Olfactory Chemistry: Low Atranol Oakmoss- Keeping the Bite

In the ongoing saga of restricted materials the one which has elicited the most concern has been oakmoss. The reason for this concern is it is one of the key components of a chypre accord. When the restrictions were first being considered there was a lot of consternation over the effect it would have on the classic chypres like Guerlain Mitsouko. One solution was to bring chemistry to the rescue to see if the oakmoss absolute could be treated to remove the chemicals which were the suspected skin sensitizers.

atranol chloroatranol

In 1992 a team at Givaudan (International Journal of Cosmetic Science, vol. 14, pg. 121-130, 1992) used the nature of these molecules and their reactivity to remove them from oakmoss absolute. Atranol and Chloroatranol (shown above) were the suspected bad actors in oakmoss absolute. What you see highlighted in red is the aldehyde function. These are not the typical aldehydes associated with perfume. Those are at the end of long carbon chains. The ones depicted in Atranol and Chloroatranol are what are called aromatic aldehydes and they are much more likely to react. The team at Givaudan took advantage of that and used that reactivity. These aromatic aldehydes in the presence of an amino acid like Leucine will form a molecule called a Schiff Base. Under the right conditions this will form a solid which will fall out of solution. Then if you filter that solid off what remains is a version of oakmoss absolute with those molecules “washed” out. After some early success with a few amino acids by themselves they found a mixture of Leucine (the one pictured) and Lysine removed the Atranol and Chloroatranol down to barely detectable amounts.

atranol schiff base

The big question left to answer was would this treated oakmoss absolute still be able to be used in perfumery. If you’ve smelled oakmoss in a perfume in the last ten years it is likely this Low Atranol Oakmoss is what you smell. It retained enough of the nature of the oakmoss that the perfumers could add in other materials to replace whatever the Atranol and Chloroatranol would have otherwise brought to the scent profile. One of the more common materials used for this purpose is one of the synthetic oakmoss replacements Evernyl which by itself was not seen as a good alternative. When combined with the Low Atranol Oakmoss it helps fill in for the missing Atranol.

The further question about whether the removal of the Atranol now made these compounds less allergenic is not as clear cut. The most recent paper on the subject published in 2014 by a group from Odense University in Denmark (Contact Dermatitis, vol. 72, pg. 75-83, 2014) showed it was much less allergenic but not completely free of causing a reaction. What this means as far as potentially further restrictions will be determined by the regulatory agencies.

When preparing this article I asked a number of perfumers if they thought oakmoss was necessary to create a chypre. All of them replied there are enough synthetic and natural materials to create any chypre effect they desire. I hope the Low Atranol Oakmoss is still allowed to be used because there is something pleasing about the bite of a good chypre and I think oakmoss is part of that.

Mark Behnke