2009-02-12

Introducing the rose alcohols



Russian version - click here

Image: a picture of a nice rose alcohol from http://www.craftdistillers.com

Rose alcohols are Citronellol, Geraniol and Nerol. They are major constituents of the rose oil and important aromachemicals in making of a rose accord (commonly used together with phenyl ethyl alcohol). A rose oil contains about 30-40% of citronellol, 20% of geraniol and 5% of nerol.

A rose accord formula may contain various proportions between PEA, citronellol and geraniol. Nerol is less common, but still widely used in rose formulae. Even the natural raw materials contains those materials in different proportions. The rose oils contains about 1% PEA, 35% of citronellol and 20% of geraniol that brings us to 1:35:20 ratio. And the absolute contains about 40-70% PEA, 6% of citronellol and 3% of geraniol that makes the ratio looks like – from 13:2:1 to 23:2:1.

If I see the 13:2:1 ratio I get an idée that the previous formula consisted of 15 druppels PEA can be enriched with 2 drops of citronellol and 1 drop of geraniol. And the amount of those alcohols can be gradually increased till I get the more rosy smell. In general the average amounts of those aromachemicals used in rose accords are – 20-60% PEA, 5-35% citronellol and 5-20% of geraniol. But the problem is that when you use rose alcohol you can get an unpleasant citronella nuance that you don’t really smell in a rose flower. Let’s have a closer look at those chemicals.

Citronellol – its smell is described as a fresh floral clean rose. But wait – I do smell citronella undertone. It’s time for some chemistry. Citronellol is a molecule that has different isomers (the compounds with similar chemical formula, but different structure). Citronellol has alpha and beta isomers and also so called stereo isomers. The first ones are a bit less important, but stereo isomers are much more interesting in perfumery – because of their structure they look like right and left hand – almost the same, but still not superposable – they are a mirror image of each other – they are called d-citronellol and l-citronellol (you may also find them as (+)-citronellol and (-)-citronellol). If you like more information on stereo isomers, please, visit a Wikipedia link - http://en.wikipedia.org/wiki/Enantiomer The d-citronellol is found to be a natural compound of citronella and ginger-grass oil. l-citronellol is a major compound of a rose oil. Both occurs in geranium oil. As aromachemical you can buy either citronellol (that contains of both l- and d- isomers and called racemic) or l-citronellol. Although the most properties of stereo-isomers are the same, the perfumery books say that l-citronellol is sweeter than racemic, has clean rosy top note and has no “mint” notes. But there is another factor that is responsible for the smell variations of different citronellols bought by different suppliers. Citronellol can be obtained by different ways – some of them gives a better quality products containing almost no impurities and other ways give citronellol of a lower grade with more impurities contributing to the smell. For example, racemic citronellol can be obtained from citronella oil by hydrogenation of geraniol component. If it’s not purified properly, you may get some other citronella constituents in citronellol. The purest citronellol is obtained chemically by reduction of citronellal. So, if you can get citronellol from different supplier – it’s important to compare the quality of their products and to choose the good one.
Citronellol can be used in rose (red and white), lily, lily of the valley and other floral accords.

Geraniol is another rose smelling aromachemical with fresh mild sweet rosy odour and dry rose-petals undertone. To my nose it reminds a bit of dried rose hips. Sometimes you can also catch some citronella notes. Geraniol occurs naturally in many essential oils like Geranium, Rose, Palmarosa, and Citronella and can be isolated from the last two oils. But it can be also made synthetically from Citral. Thus, the quality of Geraniol may also vary depending on impurities. For examle, Geraniol from Palmarosa oil is preffered to the one from Citronalla oil.

Rhodinol is the most complicated aromachemical as the word Rhodinol is used to describe a whole group of chemicals. In the first place this name was given to an impure compound isolated from rose otto. Latter it becomes a kind of synonym to the rose alcohols derived from essential oils. For example, l-citronellol isolated from Geranium oil can also be sold under the name of Rhodinol. Rhodinol C or Rhodinol ex Citronella mostly refers to a purified Citronellol from Citronella oil. Rhodinol coeur or Rhodinol ex Geranium refers to a mixture of rose alcohols from Geranium oils. Rhodinol can be found in various rose formulae – it’s used as a substitute of rose otto, geranium oils or as citronellol or rose alcohol mixture. It’s very important to collect information on Rhodinol from the supplier and figure out what kind of Rhodinol he is selling. And of course – it’s useful to compare the quality from the different suppliers.

If I compare my Rhodinol ex Citronella from the Perfumers World with Citronellol (also from the Perfumers World), I’d say that I definitely smell some Geraniol in Rhodinol, so it’s not a higher grade of citronellol, but a mixture of rose alcohols. And they both has unpleasant citronella nuances to my nose. So, I think I need to compare the suppliers and to search for a better quality.

2 opmerkingen:

Andy zei

Thank you for your Rose installation: strange as it seems one even has to worry about synthetics quality ;-)
I just opened the book "Le Livre du Parfumeur" by Félix Cola. I think you can get reprints of it at the Perfume Museum (online).
Not that you can copy /paste the formulas but it gives an introduction and sometimes is fun to read.
http://boutique.museesdegrasse.com/boutique/asp_fr/detail_livre.asp?ID=116&Det=1&TVA=2

AromaX zei

Thanks for your advice, Andy. I do appreciate your opinion on choice of perfumery books. Le Livre du Parfumeur is in French and I can't read it freely. Pity. But may be for later. I have downloaded the article on rose suggested by Octavian - let's make an effort in reading French! :o)