Material guide: phenethyl salicylate, one of the lowest vapour pressures in the library, and the strength field says low

In short: this material separates two things that get conflated, lasting a long time and having presence. It sits at the library's lowest end for vapour pressure while its strength field sits at the bottom band.

Fields

Field	Value
CAS	87-22-9
EINECS	201-732-5
First synonym	salicylic acid, phenethyl ester
Formula	C15H14O3, MW 242.274
Database category	flavor and fragrance agents
Appearance	white crystalline powder (est)
Assay	98.00 to 100.00
Melting point	39-41 C
Boiling point	370 C @ 760 mmHg; 190 C @ 5 mmHg
Flash point	> 110 C
logP	4.50 (est)
Vapour pressure	0.000002 mmHg @ 25 C (est)
Water solubility	7.856 mg/L @ 25 C (est)
Solubility	alcohol; paraffin oil; alcoholic lotion; antiperspirant; deo stick; shampoo; soap; fabric softener
Odour type	floral
Odour	balsamic; floral; rose; hyacinth; carnation
Strength	low (rank 1)
Substantivity	232 hours (20% in dipropylene glycol)
Shelf life	24 months
Occurrence	Tahitian gardenia flower; plumeria flower; Astragalus sahendi flower
Suppliers	33
Regulatory	JECFA 905, FEMA 2868, CoE 437, FLAVIS 09.753
Cosmetic uses	perfuming agents
Oral toxicity	rat LD50 > 5000 mg/kg
GHS	H315 skin irritation; H319 serious eye irritation; H335 may cause respiratory irritation
Taste descriptors	medicinal; metallic; balsamic; laundered cloth; powdery; plastic

Two extremes in one record

Vapour pressure 0.000002 mmHg.

Ranking the 654 materials in the library that have 25 or more suppliers and a vapour pressure figure, then setting aside the odourless industrial chemicals, this one sits at the bottom.

For comparison:

	Vapour pressure @ 25 C	Relative to it
ethanol	44.6 (@ 20 C)	22.3 million times faster
para-anisaldehyde	1.0	500,000 times faster
linalool	0.016	8,000 times faster
musk ketone	0.000012	6 times faster
phenethyl salicylate	0.000002	1

And the strength field on the same record reads low, at strength rank 1.

Across the ninety-odd materials I have written up, most sit at rank 3 (high). Rank 1 is uncommon, and here it shares a record with the library's lowest vapour pressure.

Why both can be true at once

Because substantivity and presence measure different things.

A low vapour pressure means it leaves slowly, hence the 232-hour substantivity figure at 20% in dipropylene glycol. But whether a material is perceived in the air depends on the ratio of its partial pressure to its odour threshold. A low vapour pressure also lowers its ability to push molecules into the air.

Osako and Nishida studied that relationship in the Japanese Journal of Hygiene in 1992. Within homologous series of aliphatic compounds, vapour pressure and odour threshold correlate very well, meaning low vapour pressure usually comes with a low threshold (easier to detect). They also found exceptions: ionised substances (acids, amines) and sulfur compounds show no good correlation, and within the alcohol and aldehyde series the rate at which threshold falls with falling vapour pressure gets smaller.

The two effects pull opposite ways, and they do not conveniently cancel. For this material, the database's verdict is that the partial pressure side wins: it lasts, and it is weak.

(The perfume engineering methods Rodrigues and colleagues reviewed in Molecules in 2021 address exactly this: they model with vapour-liquid equilibrium and Fick's law of diffusion rather than reading vapour pressure directly.)

Arctander's verdict

The database's odour description field quotes Arctander, beginning:

"This material is very well known, but not extensively used..."

33 suppliers, four regulatory bodies with numbers assigned, and I could not find it anywhere in the 954-formula corpus. Well known and little used matches what he wrote.

One possible explanation sits in the taste field: medicinal, metallic, laundered cloth, powdery, plastic. That is an unappealing list of words, while the odour field reads balsamic, rose, hyacinth, carnation. One material, two descriptions a long way apart.

(The taste field records what it is like in the mouth and the odour field what it is like in the nose, so divergence is normal. This one diverges more than most.)

It is a solid

White crystalline powder, melting at 39 to 41 C.

That is a little above body temperature, so it is solid at room temperature and softens in a hot car. Using it means making a solution first, and the solubility field lists alcohol and paraffin oil.

(logP 4.50, lipophilic. That contrasts usefully with the three-way trade-off in the isopropyl myristate article: this material is itself a combination of high melting point, high logP and extremely low volatility.)

The occurrence field

Tahitian gardenia flower, plumeria flower, and an Astragalus flower.

Three white flowers. The field gives no content percentage for any of them, so I do not know which carries the most.

(Why the percentages in that field matter, and how widely they vary, is in How much does a natural actually vary.)

What this doesn't establish

• I have not smelled it. This is database fields plus two papers.
• The vapour pressure is an estimate. "Lowest in the library" is a comparison among the 654 materials that have a vapour pressure figure and 25 or more suppliers, and only 21% of the library has that field at all. Something lower may sit among the records without it.
• "Strength low" is the database's judgement, not my measurement. How that field was assigned is not documented.
• On the "lasts but weak" mechanism I have given only a direction. Osako's work covered homologous series of aliphatic compounds, and salicylate esters are not among them.
• I could not find it in the corpus, which means those 954 formulas do not use it, not that nobody in the market does.
• I have not explained the divergence between the taste and odour fields. It may be two evaluators, two eras, two media.
• I have not tested the practical effect of a 39-41 C melting point. "Softens in a hot car" is an inference.
• The occurrence field carries no content figures, so those three flowers are a qualitative record only.