Essential oil

An essential oil is a concentrated, hydrophobic liquid containing volatile aroma compounds from plants. They are also known as volatile or ethereal oils, or simply as the "oil of" the plant material from which they were extracted, such as oil of clove. An oil is "essential" in the sense that it carries a distinctive scent, or essence, of the plant. Essential oils do not as a group need to have any specific chemical properties in common, beyond conveying characteristic fragrances. They are not to be confused with essential fatty acid.

Essential oils are generally extracted by distillation. Other processes include expression, or solvent extraction. They are used in perfumes, cosmetics and bath products, for flavoring food and drink, and for scenting incense and household cleaning products.

Various essential oils have been used medicinally at different periods in history. Medical application proposed by those who sell medicinal oils range from skin treatments to remedies for cancer, and are often based on historical use of these oils for these purposes. Such claims are now subject to regulation in most countries, and have grown correspondingly more vague, to stay within these regulations.

Interest in essential oils has revived in recent decades, with the popularity of aromatherapy, a branch of alternative medicine which claims that the specific aromas carried by essential oils have curative effects. Oils are volatilized or diluted in a carrier oil and used in massage, diffused in the air by a nebulizer or by heating over a candle flame, or burned as incense, for example.

Pepper
Piper nigrum (Piperaceae), Black pepper
Black pepper is a tropical twining plant coming from southern India. At one time Goa was the major exporter, but now black pepper is grown in all South-East Asia. The small fruits are green at first, then red, and black at last. When the half-ripened fruits are harvested and dried, black pepper is obtained with the dried skin (flesh) surrounding the seeds. When the ripe fruits are harvested and the skin removed, the naked seeds or 'white pepper' is obtained. The pepper seeds contain a volatile oil and the non-volatile compound piperine, responsible for peppers burning effect on the mucous membranes.
Spices have always been associated with warmth and sensuality, not only in the kitchen. Pepper oil recently has had a revival in perfumery. It is obtained by steam distillation of the crushed seeds and has an intensely woody, fresh and piquant odour, especially popular in masculine perfumes. Pepper oil is mainly composed of cyclic monoterpenes with 3-carene as the major component (around 35 %). Moreover, a number of hitherto unidentified sesquiterpenes probably contribute to its character.
The spicy-aromatic and musky men's perfume Extreme Polo Sport (Ralph Lauren 1998) uses as much as 6 % pepper oil.
The genus Piper has many members, several of which are utilized, e.g. long pepper, cubeb pepper, betel pepper, ashanti pepper and kava.

Peppermint
Mentha piperita (Labiatae)
Peppermint is a crossing between water mint, M. aquatica, and spearmint, M. spicata. The oldest descriptions are from the end of the 17'th century, and probably the crossing has occurred in England and was discovered there.
Peppermint oil is obtained by steam distillation of the leaves. Everybody knows it - from chewing gum, sweets, toothpaste, etc. Major production sites are a number of mid-western states in USA (around 2000 t/y). Japanese peppermint oil of fine quality is obtained in the province of Yakima from M. arvensis piperescens.
The main component of peppermint oil is (-)-menthol (ca. 50 %) followed by (-)-menthone (ca. 20 %) and (-)-menthyl acetate (ca. 10 %). A characteristic of peppermint oil is the compound (+)-menthofurane (ca. 3 %, sometimes higher) and a number of sesquiterpenes, one of them viridiflorol. The mint oils are among the most thoroughly investigated essential oils.
The menthol molecule carries three asymmetric carbon atoms, and therefore exists in four diastereomeric pairs.
(-)-Menthol, however, is the only one of these eight isomers having the special cooling effect upon the mucous membranes. (-)-Menthol forms large, transparent, colourless, tinkling, prismatic crystals with a melting point of
43 °C (picture on the right). Today it can be synthesized from number of terpenes using stereospecific hydrogenation catalysts based on rhodium(I)- or ruthenium(II)-complexes (ref. The Nobel Prize in chemistry, 2001). Pure (-)-menthol is used in large amounts for menthol cigarettes, toothpaste, etc.

Peru balsam
Myroxylon pereira (Fabaceae)
Peru balsam is obtained as a viscous resin from cuts in the bark on this tree of the pea family. It is mostly produced in El Salvador. The balsam itself (picture) is not used anymore because it is allergenic. Instead the so-called Peru balsam oil is used, made by vacuum distillation of the balsam.
Peru balsam oil has a very tenacious, sweet balsamic odour with vanilla-like nuances. It is used as a fixative in perfumes where a long-lasting sweetness is called for. Benzyl benzoate and benzyl cinnamate are some of the major components. Vanillin as well as nerolidol make their contributions too. (see alse tolu balsam)

Petitgrain
Citrus aurantium subsp. amara (Rutaceae)
Petitgrain oil is obtained by steam distillation of the leaves of Citrus species. The largest production takes place in the South American state of Paraguay from the leaves of Citrus aurantium subsp. amara.
Petitgrain oil has an intense, bitter-sweet, citrusy odour with floral and woody nuances. (-)-Linalyl acetate and
(-)-linalool in the proportion 2:1 constitutes about 80 % of the oil, but a great number of trace constituents contribute to its character.
Petitgrain oil is used as a supplement to bergamot oil in Earl Grey Tea, and in perfumes for soaps, shampoos, etc

Wormwood

Artemisia annua (Compositae), Annual wormwood, Sweet Annie, Qing Hao, Chinese wormwood
The annual wormwood is a highly aromatic herb of Eurasian origin. It has traditionally been grown in China as a medicinal plant and more recently in Europe and USA for its aromatic leaves which are used in perfumery and in flavouring beverages. One of the key components of the A. annua aroma is the doubly unsaturated terpenic ketone, artemisia ketone or 3,3,6-trimethyl-1,5-heptadiene-4-one (67 %).
In masculine perfumes of the Chypre type, artemisia (or armoise) oils are sometimes used for their fresh and stimulating herbal top notes, one great example being Kouros Fraicheur (Yves Saint Laurent 1993).
Recently, research in the Peoples Republic of China has brought a special attention to A. annua as a source of artemisinine (an endo peroxide seco sesquiterpene lactone), a compound that shows great promise as an anti-malarial agent.
Etymology: Gr. Artemis, the goddess of hunting and the moon. The wormwoods have their name from their ancient use as a remedy against intestinal worms. The alcoholic drink vermouth (~ wormwood) is made from white wine and spicy herbs, among them Artemisia absinthium.

Ylang-Ylang
Cananga odorata (Annonaceae)

The Ylang-Ylang tree is planted everywhere in the tropics because of its fragrant flowers. In the Philippines, for example, the tree is seen in almost every village. The peculiar flowers are green when they come out, but in a few days they turn yellow and become highly fragrant. On special occasions the women put them in their hair.
Ylang-ylang oil or cananga oil is obtained by steam distillation of the freshly picked flowers, especially in Madagascar and the Comores. It is a classical ingredient in perfumery. The major constituents of the oil are a number of well known powerful odorants, e.g. benzyl acetate (ca. 25 %), p-cresyl methyl ether (ca. 20 %), (-)-linalool (ca. 15 %), geranyl acetate (ca. 10 %), methyl benzoate (ca. 5 %) plus eugenol, iso-eugenol and several sesquiterpenes, among them ylangene.
p-Cresyl methyl ether is a characteristic of the Ylang-Ylang flower. The pure substance has a very powerful odour, offensive to most people. However, in lower concentration, and supplemented by the multitude of other odorants present in the flower, it supplies much of the exotic character of Ylang-Ylang.
The genus Cananga holds only four species, all with fragrant flowers. The rest of the Annonacean family usualy has flowers with a moldy or putrid smell, if they have any smell at all.

Etymology: Ylang-Ylang is Indonesian, meaning 'loosely hanging' (flowers).

Acacia
Acacia decurrens var. dealbata (Mimosaceae)

This is the 'mimosa' of the florists' shops, but actually it is an acacia from eastern Australia. True mimosas of the genus Mimosa never have yellow flowers, their flowers are somewhat differently shaped and mostly red. Anyway, this acacia and its relative from South America, cassie, Acacia farnesiana, have been used in perfumery for their diffusively sweet fragrance.

2-hydroxyacetophenone is known to be the major constituent of acacia flower oil [3], but it does not represent the full fragrance of the flowers.

Etymology: Gr. akakia, innocence, Gr. mimos, mimic, plants of the genus Mimosa often have sensitive leaves, folding up on being touched.

Agarwood
Aquilaria agallocha, A. malaccensis (Thymelaeaceae) Eaglewood, Aloe, Oud

The genus Aquilaria is found in the triangle enclosed by Bengal, Hong Kong and New Guinea, and consists of about 15 species of trees and bushes. Trees of A. agallocha, A. malaccensis and related species sometimes become infected with a mould, Phialophora parasitica, and react by producing an aromatic resin. The dark resinous heartwood from these forest trees is called agarwood, eaglewood, aloe or oud. It has an elegant, sweet-woody odour of varying character, and is one of the oldest and most famous incense materials of the Far East. The finest quality is called Kanankoh (Kyara in Japanese).

The Chinese marketed and imported agarwood thousand of years before the Europeans came to know about it. The 'aloe' of the New Testament (Joh. 19:39) might have been agarwood. In Japan, a ceremony called Kodo lets the participants experience the scent from small, heated pieces of agarwood, each with a different character and an accompanying anecdote.

Recently there has been a growing demand for agarwood. The wild trees are very rare, having been severely over harvested, but the oil is now making a comeback due to the foresight of a few families in Assam who are planting large plantations of the tree. Several other national initiatives are in progress to make this precious resource available through cultivation. Samples of agarwood oil extracted by supercritical CO2 from the oleoresin of cultivated trees are available from Eden Botanicals. It is one of the most expensive of all essential oils.

The odour-determining chemical constituents of agarwood are a multitude of oxygenated sesquiterpenes. The two shown karanones seem to be important for the 'Oriental' and fumigating character of agarwood [1].

A comprehensive bibliography on agarwood can be found at Cropwatch.

The perfume M7 (Yves Saint Laurent 2002) is declared to include agarwood oil.

Allspice
Pimenta dioica (Myrtaceae)

Soon after the discovery of America, Spanish explorers noted that the Mexican Indians used the berries from a certain bush in their warm cocoa drinks to enhance its flavour. They had to do with the fruits of a member of the Myrtle family, now known as allspice, a spice "with a flavour resembling clove, pepper as well as cinnamon", as the encyclopaedia says. The mature, unripe berries are dried and used, mostly ground, in sausages, pickles and Christmas cookies. Jamaica is one of the major exporters.

Allspice oil, or pimento berry oil, is obtained by steam distillation. Its main constituents are eugenol (up to 75 %), 1,8-cineole (eucalyptol) and the sesquiterpene caryophyllene [6]. See the relatives bay and clove.

Amber (Ambergris)
Physeter catodon (Physeteridae) Sperm Whale

The legendary amber (Fr. ambergris, grey amber) is a pathological metabolite of the sperm whale, probably arising from injuries in its intestines as a result of certain food intakes. It is abundant in steroid lipids, the tricyclic triterpene (-)-ambrein being one of the main constituents. When the excreted chunks of amber, some weighing as much as 100 kg, are exposed to sunlight and air at the surface of the sea, a number of oxidation products are gradually formed. These compounds have a pronounced odour, highly valued in perfumery since antiquity.

The most important amber odorant is (-)-ambrox. Today, it is synthesized from the diterpene sclareol, found in the plant Clary Sage. The powerful and elegant odour of (-)-ambrox is somewhat reminiscent of that of chopped bark from pine. According to Müller and Lamparsky [5] it matches the first four tonalities of aged ambergris tincture:

1. wet mossy forest soil, 2. strong tobacco, 3. balsamic sandalwood, 4. warm animal musk (the last two are:

5. seaweed/ocean, 6. fecal). (-)-Ambrox of high quality is marketed as Cetalox ® by Firmenich and as Ambrofix ® by Givaudan. Sampels may be purchased from Perfumers World.

An example of a perfume using (-)-ambrox is Drakkar Noir (Guy Laroche 1982) [43].

Ambrette seeds
Abelmoschus moschatus (Malvaceae)

Ambrette seeds come from a tropical hibiscus. The seeds contain an oil with a fatty-musky, slightly ambery odour. It's most important odoriferous components are the macrocyclic musks 5(Z)-tetradecen-14-olide and

7(Z)-hexadecen-16-olide, also called ambrettolide [6]. The oil was formerly highly appreciated in perfumery, but has now been largely replaced by synthetic musks. For example, the isomer 9-hexadecen-16-olide is made by the Swiss company Givaudan.

Musk odorants in plants are always macrocyclic lactones (see also angelica). In animals, using musks as pheromones, they may be ketones as well as lactones, see musk deer, musk rat, and civet.