Material guide · 73
Material guide: alpha-amyl cinnamaldehyde — the twin that never became a workhorse, and four columns explaining why
· 24 min read
CAS 122-40-7. One carbon from alpha-hexyl cinnamaldehyde, and the market chose the hexyl: 70 formulas against 157. Adding genre breadth this round sharpens the gap — the hexyl spans all fourteen genres with 32.4% in its largest, the amyl reaches twelve with 55.6%, well above the 35.4% baseline. Substantivity 256 hours against 400. Aquatic hazard H411 toxic against H412 harmful, and IFRA Category 9 therefore reads 1.5% against 19%. Four independent columns point the same way. A 1996 Danish study found both twins inside perfumes sold as natural.
The hexyl cinnamal guide introduced this pair of twins: one carbon apart on the side chain, both smelling of jasmine, both among the EU's 26 declarable fragrances.
That piece compared substantivity, aquatic toxicity and IFRA limits. This round adds one more column — genre breadth — and it sharpens the picture.
Four independent columns, all pointing the same way.
The short version
- 70 formulas against 157. The hexyl gets used 2.2 times as often.
- Genre breadth differs more: the hexyl spans 14/14 genres with 32.4% in its largest (below the 35.4% baseline, a workhorse); the amyl reaches 12/14 with 55.6% (1.57 times baseline, a floral specialist).
- Substantivity 256 hours against the hexyl's 400.
- Aquatic hazard H401 / H411 toxic against the hexyl's H402 / H412 harmful.
- IFRA Amendment 49 Category 9 (household cleaning): 1.5% against 19% — twelvefold.
- A 1996 Danish study found 91% of 22 perfumes "based on natural ingredients" contained target sensitisers, and both twins were on its list.
- Its natural occurrence is soybean and black tea (the hexyl's is chamomile).
About 8 minutes.
The four columns side by side
| alpha-amyl cinnamaldehyde | alpha-hexyl cinnamaldehyde | |
|---|---|---|
| CAS | 122-40-7 | 101-86-0 |
| Formula | C₁₄H₁₈O, MW 202.30 | C₁₅H₂₀O, MW 216.32 |
| Corpus appearances | 70 (7.3%) | 157 (16.5%) |
| Median dose | 6.00% | 8.00% |
| Genres | 12/14 | 14/14 |
| Largest genre | 55.6% floral | 32.4% floral |
| Corpus baseline | 35.4% | 35.4% |
| Substantivity | 256 hours at 100% | 400 hours at 100% |
| Aquatic | H401 / H411 toxic | H402 / H412 harmful |
| IFRA Category 4 | 7.0% | 9.9% |
| IFRA Category 9 | 1.5% | 19% |
| IFRA Category 10A | 1.5% | 69% |
| Suppliers | 53 | 56 |
| Occurrence | soybean, black tea | chamomile |
Supplier counts are almost identical (53 against 56) and every other column differs.
That deserves separating out: both are on the market and both are easy to buy, and one gets used more than twice as often. This is not a supply problem but a choice.
The breadth column is new this round
Last round we sorted the 954 formulas into fourteen genres by title, counting how many genres each material reaches and how concentrated it is in its largest.
The key step is the baseline: floral labels make up 35.4% of all labels in the corpus.
- Hexyl cinnamal at 32.4% — below baseline. It spreads wider than the corpus itself, so it is a workhorse.
- Amyl cinnamal at 55.6% — 1.57 times baseline. It concentrates in florals more than the corpus does.
Both smell of jasmine, and only one became something you can put anywhere.
That difference is invisible in the other columns. A 144-hour gap in substantivity and one grade of aquatic hazard do not decide whether a formulator will reach for it in a woody. The breadth column measures something else: how easily it makes sense somewhere other than a floral.
I cannot get causation out of the data. It could be that the odour itself is more floral, it could be historical inertia (the amyl is the older molecule), or it could be that the household limits push it out of functional work — and that last one comes with numbers.
A twelvefold difference in household limits
IFRA Amendment 49 treats them similarly in fine fragrance and very differently in the household categories:
| IFRA category | amyl | hexyl | Ratio |
|---|---|---|---|
| Category 4 (fine fragrance) | 7.0% | 9.9% | 1.4× |
| Category 9 (household cleaning) | 1.5% | 19% | 12.7× |
| Category 10A (other household) | 1.5% | 69% | 46× |
And GHS offers a coherent explanation.
| amyl | hexyl | |
|---|---|---|
| Sensitisation | H317 | H317 |
| Aquatic | H401 / H411 toxic | H402 / H412 harmful |
One says toxic, the other harmful — one grade apart.
To be clear: that reading comes from putting two tables side by side, and IFRA does not explain in the text how a limit was derived. Aquatic toxicity is a plausible explanation rather than a demonstrated cause.
The practical consequence is real, though: if you are making soap, detergent, candles or anything in Category 9 or 10, the amyl has almost no room and the hexyl has plenty. And the 2018 survey we cited in the hexyl piece, counting ingredient lists across 1,447 products in 131 households, found the hexyl among the most-named — not the amyl.
Some part of that 70 against 157 may run along this line.
The safety assessment
RIFM published an ingredient safety assessment for this material in 2015 (Api and colleagues, Food and Chemical Toxicology), for CAS 122-40-7.
Care is needed here. That assessment has no abstract on PubMed — I can confirm it exists and matches the right CAS, and I cannot cite its conclusions. I list it in the references to point out that a dedicated safety assessment exists to read, not to relay anything I have not read.
This is worth writing down, because RIFM assessments are easy to grab wrong. Searching "amyl cinnamal RIFM" turns up all of:
- amyl cinnamate (CAS 3487-99-8) — an ester, not an aldehyde, a different molecule
- α-amyl cinnamic aldehyde diethyl acetal (CAS 60763-41-9) — an acetal derivative
- α-amylcinnamaldehyde (CAS 122-40-7) — this one
Three different assessments with names that look alike. The same class of problem as the trade names in the jasmine piece: check the CAS, not the name.
Inside "natural" products
Someone in the thread complained about "safe naturals — that well known oxymoron". This material appears in a study that goes straight at it.
Rastogi and colleagues investigated 42 cosmetic products based on natural ingredients in Contact Dermatitis in 1996, for the content of 11 fragrance substances: geraniol, hydroxycitronellal, eugenol, isoeugenol, cinnamic aldehyde, cinnamic alcohol, α-amylcinnamic aldehyde, citral, coumarin, dihydrocoumarin and α-hexylcinnamic aldehyde.
The results:
- 91% (20/22) of the natural-ingredient-based perfumes contained 0.027%-7.706% of 1 to 7 of the target fragrances.
- 82% (18/22) contained between 1 and 5 of the chemically defined synthetic constituents of fragrance mix.
- Among the other cosmetics (shampoos, creams, tonics), 35% (7/20) contained 0.0003%-0.0820% of 1 to 3 of them.
- Relatively high concentrations of hydroxycitronellal, coumarin, cinnamic alcohol and α-amyl cinnamic aldehyde were found in some of the products.
And the paper's own conclusion is the bluntest part:
The detection of hydroxycitronellal and α-hexylcinnamic aldehyde in some of the products demonstrates that artificial fragrances, i.e., compounds not yet regarded as natural substances, may be present in products claimed to be based on natural ingredients.
That is 1996 and the market has changed. The structural problem has not: "based on natural ingredients" is not a regulated definition.
Physical properties
| Property | Value |
|---|---|
| CAS | 122-40-7 |
| Formula | C₁₄H₁₈O, MW 202.30 |
| Appearance | pale yellow to yellow clear liquid (est) |
| Boiling point | 287-290 °C |
| Flash point | > 100 °C |
| logP | 4.20 (est) |
| Water solubility | 8.545 mg/L at 25 °C (est) |
| Shelf life | 12 months or longer |
| Substantivity | 256 hours at 100% |
| Strength | medium |
| Suppliers | 53 |
| Occurrence | soybean, black tea |
| Regulatory listings | JECFA, FEMA GRAS, CoE, FLAVIS |
| GHS | H317, H401, H411 |
| Odour | sweet, floral, oily, fruity, herbal, jasmin, tropical, green, powdery |
A 12-month shelf life, same as the hexyl and shorter than most materials. Aldehydes oxidise.
Water solubility of 8.545 mg/L is three times the hexyl's 2.75, and neither goes into a water phase.
The black tea in the occurrence field is worth noting. The hexyl occurs in chamomile and this one in soybean and black tea. Neither comes from jasmine — as the hexyl piece set out, jasmine does not make this class of molecule.
What this doesn't establish
I have smelled neither and made no comparison. The whole piece sets database fields, the formula corpus, the IFRA text and two papers against each other.
For the RIFM paper I confirmed only its existence and its CAS, and cite none of its conclusions. There is no abstract on PubMed, and I do not relay what I have not read. To use that assessment, read the original.
"The household limit gap comes from aquatic toxicity" is my inference. The two tables were looked up separately and IFRA does not explain how a limit is derived.
I have no answer at all for why the breadth differs. Odour, history and regulation could all play a part, and the data can only tell me the difference exists.
The breadth method and its limits are in the workhorse piece: keyword matching on titles misfires, 21.2% of formulas get no label, and the samples differ more than twofold (70 against 157), so part of the 12/14 versus 14/14 gap may be sample size alone.
Rastogi's study is the 1996 Danish market. Thirty years on, and EU labelling rules only arrived in 2005, so those percentages cannot describe today's market. I cite it for the structural observation rather than the numbers.
The two substantivity figures (256 against 400 hours) come from two database records, both marked 100%, with no guarantee of one experiment or method.
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
A. M. Api, D. Belsito, S. Bhatia, et al., RIFM fragrance ingredient safety assessment, α-amylcinnamaldehyde, CAS registry number 122-40-7, Food and Chemical Toxicology, 82 Suppl, S20-S28 (2015). PMID 25636726. doi:10.1016/j.fct.2015.01.008
S. C. Rastogi, J. D. Johansen, T. Menné, Natural ingredients based cosmetics. Content of selected fragrance sensitizers, Contact Dermatitis, 34(6), 423-426 (1996). PMID 8879930. doi:10.1111/j.1600-0536.1996.tb02246.x
Related: alpha-hexyl cinnamaldehyde, what makes a workhorse, are naturals gentler, what IFRA limits actually limit.