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  1. #1

    Question Why does the smell of a fragrance blend change over time?

    As a natural scientist (chemist and biologist) I am always interested in understanding the basic science of the things I experience. Currently, I am wondering what could be the reason for the time-dependent alteration in the smell of a fragrance mixture. As you know, the perfume you mixed will smell different after several weeks compared to the time after you mixed it. Even after one day, it may smell different. For example I had a blend that had a very unpleasant herbal green accord right after mixing, but it was completely gone the next day.
    I think it must be chemical or physical changes. Since chemical reactions usually require some kind of activation energy (heat, UV light...) (or pH change, catalyst...) I don't think that the reason are any sort of chemical reactions. Except for a slight oxidation, maybe. But I could be wrong. Might it have something to do with the formation and distribution of micelles? Or is it just normal diffusion? Does anyone know of any scientific research/publications on this?

  2. #2
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    Default Re: Why does the smell of a fragrance blend change over time?

    Diffusion is one thing, interaction is also a big thing... reformation of molecules is also a big thing...
    Sharp smells often soften dramatically after a day or three, as you experienced.

    As a Chemist, you know that sloshes of molecules are always in motion, doing many things...
    Paul Kiler
    PK Perfumes
    http://www.PKPERFUMES.com
    In addition to Our own PK line, we make Custom Bespoke Perfumes, perfumes for Entrepreneurs needing scents for perfumes or products, Custom Wedding Perfumes, and even Special Event Perfumes.

  3. #3

    Default Re: Why does the smell of a fragrance blend change over time?

    Quote Originally Posted by polysom View Post
    Since chemical reactions usually require some kind of activation energy (heat, UV light...) (or pH change, catalyst...) I don't think that the reason are any sort of chemical reactions
    Plenty of chemical reactions are able to occur at room temperature, including those involved in maturation of perfumes.

    If you did reduce the temperature drastically to such as -78 C or so I am sure they would proceed exceedingly slowly, though. Even freezer temperature would give a very large decrease in rate.

    Might it have something to do with the formation and distribution of micelles?
    No, there are no micelles in alcoholic perfumes.

    Or is it just normal diffusion?
    No, with reasonable effort to do so, full mixing occurs without needing days or weeks of time, assuming everything is dissolved in the first place.

    That said, if speaking of timeframes such as a minute, it's entirely possible for mixing to not fully be achieved quickly. That is one possible reason why Mr Bond preferred his vodka martinis shaken not stirred.

    (Other possible and perhaps more plausible reasons include improved aeration, allowing the vermouth to more thoroughly "breathe," in other words oxidize as well as perhaps release more volatile components; and faster chilling.)

    Mendeleev did his thesis on the general question of alcohol/water solutions not being as simple as one might imagine. As a consequence, the final state at the microscale as to what extent and manner ethanol molecules are hydrated is not achieved immediately with stirring. That is not relevant to odor released into the air, but may be relevant to taste of vodka, to a supertaster anyway.

    Does anyone know of any scientific research/publications on this?
    Try searching for acetal formation and formation of Schiff bases. I have not saved anything in particular.

  4. #4

    Default Re: Why does the smell of a fragrance blend change over time?

    Thanks for your answers. This is becoming a much more interesting topic than I first imagined. Will do some research...

  5. #5

    Default Re: Why does the smell of a fragrance blend change over time?

    Im not a chemist by any means, but at the very simplest-- common scent molecules are often alcohols, aldehydes, acids, esters, acetals, ketones, etc that when introduced to each other will all start to interact, break down into constituent parts, and reform new ones, moving towards a new equilibrium. This is just the way the organic chemistry world works, as far as I have learned.

  6. #6

    Default Re: Why does the smell of a fragrance blend change over time?

    I believe one shouldn't overestimate how much goes on.

    E.g. if you use musk ketone at some percentage, you will find essentially the same percentage later; if you use so much citronellol and so much geranyl acetate that will smell different than starting with citronellyl acetate and geraniol, that difference will generally sustain.

    I shared with another member here an excellent (IMO anyway) illustration of how one can see for oneself that transesterification doesn't occur much by naming two ingredients where it would be a screaming note change if it occurred much at all but in practice it clearly doesn't happen, but for the life of me I can't recall the example nor think it up again.

    Or, consider that GC/MS's do generally reflect formula rather than being all scrambled.

    It's really not a hot soup of highly reactive entities, not even close.

    Your general thought is certainly right but in practice the major ones in maturatioyou absolutely can smell or even see are the above. Plus, over time there degradations, which I would consider distinct from maturation, of which oxidation is likely the worst culprit.

  7. #7

    Default Re: Why does the smell of a fragrance blend change over time?

    This reminds me of an experiment I did during my chemistry studies. I put an alcohol and a ketone in two flasks. Both can react to form an acetal. In one flask I added some acid. Then I put both flasks in a dark cupboard for 2 months. In the flask with acid a yellow substance with a sweet smell was formed. In the flask without acid nothing happened at all (I did a GC analysis to make sure). What I want to say is that just because organic compounds are together, they do not necessarily react. Many reactions need a change in pH or some form of activation energy.
    I have read again about Schiff bases in my old notes from my studies. Aldehydes and ketones can really react with nucleophilic nitrogen bases (e.g. primary and secondary amines) to form Schiff bases, azomethines or enamines. But only if the base has a high pKs of 9-11. Otherwise you also need some acid for this (or maybe wait a very long time).

    I found two interesting references in the internet about the chemistry in perfume aging.
    https://pubmed.ncbi.nlm.nih.gov/19456979/
    https://www.chemistryworld.com/featu...m/9003.article

    They also mention acetal formation and imines formation (at 37 degrees and in daylight).

    I will make an experiment, I will mix methyl anthranilate (nucleophilic nitrogen base with low pKs) and hexyl cinnamic aldehyde, put one sample in the sun and one in the dark and see if some Schiff base will be formed.




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