Aldehydes

Sparkling and slightly metallic, with waxy, soapy cleanliness, citrus peel and a freshly laundered impression.

In perfumery, “aldehydes” does not refer to a plant but to a group of molecules. It mainly means the straight-chain, saturated aldehydes with eight to twelve carbon atoms – octanal, decanal, undecanal and dodecanal – plus the branched 2-methylundecanal. Nature knows them well. Octanal and decanal are among the main aldehydes in orange and mandarin peel oil, dodecanal occurs in orange, lemon and lime, and coriander is one of the plants with the highest contents of decanal, undecanal and dodecanal. Perfumery aldehydes, however, come from synthesis.

Aliphatic aldehydes are produced industrially and are chemically identical to the molecules in citrus peel. One important route is hydroformylation: an alkene is extended by a CHO group using carbon monoxide and hydrogen, for example decene to undecanal or heptene to octanal. A second route starts from the fatty alcohol of the same chain length, from which two hydrogen atoms are removed – this is how dodecanal is made from dodecanol over copper or silver catalysts. The branched 2-methylundecanal can be made from methyl nonyl ketone by the Darzens reaction described in 1904.

Aliphatic aldehydes give a composition radiance and diffusion: in small amounts they make floral and citrus accords seem brighter, fresher and more “airy” and carry them outward in the opening. Their soapy, clean effect is typical, which is why they are also widely used in soaps and detergents; 2-methylundecanal is also used for conifer and fir notes. Because aldehydes react easily with air and are very powerful odorants, they are dosed sparingly and usually diluted. In our range, aldehydes appear in 27 fragrances, 25 in the top and 2 in the heart note.

Aldehydic · Fresh and soapy · Mainly top note

As synthetic aroma chemicals, aldehydes are available all year round, independent of harvest and season.

In our fragrances, it often appears alongside Moschus, Rose, Vanille, Bergamotte, Patschuli, Amber, Jasmin.

The name “aldehyde” was coined by the chemist Justus von Liebig in the 1830s as a contraction of “alcohol dehydrogenatus” – alcohol from which hydrogen has been removed. Modern perfumery began in the late 19th century with the synthesis of aroma chemicals. In 1904 the French chemist Georges Darzens published a general method for synthesising aldehydes; it was also used to make 2-methylundecanal for the first time. At the beginning of the 20th century aliphatic aldehydes found their way into floral compositions.

• The peach-scented “aldehyde C-14” is chemically not an aldehyde at all but an eleven-carbon lactone.
• If coriander leaves taste soapy to you, aldehydes are probably the reason: in 2012 a study with more than 14,000 participants found a genetic variant near an olfactory receptor that responds to aldehydes.
• “Aldehyde C-12” is ambiguous: dodecanal and 2-methylundecanal share the formula C₁₂H₂₄O but smell different – one waxy and soapy, the other herbaceous and amber-like.

Aldehydes carry a formyl group, –CHO, at the end of the chain: a carbon atom double-bonded to oxygen and bearing one hydrogen atom. The aliphatic aldehydes of perfumery form a homologous series whose members each differ by one CH₂ unit: octanal (C₈H₁₆O, PubChem CID 454), decanal (C₁₀H₂₀O, CID 8175), undecanal (C₁₁H₂₂O, CID 8186) and dodecanal (C₁₂H₂₄O, CID 8194). 2-Methylundecanal (C₁₂H₂₄O, CID 61031) is a branched isomer of dodecanal with one asymmetric carbon atom. The odour changes with chain length: short aldehydes smell pungent, from eight to twelve carbon atoms the impression becomes pleasantly fatty and floral, octanal comes across as fruity, and dodecanal is regarded as the model of the fatty-aldehydic odour. The formyl group is reactive: aldehydes oxidise easily in air. For more stable formulations they are therefore sometimes converted into acetals or nitriles.