Material guide: benzophenone — the supplier calls it "very faint" and the substantivity field says 394 hours

About 5 minutes.

Short version

• Name: benzophenone, also diphenylketone, CAS 119-61-9
• Formula C13H10O, MW 182.22; FEMA 2134, JECFA 831, FLAVIS 07.032, CoE 166
• Odour: balsamic type — balsamic, rose, metallic, powdery, geranium, herbal
• Strength: medium (smell at 10% or less), rank 2
• Substantivity: 394 hours; vapour pressure 0.001 mmHg
• Appearance: white crystalline powder, melting at 47–51 °C
• Assay: 98.00 to 100.00; shelf life 36 months or longer
• Suppliers: 41
• GHS: H351 suspected of causing cancer, H400/H410 aquatic toxicity
• Storage: cool, dry, sealed, protected from heat and light

One thing first. This is not the benzophenone-3 (oxybenzone) on a sunscreen label, and "add it for UV protection" gets the mechanism backwards. That is Add benzophenone for UV protection. This article is about it as a fragrance material.

"Very faint" and 394 hours

The supplier descriptions the database carries complement each other well:

"faint, sweet rose, light herbal nuance like geranium"

"very faint powdery-rosy geranium-like odor with a slightly metallic note"

"sweet aromatic slightly-rose fruity-vinyl"

And the substantivity field says 394 hours.

Faint and persistent together sounds contradictory, but it is a class with size to it.

Pulling every material with at least ten suppliers that has values in both the strength and substantivity fields gives 1,193 records. Of those, 189 — 15.8% — are low or medium strength with substantivity of 350 hours or more.

Who is in that class:

Material	Suppliers	Substantivity	Odour type
Vanillin	193	400 h	vanilla
Patchouli oil	148	400 h	woody
Raspberry ketone	112	400 h	berry
Sandalwood oil	81	400 h	woody
Cinnamyl alcohol	79	371 h	balsamic
Coumarin	74	364 h	tonka
benzophenone	41	394 h	balsamic

One in six commonly stocked materials belongs to this class, and this class is what carries the weight in a formula. Low strength does not mean low dose — hexyl salicylate reads low in the strength field and has a median formula dose of 7%.

That is also the subject of the other article this round: a formula five people diagnosed, where the two largest materials were both medium strength, together made up half the aroma material, and nobody mentioned either (Five people diagnosed the same formula). Understated materials are not understated on the weight table.

It is a solid

Melting point 47–51 °C, so at room temperature it is a white crystalline powder.

That matters more in practice than the odour does. You cannot measure it with a pipette, and you cannot drop it in and wait for it to disperse. So:

• Weigh it; do not count drops. There is no drop to count.
• Make a solution first. Alcohol, fixed oils and paraffin oil are all in the solubility field; 10% in ethanol or DPG is the usual move.
• A solution can drop out at low temperature. At 10% a material melting at 47–51 °C is usually fine, but concentrate it and you need to watch. Telling apart the particles at the bottom of a bottle is Particles in the bottle.

Solid aroma materials are not unusual — coumarin, vanillin and heliotropin all are.

One sentence buried in the solubility field

Besides listing solvents, the solubility field slips in a phrase: "non-discoloring in most media".

That marking is not common. Of the 3,156 materials with ten or more suppliers, only 213 (6.7%) carry it.

For anyone making soap, candles or household products it is worth something — plenty of balsamic and phenolic materials will yellow a finished product. But note it says most media, not all, and it is a supplier's claim rather than a test report.

The occurrence field: it really does grow in plants

The occurrence field reads arisaema ciliatum, arisaema tortuosum — two Arisaema species — and the notes field adds that it is present in grapes.

That is the reverse of its relative oxybenzone, whose occurrence reads "not found in nature" while its natural_synthetic field says "natural". There are 306 records where those two fields contradict each other, counted in My database can't settle the synthetic-versus-natural argument.

On this record the two fields agree, which in this database is worth noting on its own.

The GHS field is not empty

H351 — Suspected of causing cancer H400 — Very toxic to aquatic life H410 — Very toxic to aquatic life with long lasting effects

The background: of 42,225 records, only 359 (0.9%) carry a GHS entry, rising to 337 of 3,156 (10.7%) among materials with ten or more suppliers. Among those that do, four carry H351 — acetaldehyde, benzophenone, musk xylol and (Z)-aconitic acid.

The acute toxicity numbers are not high: oral rat LD50 > 10000 mg/kg, dermal rabbit LD50 3535 mg/kg. Low acute toxicity and a suspected-carcinogen classification are different endpoints and do not cancel each other out.

And H410 is about water bodies — what happens after it goes down a drain — not about the dose on your skin. That layer is separated out in An environmentally friendly musk.

These figures are bounded by that 0.9% coverage and cannot be read as "everything else is fine".

Why it turns up in photochemistry textbooks

The notes field also carries this:

"Benzophenone is a common photosensitizer in photochemistry. It crosses from the S1 state into the triplet state with nearly 100% yield. The resulting diradical will abstract a hydrogen atom from a suitable hydrogen donor to form a ketyl radical."

When Cuquerella and colleagues reviewed photosensitized DNA damage in Accounts of Chemical Research in 2013, this is the molecule they picked as the classical and paradigmatic chromophore.

The practical implication for a formula is limited — those are photochemistry-experiment conditions, not the inside of a perfume bottle. But it explains why this record's storage field goes out of its way to say "protected from heat and light", and why adding it as UV protection points the wrong way.

How to use it

• Evaluate at 10% or less, as the field recommends.
• Use it as a long-lasting powdery rose/geranium background, not a lead. Its odour field carries rose and geranium, so it joins the line that runs through PEA and citronellol.
• Weigh it, and make a solution first.
• Store it away from light. Its own field says so.
• Do not use it as a UV additive. The reasons are in the other article.

What this doesn't establish

• I have not smelled it. The whole article is fields, database-wide counts and one paper.
• "Very faint" is the supplier's description, not my judgement, and supplier descriptions disagree with each other by nature.
• The 189 "low/medium strength × long substantivity" records come from my own thresholds (≥10 suppliers, ≥350 hours); change the thresholds and the number changes. And 400 is the ceiling of the substantivity field (That "400 hours" for Ambroxan), so the long end of that column is compressed to begin with.
• "Non-discoloring" is a supplier marking. I have not tested it and have not looked into which media it fails in.
• The four H351 records are bounded by the 0.9% coverage and are not a complete list.
• The acute toxicity data come from literature dated 1973 to 1983, as the field itself states.
• I did not check current EU cosmetic regulation. The regulatory field lists only JECFA, FEMA GRAS, CoE and FLAVIS, with no IFRA entry, which does not mean there is no restriction.
• The photosensitizer passage describes photochemistry-experiment conditions. I have no measurements of a perfume formula under light.