Material guide · 162
Material guide: 2-methyl undecanal (aldehyde C-12 MNA) — one wrong boiling point that dragged the vapour pressure with it
· 17 min read
CAS 110-41-8, 40 suppliers, C12H24O. Its boiling point field carries two values at the same pressure, 171 °C and 233 °C, 62 degrees apart. The homologous series settles it: 2-methyl decanal, one carbon shorter, is registered at 170 °C, and adding a carbon cannot raise a boiling point by one degree. Straight-chain undecanal is 223 °C, so a branched twelve-carbon aldehyde landing near 233 is the sensible reading. What makes this interesting is that the error did not stop at the boiling point. Its vapour pressure reads 1.428 mmHg marked est, and the relationship I fitted across 8,048 materials returns 1.94 for a boiling point of 171 and 0.039 for 233, while dodecanal, the same molecular formula, is registered at 0.034. That estimated vapour pressure looks like it was computed from the wrong boiling point. In the corpus, merging five spellings gives 67 formulas at a median dose of 1.00%, and its odour field runs to ten words including metallic and gassy.
About a 4 minute read.
The short version
- Name: 2-methyl undecanal, trade code aldehyde C-12 MNA, CAS 110-41-8, 40 suppliers
- C12H24O, molecular weight 184.32; odour type aldehydic
- Odour: fresh, amber, aldehydic, mossy, citrus, tuberose, metallic, waxy, coumarinic, gassy
- High strength (rank 3), evaluate at 1% or less; substantivity 388 hours
- Its boiling point field carries 171 °C and 233 °C at the same pressure
- And its vapour pressure looks like it was estimated from the wrong one
- 67 formulas in the corpus once five spellings are merged, median dose 1.00%
Sixty-two degrees apart
The bp field:
171.00 °C. @ 760.00 mm Hg | 233.00 °C. @ 760.00 mm Hg
One pressure, two values, sixty-two degrees apart.
I have just swept the database: 208 materials are in this
state, and nine in ten resolve through the (est) marker by keeping the unmarked value.
Neither of this record's values is marked, putting it among the twenty that do not resolve.
The homologous series settles it
Aldehyde boiling points rise regularly with carbon count, roughly 20 degrees per carbon. Placing this material in its series:
| Material | Carbons | Structure | Boiling point @760 | Vapour pressure |
|---|---|---|---|---|
| decanal (aldehyde C-10) | 10 | straight | 207–209 | 0.207 |
| undecanal (C-11 undecylic) | 11 | straight | 223 | 0.083 |
| 2-methyl decanal (C-11 MOA) | 11 | branched | 170 | 0.102 |
| 2-methyl undecanal (C-12 MNA) | 12 | branched | 171 or 233 | 1.428 |
| dodecanal (C-12 lauric) | 12 | straight | (185 @100 mmHg) | 0.034 |
The third row is the key: 2-methyl decanal, one carbon shorter, is registered at 170 °C.
If this material were 171, adding a carbon would have raised the boiling point by one degree. Homologous series do not work that way.
Straight-chain undecanal is 223 °C. Branching lowers a boiling point by a dozen degrees or so, but this material carries one more carbon than undecanal. Put the two effects together and 233 is where it should land.
So 233 is right and 171 is the spare one.
(Incidentally, 2-methyl decanal's own 170 °C looks suspect for the same reason: if straight-chain undecanal is 223, a branched eleven-carbon aldehyde should not fall to 170. Those two numbers may share a wrong source, which I did not pursue.)
And the error did not stop at the boiling point
This record's vapour pressure reads 1.428 mmHg and carries (est). An estimate.
I fitted the relationship between vapour pressure and boiling point across 8,048 materials:
boiling point ≈ 181.5 − 36.5 × log10(vapour pressure)
Running it backwards on the two candidate boiling points:
| Boiling point fed in | Vapour pressure the relationship returns |
|---|---|
| 171 °C | 1.94 mmHg |
| 233 °C | 0.039 mmHg |
The database registers 1.428, which is close to the 171 side.
And its straight-chain isomer dodecanal registers a vapour pressure of 0.034, almost exactly what 233 °C predicts at 0.039.
That estimated vapour pressure looks like it was computed from the wrong boiling point.
One error produced a second, and the two are consistent with each other. It is the most complete propagation of an error I have found in this database.
(I noticed in #112 that this material's vapour pressure is 42-fold from dodecanal's and recorded it as an anomaly. Only this round did I learn where it came from.)
And that 388 hours follows the same way
The odor_substantivity field reads 388 hours @100%.
I have computed how vapour pressure relates to substantivity: roughly 5.85-fold per decade of vapour pressure. If the vapour pressure really were 1.428, this material would sit in the same bracket as dextro-limonene (1.55, four hours), not at 388.
With the corrected 0.039 it fits. Its same-formula isomer dodecanal (0.034) is registered at 368 hours, close to this record's 388.
The substantivity field is right and the vapour pressure field is wrong. Reason from the vapour pressure and you arrive at the opposite conclusion.
What it smells like
The odour field runs to ten words:
fresh, amber, aldehydic, mossy, citrus, tuberose, metallic, waxy, coumarinic, gassy
The evaluation description is blunter:
Gassy, diffusive, metallic, waxy, with coumarin and citrus nuances.
Metallic and gassy are the signature of an aliphatic aldehyde. At low concentration this class reads as bright and forceful; overdose it and you get an unlit gas ring. Hence the recommendation to evaluate at 1% or less, and the strength rank of 3.
And it is branched, with a methyl group on carbon 2. That methyl suppresses the waxiness of a straight-chain aldehyde and buys a brighter, cleaner effect. Its straight-chain sibling dodecanal (C-12 lauric) has an odour field of fatty, citrus and waxy: no metallic and no gassy.
Almost absent from nature
The occurrence field holds two entries:
kumquat oil; rue
Two sources, neither quantified. Dodecanal's occurrence list is far longer.
Its notes field is one line, Used as a food additive [EAFUS], and its regulatory field carries
all four of JECFA, FEMA GRAS, CoE and FLAVIS, with FEMA 2749.
Dose and storage
The corpus writes it five ways (aldehyde c-12 mna 60 times, aldehyde mna 6, and so on), merging
to 67 formulas:
| Dose | |
|---|---|
| Median | 1.00% |
| Quartiles | 0.50% – 2.50% |
| Max | 15.0% |
The overall median for strength rank 3 is 0.76%, so this runs slightly above its rank.
Its shelf life is 12 months and it needs nitrogen, because like every aldehyde it oxidises to the carboxylic acid in air.
What this doesn't establish
- I measured neither the boiling point nor the vapour pressure. "233 is right" is an inference from the homologous series, and "the vapour pressure came from the wrong boiling point" comes from feeding the database's values into a relationship I fitted myself.
- That relationship has a residual standard deviation of 34 °C. It can separate 171 from 233; it cannot supply a precise value.
- I flagged 2-methyl decanal's 170 °C as suspect without pursuing it.
- "One error produced a second" is the simplest explanation, not the only one. The two fields might have been copied from two different wrong sources.
- The RIFM assessment covers its dimethyl acetal (CAS 68141-17-3), not the material itself. I could not find one for 110-41-8.
- The odour reading (the methyl suppressing waxiness) is a general principle, not a measured comparison of these two records.