In short
Ethyl cyclopentenolone is the ethyl homologue of cyclotene, a very powerful maple and caramel material. It is often supplied at 50% in propylene glycol.
What Ethyl Cyclopentenolone smells like
ChemicalBook describes ethyl cyclopentenolone at 1% as sweet, caramel, maple and fenugreek; a Parchem specification lists sweet, brown, caramellic, maple, brown sugar, rum, whiskey and furanone. An aroma supplier calls it a very powerful maple-caramellic, coffee-roast material with nutty, burnt-sugar facets. PubChem links it to natural-product databases.
- Leading note
- Maple
- Clear facets
- Caramel
- Supporting facets
- Brown sugar
- Faint facets
- Roasted coffee, rum
- Character
- Powerful, warm
What makes Ethyl Cyclopentenolone distinctive
Darker and more layered than cyclotene, with roast and rum beside the maple.
How Ethyl Cyclopentenolone is used
Used in traces for maple, caramel and roasted effects in gourmand accords.
Typical role: modifier (used in small amounts to change the character of a blend).
How Ethyl Cyclopentenolone differs from similar materials
- Cyclotene
- Cyclotene gives a clean maple-syrup sweetness; its ethyl homologue is darker and more layered, with roast and rum facets, according to a supplier.
Each difference compares the published descriptions of the two materials. Smell varies with grade, supplier and dilution; compare them side by side on blotters before substituting one for another.
Formulation considerations
Very powerful; one supplier gives about 0.005% in fine fragrance.
Identity and classification
- Type
- Aroma chemical
- Origin
- Occurs in nature
- Odour family
- Gourmand / Woody
- Note position
- Heart note
- Physical form at room temperature
- Solid
- Also known as
- 3-Ethyl-2-hydroxy-2-cyclopenten-1-one
- CAS number
- 21835-01-8
- Molecular formula
- C7H10O2
- Molecular weight
- 126.15 g/mol
- IUPAC name
- 3-ethyl-2-hydroxycyclopent-2-en-1-one
The CAS number, formula and molecular weight are taken from PubChem compound 62752, whose own record lists this CAS number; checked 24 October 2026.
Safety and compliance
Hazard classification of the neat substance, as PubChem summarises it, read 26 October 2026. Companies notifying the ECHA C&L Inventory report it as not meeting the GHS hazard criteria (1,407 of 1,448 reports). Unless it is harmonised, this is the notifiers' own classification, not a binding one.
This page is general information, not a safety assessment or a specification. Confirm identity, composition, IFRA status and allergen content from your supplier's documents for the lot you hold.
Materials it works with
-
Cyclotene
Aroma chemical · Gourmand / Woody — maple, caramel, nutty, sweet
-
Maltol
Aroma chemical · Gourmand / Fruity — caramel, sweet, bready, cooked fruit
-
Fenugreek Absolute
Absolute · Gourmand / Spicy — maple, curry, celery, hay
Used in formulas and accords
Used in 5 published formulas
Ethyl Cyclopentenolone is an ingredient in 3 perfume formulas and 2 accords in the Formula & Accord Library.
Community formulas
RUŌOD House Originals
Original compositions by RUŌOD House.
Further reading
Questions about Ethyl Cyclopentenolone
Is Ethyl Cyclopentenolone natural or synthetic?
The molecule occurs in nature. Commercial Ethyl Cyclopentenolone may be made by synthesis or obtained from natural sources, so check the supplier's specification if the distinction matters to you.
What is the CAS number of Ethyl Cyclopentenolone?
21835-01-8. It was checked against PubChem on 24 October 2026.
Which published formulas use Ethyl Cyclopentenolone?
Ethyl Cyclopentenolone is used in 5 published formulas in the RUŌOD Lab Formula & Accord Library, including Burnt Sugar Smoke Accord, Ginger Biscuit Tin and Hazelnut Accord. Each is listed with a link under "Used in formulas and accords" on this page.
Sources
- PubChem — compound 62752, checked 24 October 2026.
- PubChem — GHS classification (the ECHA C&L Inventory notifications and any harmonised EU entry), read 26 October 2026.
- ChemicalBook — 21835-01-8 — odour database.
- Parchem — ethyl cyclopentenolone — distributor's description.
- Olfactory profile: the RUŌOD Lab team's synthesis of the published descriptions above, reviewed 24 October 2026. Evidence: more than one published description. Classification and the short description: revision 1. Descriptions of odour are judgement, not measurement.