Alpha-isomethyl ionone (CAS 127-51-5) — Floral Heart Note Fragrance Ingredient
Alpha-isomethyl ionone
CAS 127-51-5
What Is Alpha-isomethyl ionone?
Alpha-isomethyl ionone is a synthetic floral musk used in perfumes and personal care products. You’ll encounter it in fabric softeners, shampoos, and luxury fragrances where it adds a velvety violet-like softness. This versatile ingredient matters because it bridges floral and woody accords, creating long-lasting scent trails without overpowering other notes. Its subtle powdery character makes it a perfumer’s secret weapon for adding sophistication.
Safety Profile
GENERALLY SAFEWhat Does Alpha-isomethyl ionone Smell Like?
Alpha-isomethyl ionone unfolds like a silk scarf – initially crisp with violet leaf sharpness that quickly softens into a powdery embrace. The heart reveals orris-like richness with nuances of raspberry jam sweetness and cedarwood dryness. As it settles, it leaves a skin-hugging muskiness reminiscent of vintage face powder stored in a wooden vanity. Unlike its ionone cousins, this variant has superior tenacity, evolving over hours while maintaining floral delicacy amidst stronger base notes.
Scent Profile
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
Provides the velvety floralcy that makes J’adore’s white flowers feel luxurious rather than sharp. Blends seamlessly with ylang-ylang and damask rose.
Forms the powdery-woody backbone that supports this fragrance’s grapefruit-quince top notes, preventing them from becoming too tart.
2D Molecular Structure
SMILES: CC(=O)C(C)=CC1C(C)=CCCC1(C)C
Chemistry, Properties & Perfumer Guide
The Chemistry
Alpha-isomethyl ionone belongs to the ionone class of cyclic terpenoids, specifically a methylated derivative of gamma-ionone. Industrially produced via acid-catalyzed cyclization of pseudoionone, this chiral molecule exists as stereoisomers that influence its odor profile. The synthetic process allows precise control over the methyl group positioning, creating a more stable and consistent material than natural ionones from orris root.
Physical & Chemical Properties
| Appearance | Colorless to pale yellow liquid |
|---|---|
| Boiling Point | 266 °C (estimated) |
| Density | 0.93-0.94 g/cm³ |
| Refractive Index | 1.497-1.502 |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 5-12% | Up to 20% | Floral-musk core |
| Soap | 0.5-2% | Up to 3% | Powdery dry-down |
Classic Accords
Tip: Use with ionone beta to create dimensional violet effects without excessive powderiness.
Alternatives & Comparisons
More violet-forward with less muskiness. Preferred for soliflores requiring clearer floralcy.
Safety, Regulatory & Sustainability
⚠ Regulatory Disclaimer
General reference only. IFRA, REACH, EU Cosmetics Regulation standards update periodically. Consult current IFRA Standards Library before formulating. Not legal or regulatory advice.
IFRA Status
No restrictions under IFRA 49th Amendment. Considered safe at current usage levels.
RIFM Assessment
Evaluated as safe for current fragrance use patterns (RIFM, 2015).
Sustainability
Synthetic production avoids overharvesting of orris root. Manufacturing uses renewable citral feedstocks in some processes. Biodegradation studies show moderate environmental persistence.
Explore Alpha-isomethyl ionone
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References
- Brenna et al. (2002). Ionones and Damascones: Structure-Odor Relationships. Chemistry & Biodiversity. DOI 10.1002/cbdv.200590001
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Mar 2026.
Report a data errorPhysicochemical Properties
DTXSID: DTXSID7027047
Physical Properties
| Molecular Weight | 206.329 g/mol🔬 EPA CompTox |
| Density | 0.93 g/cm^3🔬 EPA CTX |
| Boiling Point | 264.467 °C🔬 EPA CTX |
| Melting Point | -15.6 °C🔬 EPA CTX |
| Flash Point | 118.15 °C🔬 EPA CTX |
| Refractive Index | 1.508 Dimensionless📊 OPERA |
| Molar Volume | 221.967 cm^3/mol📊 OPERA |
Partition & Solubility
| LogP (Octanol-Water) | 4.536 Log10 unitless🔬 EPA CTX |
| LogD (pH 5.5) | 4.3 Log10 unitless📊 OPERA |
| LogD (pH 7.4) | 4.3 Log10 unitless📊 OPERA |
| LogKoa (Octanol-Air) | 6.9 Log10 unitless📊 OPERA |
| Water Solubility | 0 mol/L🔬 EPA CTX |
| Henry's Law Constant | 0 atm-m3/mole📊 OPERA |
Transport Properties
| Vapor Pressure | 0.006 mmHg🔬 EPA CTX |
| Surface Tension | 31.72 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 | 2 count💻 Computed |
| Aromatic Rings | 0 count💻 Computed |
| Molar Refractivity | 66.183 cm^3/mol📊 OPERA |
| Polarizability | 26.237 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.
