Material guide: camphene — the puzzle left open last time resolves as "camphene" not being one thing

About 5 minutes.

Short version

• Name: camphene, CAS 79-92-5, C10H16, MW 136.24
• FEMA 2229, JECFA 1323, FLAVIS 01.009, CoE 2227, structure class I
• Odour type: woody; eleven words in the odour field — woody, herbal, fir needle, camphoreous, terpenic, cooling, pine, citrus, green, minty, spicy
• Strength: medium (smell at 10% or less), rank 2
• Substantivity: the field reads "< 1 hour at 10% in DPG" — the very short end of that column
• Vapour pressure 3.0 mmHg; melting point 51.2 °C, a crystalline solid at room temperature
• Flash point 35.0 °C; GHS H228 flammable solid, H319 eye irritation 2A, H400/H410
• Assay: 80.00 to 100.00
• Suppliers: 39

The puzzle left open last round

When I wrote Who wrote the odour field, I used vocabulary overlap between the two describers to find cases. Most "zero overlap" materials resolve as a difference in dose — one smelled it at 25%, the other at 10%, which is not disagreement.

Camphene would not resolve, because both stated 10%:

Luebke (1997): at 10.00% in dipropylene glycol. woody herbal fir needle camphor terpenic.

Mosciano (2000): at 10.00%. Camphoraceous, cooling, piney woody with terpy nuances. It has citrus and green minty and green spicy notes.

Same concentration; one says fir needle and woody, the other citrus and green minty. Only "camphor" barely lines up.

I left it as an open question. The answer is in another field.

The answer is in the formulations field

The formulations field says:

commercial product may contain approx 20% tricyclene. … grades of purity: commercial, 75% or greater.

And the assay field reads 80.00 to 100.00 — a twenty-point range.

Look at the supplier entries carried in the solubility field, and the same database lists, side by side:

"Camphene 95%" … "Camphene 46%" … "Camphene 94%"

One supplier sells both a 46% and a 94% "camphene".

So those two describers may genuinely have smelled different things. Both wrote "10% camphene solution", but if one bottle of starting material was 94% and another 46%, the two solutions differ substantially.

Nobody misremembered. There is more than one product under this name.

(How wide assay ranges get, and the three causes behind wide ones, is measured in How wide is the assay window. Camphene is the representative of the "the synthesis does not run clean" class.)

Why the tricyclene is there

Camphene is not picked off a tree — industrially it is made by isomerising α-pinene, which comes from turpentine.

Huang and colleagues tested titanate nanotubes as solid acid catalysts for solvent-free α-pinene isomerisation in RSC Advances in 2020. Their best result:

The highest conversion was up to 97.8% with selectivity to camphene of 78.5% under mild reaction conditions, and the catalyst also showed outstanding reusability after four runs.

Note the gap between those two numbers. A conversion of 97.8% says almost all the α-pinene reacted; a selectivity of 78.5% says under four fifths of it became camphene.

The rest is other products — and tricyclene is one of them, being a sibling on the same carbocation rearrangement pathway.

So the 80-to-100 assay range is not slack quality control. It is the shape of the reaction.

(That paper's subject is the catalyst, not camphene's odour. I cite it to explain where the range comes from.)

A solid melting at 51 °C with a flash point of 35 °C

This set of numbers is worth stopping on:

Melting point	51.2 °C
Flash point	35.0 °C
Boiling point	159–160 °C
Vapour pressure	3.0 mmHg @ 20 °C

The flash point is 16 degrees below the melting point. While it is still a solid, the vapour it gives off is already ignitable.

That is why the GHS hazard statement reads H228 — flammable solid, rather than the H226 of an ordinary liquid aroma material.

In practice:

• It is a crystalline solid at room temperature (the appearance field reads "colorless to light yellow crystalline solid"), so weigh it rather than dropping it.
• A 35 °C flash point matters for shipping. Those rules are in Shipping a flammable liquid — though this one classifies as a solid, so a different entry applies and needs checking separately.
• The storage field says away from heat and light; shelf life 24 months.

Substantivity under 1 hour

The raw substantivity string is "< 1 hour(s) at 10.00 % in dipropylene glycol", and the numeric column keeps 1.0.

This is the very short end of this database. For comparison, cis-3-hexenyl acetate is 4 hours, and the ceiling of the substantivity field is 400.

With a vapour pressure of 3.0 mmHg — the top 12.7% database-wide — the direction is consistent: this material moves fast.

Note that the inequality sign is dropped by the numeric column again. "< 1" and "1" are not the same statement, and only the second survives.

Where it occurs

The occurrence field is one of the longest I have seen, and it carries percentages: angelica root oil at 1.88%, galangal oil at 0.50%, ajowan seed oil at trace, yarrow flower oil (Iran) at 3.10% — the list runs for several lines.

The molecule is widespread in conifer and Apiaceae essential oils, and it is usually not a main constituent in them.

"Fir needle" and "pine" in the odour field are not metaphors; they are its actual provenance.

How to use it

• Evaluate at 10% or less, as the field recommends.
• Ask about purity when buying. An 80-to-100 spec range plus 46% and 94% products in the market makes this one worth confirming.
• It is a top note, and an extreme one. Substantivity under an hour. For sustained pine or camphor, this is not the material.
• Weigh it; it is a solid. Melting point 51 °C.
• Mind the flammable-solid classification. The flash point is below the melting point.
• It carries FEMA, JECFA, FLAVIS and CoE numbers, so its food rules are traceable.

What this doesn't establish

• I have not smelled it, and I have not compared a 46% against a 94% product. "The two describers may have smelled different things" is an explanation derived from fields, not something I verified.
• I do not know which purity of sample either of them used. The description field states the solution concentration, not the starting material's specification. That is the biggest gap in this explanation.
• Huang's paper is about the catalyst. The 78.5% selectivity is their system's best result, not an industry figure, and not a claim about what commercial camphene contains.
• "Tricyclene and camphene come from the same rearrangement pathway" is a general statement of terpene chemistry. I did not consult the mechanistic literature for that reaction.
• The formulations field's "approx 20% tricyclene" carries no source or date.
• The percentages in the supplier entries (46%, 94%, 95%) are part of product names; I did not check them against analytical values.
• GHS classifications are supplier-declared and may differ between suppliers.