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Alpha-iso-Methylionone (CAS 127-51-5) is a synthetic fragrance compound derived from ionone, known for its woody, floral-violet scent. Key facts:
Scent Profile:
Rich woody-violet aroma with fruity undertones, used to enhance floral or oriental perfumes.
Applications:
Perfumery: Base note in fine fragrances, soaps, detergents, and cosmetics.
Fixative: Extends scent longevity by slowing evaporation.
Chemical Structure:
Isomer of methylionone; differs in methyl group position on the ionone ring.
Allergen: Recognized as a skin sensitizer (EU requires labeling if ≥0.001% in leave-on products).
IFRA Compliance: Restricted to safe levels in formulations (typically ≤0.4%).
Stability: Non-photosensitizing; suitable for sun-exposed products.
Why Used: Affordable alternative to natural violet extracts, adds depth to scent compositions.
Caution: Patch-test in skincare due to sensitization risk.
alpha-iso-Methylionone (CAS 127-51-5) is a synthetic terpenoid ketone used primarily in perfumery. Here are its key chemical characteristics:
IUPAC Name:
(E)-1-(2,6,6-Trimethylcyclohex-2-en-1-yl)pent-1-en-3-one
Molecular Formula: C₁₄H₂₂O
Core Structure:
Cyclic moiety: 2,6,6-Trimethylcyclohex-2-enyl ring (derived from ionone backbone).
Chain moiety: Unsaturated ketone (α,β-unsaturated enone: −CH=CH−C(O)CH₃).
"iso" designation: Methyl group (−CH₃) attached at the C1 position of the cyclohexenyl ring (distinguishing it from α-methylionone).
Stereoisomers: Exists as cis/trans isomers due to the double bond in the side chain (the E-isomer is most common).
Chiral Centers: The cyclohexenyl ring has chiral centers at C1 and C6, leading to enantiomers (typically used as a racemic mixture).
Produced via acid-catalyzed aldol condensation:
Citral (or pseudoionone) + acetone → ionone intermediate.
Methylation: Selective allylic methylation at C1 of the ionone ring.
Functional Groups: α,β-Unsaturated enone (electrophilic, Michael acceptor).
Reactivity:
Prone to oxidation under strong conditions.
Can undergo Diels-Alder reactions (diene character in ring).
Solubility: Insoluble in water; soluble in ethanol, oils.
Boiling Point: ~295°C (decomposes).
The "iso" prefix indicates methyl substitution on the ring carbon adjacent to the side chain (C1), unlike α-methylionone where methylation is on the side chain.
IR: Strong C=O stretch at ~1670 cm⁻¹; C=C at ~1600 cm⁻¹.
NMR: Characteristic vinyl proton signals (δ 5.5–6.5 ppm).
Practical Note: Its α,β-unsaturated ketone structure contributes to both its violet-like scent and potential skin sensitization (ability to form protein adducts). This reactivity is regulated in cosmetics (IFRA limits).
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