2-aminobenzaldehyde and 3(Z)-hexen-1-ol
Robinia pseudoacacia (Fabaceae) False Acacia
For unknown reasons robinia is often wrongly called acacia. Linné consequently named it pseudoacacia (Lat. pseudo, false). Acacias, however, are tropical and subtropical members of the mimosa family. Robinia is a tall, North American tree with clusters of white flowers in the springtime. Since the beginning of the 16'th century it has been planted as an ornamental tree in Europe.
The fragrance of the flowers is fine and sweet, being dominated by the aromatic aldehyde 2-aminobenzaldehyde [5]. The leaves are rich in the unsaturated aliphatic alcohol 3(Z)-hexen-1-ol, called leaf alcohol. In perfumery terms, this odorant has a typical 'green' odour reminiscent of freshly cut grass [55].
P.S. Robinia wood is resistant to rot because of its high level of flavonoids (around 6 % of the dry material), for instance robinethin, dirobinethin and taxifolin. Methanolic extracts from the wood of robinia has shown to be just as effective as traditional impregnating chemicals like pentachlorophenol and chromated copper arsenate [85].
aroma impact compounds in rocket
Eruca sativa (Cruciferae) Rucola, Roquette
This crucifer, a long known salad green from the Mediterranean area, has a rich nutty-green flavour with a subdued mustard-like pungency. It is a piquant addition with lettuce, salads, as a topping on pizzas, etc.
Jirovetz et al. analysed the headspace from freshly cut rocket leaves using solid phase micro extraction with GC, GC-MS, and olfactometry. More than 50 constituents could be identified. Characteristic aroma impact compounds were found to be methylthioalkyl isothiocyanates and -nitriles together with (Z)-3-hexen-1-ol and -esters. The following compounds were found in more than 5 % concentration: 4-methylthiobutyl isothiocyanate (14 %), 5-methylthiopentanonitrile (5 %), 5-methylthiopentyl isothiocyanate (9 %), (Z)-3-hexen-1-ol (11 %), (Z)-3-hexen-1-yl butanoate (11 %), (Z)-3-hexen-1-yl 2-methylbutanoate (5 %) [178]. Likewise, Miyazawa et al. found 4-methylthiobutyl isothiocyanate and 5-methylthiopentanonitrile to be major components [179].
See also watercress.
Etymology: Lat. eruca, from Lat. roc, harsh; Lat. sativa, cultivated.
isobutyl angelate, 2-methylbutyl angelate, and chamazulene
Roman chamomile
Chamaemelum nobile (Anthemis nobilis) (Compositae)
Roman chamomile is a herbaceous perennial native to western Europe and
North Africa. It is a close relative to the true chamomiles of genus Chamomilla
(Matricaria), and the flowers, containing anti-inflammatory and
sedative ingredients, have been used in much the same way.
Roman chamomile oil is produced from cultured varieties of the herb (var.
flora plena syn. var. ligulosa) in several countries.
The oil is obtained by steam distillation of the freshly dried flowers
as a bluish liquid with a strong, aromatic odour characteristic of the
flowers. Roman chamomile oil is especially suited for top notes in masculine
perfumes, where it provides a heady, sweet-herbal diffusion of considerable
radiance.
The major constituents of Roman chamomile oil are esters of angelic acid
(2-methyl-2(Z)-butenoate) and tiglic acid (2-methyl-2(E)-butenoate), e.g.
the isobutyl- and 2-methylbutyl esters. The bluish colour of the oil is
due to the sesquiterpenoid chamazulene (C14H16) [6] [86]. The photo on
the right shows the freshly distilled oil (dark blue) on top of the water
phase.
Etymology: Gr. khamai, on the ground, low; Gr. melon,
apple, because of the pleasant and somewhat apple-like odour of the plant;
Lat. nobilis, noble.
rose alcohols, methyleugenol, beta-damascenone and (-)-cis-rose oxide
Rose
Rosa damascena (Rosaceae) Damask rose
The true wild roses add up to a few hundred species from the temperate
and subtropic zones on the northern hemisphere, including North Africa,
Ethiopia, Himalaya and the Philippines. The crossings and grown varieties
are more than tenfold that number.
The rose is the most celebrated of flowers, symbol of love and beauty.
The precious rose oil is obtained by careful steam distillation of the
freshly picked flowers of the Damask rose, Rosa damascena, mainly
in Bulgaria, Turkey, Morocco and China. It takes several hundred man-hours
to pick the 3-4 tonnes of flowers needed to produce 1 kg of rose oil,
which makes rose oil one of the most expensive essential oils.
Following the development of organic chemistry, continued investigations
have been carried out to identify the
odour impact compounds in rose oil. Prior to 1959 no real progress was
achieved in spite of the identification of all constituents present in
more than 1 % concentration (corresponding to 83 % of the oil). A break-through
came in 1959 with the discovery of (-)-cis-rose oxide, present in 0.5
% concentration. This cyclic monoterpene ether is responsible for the
highly volatile, floral-green top note in rose oil. Moreover, in 1970,
beta-damascenone was identified in 0.1 % concentration, supplying a floral-fruity
character with a plum-like shading. Because of the extremely low odour
threshold of this compound, it has a much higher odour impact than citronellol,
present in 330 times greater concentration [3]. However, rose oxide and
beta-damascenone appear to be rearrangement products that are formed during
the steam distillation process from labile progenitors [87]. The major
constituents of rose oil are (-)-citronellol, certain specific paraffines,
geraniol and nerol, phenethyl alcohol, and methyleugenol - in decreasing
order. Some of the important minor- and trace constituents are (-)-cis-rose
oxide, beta-damascenone, beta-ionone, beta-damascone, 1-p-menthen-9-al,
and rose furan. More than 350 compounds have been identified [5] [88]
[89].
3,5-dimethoxytoluene
The name 'tea rose' is the result of a misunderstanding - the rose was created in the Fa Tee nursery near Canton
in China! In 1810 it was discovered by an Englishman who sent a specimen to England. It is the ancestor behind several yellow and yellowish modern roses.
However, the scent of these roses is rather different from that of traditional roses. Surprisingly, their scent is strongly influenced by the aromatic compound orcinyl dimethyl ether, or 3,5-dimethoxy-toluene, which is chemically related to the oakmoss odorants [89]. This phenol ether has a warm and sweet, nut-like, earthy-mossy odour - according to Arctander.
eugenol
The rugosa rose origins in Japan or northern China (it is also called Kamchatka rose). It is a hardy bush with densely thorny stems and plenty of root suckers. The leaves have a corrugated surface and are shiny green. Rugosa rose has become an invasive specimen in several parts of the world. In Denmark, for example, it spreads along the coastline as it thrives in sandy soils, outperforming native plant communities (the seeds float and tolerate salty waters for several months). Nevertheless, the fragrant flowers and fleshy hips are beloved.
The flowers have most of their volatiles in common with the damask rose, but are characterized by a spicy note from eugenol in their deep sweetness [130]. An interesting, complete phytochemical review of Rosa rugosa was undertaken by Hashidoko [131].
The palette of rosy-smelling odorants is large. One newer achievement utilizes the
fact that the isobutenyl group common of many terpenes is rather isosteric with a phenyl group. By 'replacing' the isobutenyl group with a phenyl group in citronellol, for example, the odour character isn't changed much, but instead the more substantive odorant Phenoxanol ® (IFF) is achieved. The vapor pressure of Phenoxanol is ten times lower than that of citronellol. However, the odour threshold is also about ten times lower! Moreover, Phenoxanol has a richer and smoother odour than citronellol [43].
citronellol and Phenoxanol ®
(+)-borneol, (+)-bornyl acetate, (+)-camphor, (+)-alpha-terpineol, (+)-verbenone and 1,8-cineole
Rosemary
Rosmarinus officinalis (Labiatae)
Rosemary is a typical member of the Mediterranean coastal 'macchia' vegetation.
It is an aromatic shrub with an intense and pleasant smell. In the antiquity
rosemary was associated with Aphrodite, the goddess of love. Although
the only member of the genus Rosmarinus, it is found in numerous
chemotypes and cultivars.
Rosemary oil is obtained by steam distillation of the flowering tops,
mainly in Spain, Morocco and Tunisia. One of the first perfumes made by
distillation was based on rosemary oil, namely the Hungarian queen's-water,
'Aqua Reginae Hungariae'. It is told that the Hungarian Queen Isabella,
suffering heavily from rheumatism, used this perfume with beneficial results.
She became young and beautiful again, and the King of Poland offered to
marry her.
Good qualities of rosemary oil have a pleasant fresh odour with characteristic
resinous nuances and slightly bitter undertones. (+)-Borneol and (+)-verbenone
are important constituents. (+)-Borneol has a dry-camphoraceous, woody-peppery
odour, (+)-verbenone possesses an odour reminiscent of camphor, menthol
and celery. (+)-Alpha-pinene, (+)-bornyl acetate, (+)-camphor and 1,8-cineole
are characteristic too [90] [91] [92].
Rosemary oil is extensively used in perfumery. The dried and broken leaves
are used as a spice.
Etymology: Lat. rosmarinus, from Lat. ros, dew, and
Lat. marinus, sea.
2-undecanone, 'rue ketone',
and 2-nonanone
Ruta graveolens (Rutaceae) Common rue
Rue is chiefly mentioned here because it has given name to the rue family, Rutaceae, including many fragrant plants, not least the Citrus species. There are about 60 species of the genus Ruta having a natural distribution from the Canary Islands via the Mediterranean countries and Central Europe to eastern Siberia. Common rue is a perennial herb from the Mediterranean area. It has been grown as a medicinal plant, for instance in Switzerland, Austria and southern Germany, where it may be found growing wild, especially on warm and dry, calcareous ground. It was always kept in the gardens of the monasteries as it was considered to be of benefit to chastity.
The whole plant has a penetrating odour due to an essential oil with a great prevalence of straight chain aliphatic
2-ketones. 2-Undecanone or 'rue ketone' (47 %), and 2-nonanone (19 %) are the major constituents [93].