Geraniol

Absorption

The profile of the geraniol concentrations in rat blood following oral administration of the emulsified formulation was characterized by a peak concentration at 30 min of about 270 μg/mL and an area under concentration (AUC) similar to that obtained by the intravenous administration of the same geraniol dose, indicating an absolute bioavailability of 92% . Geraniol appears able to permeate directly from the bloodstream to the central nervous system following its oral administration to rats, reaching detectable amounts in the CSF; peak concentration in the CSF was found to be about 2.5 μg/mL and was observed 30 min after oral administration .

Description

Geraniol has a characteristic rose-like odor. Geraniol may be prepared by fractional distillation from those essential oils rich in geraniol, or synthetically from myrcene; commercial geraniol cannot be classified according to its alcohol content, as most of the recurring impurities are alcoholic in nature (nerol, citronellol, tetrahydrogeraniol). Gas-chromatography techniques may be usefully employed to determine the geraniol content in a product.

Chemical properties

colourless to pale yellow liquid with an odour of roses

Chemical properties

Geraniol occurs in nearly all terpene-containing essential oils, frequently as an ester. Palmarosa oil contains 70–85% geraniol; geranium oils and rose oils also contain large quantities. Geraniol is a colorless liquid, with a floral, rose-like odor.
Since geraniol is an acyclic, doubly unsaturated alcohol, it can undergo a number of reactions, such as rearrangement and cyclization. Rearrangement in the presence of copper catalysts yields citronellal. In the presence of mineral acids, it cyclizes to form monocyclic terpene hydrocarbons, cyclogeraniol being obtained if the hydroxy function is protected. Partial hydrogenation leads to citronellol, and complete hydrogenation of the double bonds yields 3,7-dimethyloctan-l-ol (tetrahydrogeraniol). Citral may be obtained from geraniol by oxidation or by catalytic dehydrogenation. Geranyl esters are prepared by esterification.
Geraniol is one of the most frequently used terpenoid fragrance materials. It can be used in all floral, rose-like compositions and does not discolor soaps. In flavor compositions, geraniol is used in small quantities to accentuate citrus notes. It is an important intermediate in the manufacture of geranyl esters, citronellol, and citral.

Chemical properties

Geraniol has a characteristic rose-like odor The physical constants vary for the various commercial products, depending on the total geraniol content; specifc gravity and refractive index may be indicative of the purity of the product Commercial geraniol cannot be classifed according to its alcohol content, as most of the recurring impurities are alcoholic in nature (nerol, citronellol, tetrahydrogeraniol) Gas chromatography techniques may be usefully employed to determine the gera- niol content in a product.

Occurrence

The presence of geraniol in nature has been reported in more than 160 essential oils: ginger grass, lemongrass, Ceylon and Java citronella, tuberose, oak musk, orris, champaca, ylang-ylang, mace, nutmeg, sassafras, Cayenne Bois-de-Rose, Acacia farnesiana, geramium clary sage, spike, lavandin, lavender, jasmine, coriander, carrot, myrrh, eucalyptus, lime, mandarin petitgrain, bergamot petitgrain, bergamot, lemon, orange and others The essential oils of palmarosa and Cymbopogon winterianus contain the highest levels of geraniol (approx 80 to 95%) Also reported in numerous other sources including apple juice, citrus peel oils and juices, bilberry, cranberry, other berries, guava, papaya, cinnamon, ginger, corn mint oil, mustard, nutmeg, mace, milk, coffee, tea, whiskey, honey, passion fruit, plums, mushrooms, mango, starfruit, cardamom, coriander leaf and seeds, litchi, Ocimum basilicum, myrtle leaf, rosemary, clary sage, Spanish sage and chamomile oil

The Uses of Geraniol

Geraniol is used in the synthesis of insect repellant. It is also used in the synthesis of Angelicoin A and Herecinone J, which inhibit collagen-induced platelet aggregation.

The Uses of Geraniol

Geraniol was used in field evaluation of synthetic herbivore-induced plant volatiles as attractants to beneficial insects.It was used to evaluate the tumor-suppressive potency of isoprenoids in vitro and in vivo.

The Uses of Geraniol

geraniol is perfuming and with tonic properties. It is a primary constituent in many essential oils, including citronella, lavender, lemongrass, orange flower, and ylang-ylang.

Indications

Geraniol is approved for use within allergenic epicutaneous patch tests which are indicated for use as an aid in the diagnosis of allergic contact dermatitis (ACD) in persons 6 years of age and older.

Background

Geraniol is a monoterpene that is found within many essential oils of fruits, vegetables, and herbs including rose oil, citronella, lemongrass, lavender, and other aromatic plants. It is emitted from the flowers of many species of plant and is commonly used by the food, fragrance, and cosmetic industry. Geraniol has demonstrated a wide spectrum of pharmacological activities including antimicrobial, anti-inflammatory, antioxidant, anti-cancer, and neuroprotective to name a few . Interestingly, geraniol has also been shown to sensitize tumour cells to commonly used chemotherapies including Fluorouracil and Docetaxel and represents a promising cancer chemopreventive agent . Due to its anticancer effects, geraniol has been found to be effective against a broad range of cancers including breast, lung, colon, prostate, pancreatic, skin, liver, kidney and oral cancers .
These pharmacologic effects are clinically important as geraniol is classified as generally-recognized-as-safe (GRAS) by the Flavor and Extract Manufacturers Association (FEMA) and the Food and Drug Administration (FDA) of the United States. Sensitivity to geraniol may be identified with a clinical patch test.

Definition

ChEBI: A monoterpenoid consisting of two prenyl units linked head-to-tail and functionalised with a hydroxy group at its tail end.

Preparation

A convenient route for the production of geraniol and nerol consists of the hydrogenation of citral, which is used in large quantities as an intermediate in the synthesis of vitamin A. Large-scale processes have, therefore, been developed for producing geraniol. Currently, these are far more important than isolation from essential oils. Nevertheless, some geraniol is still isolated from essential oils for perfumery purposes.
1) Isolation from essential oils: Geraniol is isolated from citronella oils and from palmarosa oil. Fractional distillation of, for example, Java citronella oil (if necessary, after saponification of the esters present) yields a fraction containing about 60% geraniol, as well as citronellol and sesquiterpenes. Aproductwith a higher geraniol content and slightly different odor quality for use in fine fragrances is obtained by fractionating palmarosa oil after saponification of the geranyl esters.
2) Synthesis from β-pinene: Pyrolysis of β-pinene yields myrcene, which is converted into a mixture of predominantly geranyl, neryl, and linalyl chloride by addition of hydrogen chloride in the presence of small amounts of catalyst, for example, copper(I) chloride and an organic quaternary ammonium salt. After removal of the catalyst, the mixture is reacted with sodium acetate in the presence of a nitrogen base (e.g., triethylamine) and converted to geranyl acetate, neryl acetate, and a small amount of linalyl acetate.
Geraniol is obtained after saponification and fractional distillation of the resulting alcohols. 3) Synthesis from linalool: A 96% pure synthetic geraniol prepared by isomerization of linalool has become commercially available. Orthovanadates are used as catalysts, to give a >90% yield of a geraniol–nerol mixture. Geraniol of high purity is finally obtained by fractional distillation. A considerable portion of commercially available geraniol is produced by a modified process: linalool obtained in a purity of about 65% from α-pinene is converted into linalyl borates, which rearrange in the presence of vanadates as catalysts to give geranyl and neryl borates. The alcohols are obtained by hydrolysis of the esters.
4) Synthesis from citral: Citral has very recently come to be produced petrochemically in very large quantities, so partial hydrogenation of citral has become a very economical route for the production of geraniol. A high selectivity for this reaction can be achieved by the use of special catalysts [106] or by special reaction techniques.

Aroma threshold values

Detection: 4 to 75 ppb.

Taste threshold values

Taste characteristics at 10 ppm: sweet foral rose, citrus with fruity, waxy nuances.

General Description

Colorless to pale yellow oily liquid with a sweet rose odor.

Reactivity Profile

An unsaturated aliphatic hydrocarbon and an alcohol. Flammable and/or toxic gases are generated by the combination of alcohols with alkali metals, nitrides, and strong reducing agents. They react with oxoacids and carboxylic acids to form esters plus water. Oxidizing agents convert them to aldehydes or ketones. Alcohols exhibit both weak acid and weak base behavior. They may initiate the polymerization of isocyanates and epoxides.

Flammability and Explosibility

Non flammable

Anticancer Research

Starting from antitumor activity against several cell lines by an arrest occurring atthe G0/G1 cell cycle and ultimately with an increase of apoptosis, this molecule wasfound to interfere with the mevalonic cycle enzyme. Suppression of prenylation ofproteins leads to the inhibition of DNA synthesis, and the suppression of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) leads to a reduction of the mevalonate pool andthus limits protein isoprenylation. In the same way, a reduction of cholesterol biodisponibilitywas controlled (Pattanayak et al. 2009; Ni et al. 2012; Dahham et al.2016).

Safety Profile

Poison by intravenous route. Moderately toxic by ingestion, subcutaneous, and intramuscular routes. A severe human skin irritant. Combustible liquid. When heated to decomposition it emits acrid smoke and irritating fumes.

Synthesis

By fractional distillation from those essential oils rich in geraniol, or synthetically from myrcene.

Metabolism

Not Available

Metabolism

Geraniol is metabolized in the rabbit by ω-oxidation and by reduction of an α β-unsaturated bond (Parke, 1968). The products of geraniol metabolism are 'Hildebrandt acid' and 7-carboxy-3-methylocta-6-enoic acid. The latter acid is optically active (Williams, 1959).

Hazards

Geraniol is classified as D2B (Toxic materials causing other effects) using the Workplace Hazardous Materials Information System (WHMIS).

Purification Methods

Purify geraniol by ascending chromatography or by thin layer chromatography on plates of kieselguhr G with acetone/water/liquid paraffin (130:70:1) as solvent system. Hexane/ethyl acetate (1:4) is also suitable. Also purify it by GLC on a silicone-treated column of Carbowax 20M (10%) on Chromosorb W (60-80 mesh). [Porter Pure Appl Chem 20 499 1969.] Store it in full, tightly sealed containers in the cool and protect from light. It has a pleasant odour. [cf p 681, Beilstein 1 IV 2277.]