3,7-Dimethyl-7-hydroxyoctanal

Description

Hydroxycitronellal has an intense, sweet, floral, lily-type odor. It may be prepared by hydration of natural citronellal obtained from Java citronella or from Eucalyptus citriodora; P-pinene is converted to myrcene, which on hydration may yield either linalool or a mixture of geranoil and nerol; the latter mixture can be hydrogenated to citronellol and subsequently converted to citronellal and hydroxycitronellal; also by hydrogenation of 3,7-dimethyl- 7-hydroxy-2-octen-2-al over palladium carbon in ethyl acetate solution.

Chemical properties

clear colourless liquid

Chemical properties

This is a colorless, slightly viscous liquid with a floral odor reminiscent of linden blossom and lily of the valley. Commercially available “hydroxycitronellal” is either optically active or racemic, depending on the starting material used. Hydroxydihydrocitronellal prepared from (+)-citronellal, for example, has a specific relation α20 D +9 to +10°.
Hydroxydihydrocitronellal is relatively unstable toward acid and alkali and is, therefore, sometimes converted into more alkali-resistant acetals, particularly its dimethyl acetal.
Because of its fine, floral odor, hydroxydihydrocitronellal is used in large quantities in many perfume compositions for creating linden blossom and lily of the valley notes. It is also used in other blossom fragrances such as honeysuckle, lily, and cyclamen.

Chemical properties

Hydroxycitronellal has a sweet, floral, lily-type odor

Occurrence

Reported found in pepper

The Uses of 3,7-Dimethyl-7-hydroxyoctanal

7-Hydroxycitronellal shows fungicide activity the strains of Candida tropicalis.

The Uses of 3,7-Dimethyl-7-hydroxyoctanal

Hydroxycitronellal is a fragrance for use in various perfumes, antiseptics, insecticides and household products; some perfumery uses (sweet pea Pois De Senteur; gardenia; cherry; melon; mint).

Preparation

The most important synthetic routes to hydroxydihydrocitronellal are listed as follows.
1) Synthesis from citronellal: One of the oldest routes to hydroxydihydrocitronellal is the hydration of the citronellal bisulfite adduct (obtained at low temperature) with sulfuric acid, followed by decomposition with sodium carbonate. A more recent development is hydration of citronellal enamines or imines, followed by hydrolysis.
2) Synthesis from citronellol. Citronellol is hydrated to 3,7-dimethyloctane-1,7- diol, for example, by reaction with 60% sulfuric acid. The diol is dehydrogenated catalytically in the vapor phase at low pressure to give highly pure hydroxydihydrocitronellal in excellent yield.The process is carried out in the presence of, for example, a copper–zinc catalyst; at atmospheric pressure, noble metal catalysts can also be used.
3) Synthesis from 7-hydroxygeranyl/-neryl dialkylamine: The starting material can be obtained by treatment of myrcene with a dialkylamine in the presence of an alkali dialkylamide, followed by hydration with sulfuric acid. The 7-hydroxygeranyl/-neryl dialkylamine isomerizes to the corresponding 7-hydroxyaldehyde enamine in the presence of a palladium(II)- phosphine complex as catalyst. Hydrolysis of the enamine gives 7-hydroxydihydrocitronellal [151].

Definition

ChEBI: The tertiary alcohol arising from addition of water across the C2C double bond of citronellal.

Background

Hydroxycitronellal is a synthetic fragrance that is widely used in many cosmetics and hygiene products such as deodorants, soaps, antiseptics, and other household items. It has the smell of lilac, lily, and lily of the valley . Hydroxycitronellal has also been shown to be a dermatologic irritant and allergen, and as a result commercially available products are restricted by the International Fragrance Association (IFRA) to contain only 0.1-3.6%.
Sensitivity to hydroxycitronellal may be identified with a clinical patch test.

Indications

Hydroxycitronellal is approved by the FDA 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.

Taste threshold values

Taste characteristics at 50 ppm: sweet, waxy, green, floral and melon notes.

Flammability and Explosibility

Not classified

Trade name

Laurinal® (Takasago).

Contact allergens

Hydroxycitronellal is a classical fragrance allergen, found in many products. It is contained in “fragrance mix.” It has to be listed by name in the cosmetics of the EU.

Safety Profile

A skin irritant. Combustible liquid. When heated to decomposition it emits acrid smoke and irritating fumes. See also ALDEHYDES.

Synthesis

By hydration of natural citronellal obtained from Java citronella or from Eucalyptus citriodora; β-pinene is converted to myrcene, which on hydration may yield either linalool or mixture of geranoil and nerol; the latter mixture can be hydrogenated to citronellol and subsequently converted to citronellal and hydroxycitronellal; also by hydrogenation of 3,7-dimethyl-7-hydroxy-2- octen-2-al over palladium carbon in ethyl acetate solution.

Metabolism

Studies in rabbits have shown that hydroxycitronellal is converted to two primary metabolites: reduction to the alcohol 7-hydroxycitronellol and oxidation to the carboxylic acid 7-hydroxycitronellylic acid . On average, about 50% of hydroxycitronellal is excreted as 7-hydroxycitronellylic acid which is therefore regarded as the major metabolite .