Linalol

Linalool has the formula C₁₀H₁₈O and a molar mass of 154.25. Its systematic name is 3,7-dimethylocta-1,6-dien-3-ol. Together with geraniol, nerol and citronellol, linalool is one of the rose alcohols. The word linalool is based on linaloe, a type of wood, and the suffix -ol. In food manufacturing it may be called coriandrol.

Occurrence

Both enantiomeric forms are found in nature. (S)-linalool is found, for example, as a major constituent of the essential oils of coriander, cymbopogon and sweet orange flowers. (R)-linalool is present in lavender, bay laurel and sweet basil, among others. Over 200 species of plants produce linalool, notably from the families Lamiaceae (mint and other herbs), Lauraceae (laurels, cinnamon, rosewood) and Rutaceae (citrus fruits). Linalool is a major contributor to the fragrance of coriander. In coriander seeds it comprises about two thirds of the volatile components. The essential oil of coriander leaves and seeds contains linalool as its major constituent. In bergamot oil, linalool at 9% and linalyl acetate at 30% are among the key ingredients. Linalool is also among the major constituents of geranium oil. Linalool is among the substances in the tree Aniba rosodora, one of the commercially important sources of rosewood oil.

Other natural sources

Camphor laurel has six different chemical variants, called chemotypes, and one of them is rich in linalool. This linalool type is commonly found in Taiwan and Japan, and its oil contains 80 to 85% linalool; another source gives a wider range of 58 to 92%. The linalool in rosewood oil is mostly the dextro (S) enantiomer, typically above 90%, though the share varies with the source material and the extraction technique. Trees of the genus Dalbergia, such as Brazilian rosewood and Indian rosewood, have never been a source of rosewood oil.

The Indian lavender tree, Bursera delpechiana, was taken from Mexico to India in 1912 and has been used there as a source of linalool. Distilling the mature fruits instead of the wood gave the Indian oil a better odor and a longer persistence.

Chemistry and history

In higher plants linalool is formed by rearrangement of geranyl pyrophosphate. Isomerization of linalool gives geraniol and nerol. Linalool is classified as an acyclic monoterpenoid. In plants it is a metabolite, a volatile oil component, an antimicrobial agent and an aroma compound. Linalool exhibits antimicrobial and antifungal properties. Esters of linalool are called linalyl; linalyl pyrophosphate, for example, is an isomer of geranyl pyrophosphate. Linalool was first synthesized in the laboratory of Leopold Ružička in 1919. The hydroxy group at carbon 3 is the main contributor to both the odor quality and the potency of linalool.

Physical properties

Linalool dissolves in water only to about 1.589 g/l. It is soluble in alcohol, ether, fixed oils and propylene glycol, and insoluble in glycerin. The racemic form has the CAS number 78-70-6, the (R)-form 126-91-0 and the (S)-form 126-90-9.

Regulation

Under EU Cosmetics Regulation 1223/2009, Annex III, linalool must be declared on the label when present above 0.001% in leave-on products or above 0.01% in rinse-off products. Declaration of an allergen on the label is a labelling obligation and not an automatic ban. The US Food and Drug Administration lists linalool in the Code of Federal Regulations among the substances generally recognized as safe, synthetic flavoring substances and adjuvants.

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