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  1. #1
    Basenotes Member
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    Dec 2012

    Default Why does a natural isolate apparently smell different to its synthetic counterpart?

    I'm reading a lot about natural isolates at the moment in an attempt to reconstruct certain absolutes and essential oils.

    One thing I've noticed is it's often said that the natural version of a particular compound smells different to its synthetic equivalent. For example, Hermitage Oils says this about benzyl acetate:

    "This incredibly beautiful material is the result of a fractional distillation of ylang ylang flowers and it shows. Whereas synthetic benzyl acetate is all about jasmine, this completely natural isolate is all about ylang ylang in perfect harmony with jasmine."

    I'm not a chemist so I can't wrap my head around why this would be the case.

    Also, I've heard that certain compounds can smell different depending on the supplier/manufacturer (e.g. ambroxide). Why would this be the case?

    My uneducated assumption was that a compound is a compound so where it comes from or how it's synthesised shouldn't determine its smell, but I'm sure it's much more complicated than this...

    I'm looking forward to hearing an explanation!

    Many thanks

  2. #2

    Default Re: Why does a natural isolate apparently smell different to its synthetic counterpart?

    The answer comes down, mostly, to purity. There are other factors, like isomerism, which come into play.

    Chemicals when synthesized synthetically will contain byproducts (which can smell completely different), and sometimes in more than trace amounts. Many factors, including starting material, will affect what byproducts result from synthesis. Also, on occasion, noticeable residual levels of solvent. I have smelled, just fleetingly, acetone in many methyl ionones for example. This chemical doesn't occur naturally, but the cheaper the product, e.g. the less money spent on cleaning it up, the more you will notice these off notes.

    When synthesized synthetically, many perfumery chemicals result in racemic mixtures. Take citronellol, for example; the L is found in rose and geranium, the D in citronella. They smell similar, the latter more lemon, and the former more floral. A citronellol ex geranium will smell different than one ex citronella, and different still from one synthesized synthetically which is a 50:50 mixture of the two -- even if one has essentially pure samples.

    More often, both synthetic and natural variants will contain noticeable impurities, from either synthesis or extraction, which alter the smell. This is why geraniol ex palmarosa, geraniol ex geranium (both of which should be trans) and trans-geraniol synthetic smell different. Both smell similar to the synthetic, though like the respective oils from which they came; and after an hour, all three are relatively indistinguishable. Though the two natural extracts do smell rather different for the first few minutes on blotter.

    Price and time influence greatly how a fragrance house or manufacturer will process their chemicals / naturals. I have just had a look at the Hermitage page. 85 pounds for 10mls is, of course, alarmingly expensive and unaffordable in just about any but the most lavish niche products; and even then, not in but a fraction of the average concentration of benzyl acetate in white floral perfumes. It also isn't sustainable to have your benzyl acetate always coming from ylang. The logical thing to do, then, is to use synthetic benzyl acetate, and a touch of real ylang oil (if you like the effect), though some have objections -- for myriad reasons -- to using synthetics in the first place, which is why, I suspect, this product exists at all.

  3. #3
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    pkiler's Avatar
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    Dec 2007
    Southern California

    Default Re: Why does a natural isolate apparently smell different to its synthetic counterpart?

    Quote Originally Posted by fragrantregard View Post
    The answer comes down, mostly, to purity. There are other factors, like isomerism, which come into play..
    yes to everything Harry says.

    How I characterize this in a soundbite form, that each processing of the molecules has their own set of tag along impurities, and these impurities are the major difference in smell between them.
    Paul Kiler
    PK Perfumes
    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.

  4. #4

    Default Re: Why does a natural isolate apparently smell different to its synthetic counterpart?

    Additionally, besides optical isomers (which may be expressed as D vs L, - vs +, R vs S, for example L-linalool vs D-linalool vs racemic mixture which all smell quite different) and cis vs trans differences (what direction "branching off" occurs after a double bond,) it's possible for double bonds to be in different positions as well between synthetic versions and the natural product, which is a pretty major change in the molecule.

    The only example coming to mind is synthetic ambrettolide as commonly sold vs natural but there may well be more.

    If the same in all regards -- everything all in the same position -- and no smellable impurities in either synthetic or natural product then there will be no difference in smell. Any of these can cause difference, sometimes important, sometimes not.

    And not all synthetics going by the same name will smell the same, either generally for reason of different mix of isomers, or smellable impurities.

    In rare cases impurities can smell stronger than the named product. The only example I've personally experienced of this was cinnamic alcohol where the cinnamic aldehyde impurity was so strong it almost might as well have been cinnamic aldehyde with inert diluent. Other cinnamic alcohols have no such noticeable problem. Same product name, different smell.

    Poorly stored or expired material but sold anyway, or bad manufacturer and bad or no incoming organoleptic inspection vs everything done right.

    Of course that can happen with naturals too, probably moreso.

  5. #5

    Default Re: Why does a natural isolate apparently smell different to its synthetic counterpart?

    And getting back to your specific question:

    Now personally I don't take anything said by Hermitage about a product too seriously after the Sacred Jasmine Sambac Absolute debacle. That's me, many people do, perhaps nearly all.

    However let's say this is right about this product: "this completely natural isolate is all about ylang ylang in perfect harmony with jasmine."

    A common isolation method is fractional distillation. Benzyl acetate will be among the first or perhaps the first to distill off of ylang and thus could be largely, but imperfectly, separated. Other ylang components will come with it, particularly earlier-distilling ones while little of late-distilling ones.

    In other words, some Ylang-Ylang Extra materials will be included too with the "isolated" benzyl acetate, but very little Ylang-Ylang I, II, or especially III materials, probably nothing smell-able.

    So it will smell different from pure benzyl acetate, perhaps in a desired way, plausibly with noticeable ylang, though I must say mysefl I have not thought "ylang-ylang" on smelling natural benzyl acetate from differing providers.

    As some ylang-ylang can be 25% benzyl acetate, deriving from ylang is doable, but of course the result could readily cost 4 times what ylang oil complete will.

    EDIT: The 25% figure is from EODB. Even the Extra fractions offered by EB and Plant Therapy have only a fraction that much benzyl acetate, though. For example, in the EB product benzyl acetate is only the 7th most prevalent component, at under 6%. So a high value may be particular to some ylang-ylang rather than common.

    White Lotus Aromatics sells the Superior Extra, which they say is from the only the first 45 minutes of distillation rather than the first 90 as with Extra and so might be more enriched in benzyl acetate, but their CoA doesn't list any components whatsoever so I can't determine how much benzyl acetate may be in it.

    Alternatively to obtain natural benzyl acetate isolate a higher-tech method of separation might be used such as spinning-band distillation. I would expect many natural isolates are done this way, but not necessarily if actually desiring odor-affecting-amounts of some other components to come with it.
    Last edited by Bill Roberts; 9th June 2020 at 06:36 PM.

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