4-Methylpentanoic acid (CAS 0646-07-01) — Balsamic Base Note Fragrance Ingredient
4-Methylpentanoic acid
CAS 0646-07-01
What Is 4-Methylpentanoic acid?
4-Methylpentanoic acid is a synthetic fragrance ingredient with a sharp, cheesy odor that perfumers use in trace amounts to add animalic complexity. It’s found in some niche perfumes and functional fragrances. This molecule matters because it can recreate the natural muskiness found in certain animal-derived materials, offering a vegan alternative when used skillfully in blends.
Safety Profile
USE WITH AWARENESSWhat Does 4-Methylpentanoic acid Smell Like?
4-Methylpentanoic acid assaults the nose with an initial punch of sweaty, goat-like musk that borders on unpleasant at full strength. As it diffuses, the sharpness mellows into a warm, animalic hum reminiscent of aged leather and human skin. The dry-down reveals a surprisingly soft, slightly nutty character that blends well with woody bases. Perfumers use it like a stiletto—dangerously sharp alone, but capable of adding thrilling edge when precisely dosed in chypres or leather compositions.
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
Used here to amplify the urinous civet note, creating the controversial animalic growl that defines this iconic masculine. The acid’s sharpness cuts through the heavy honeyed florals.
Provides the intimate skin-musk illusion in this legendary composition. The molecule’s nutty dry-down blends seamlessly with costus and ambrette.
Chemistry, Properties & Perfumer Guide
The Chemistry
4-Methylpentanoic acid is a branched-chain fatty acid with the molecular formula C6H12O2. Unlike its straight-chain counterparts, the methyl branch at the 4-position creates steric hindrance that alters both volatility and olfactory character. Industrially synthesized via oxidation of 4-methyl-1-pentanol or through Grignard reactions, this achiral molecule exhibits higher odor potency than linear hexanoic acid due to its compact structure.
Physical & Chemical Properties
| Appearance | Colorless to pale yellow liquid |
|---|---|
| Boiling Point | 196-198 °C |
| Density | 0.92 g/cm³ |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 0.01-0.1% | Up to 0.3% | Extreme overdosing causes foul odors |
| Functional Fragrance | 0.001-0.01% | Up to 0.05% | Masking agent in cleaning products |
Classic Accords
Tip: Always pre-dilute to 1% in ethanol before incorporating to prevent overwhelming a blend.
Alternatives & Comparisons
Less aggressive sibling with similar muskiness but smoother dairy tones. Preferable for skin-contact applications requiring softer animalics.
Safety, Regulatory & Sustainability
⚠ Regulatory Disclaimer
General reference only. Consult current IFRA Standards Library before formulating.
IFRA Status
No specific restrictions under IFRA 51st Amendment. General recommendations for carboxylic acids apply.
GHS Classification
RIFM Assessment
RIFM evaluation ongoing. Preliminary data suggests safe use below 0.3% in leave-on products.
Sustainability
As a purely synthetic material, 4-methylpentanoic acid doesn’t deplete natural resources. Production typically uses petrochemical feedstocks, though bio-based synthesis routes from fermented sugars are under development. Waste streams require neutralization due to acidity.
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References
- Arctander S. (1969). Perfume and Flavor Chemicals. Montclair, NJ.
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.
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