2-Methyl-2-pentenoic acid (CAS 16957-70-3) — Balsamic Middle Note Fragrance Ingredient
2-Methyl-2-pentenoic acid
CAS 16957-70-3
What Is 2-Methyl-2-pentenoic acid?
2-Methyl-2-pentenoic acid is a synthetic fragrance ingredient used to add fruity, cheesy, or sweaty notes to perfumes. It’s found in some niche fragrances aiming for unconventional olfactory effects. This molecule matters because it can create surprising contrasts in compositions, adding a touch of animalic or fermented character that makes fragrances more complex and intriguing.
Safety Profile
USE WITH AWARENESSWhat Does 2-Methyl-2-pentenoic acid Smell Like?
2-Methyl-2-pentenoic acid delivers a paradoxical olfactory profile – opening with a sharp, almost cheesy sourness that evolves into a sweaty, animalic warmth. The initial impression recalls overripe fruit or aged cheese, but at proper dilution reveals a complex fruity-sweaty character reminiscent of human perspiration. The dry-down retains a subtle fermented fruit nuance that blends surprisingly well with floral and woody notes, adding depth and realism to animalic accords.
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
Used here to amplify the controversial blood-and-sweat accord, contributing a metallic, bodily realism that makes this fragrance deliberately provocative.
Provides animalic depth to the musky core, enhancing the skin-like quality with its sweaty-fruity facets.
2D Molecular Structure
SMILES: CC\C=C(/C)C(O)=O
Chemistry, Properties & Perfumer Guide
The Chemistry
2-Methyl-2-pentenoic acid is an unsaturated carboxylic acid with a branched chain structure. As a synthetic material, it’s typically produced through controlled oxidation or dehydration reactions of precursor alcohols. The double bond at position 2 creates geometric isomerism (E/Z forms), with each isomer displaying slightly different odor characteristics. The molecule’s polarity allows it to interact with both hydrophilic and hydrophobic fragrance components.
Physical & Chemical Properties
| Appearance | Colorless to pale yellow liquid |
|---|---|
| Odor Threshold | Extremely low (ppb range) |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 0.01-0.1% | Up to 0.5% | Used sparingly for animalic effects |
| Functional Fragrance | Not used | N/A | Too challenging for mass market |
Classic Accords
Tip: Always pre-dilute to 1% or lower before incorporating into blends to avoid overwhelming compositions.
Alternatives & Comparisons
Offers similar sweaty-cheesy notes but with more pronounced foot odor character, useful when a stronger animalic punch is needed.
Safety, Regulatory & Sustainability
⚠ Regulatory Disclaimer
General reference only. Consult current IFRA Standards Library before formulating.
IFRA Status
Not currently restricted by IFRA standards, but recommended for low-level use due to potency.
GHS Classification
RIFM Assessment
Limited safety data available; recommended for professional use only at current knowledge levels.
Sustainability
As a synthetic material, production can be controlled to minimize environmental impact. No known issues with sourcing or supply chain. Biodegradability studies are limited but expected to be moderate due to the carboxylic acid group.
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References
- Brenna et al. (2002). Stereodifferentiation of chiral unsaturated carboxylic acids. Journal of Agricultural and Food Chemistry.
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.
Report a data errorIngredient Data Sheet
CAS 16957-70-3Physical Properties
| Molecular Weight | 114.14 g/mol🔬 PubChem |
| LogP (Octanol-Water) | 1.4🔬 PubChem |
| Boiling Point | 198.5 °C🔬 EPA CompTox |
| Vapor Pressure | 0.0122 mmHg @ 25°C📊 OPERA |
| Flash Point | 104 °C🔬 EPA CompTox |
| Involatility Index | 0.0012💻 Calculated |
| log Kp (skin permeability) | -2.402💻 Calculated |
Volatility & Performance
| Fragrance Note | Heart💻 Calculated |
| Volatility Class | Very slow💻 Calculated |
| Persistence Score | 2.4 / 5💻 Calculated |
Odor & Flavor
| Primary Descriptors | caramelgreenstrawberrysweet• leffingwell |
| 2-Methyl-2-pentenoic acid has a fruity odor.📖 Fenaroli | |
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: DTXSID30884951
Physical Properties
| Molecular Weight | 114.144 g/mol🔬 EPA CompTox |
| Density | 0.982 g/cm^3🔬 EPA CTX |
| Boiling Point | 198.5 °C🔬 EPA CTX |
| Melting Point | 23.7 °C🔬 EPA CTX |
| Flash Point | 106.033 °C🔬 EPA CTX |
| Refractive Index | 1.454 Dimensionless📊 OPERA |
| Molar Volume | 115.618 cm^3/mol📊 OPERA |
Partition & Solubility
| LogP (Octanol-Water) | 1.9 Log10 unitless🔬 EPA CTX |
| LogD (pH 5.5) | 0.842 Log10 unitless📊 OPERA |
| LogD (pH 7.4) | -0.965 Log10 unitless📊 OPERA |
| LogKoa (Octanol-Air) | 4.79 Log10 unitless📊 OPERA |
| Water Solubility | 0.098 mol/L📊 OPERA |
| Henry's Law Constant | 0 atm-m3/mole📊 OPERA |
Transport Properties
| Vapor Pressure | 0.012 mmHg🔬 EPA CTX |
| Viscosity | 2.324 cP📊 OPERA |
| Surface Tension | 29.491 dyn/cm📊 OPERA |
| Thermal Conductivity | 143.031 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 | 2 count💻 Computed |
| Aromatic Rings | 0 count💻 Computed |
| Molar Refractivity | 31.311 cm^3/mol📊 OPERA |
| Polarizability | 12.413 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.
