Hydroxycitronellal

• 📂 CAS N° — 107-75-5

• ⚖️ MW — 172.26 g/mol

• 📝 Odor Type — Floral (Muguet / lily of the valley)

• 📈 Odor Strength — Medium

• 👃🏼 Odor Profile — Sweet-floral, at first delicate and refreshingly mild, but often increasing in odor strength after short olfactory study. The floral notes are mild, light and resemble Lily of the Valley. The tenacity is good, and the odor diffusion increases significantly when the material is properly blended with lower boiling odorants or modifiers.

  There is a marked difference in the top note of this material from different suppliers. Only few manufacturers make a material with a truly uniform, delicately floral odor performance from the very first (initial) note to the terminal notes. The odor will remain for days, weeks or even longer, but the material on a testing blotter is obviously exposed to air attack and polymerization. 

  A good way - but a very strict one - to evaluate this aldehyde is in lukewarm water.  It is sufficiently soluble that it will show water-insoluble impurities strongly enhanced on this test. A very tine grade of  Hydroxycitronellal will have almost the same odor on this test as it has on a perfume blotter.

• 👅 Flavor Profile — Hydroxycitronellal has a sweet-floral taste but shows a bitter aftertaste at concentrations higher than 20 ppm, sometimes even much lower than that.

• ⚗️ Uses — This aldehyde is one of the most frequently used  floralizing perfume materials. Originally introduced as a muguet material it finds its way into almost every type of floral fragrance, and many non-floral ones. It’s concentration in perfumes may vary from about 1% (which rarely gives effects unless supported by parallel materials) up to 30 or 40% in straight floral types.

  It is almost a must in Muguet (at certain price levels) and peony, Lily, sweet pea, Narcisse, linden blossom, etc. and it had a monopoly on these types for more than 40 years during which period not one material appeared that could truly replace Hydroxy- citronellal. And even after the appearance of one of several very good, perhaps superior - Materials, the demand of hydroxycitronellal kept increasing Endless discussions about its possibly irritating effect on the human skin have hardly died out yet - but Hydroxy - citronellal has now reached and by-passed the one-million-pounds per year mark in a volume class reserved for comparatively few perfume materials.

  For soap perfumes it is customary to use a slightly more “rough” grade of this material. Power is often of paramount interest to the soap manufacturer when it comes to perfuming, and the very pure grade materials with delicate odors often fail to yield the desirable power in a soap. High-grade Hydroxycitronellal is used sparingly in flavor compositions as a floralizer in many types of flavor: Berry complexes, Citrus, Violet, Cherry, etc. and in general, a discrete touch of floral note in a flavor tend to give impression of “richness” or “body” which are highly desirable virtues. 

  In some cases, a complete new get base is added to a flavor fruit, mint, Etc. — to land this rounding off effect. The amounts needed are mere traces.

  Hydroxycitronellal enters these flavor types in the concentration equal to 0.3 to 15 ppm in the finished product.

WHAT IS HYDROXYCITRONELLAL?

Hydroxycitronellal (7-hydroxy-3,7-dimethyloctanal) is an odorant used in perfumery. Its molecular formula is C10H20O2.

It derives from a citronellal. 7-Hydroxy-3, 7-dimethyloctanal, also known as 3, 7-dimethyl-7-hydroxyoctan-1-al or 7-hydroxycitronellal, belongs to the class of organic compounds known as medium-chain aldehydes.

DISCOVERY AND FIRST USES

The discovery, preparation and marketing of this aldehyde is attributed to Knoll and Co. (I suppose incorporated by BASF in 1975, then sold in 2002 to the American company Abbott) in 1905-1908.

According to Rifm, the material is In public use since the 1920s. Another preparation by hydration of citronellal happened in 1967 by the renowned Bedoukian.

However, the first large use is reported to be in the 1940’s with the launch of L’air du temps and other emerging brands like Dior, Balenciaga and Balmain were going to launch designer fragrances.

Note — RIFM has completed an official safety assessment for this ingredient and concluded that hydroxycitronellal is a weak skin sensitizer. These findings have been approved by the expert panel for fragrance safety, an independent expert advisory board, and are awaiting peer reviewed publication. IFRA has set a Standard for acceptable concentrations of hydroxycitronellal that can be used in a variety of consumer products. Separately in a large patch test study 98.3% of people self reported they did not have a reaction to hydroxycitronellal.

PRODUCTION AND SYNTHESIS

Reaction of citronellal with diethanolamine produces the oxazolidine derivative. If this product is dissolved in 98% sulfuric acid, two things happen. Firstly, the nitrogen atom is protonated to form the hydrogen sulfate salt. This process no doubt helps the organic material to dissolve in the acid. Sulfuric acid then adds across the double bond at the far end of the molecule to give the sulfate ester. If the sulfuric acid solution of this product is added to water, both the sulfate ester and the oxazolidine ring are hydrolysed under the acidic aqueous conditions to give hydroxycitronellal (C. Sell)

POLARITY

The polarity, solubility, surface activity and stability of fragrance materials can explain their behavior in diverse environments. For example, hydroxycitronellal contains two polar groups, hydroxyl and aldehydic. Its polarity enables it to compete for space on the surface of a micelle, leading to either a decrease in viscosity or a breaking of an emulsion (De Monchy Aromatics)

Sources and informations:

1. Howard, G.; Butler, H.; Jouhar, A.J.; Poucher, W.A. (1991). Poucher's Perfumes, Cosmetics and Soaps : Volume 1: The Raw Materials of Perfumery (9 ed.). Springer Netherlands. p. 183. doi:10.1007/978-94-010-9672-0. ISBN 9789401096720.

2. "Octanal, 7-hydroxy-3,7-dimethyl-". webbook.nist.gov. Retrieved 2015-12-30.

3. "Compound Report Card". www.ebi.ac.uk. Retrieved 2015-12-30.

4. National Center for Biotechnology Information (2021). PubChem Compound Summary for CID 7888, Hydroxycitronellal. Retrieved January 10, 2021 from https://pubchem.ncbi.nlm.nih.gov/compound/Hydroxycitronellal.

5. Perfume and flavor chemicals, S. Arctander, Denmark 1969. 

6. The fragrance conservatory, https://fragranceconservatory.com/ingredient/hydroxycitronellal

7. The Chemistry of Fragrances, David Pybus and Charles Sell; Quest International, Ashford,Kent, UK 

8. Chemistry and Technology of Flavors and Fragrances, Edited by David J. Rowe (De Monchy Aromatics Ltd Poole, UK)

9. Monographs on fragrance raw materials. 1. Perfumes - Addresses, essays, lectures, I. Opdyke D L J II. Research Institute for Fragrance Materials III. 'Food and cosmetics toxicology' 668'.54 TP983 78-41218 ISBN 0 08 023775-4