Material guide · 78
Material guide: cis-3-hexenyl acetate — the smell of cut grass, and it is a plant's alarm signal
· 23 min read
CAS 3681-71-8. A hundred and three suppliers, among the highest counts in this series. Its substantivity field reads "< 4 hours at 100%" — with a less-than sign, and the shortest this series has met. It appears in 79 of 954 formulas at a median dose of 0.60%. Its role in nature is far better known than its role in perfume: a 2008 study exposed poplar saplings to naturally wound-emitted concentrations of it, and when those leaves were later fed on by gypsy moth larvae they carried higher jasmonic acid and had their defence genes primed. The smell of cut grass is a warning, and trees listen.
Start with the substantivity field, because how it is written is part of this piece:
< 4 hours at 100%
That less-than sign.
We've written about substantivity records carrying a greater-than sign — 206 of them database-wide, each a lower bound rather than a measurement. This one runs the other way: it means the neat material was gone from the blotter before four hours, which is where somebody looked.
It is the shortest in this series. Dimethyl sulfide reads 4 hours, and this one does not reach 4.
The short version
- CAS 3681-71-8, C₈H₁₄O₂, MW 142.20, 103 suppliers — among the highest counts in this series.
- Substantivity < 4 hours at 100%. Strength rated high, recommend smelling at 10% or less.
- It appears in 79 of 954 formulas (8.3%) at a median dose of 0.60%.
- Odour: fresh, green, sweet, fruity, banana, apple, grassy, pear, melon.
- Its GHS entry has exactly one line: H226, flammable liquid and vapour. No sensitisation, no aquatic hazard — rare among the materials this series has covered lately.
- Its real fame is in plant science. A 2008 study exposed poplar saplings to naturally wound-emitted concentrations of it; when those leaves were subsequently fed on by gypsy moth larvae, they showed higher jasmonic acid and linolenic acid, and their defence-related genes had been primed.
- The paper's conclusion: woody plants can detect and use it as a signal to prime defences before actually experiencing damage.
About 8 minutes.
That less-than sign
How the field is written deserves its own note.
| Material | Substantivity |
|---|---|
| Calone | > 600 hours at 10% |
| isoeugenol | 400 hours at 100% |
| dihydro-β-ionone | 9 hours at 100% |
| dimethyl sulfide | 4 hours at 100% |
| cis-3-hexenyl acetate | < 4 hours at 100% |
The two signs mean opposite things, and both mean the measurement was cut off.
> 600= still detectable at 600 hours, so the true value is at least 600.< 4= already gone at the earliest check, presumably four hours, so the true value is under 4.
Neither is a measured number. Both are the edge of the measuring range.
The practical upshot: this is purely an opening material. It does not last through a film on a blotter.
And its median dose in formulas is 0.60%. 24.6% of corpus material entries sit below 1%, and this one is in that group.
The odour field straddles two worlds
fresh, green, sweet, fruity, banana, apple, grassy, pear, melon
Five of the nine words are specific foods.
That is characteristic of the green leaf volatile family: they are simultaneously the smell of a damaged plant and the smell of ripening fruit, because both come from the same biochemistry — oxidative cleavage of fatty acids.
The occurrence field supports it:
apple, bilberry, celery, chamomile flower oil (trace), champaca concrete @ 0.01%, cornmint oil @ 0.04%, dill leaf, guava fruit, guava fruit headspace, Réunion @ 1.30%…
Guava headspace at 1.30%, one of the highest figures in that field.
In a formula its job is usually to push fruit toward freshly-picked, or to give a green accord a believable leaf at the start. It cannot hold structure; it handles the first few minutes.
It is a plant's alarm
This is what is genuinely worth knowing about the material, and it has nothing to do with perfume.
Green leaf volatiles are a group of molecules plants release immediately on tissue damage, and this is among the principal ones. The smell of cut grass is them.
And plants listen.
Frost and colleagues ran a cleanly designed experiment in New Phytologist in 2008.
Their question: herbivore-induced plant volatiles, besides attracting the herbivores' natural enemies, can serve as signals within plants to induce or prime defences. But which compounds in those blends act as signalling molecules is largely unknown, particularly in woody plants.
The method:
- Leaves of hybrid poplar saplings, exposed in vivo to naturally wound-emitted concentrations of cis-3-hexenyl acetate
- Then fed upon by gypsy moth larvae
- Volatiles collected throughout; leaf tissue taken to measure phytohormones and defence gene expression
The result:
Relative to controls, exposed leaves had higher concentrations of jasmonic acid and linolenic acid following gypsy moth feeding. Furthermore, it primed transcripts of genes that mediate oxylipin signaling and direct defenses, as determined by both qRT-PCR and microarray analysis using a microarray containing c. 5,400 unique gene models. Moreover, it primed the release of terpene volatiles.
And their conclusion is explicit:
The widespread priming response suggests an adaptive benefit to detecting it as a wound signal. Thus, woody plants can detect and use it as a signal to prime defenses before actually experiencing damage.
A tree smells that its neighbour has been bitten and switches its defences on in advance.
And that signalling molecule is the one in your bottle.
Nor is this confined to trees. Desmedt and colleagues published a molecular analysis of the same molecule in rice in the Journal of Experimental Botany in 2023, titled "Molecular analysis of broad-spectrum induced resistance in rice by the green leaf volatile Z-3-hexenyl acetate". Woody and herbaceous, insects and pathogens, one molecule.
Why it does not last four hours
This is consistent with its biological role.
An alarm signal needs to be fast, not durable.
- It has to be released in quantity at the moment of damage
- It has to travel quickly to neighbouring plants
- And it has to disappear quickly, or the signal stops meaning anything — an alarm that never stops is not an alarm.
Boiling point 165-167 °C, flash point 57 °C, water solubility 0.9 g/L. A small light ester, built to leave.
(To be clear: "built to" is a figure of speech. Evolution does not build, and what I am describing is an observed consistency rather than a demonstrated cause. The paper makes no such claim.)
Physical properties
| Property | Value |
|---|---|
| CAS | 3681-71-8 |
| Formula | C₈H₁₄O₂, MW 142.20 |
| Appearance | colourless clear liquid (est) |
| Boiling point | 165-167 °C at 760 mmHg |
| Flash point | 57 °C |
| logP | 1.90 (est) |
| Water solubility | 0.9 g/L at 20 °C (experimental) |
| Substantivity | < 4 hours at 100% |
| Strength | high, recommend smelling at 10% or less |
| Shelf life | 18 months or longer |
| Suppliers | 103 |
| Regulatory listings | JECFA, FEMA GRAS, CoE, FLAVIS |
| GHS | H226 flammable liquid and vapour (that is the whole entry) |
One GHS line, and it is flammability rather than toxicity. That is rare among this series' recent materials — hexyl cinnamal carries H317 sensitisation, dihydro-β-ionone H411 aquatic toxicity, isoeugenol five statements. This one is only flammable.
A 57 °C flash point is on the low side, below most fragrance materials, so treat it as combustible in shipping and storage. It is still a long way from dimethyl sulfide's −36.7 °C.
Water solubility of 0.9 g/L is 900 mg/L, high for a fragrance material, so it will go into a water-containing product.
An 18-month shelf life. It is an ester and will hydrolyse — moisture is its enemy, so keep the cap tight.
What this doesn't establish
I have not smelled it. The whole piece sets database fields, the formula corpus and two papers against each other.
"< 4 hours" is the database's record, and I have no source for exactly what that sign means. I read it as "already undetectable at the earliest check", which is a reasonable reading of the notation rather than a definition the database supplies.
Frost's study used hybrid poplar and gypsy moth larvae under controlled conditions at "naturally wound-emitted concentrations". That is not a concentration any perfume produces, and the abstract does not quantify it.
"An alarm that never stops is not an alarm" is my figure of speech, not the paper's argument. That paper does not discuss why the molecule is volatile. Setting its short substantivity beside its signalling function is an observation, not a causal claim.
Of Desmedt's paper I read only the title and authors. I cite the scope its title states — broad-spectrum induced resistance in rice — and no results or figures.
Guava headspace at 1.30% is a number in the database's occurrence field, with no primary source, and natural compositions shift with origin and method. Treat it as an order of magnitude, not a specification.
The 79 corpus formulas were found under the spelling cis-3-hexenyl acetate. Formulas writing it as (Z)-3-hexen-1-yl acetate or otherwise would have been missed.
The GHS classification is what the database records, not a complete regulatory determination. Work from the SDS for your own batch and the current IFRA standard.
References
C. J. Frost, M. C. Mescher, C. Dervinis, J. M. Davis, J. E. Carlson, C. M. De Moraes, Priming defense genes and metabolites in hybrid poplar by the green leaf volatile cis-3-hexenyl acetate, New Phytologist, 180(3), 722-734 (2008). PMID 18721163. doi:10.1111/j.1469-8137.2008.02599.x
W. Desmedt, M. Ameye, O. Filipe, et al., Molecular analysis of broad-spectrum induced resistance in rice by the green leaf volatile Z-3-hexenyl acetate, Journal of Experimental Botany, 74(21), 6804-6819 (2023). PMID 37624920. doi:10.1093/jxb/erad338
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