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.
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.
Hydroxycitronellal has a sweet, floral, lily-type odor
7-Hydroxycitronellal shows fungicide activity the strains of Candida tropicalis.
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).
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].
ChEBI: The tertiary alcohol arising from addition of water across the C2C double bond of citronellal.
Taste characteristics at 50 ppm: sweet, waxy, green, floral and melon notes.
Flammability and Explosibility
Not classified
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.
A skin irritant.
Combustible liquid. When heated to
decomposition it emits acrid smoke and
irritating fumes. See also ALDEHYDES.
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.
