Indole (CAS 120-72-9) — floral heart Note Fragrance Ingredient
Indole
CAS 120-72-9
What Is Indole?
Indole is a fascinating fragrance ingredient found in both flowers and animal secretions. You’ll encounter it in jasmine perfumes and some unexpected places like fecal matter – purified indole smells floral, while concentrated forms are intensely animalic. This dual nature makes indole special. It’s the chemical bridge between delicate florals and primal muskiness, allowing perfumers to create depth and intrigue in fragrances.
Safety Profile
USE WITH AWARENESS
What Does Indole Smell Like?
Indole presents a mesmerizing duality – at high dilution, it’s a radiant floral reminiscent of jasmine blossoms with a honeyed sweetness. Concentrated, it transforms into an animalic, almost fecal intensity that adds primal depth. As a heart note, indole evolves from initial floral brightness into a warm, slightly narcotic dry-down. Its tenacity allows it to bridge between top and base notes, carrying floralcy into deeper accords. The molecule behaves differently in various contexts – in white florals it enhances their naturalness, while in chypres it provides an intriguing animalic counterpoint.
Scent Profile
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
Indole provides the narcotic jasmine heart that makes this fragrance so addictive. It’s carefully balanced with fruity top notes to maintain elegance while delivering the flower’s full sensual spectrum.
This jasmine soliflore uses indole masterfully to recreate the flower’s natural indolic profile – both the intoxicating bloom and the darker, earthier facets that emerge at night.
One of perfumery’s most famous jasmine compositions relies on indole to achieve its legendary floral richness. The indole adds necessary depth to prevent the floral notes from becoming cloying.
Indole’s animalic side is amplified here to create the fragrance’s otherworldly character. It blends with amber notes to produce an intense, almost extraterrestrial floral signature.
This daring jasmine pushes indole’s animalic aspects to their limits, creating a fragrance that’s simultaneously beautiful and challenging – like flowers growing on a dung heap.
2D Molecular Structure
SMILES: N1C=CC2=C1C=CC=C2
Chemistry, Properties & Perfumer Guide
The Chemistry
Indole is an aromatic heterocyclic compound with a bicyclic structure consisting of a benzene ring fused to a pyrrole ring. As a secondary metabolite, it occurs naturally in plants like jasmine and orange blossoms, as well as in animal secretions. Industrially, indole is synthesized via the Fischer indole synthesis from phenylhydrazine and pyruvic acid, or through cyclization of o-ethylaniline. The molecule’s planar structure and electron-rich π-system make it highly reactive in electrophilic substitution reactions. While indole itself isn’t chiral, many of its derivatives in nature are optically active.
Physical & Chemical Properties
| Boiling Point | 254 °C |
|---|---|
| Melting Point | 52.5 °C |
| Density | 1.22 g/cm³ |
| Vapor Pressure | 0.01 mmHg |
| Solubility | 3560 mg/L (at 25 °C) |
| XLogP | 2.1 |
| Appearance | Leaflets (water, petroleum), crystals (ether) |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 0.1-1% | Up to 2% | Powerful floral enhancer |
| Functional Fragrance | 0.01-0.1% | Up to 0.5% | Requires careful dosing |
| Jasmine Absolute | 2-5% | Up to 8% | Natural component |
| Animalic Accords | 0.5-3% | Up to 5% | For bold compositions |
Classic Accords
+ Civet + Musk = Animalic Base
+ Orange Blossom + Tuberose = White Floral
+ Sandalwood + Vanilla = Oriental Floral
Tip: Balance indole’s intensity with fresh top notes and warm base notes to prevent it from dominating the composition.
Alternatives & Comparisons
More intensely animalic than indole, used when a stronger fecal character is desired in very small quantities.
Provides floral character without the animalic aspects, useful for cleaner jasmine effects.
Green-floral alternative that can provide some floralcy without indole’s challenging facets.
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 IFRA restrictions. FEMA GRAS 2593.
GHS Classification
H319 Eye irritation
RIFM Assessment
RIFM assessment confirms safe use at current levels in fragrance applications.
Sustainability
Most indole used in perfumery is synthesized from petrochemical sources, though identical molecules exist in nature. Synthetic production avoids the ecological impact of harvesting natural sources like jasmine flowers. The synthesis route is relatively efficient with minimal hazardous byproducts. Future green chemistry approaches may enable bio-based production through microbial fermentation.
Explore Indole
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Industry & Science Data
References
- PubChem Compound Summary for CID 798 (Indole) PubChem 798
- Brenna et al. (2002). Industrial synthesis of indole derivatives. Chemical Reviews. DOI:10.1021/cr0102925
- FEMA (2011). GRAS assessment of indole. Food Technology. FEMA 2593
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Mar 2026.
Physicochemical Properties
DTXSID: DTXSID0020737
Physical Properties
| Molecular Weight | 117.151 g/mol🔬 EPA CompTox |
| Density | 1.22 g/cm^3🔬 EPA CTX |
| Boiling Point | 253.4 °C🔬 EPA CTX |
| Melting Point | 52.221 °C🔬 EPA CTX |
| Flash Point | 108.613 °C🔬 EPA CTX |
| Refractive Index | 1.681 Dimensionless📊 OPERA |
| Molar Volume | 101.872 cm^3/mol📊 OPERA |
Partition & Solubility
| LogP (Octanol-Water) | 2.14 Log10 unitless🔬 EPA CTX |
| LogD (pH 5.5) | 2.291 Log10 unitless📊 OPERA |
| LogD (pH 7.4) | 2.291 Log10 unitless📊 OPERA |
| LogKoa (Octanol-Air) | 7.46 Log10 unitless📊 OPERA |
| Water Solubility | 0.035 mol/L🔬 EPA CTX |
| Henry's Law Constant | 0 atm-m3/mole🔬 EPA CTX |
Transport Properties
| Vapor Pressure | 0.012 mmHg🔬 EPA CTX |
| Viscosity | 3.937 cP📊 OPERA |
| Surface Tension | 49.868 dyn/cm📊 OPERA |
Molecular Descriptors
| Topological Polar Surface Area | 15.79 Ų💻 Computed |
| H-Bond Donors | 1 count💻 Computed |
| H-Bond Acceptors | 0 count💻 Computed |
| Rotatable Bonds | 0 count💻 Computed |
| Aromatic Rings | 2 count💻 Computed |
| Molar Refractivity | 38.529 cm^3/mol📊 OPERA |
| Polarizability | 15.274 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.
