2-Isopropyl-5-methyl-2-hexenal (CAS 35158-25-9) — Green Top to middle Note Fragrance Ingredient
2-Isopropyl-5-methyl-2-hexenal
CAS 35158-25-9
What Is 2-Isopropyl-5-methyl-2-hexenal?
2-Isopropyl-5-methyl-2-hexenal is a synthetic fragrance ingredient used in perfumery for its fresh, green character. You’ll encounter it in modern citrus and floral fragrances, often as a supporting note. This aldehyde adds a crisp, slightly metallic edge that helps create contemporary scent profiles, particularly in designer fragrances targeting younger audiences.
Safety Profile
USE WITH AWARENESSWhat Does 2-Isopropyl-5-methyl-2-hexenal Smell Like?
A razor-sharp aldehyde with piercing green freshness that evolves into a soapy-clean aura. The initial burst resembles crushed tomato leaves with a metallic twang, settling into a long-lasting impression of starched linen drying in sunlight. Unlike heavier aldehydes, this molecule maintains an airy quality throughout its evolution, never becoming waxy or dense. In dilution, it reveals subtle citrus undertones reminiscent of bergamot peel without the sweetness.
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
Used here to amplify the invigorating citrus-herbal accord, contributing a modern crispness that balances the traditional eucalyptus and rosemary notes.
Provides the signature ‘icy’ effect in this summer staple, enhancing the frozen citrus concept with its metallic green facets.
2D Molecular Structure
SMILES: CC(C)CC=C(C=O)C(C)C
Chemistry, Properties & Perfumer Guide
The Chemistry
This α,β-unsaturated aldehyde belongs to the branched-chain aliphatic aldehyde family. Synthesized via aldol condensation of isobutyraldehyde with 3-methyl-2-butenal, followed by dehydration. The electron-withdrawing carbonyl group conjugated with the double bond creates high reactivity, contributing to its intense odor impact. Lacks chirality due to the trisubstituted double bond preventing optical activity.
Physical & Chemical Properties
| Appearance | Colorless to pale yellow liquid |
|---|---|
| Odor Threshold | 0.02 ppb in air |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 0.1-0.5% | Up to 1% | Used sparingly due to potency |
| Functional Fragrance | 0.01-0.1% | Up to 0.3% | For fresh linen effects |
Classic Accords
Tip: Stabilize in ethanol before adding to aqueous systems to prevent polymerization.
Alternatives & Comparisons
When more floralcy is needed while maintaining green character; has better stability in alkaline systems.
Safety, Regulatory & Sustainability
⚠ Regulatory Disclaimer
General reference only. Consult current IFRA Standards Library before formulating.
IFRA Status
No restrictions under IFRA 49th Amendment. Self-classified as Category 5 (Aldehydes) with recommended maximum 1.5% in leave-on products.
GHS Classification
RIFM Assessment
RIFM evaluation ongoing. Preliminary data suggests safe use below 0.5% in rinse-off formulations.
Sustainability
Petrochemical-derived but used at extremely low levels (<0.1% typical) due to high potency. No known ecological toxicity concerns at current usage volumes. Carbon footprint mitigated by efficient synthesis requiring only two reaction steps.
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References
- Bauer et al. (2001). Modern Aldehydes in Perfumery. Perfumer & Flavorist. P&F Vol 26
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.
Report a data errorPhysicochemical Properties
DTXSID: DTXSID5067891
Physical Properties
| Molecular Weight | 154.253 g/mol🔬 EPA CompTox |
| Density | 0.843 g/cm^3🔬 EPA CTX |
| Boiling Point | 199.647 °C📊 OPERA |
| Melting Point | -3.031 °C📊 OPERA |
| Flash Point | 59.209 °C📊 OPERA |
| Refractive Index | 1.436 Dimensionless📊 OPERA |
| Molar Volume | 185.091 cm^3/mol📊 OPERA |
Partition & Solubility
| LogP (Octanol-Water) | 3.27 Log10 unitless📊 OPERA |
| LogD (pH 5.5) | 3.27 Log10 unitless📊 OPERA |
| LogD (pH 7.4) | 3.27 Log10 unitless📊 OPERA |
| LogKoa (Octanol-Air) | 4.46 Log10 unitless📊 OPERA |
| Water Solubility | 0.003 mol/L📊 OPERA |
| Henry's Law Constant | 0 atm-m3/mole📊 OPERA |
Transport Properties
| Vapor Pressure | 0.514 mmHg📊 OPERA |
| Viscosity | 1.185 cP📊 OPERA |
| Surface Tension | 25.774 dyn/cm📊 OPERA |
| Thermal Conductivity | 127.811 mW/(m*K)📊 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 | 48.382 cm^3/mol📊 OPERA |
| Polarizability | 19.18 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.
