarboxylation of pentene. The branched structure creates steric hindrance that affects its volatility and odor profile compared to straight-chain counterparts. While not chiral itself, it’s often used to synthesize chiral esters in flavor chemistry.
Physical & Chemical Properties
| Boiling Point | 194-195 °C |
|---|---|
| Density | 0.92 g/cm³ |
| Flash Point | 82 °C |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 0.01-0.1% | Up to 0.5% | Used as trace modifier |
| Flavorings | 1-10 ppm | Up to 50 ppm | Cheese/dairy applications |
Classic Accords
Tip: Dilute to 1% in ethanol before blending to avoid overwhelming compositions.
Alternatives & Comparisons
More intensely sweaty, used when projecting stronger body odor nuances is desired.
Straight-chain variant with sharper, more vomit-like character at high concentrations.
Safety, Regulatory & Sustainability
⚠ Regulatory Disclaimer
General reference only. Consult current IFRA Standards Library before formulating.
IFRA Status
No IFRA restrictions. Generally recognized as safe at typical usage levels.
GHS Classification
RIFM Assessment
RIFM evaluation confirms safe use current levels based on exposure modeling.
Sustainability
As a petrochemical derivative, 2-ethylbutyric acid has moderate environmental impact. Some manufacturers are exploring bio-based production routes using fermentation of sugar feedstocks to reduce carbon footprint.
Explore 2-Ethylbutyric acid
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References
- Burdock, G.A. (2010). Fenaroli’s Handbook of Flavor Ingredients. CRC Press. ISBN 9781420090772
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.
Report a data errorIngredient Data Sheet
CAS 88-09-5Physical Properties
| Molecular Weight | 116.16 g/mol🔬 PubChem |
| LogP (Octanol-Water) | 1.7🔬 PubChem |
| Boiling Point | 99 °C🔬 EPA CompTox |
| Vapor Pressure | 0.18 mmHg @ 25°C📊 OPERA |
| Flash Point | 87 °C🔬 EPA CompTox |
| Involatility Index | 0.018💻 Calculated |
| log Kp (skin permeability) | -2.202💻 Calculated |
| SMILES | CCC(CC)C(=O)O🔬 PubChem |
Volatility & Performance
| Fragrance Note | Top💻 Calculated |
| Volatility Class | Slow💻 Calculated |
| Persistence Score | 1 / 5💻 Calculated |
Odor & Flavor
| Primary Descriptors | earthyfruitynutty• leffingwell |
| “Oily-fruity, acidulous odor, not as "rancid" as that of Caproic acid.”📖 Arctander | |
| 2-Ethylbutyric acid has a rancid, oily-fruity, acidulous odor.📖 Fenaroli | |
Flavor Notes (Arctander)
| “Fruity-earthly, acid taste with a Nut-like undertone. The acid finds use in flavor compositions for imitation Nut and Walnut and in various fruit complexes.”📖 Arctander |
Sensory Thresholds
| Odor Detection Threshold | 3.535 ppm (n=4)📖 van Gemert |
Regulatory Status
| FEMA Number | FEMA 2429⚖️ FEMA GRAS |
| GRAS Status | Generally Recognized as Safe⚖️ FEMA GRAS |
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: DTXSID2041418
Physical Properties
| Molecular Weight | 116.16 g/mol🔬 EPA CompTox |
| Density | 0.92 g/cm^3🔬 EPA CTX |
| Boiling Point | 194 °C🔬 EPA CTX |
| Melting Point | -20.857 °C🔬 EPA CTX |
| Flash Point | 87 °C🔬 EPA CTX |
| Refractive Index | 1.425 Dimensionless📊 OPERA |
| Molar Volume | 122.578 cm^3/mol📊 OPERA |
Partition & Solubility
| LogP (Octanol-Water) | 1.68 Log10 unitless🔬 EPA CTX |
| LogD (pH 5.5) | 1.046 Log10 unitless📊 OPERA |
| LogD (pH 7.4) | -0.731 Log10 unitless📊 OPERA |
| LogKoa (Octanol-Air) | 4.76 Log10 unitless📊 OPERA |
| Water Solubility | 0.155 mol/L🔬 EPA CTX |
| Henry's Law Constant | 0 atm-m3/mole🔬 EPA CTX |
Transport Properties
| Vapor Pressure | 0.186 mmHg🔬 EPA CTX |
| Viscosity | 2.782 cP📊 OPERA |
| Surface Tension | 28.579 dyn/cm📊 OPERA |
| Thermal Conductivity | 140.688 mW/(m*K)📊 OPERA |
Molecular Descriptors
| Topological Polar Surface Area | 37.3 Ų💻 Computed |
| H-Bond Donors | 1 count💻 Computed |
| H-Bond Acceptors | 1 count💻 Computed |
| Rotatable Bonds | 3 count💻 Computed |
| Aromatic Rings | 0 count💻 Computed |
| Molar Refractivity | 31.369 cm^3/mol📊 OPERA |
| Polarizability | 12.436 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.
