Material guide: geranyl nitrile — made to replace citral, and retired itself

About a 4 minute read.

The short version

• Name: geranyl nitrile, sold as Citralva (IFF), CAS 5146-66-7
• Odour type: citrus; evaluation: citrus, lemon, nitrile, aldehydic, metallic
• Strength medium (rank 2), evaluate at 10% or less; substantivity 56 hours at 100%
• Vapour pressure 0.025 mmHg; oral rat LD50 3,100 mg/kg
• Suppliers: 20, while the category field says information only
• cosmetic_uses says both "not used anymore" and "perfuming agents"

Two contradictory statements in one cell

cosmetic_uses: "not used anymore; perfuming agents".

Separated by a semicolon.

I wrote about three retirement flags across three fields (musk ambrette). This record goes further — the contradiction happens inside a single field.

And category reads "information only not used for fragrances or flavors." Two fields, plus one field's internal contradiction, make three statements.

And it has 20 suppliers.

Why it exists

The notes field is two words: "citrus odourant."

But its name says more. Geranyl nitrile's structure is geranial with its aldehyde group replaced by a nitrile — and geranial together with its isomer neral is citral.

Citral is one of the most important lemon molecules, and it has an old industrial problem: it is unstable in alkaline media. Soap, detergent and cleaning products are alkaline, and citral discolours and drifts in them.

Replace the aldehyde with a nitrile and that problem disappears. A nitrile group does not oxidise or take part in those reactions the way an aldehyde does — and the smell changes as the price.

The evaluation field records that price honestly:

at 10.00% in dipropylene glycol. citrus lemon nitrile aldehydic metallic (Luebke 1992)

Neither "nitrile" nor "metallic" is a compliment. This is a thing that smells like lemon and audibly is not.

And nitriles have a problem of their own

Kaplita and Smith open their 1986 Toxicology and Applied Pharmacology paper:

Reports from several laboratories agree that many, but not all, aliphatic nitriles undergo hepatic biotransformation in mice and rats to release free cyanide, but the mechanisms at work in these reactions remain in doubt.

They used butyronitrile, propionitrile and their α-carbon-hydroxylated homologues, testing whether various pretreatments changed mortality in mice — inducing or depleting cytochrome P450 made no difference, while dimethyl sulfoxide reduced mortality.

Read "many, but not all" and "the mechanisms remain in doubt" together. This paper does not say geranyl nitrile releases cyanide. It says some compounds in this class do.

But that is enough to complicate the safety assessment of a whole class of materials, and this record's category and cosmetic uses fields may be reflecting that outcome. (I checked no regulatory decision; this is inference.)

And the problem it was meant to replace is still there

The other half of the citral story is the more interesting one.

Hagvall and colleagues, in the same journal in 2008:

Geraniol, a widely used fragrance chemical, is considered to be a weak allergen, although its chemical structure does not indicate it to be a contact sensitizer. We have shown that geraniol autoxidizes and forms allergenic oxidation products. In the literature, it is suggested but not shown that geraniol could be metabolically activated to geranial.

They incubated geraniol with a "skin-like CYP cocktail" of cutaneous cytochrome P450 isoenzymes, and got geranial, neral, 2,3-epoxygeraniol and 6,7-epoxygeraniol.

Geranial plus neral is citral.

So your skin turns geraniol into citral. A molecule whose structure gives no sign of being a sensitiser gets made into one by the skin's own enzymes.

Which complicates "replace the aldehyde with a nitrile" — you can avoid citral in the bottle, but if the formula contains geraniol, the skin makes some anyway.

Where its physical properties land

Vapour pressure 0.025 mmHg, substantivity 56 hours (measured neat).

I computed three bands: 0.01 to 1 mmHg is the heart, median 24 hours. This sits at the long end of that band.

For a citrus material, 56 hours is very long. An ordinary citrus top note runs about four — which is nitriles' other selling point: they outlast the corresponding aldehydes by a wide margin.

How to use it

• First confirm you can get it and may legally use it. The category field says information only and the cosmetic uses field is arguing with itself. Check the supplier specification and current IFRA.
• If you do use it, evaluate at 10% or less. The metallic facet is obvious at higher concentration.
• Its position is "lemon inside an alkaline product" — soap and detergent, not fine fragrance.
• 56 hours of substantivity survives functional product conditions.
• Oral LD50 3,100 mg/kg; acute toxicity is not the main issue.

What this doesn't establish

• I have not smelled it. This is fields, whole-database statistics, and two papers.
• Kaplita 1986 did not test geranyl nitrile. It tested butyronitrile and propionitrile, and its conclusion says "many, but not all." I have no data on whether this material releases cyanide.
• "Nitrile safety concerns drove its retirement" is inference; I checked no regulatory decision or IFRA text.
• "Citral is unstable in alkaline media" is industry common knowledge, cited from no study.
• Hagvall 2008 used an in vitro skin-like enzyme system, not measurements on living skin, and I have no figures for how much is formed.
• The occurrence field says "not found in nature", and I have measured that this claim is sometimes wrong; I did not verify it here.