4-Decenal, 5,9-dimethyl- (CAS 689-65-6) — Citrus Top to middle Note Fragrance Ingredient

ByThe Good Scents
Citrus · Green

4-Decenal, 5,9-dimethyl-

CAS 689-65-6

Origin
synthetic
Note
Top to middle
IFRA
Use with awareness
Data as of: Apr 2026

What Is 4-Decenal, 5,9-dimethyl-?

4-Decenal, 5,9-dimethyl- is a synthetic fragrance ingredient rarely encountered by name in consumer products. It’s typically listed simply as ‘fragrance’ in formulations. This aldehyde contributes fresh, marine, and slightly citrusy nuances to modern perfumery, often used to create aquatic or ozonic effects in body care products and fine fragrances.

Safety Profile

USE WITH AWARENESS
Generally safeUse with awarenessProfessional use
✓ IFRA-approved within limits
⚠ Potential skin sensitizer at high concentrations
CAS
689-65-6
Formula
Mixture
MW
Variable
Odor Family
Citrus · Green
Layer 1 · Enthusiast

What Does 4-Decenal, 5,9-dimethyl- Smell Like?

5,9-dimethyl-4-decenal bursts with a crisp, marine freshness reminiscent of ocean spray hitting sun-warmed rocks. The initial impression is ozonic and slightly metallic, like crushed seashells, evolving into a clean citrus-musk heart with hints of watermelon rind and cucumber water. As it dries down, it reveals a subtle woody-ambery undertone that prevents the freshness from becoming shrill. The overall effect is modern and minimalist – the olfactory equivalent of polished steel and sea breeze.

Scent Profile

In Famous Fragrances

Fragrance associations may not reflect actual formulations.

Cool Water(Davidoff, 1988)

Used to amplify the marine freshness, contributing to the signature ‘blue’ aquatic effect that defined 90s masculine perfumery.

L'Eau d'Issey(Issey Miyake, 1992)

Provides the crystalline water accord that makes this fragrance smell like raindrops on lotus leaves.

Layer 2

Chemistry, Properties & Perfumer Guide

The Chemistry

5,9-dimethyl-4-decenal belongs to the family of branched-chain unsaturated aldehydes. While not found in nature, its structure mimics certain marine-derived odorants. Industrial synthesis typically involves the hydroformylation of corresponding dienes, followed by selective hydrogenation. The Z/E isomer ratio significantly impacts the odor profile, with the Z-isomer being more marine and the E-isomer more citrusy.

Physical & Chemical Properties

AppearanceColorless to pale yellow liquid
Odor Threshold0.00002 ppm in water

Perfumer Guide

Note Position
Top to middle
Volatility
Moderate (2-4 hours)
Blending
Good with citrus and musks
ApplicationTypical %RangeNotes
Fine Fragrance0.1-0.5%Up to 1%For aquatic/marine effects
Body Care0.01-0.1%Up to 0.2%Freshness booster

Classic Accords

Tip: Use at trace levels with ionones to create a ‘wet stones’ effect.

Alternatives & Comparisons

1
2,6-dimethyl-5-heptenal CAS 106-72-9

More citrusy and less marine, suitable when a fruitier top note is desired.

Layer 3

Safety, Regulatory & Sustainability

⚠ Regulatory Disclaimer

General reference only. Consult current IFRA Standards Library before formulating.

IFRA Status

No specific restrictions under IFRA 49th Amendment.

GHS Classification

H315 Skin irritation H317 May cause allergic skin reaction

RIFM Assessment

RIFM assessment ongoing; preliminary data suggests safe use at current industry levels.

Sustainability

As a synthetic material, production involves petrochemical feedstocks. Some manufacturers are exploring bio-based routes using fermentation-derived intermediates. The material’s high potency means minimal quantities are required, reducing environmental load compared to less powerful ingredients.

Explore 4-Decenal, 5,9-dimethyl-

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References

  1. Brenna et al. (2003). Stereoisomeric flavor compounds. Chemical Reviews. DOI:10.1021/cr010409+

Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.

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