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Pharmacognosy I
Mosul University/ college of Pharmacy
L.A. Dilbreen Barzanji
 ‘Volatile’ or ‘essential’ oils are the odorous and volatile
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products of various plant and animal species.
They have a tendency to undergo evaporation on being
exposed to air even at an ambient temperature.
They differ entirely in both chemical and physical
properties from fixed oils.
They are secreted in oil cells, in secretion ducts or cavities
or in glandular hairs. They frequently associated with other
substances such as gums and resins and themselves tend to
resinify on exposure to air.
Large quantities of volatile oils are produced annually; as
examples, for lemon oil, eucalyptus oil, clove leaf oil and
peppermint oil world production annually runs into several
thousand metric tons each.
Uses of volatile oils:
Volatile oils are used for their therapeutic action:
 for flavouring agent (e.g. oil of lemon)
 in perfumery (e.g. oil of rose)
 starting materials for the synthesis of other
compounds (e.g. oil of turpentine)
For therapeutic purposes they are administered as:
 Inhalations (e.g. eucalyptus oil)
 Orally (e.g. peppermint oil)
 Gargles and mouthwashes (e.g. thymol)
 Transdermaly (many essential oils including those of
lavender, rosemary and bergamot are employed in
practice of aromatherapy).
 Oils with a high phenol content, e.g. clove and thyme,
have antiseptic properties
 carminatives
 antispasmodics
Composition of volatile oils
 with the exception of oils derived from glycosides (e.g. bitter
almond oil and mustard oil) volatile oils are generally mixtures
of hydrocarbons and oxygenated constituents are present; in
others (e.g. oil of gloves) the bulk of the oil consists of
oxygenated compounds.
 The odour and taste of volatile oils is mainly determined by these
oxygenated constituents, which are to some extent soluble in
water (note orange-flower water, rose water, etc.) but more
soluble in alcohol (note tincture or essence of lemon, etc.).
 Many oils are terpenoid in origin; a smaller number such as those
of cinnamon and clove contain principally aromatic (benzene)
derivatives mixed with the terpenes. A few compounds (e.g.
thymol and carvacrol), although aromatic in structure, are
terpenoid in origin.
Note box 1: terpenoids
 Terpenoids are compounds derived from combination
of two or more isoprene units, isoprene is a five
carbon unit, chemically known as 2-methyl-1,3butadiene.
 According to isoprene rule proposed by Leopold
Ruzicka, terpenoids arise from head-to-tail joining of
isoprene units. Carbon 1 is called the ‘head’ and carbon
4 is the ‘tail’.
 Terpenoids are classified into: monoterpenes,
sesquiterpenes, diterpenes, triterpenes, tetraterpenes
and polymeric terpenoids.
Note box 2: monoterpenes
 Monoterpenes, 10-carbon containing terpenoids, are
composed of 2 isoprene units, and found abundantly
in plants, e.g. (+)-limonene from lemon oil, and (-)linalool from rose oil.
 Many monoterpenes are the constituents of plant
volatile oils or essential oils.
 Monoterpenes occur in plants in various structural
forms; some are cyclic while others are acyclic.
 They also contain various types of functional group,
and depending on their functional group they can be
classified as simple hydrocarbons, alcohols, ketones,
aldehydes, acids or phenols.
Evaluation of volatile oil
 Various pharmacopoeial procedures are given for the evaluation
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of volatile oils.
Odour and taste are obviously important in preliminary
examination.
Physical measurements including optical rotation, relative
density and refractive index are regularly employed for
identification and assessment of purity; similarly. thin layer
chromatograms (TLC).
Capillary gas chromatographic profiles are used to determine the
proportions of individual components of certain oils. Advances
in gas chromatography have now made possible detection of
adulteration with synthetic material or unwanted other oils.
Other general tests described in BP include examination for
fixed or resinified oils (residue after evaporation), foreign esters
(conversion to a crystalline deposit) and presence of water
(turbidity of a carbon disulphide solution).
Preparation of volatile oils:
 Modern volatile oils stills contain a raw material on
perforated trays or in perforated basket.
 The still contains a water at the base which is heated
by steam coils, and free steam under pressure may also
be passed in.
 Tough materials such as barks, seeds and roots may be
comminuted to facilitate extraction but flowers are
usually placed in the still without further treatment as
soon as possible after collection. Distillation is
frequently performed in the field.
 The distillate which consist of a mixture of oil and
water, is condensed and collected in a suitable receiver
which is usually a large glass jar with one outlet near
the base and another near the top.
 The distillate separates into 2 layers, the oil being
withdrawn through the upper outlet and the water
from the lower outlet, or vice versa in the case of oils,
such as oil of cloves, which are heavier than water.
 The oil-saturated aqueous layer may be returned to the
still or may form an article for commerce, as in the case
of rose water and orange-flower water.
Peppermint leaf and peppermint oil
 The fresh leaves of Mentha piperita (F. Labiatae) is required to
contain not less than 1.2% of volatile oil. The oil is obtained from
the same plant by steam distillation using the flowering tops.
 The peppermint oil was required to contain not less than 44% of
free alcohols calculated as menthol, 15-32% of ketones calculated
as menthone, and 4.5-10% of esters calculated as menthyl
acetate.
 Menthol is terpene alcohol occurs as a white crystalline solid,
topical application of menthol to the skin causing refreshing
cooling sensation followed by a slight burning and pickling
sensation.
Uses:
 Peppermint oil used as inhalation (for coughs and colds),
decongestant, antitussive, analgesic,
anesthetic, counterirritant, anti-pruritic, enteric coated capsules containing
peppermint oil used for irritable bowel syndrome.
Spearmint oil
Spearmint or ordinary garden mint consists of the dried
leaf and flowering top of Mentha spicata.
Oil of spearmint contains (-)-carvone, (-)-limonene,
phellandrene and esters.
Uses:
 Oil of spearmint finds wide application especially in
the flavouring of chewing gums and toothpastes. The
oil does not possess the medicinal virtue of
peppermint oil.
Natural camphor
Natural camphor is a white, dextrorotatory ketone, C10H16O,
obtained from the wood of Cinnamomum camphora.
Camphor occurs in small, colorless crystals or in transparent
fibrous blocks. It has a characteristic odour and a pungent,
aromatic taste, which is followed by a sensation of cold.
Camphor oil contains in addition to camphor , safrole,
borneol, vanillin and terpineol, a number of sesquiterpens.
Uses: camphor is used externally as rubefacient, and
internally as a mild antiseptic and carminative.
Eucalyptus oil
Oil of eucalyptus is distilled from the fresh leaves of various species
of Eucalyptus (f. Myrtaceae) and rectified.
Only a ceratin number of species produce oils suitable for
medicinal use. The chief requirement is a high cineole content
and the absence of appreciable quantities of phellandrene and
aldehydes.
Suitable oils are derived from E. polybractea, E. smithii, E. globules
and E. australiana.
Oil of eucalyptus is a colourless or pale yellow liquid. It has an
aromatic and compharaceous odour; a pungent, camphoraceous
tast, which is followed by a sensation of cold. It is required to
contain not less than 70.0% of cineole.
Eucalyptus oil is much used for alleviating the symptoms of
nasopharyngeal infections, for treating coughs and as a
decongestant. It is taken internally in the form of mixtures,
inhalations, lozenges and pastilles and applied externally as
ointments and liniments.
Caraway fruit and oil
 Caraway consists of the dried ripe fruits of Carum carvi
(f. Umbelliferae), a biennial herb about 1 m high. It
occurs both wild and cultivated in central and
noerthern Europe.
 Caraway contains about 3-7% of volatile oil.
 Caraway oil consists largely of the ketone carvone and
the terpene limonene.
 Uses: the fruits and oil are used in medicine for
flavouring and as carminatives. The carminative and
antispasmodic properties have been experimentally
verified.
Dill oil
 Dill consists of the dried, ripe fruits of Anethum
graveolens (f. Umbelliferae), a small annual
indigenous to southern Europe.
 The Dill oil resembles oil of caraway in containing
carvone and limonene. The European fruits yield
about 3-4% of volatile oil, which should contain from
43-63% of carvone.
 Uses: dill is used as carminative and flavor; it is much
used in infant’s gripe water.
Coriander and coriander oil
 Coriander is the dried nearly ripe fruit of Coriandrum
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sativum, an annually about 0.7 m high with white pinkish
flower.
Coriander fruit contain up to 1.8% of volatile oil.
The distilled oil contains 65-70% of (+)-linalool
(coriandrol), depending on the source, and smaller
amounts of α-pinene, γ-terpinene, limonene and p-cymene
together with various non-linalool alcohols and esters.
The unripe plant has an pleasant, mousy odour, which is
also present in oil distilled from unripe fruits (mainly
aldehydes such as n-decanal ).
Uses: pharmaceutically coriander and its oils are used as
flavouring agent and carminative.