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Filbertone

FRUITS, VEGETABLES AND NUTS / nutty · warm · sweet

Filbertone

Category	FRUITS, VEGETABLES AND NUTS
Subcategory	nutty · warm · sweet
Origin
Volatility	Top Note
Botanical	N/A — aroma chemical (naturally found in hazelnuts, Corylus avellana)
Appearance	colorless to yellow clear liquid
Odor Strength	High
Producing Countries	Synthetic molecule — manufactured by major aroma chemical companies worldwide
Pyramid	Top

Roasted hazelnuts split open on a hot pan. A sharp, fatty-metallic note flashes first, then a warm, buttery sweetness settles in — the smell of praline before the sugar. Filbertone is the single molecule responsible for hazelnut's character impact, and a potent aroma chemicals a perfumer can reach for.

Scent
The Full Story
Fun Fact
Extraction & Chemistry
In Perfumery

Scent

First impact: fatty, metallic, almost abrasive — the scorch of a hot nut roasting, not the smooth sweetness of a finished praline. A buttery warmth follows within seconds, carrying the specific roasted-kernel quality that separates hazelnut from almond or walnut. The metallic edge is more pronounced than in 5-methyl-2-heptanone (filbertone B, CAS 409-02-9), which reads as the same family but flatter, less incisive. On a smelling strip, the initial blast dissipates in under thirty minutes; a faint, warm, toasted residue lingers for approximately two hours before vanishing. The molecule is a sprinter, not a marathoner.

Evolution over time

Immediately

Sharp, metallic, fatty flash — roasted hazelnut kernel split open. The (R)-enantiomer's buttery-chocolate facet dominates the opening alongside a biting, almost abrasive metallic edge from the (S)-enantiomer.

After a few hours

The metallic attack fades within 30 minutes. A warm, toasted, faintly sweet residue remains — closer to praline than to raw nut. On blotter, barely perceptible after 2 hours. Substantivity is very low for such a powerful molecule.

After a few days

Effectively absent. MW 126.20 and high vapour pressure (1.25 mmHg @ 25C) ensure near-complete evaporation within hours. On fabric, a faint warm ghost may persist for 6-8 hours under favourable conditions.

The Full Story

Filbertone ((E)-5-methyl-2-hepten-4-one, CAS 81925-81-7, MW 126.20) is the character impact compound of hazelnuts. Identified in roasted Corylus avellana by Guentert, Bruening, Emberger, and Hopp in 1991, it was the missing piece that explained why hazelnut aroma had resisted reconstruction for decades. The molecule is an aliphatic unsaturated ketone — structurally simple, olfactorily devastating.

Explore all seven extraits in the Discovery Set.

Chirality

Filbertone has a stereocenter at C-5, producing two enantiomers with distinct odour profiles. The (-)-(5R)-(E) isomer (CAS not assigned separately in commercial supply) smells of butter, chocolate, and roasted nuts. The (+)-(5S)-(E) isomer is fattier, more metallic, with a balsamic undertone. The (R)-enantiomer is roughly ten times more potent — its odour threshold is an order of magnitude lower than the (S)-form. In nature, hazelnuts contain a slight excess of the (S)-enantiomer, with the ratio varying by cultivar and roasting conditions. Commercial filbertone is typically sold as the racemic (E)-mixture.

Natural Occurrence

Filbertone occurs naturally in roasted hazelnuts (Corylus avellana) at trace concentrations — typically 0.5 to 5 ppm depending on cultivar, origin, and degree of roasting. It is also a minor volatile component of chocolate. Despite its natural occurrence, the compound used in perfumery and flavour work is synthesised — either via Grignard reaction of sec-butyl magnesium bromide with crotonaldehyde followed by oxidation, or via aldol condensation routes using butanone and acetaldehyde intermediates. Both pathways yield a nature-identical product.

Potency and Dosage

Filbertone is extraordinarily potent. Odour strength is rated 8/10 on the TGSC scale; impact in blends reaches 9/10. It is commonly supplied pre-diluted to 1% in triethyl citrate because the pure material overwhelms at standard working concentrations. Recommended use levels in fragrance compositions range from 0.002% to 2%, with most perfumers working at approximately 0.1% in the final concentrate. At that level, it delivers a clean nutty-green quality without becoming identifiably 'hazelnut.' Above 0.5%, the hazelnut signature becomes unmistakable.

Did You Know?

Did you know?

Filbertone was only identified as the character impact compound of hazelnuts in 1991 — centuries after humans began roasting and eating them. Guentert, Bruening, Emberger, and Hopp published the identification in Zeitschrift fuer Lebensmittel-Untersuchung und -Forschung (1991, 192(2):108-110), resolving a long-standing puzzle in flavour chemistry. The delay was partly due to the molecule's extraordinarily low odour threshold: it dominates hazelnut aroma at concentrations so small they escaped early analytical methods.

Extraction & Chemistry

Extraction method: Fully synthetic (nature-identical). No natural essential oil or absolute of hazelnut exists for perfumery use. Two principal industrial synthesis routes: (1) Grignard route: sec-butyl magnesium bromide reacts with crotonaldehyde to yield 5-methyl-2-hepten-4-ol, which is then oxidised (sodium dichromate or catalytic methods) to the target ketone (US Patent 4,563,365). (2) Aldol condensation route: butanone condenses with acetaldehyde to form 3-methyl-3-penten-2-one; catalytic hydrogenation gives 3-methyl-2-pentanone; a second aldol condensation with acetaldehyde yields filbertone (CN Patent 101597223B). This route avoids Grignard reagents and stoichiometric oxidants, offering cleaner industrial scalability. The product is a colourless to pale yellow mobile liquid. Commercial grades are typically >97% purity (Sigma-Aldrich, mixture of E/Z isomers). Supplied pure or pre-diluted to 1% in triethyl citrate (TEC) due to extreme potency.

Molecular Formula	C8H14O (MW 126.20)
CAS Number	81925-81-7
Botanical Name	N/A — aroma chemical (naturally found in hazelnuts, Corylus avellana)
IFRA Status	No dedicated IFRA standard. RIFM safety assessment exists (CAS 81925-81-7); in silico evaluation conducted with read-across analogs due to insufficient direct toxicological data. No category-specific limits published under the 51st Amendment. General RIFM guidance for aliphatic ketones applies.
Synonyms	5-methyl-2-hepten-4-one; filbert heptenone; (E)-5-methylhept-2-en-4-one
Physical Properties
Odor Strength	High
Lasting Power	2 hours (at 100%)
Appearance	colorless to yellow clear liquid
Boiling Point	170–173 °C @ 760 mmHg
Flash Point	126 °F TCC (52.22 °C)
Specific Gravity	0.845–0.852 @ 25 °C
Refractive Index	1.440–1.445 @ 20 °C

In Perfumery

Top-note modifier of extreme potency. Filbertone functions at sub-threshold doses as a naturaliser and texture agent — it adds a warm, roasted undertone to compositions without being identifiable as hazelnut. At 0.002–0.05%, it enriches citrus openings with a subliminal fatty-green warmth. At 0.1–0.5%, the nutty character becomes perceptible, making it a signature material in gourmand, praline, and chocolate accords. Its primary functional roles: (1) top-note booster in exotic fruit and citrus structures, where it adds volume and a flash of warmth; (2) signature note in gourmand compositions alongside vanilla, tonka, and cocoa; (3) naturaliser for woody and sandalwood bases, where trace amounts introduce an organic, lived-in quality. The molecule pairs structurally with Sandalore (CAS 65113-99-7) for nutty-sandalwood fusions, with ethyl maltol for praline accords, and with pyrazines (2-acetyl-3-methylpyrazine, CAS 13925-00-3) for roasted-coffee effects. TGSC rates odour strength at 8/10 and impact at 9/10 — among the highest for any single aroma chemical. IFRA/RIFM: a RIFM safety assessment exists (Fragrance Material Safety Assessment Center, CAS 81925-81-7). The molecule is not individually restricted under a dedicated IFRA standard as of the 51st Amendment, but its in silico evaluation flagged insufficient toxicological data, leading to read-across analog assessment. No specific category limits have been published. Comply with general RIFM guidance for structurally analogous aliphatic ketones. No confirmed presence in the current Premiere Peau collection.