Linalool · Lablypedia

A colorless oil, 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 has uses in manufacturing of soaps, fragrances, food additives as flavors, household products, and insecticides. Esters of linalool are referred to as linalyl, e.g. linalyl pyrophosphate, an isomer of geranyl pyrophosphate.

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 (dextro-linalool) is found, for example, as a major constituent of the essential oils of coriander (Coriandrum sativum L.), cymbopogon (Cymbopogon martini var. martinii), and sweet orange (Citrus sinensis) flowers. (R)-linalool (laevo-linalool) is present in lavender (Lavandula officinalis), bay laurel (Laurus nobilis), and sweet basil (Ocimum basilicum), among others.

Each enantiomer evokes distinct neural responses in humans, so each is classified as possessing distinct scents. (S)-(+)-Linalool is perceived as sweet, floral, petitgrain-like (odor threshold 7.4 ppb) and the (R)-form as more woody and lavender-like (odor threshold 0.8 ppb).

Over 200 species of plants produce linalool, notably from the families Lamiaceae (mint and other herbs), Lauraceae (laurels, cinnamon, rosewood), and Rutaceae (citrus fruits), but also birch trees and other plants, from tropical to boreal climate zones.

Aniba rosaeodora
Lavandula
Cinnamomum tamala
Cannabis sativa
Basil
Solidago (goldenrod)
Artemisia vulgaris (mugwort)
Humulus lupulus (hop)

It was first synthesized in the laboratory of Leopold Ružička in 1919.

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Production

Linalool is produced commercially from several terpenes and terpenoid precursors, which are often components of terpentine. 2-Pinanol, derived from pinene, gives linalool upon pyrolysis.

Biosynthesis

In higher plants linalool is formed by rearrangement of geranyl pyrophosphate (GPP). With the aid of linalool synthase (LIS), water attacks to form the chiral center. LIS appears to show a limonene synthase-type catalysis through a simplified "metal-cofactor-binding domain [where the majority] of the residues involved in substrate...binding [are] in the C-terminal part of the protein" suggesting stereoselectivity and the reasoning behind why some plants have varying levels of each enantiomer.

Odor and flavor

Linalool has complex odor and flavor properties. Its odor is similar to floral, spicy wood, somewhat resembling French lavender plants, bergamot oil or lily of the valley. It has a light, citrus-like flavor, sweet with a spicy tropical accent. The aroma of the racemic mixture is described as citrus, floral, sweet, bois de rose, woody, green, blueberry, orange, terpenic, waxy, and rose. The aroma of the laevo enantiomer is described as fresh, floral, woody, natural, and lavender, whilst the dextro enantiomer is described as sweet, floral, petitgrain, and lavender.

Linalool is used as a scent in perfumed hygiene products and cleaning agents, including soaps, detergents, shampoos, and lotions. It exhibits antimicrobial and antifungal properties.

Chemical derivatives

Linalool is hydrogenated to give dihydro- and tetrahydrolinalool, which are fragrances that are more resilient toward oxidants, as might be found in household cleaning products. Linalyl acetate, a popular scent, is produced by esterification of linalool (as well as occurring naturally). Isomerization of linalool gives geraniol and nerol.

Conversion of linalool to its dimethylcarbamate yields a compound that is known as "Pepperwood".

Linalool oxide is another example of a compound that is made from linalool starting material. There is a total of eight stereoisomeric forms of terpene linalool oxide.

Additional commercially available esters of linalool besides the acetate include: linalyl cinnamate, linalyl formate, linalyl isobutyrate, linalyl propionate & linalyl benzoate (c.f. Givaudan website) .

Elintaal (ethyl linalyl acetal) is another linalool based product, as is geranylacetone (q.v.).

Safety

Linalool can be absorbed by inhalation of its aerosol and by oral intake or skin absorption, potentially causing irritation, pain and allergic reactions. Some 7% of people undergoing patch testing in Europe were found to be allergic to the oxidized form of linalool.

The US Food and Drug Administration (FDA) lists linalool in the Code of Federal Regulations under substances generally recognized as safe, synthetic flavoring substances and adjuvants.