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Volatile Oils:- Full details note

Volatile Oils

Volatile oils are odorous principle compounds obtained from plants and animal source.
Volatile evaporate at ordinary temperature, that’s why they are known as etheral oils. They are also known as essential oils as they represent the essence/odorous constituents of plants.
Examples of volatile oils obtained from animals are musk from musk bear and amber from sperm whale.

Properties of Volatile Oils

• They have low boiling points and evaporate at room temperature.
• Volatile oils are usually colorless liquids but may become darker in color/ resinified (rubber like) upon exposure to air/ light due to oxidation.
• They have high refractive indices.
• They are lighter than water (except for clove oil).
• They have characteristic odor.
• They are optically active.
• They are immiscible with water but soluble in organic solvents like alcohol, ether etc.

Difference between Volatile oils & Fixed oils

• Volatile oils are made up of isoprene units; phenyl propanoids whereas fixed oils are esters of fatty acids with alcohol glycerol.
• They evaporate at room temperature whereas fixed oils do not.
• Unlike fixed oils they do not leave greasy mark/ spot on paper.
• Volatile oils can be distilled from their sources.
• Volatile oils cannot be saponified with alkalies.
• Volatile oils are resinified upon exposure to air/ oxygen unlike fixed oils which are rancified upon exposure to air.

Occurrence

Volatile oils can occur in specialized secretory structures in different parts of the plants depending on the family e.g.
1. Glandular hair of leaves and stem in labiatae (e.g. peppermint, spearmint etc.)
2. Oil ducts or vitae in umbelliferae (e.g. fennel, caraway etc.)
3. In modified parenchyma in family piperaceae (e.g. Cubeb)
4. In mesophyll of Eucalyptus leaves
Chiefly volatile oils are present in/;• Flowers where they act as repellent to protect flower from insects or attractant to facilitate fertilization.
• Bark and leaves of cinnamon
• Peel of orange and lemon contain large amount of volatile oils

Methods of Obtaining Volatile Oils

1. Distillation

Being volatile they are generally obtained by distillation. Depending on the nature of drugs different types of distillation methods are used.
• Water distillation
• Water & steam distillation
• Direct steam distillation
• Destructive distillation

Water distillation:

This method is suitable for dried plant material which can withstand boiling. The material is boiled in a distillation chamber until the water and oil is completely evaporated and collected in condensing chamber. After sometimes the two layers are separated, and oil layer can be removed.

Water & steam distillation:

This method is applied to fresh/dry plant material which can be affected by boiling e.g. cinnamon oil, clove oil etc.
The drug material is ground and covered with water. Steam is passed through the drug. After
condensation, the oil layer is separated from aqueous layer.

Direct steam distillation:

This method is used for fresh drugs which contain moisture. Steam is passed through the freshly collected drug and the vapors from the top of the distillation chamber are transferred to the condensing chamber. The oil layer is removed after condensation.

Destructive distillation:

This method is rarely used when members of Pinaceae family are heated in the absence of air, decomposition occurs resulting in the formation of volatile oil. E.g. turpentine oil.
The main disadvantage of distillation is decomposition of compounds/volatile oils due to high temperatures and hydrolysis used. It is also time consuming.

2. Expression

This method is suitable for volatile oils which are heat sensitive (thermolabile) and can be decomposed during distillation e.g. lemon and orange oil. These oils are present in oil glands which are present in peel of fruit.Two processes are generally used:

Sponge method:

The rind/skin of fruit is separated from peel and soaked in water to render it soft. It is then expressed by one hand and the oil which is expressed out is absorbed by a sponge in the other hand. The oil is collected in a vessel. The whole process is carried out in a dark cool room to avoid decomposition.

Ecuelle method: (French for Needle-like)

In this method oil is expressed by rupturing oil glands with sharp projections. The oil is collected by spraying water on injured peel. The oil is separated from the aqueous layer.

3. Extraction

Extraction with non-volatile solvents/enfleurage:
When amount of essential oil in a freshly plant material e.g. in flowers, is very small the removal is not commercially feasible, we use enflurage method. In this method an odorless fixed oil like olive oil is spread as a thin film on glass plate. The flower petals are placed in this oil for a few hours. After the oil has absorbed maximum amount of essential oil, it is removed and volatile oil is extracted with alcohol. This method was frequently used for production of perfumes.

Extraction with volatile solvents:

In perfume industry, the modern method for essential oil production is extraction with volatile solvents e.g. petroleum ether, benzene etc.
Advantages:
• Main advantage of this method over distillation is that decomposition of oil constituents does not occur and we can obtain essential oil for perfumes without any change in the characteristic aroma/fragrance.
Disadvantages:
• It is an expensive method.

4. Chemical Methods (Enzymatic hydrolysis of glycosides)

Sometimes volatile oils can be produced by enzymatic hydrolysis of glycosides e.g. allyl isothiocyanate (sulfur containing volatile oil) is obtained by hydrolysis of glycoside sinigrin with myrosin.

Chemistry and Biosynthesis of Volatile Oils

Chemical constituents of volatile oils are divided into:
• Terpenoids
• Phenylpropanoids

Terpenoids (Terpenes)

Volatile oils are mono or sesqui terpenes. Terpenes are defined as “Natural products whose structure consists of isoprene units.”
These isoprene units are derived from acetate-mevalonate pathway. Isoprene units are joined together in head to tail manner/fashion.screenshot 2021 04 11 13 49 40 196 com7758210599847155805An isoprene unit is a 5-carbon unit with two double bonds. Monoterpenes consist of two isoprene units. Sesqui-terpenes consist of three isoprene units. Diterpenes consist of four isoprene units and triterpenes consists of 6 isoprene units. Terpenes usually found in volatile oils are monoterpene alcohol, aldehydes, ketones, oxides and esters.

Phenylpropanoids:

screenshot 2021 04 11 13 51 19 894 com3583859905084147589They are derived from schikimic acid pathway. These compounds contain an aromatic ring (C-6 phenyl ring) and a propane side chain. The precursors for phenylpropanoids are cinnamic acid and para- hydroxycinnamic acid, which in turn are synthesized from phenylalanine and tyrosine respectively.Phenylpropanoids generally found in volatile oils are phenols and phenol-ethers. Volatile oils generally consist of
• Eleoptenes (un-oxidized)
• Stearoptenes (oxidized)
The characteristic odour and flavor of volatile oil is due to stearoptenes.

Eleoptenes:

Eleoptenes are the hydrocarbon portion of volatile oil which is liquid at room temperature.

Stearoptenes:

Stearoptenes are the oxidized hydrocarbon portion of volatile oil. They are usually solid except for few. Methanol, thymol, anethole are solid stearoptenes whereas cineol (eucalyptol), eugenol and methylsalicylate are liquid stearoptenes.

Chemical Tests for Identification of Volatile oils

Saudan III:
Alcoholic solution of saudan III produces red color with volatile oils.
Tincture of alkane:
It also produces red color with volatile oils.

Storage of Volatile oils

V.Os can be oxidized during storage in air, moisture and light resulting in change of color, viscosity and odor. V.Os should be stored in closed in containers fully filled, away from light in amber glass containers.

Commercial and Medicinal Use of Volatile Oils

• Flavoring agent
• Perfuming agent
• In beverages
• In cosmetics
• Carminative e.g. umbelliferous fruits
• Anthelmintic e.g. chenopodium oil
• Diuretic e.g. juniper
• Antiseptic e.g. eucalyptus
• Counter-irritant e.g. wintergreen (due to methylsalicylate)
• Local anesthetic e.g. clove oil, methanol
• Sedative e.g. jatamansi
• Insect repellant e.g. citronella

Classification of V.Os

A. Hydrocarbon V.Os:
Hydrocarbons occur mainly in all V.Os. Limonene is the most common monocyclic terpenes/turpenes.
Turpentine oil:
It is obtained by distillation from oleoresin of Pinus palustris/ P.longifolia, family Pinaceae. It is colorless liquid with characteristic odor and taste.
Uses:
• Expectorant
• Rubefacient
• Counter-irritant• Antiseptic

Cubeb:

Cubeb oil is obtained from Cubeba officinalis, family piperaceae.
Chemical constituents:
It contains essential oils and fixed oils. Main constituents are cubebic acid, cibeol (cineole) and cubebene.
Uses:
• Expectorant
• Used in mouthwashes

2. Alcoholic V.Os:

• Alcohols found in V.Os can be acyclic, cyclic or di-cyclic aliphatic alcohols like ethanol, methanol and other high molecular weight alcohols are also present.
• Being water they are removed during distillation process but terpene alcohols remain in V.Os like acyclic terpene alcohols e.g. geraniol, citronella and linalool.
• Monocyclic alcohols include menthol, cineol and terpineol. Di-cyclic alcohols include borneol. Sesqui- terpene alcohols include zingiberol.

Peppermint oil:

It is obtained from aerial parts of Mentha piperita, family labiatae.
Chemical constituents:
Peppermint in longer days contains menthol as a major constituent and methyl acetate in lower quantities. But in shorter days it contains methyl acetate in large quantities and menthol in small
quantities.
• Peppermint oil is obtained by steam distillation from the aerial parts of peppermint.
Uses:
• Flavoring agent
• Carminative
• Stimulant
• Stomachache
• Relieves vomiting and nausea
• Leaves are applied externally for relieving pain as it has mild local anesthetic and analgesic effect due to menthol.
• Menthol is used in different analgesic preparations.
• It is also used in mouthwashes, toothpastes, chewing gums, cough drops etc.
• Also used in rheumatism, neuralgia, headache and toothache.screenshot 2021 04 11 14 00 17 639 com1179272454027570771

Coriander oil:

It is dried fruit of Coriandrum sativum, family umbelliferae.
Chemical constituents:
It contains volatile oil up to 1%. Main constituent is linalool. It also contains pinene, geraniol, borneol and phellandrene.screenshot 2021 04 11 14 02 05 402 com7057419441480999987It is colorless to pale yellow liquid with characteristic odor and color.
Uses:
• Antispasmodic
• Stomachache
• Diuretic
• Used externally for rheumatism
• Flavoring agent
• Carminative
• Tonic

Cardamom oil:

It consists of dried ripe fruit of Elettaria cardamomum, family zingiberaceae.
Chemical constituents:
It contains volatile oil (3.8%), resins, fixed oils, starch and calcium oxalate. V.O consists of eucalyptol (cineole), borneol and limonene.
Uses:
• Aromatic
• Carminative
• Stimulant
• Diuretic
• Flavoring agent
• Diarrhea
• Headache
• Respiratory disorders like asthma, cough, bronchitis

3. Ketonic V.Os:

Caraway
It consists of dried ripe fruit of Carum carvi family umbelliferae.
Chemical constituents:
It contains volatile oils, resins, fixed oils, proteins, coloring matter and calcium oxalate. V.O or caraway oil B.P consists of carvone, hydrocarvone, carveol and dihydrocarveol.
Uses:
• Condiment
• Carminative
• Antispasmodic
• Flavoring agent

Camphor:

It is a ketone obtained from Cinnamomum camphora, family lauraceae.
It is synthesized from pinene. Natural camphor occurs as a crystallized product as a woody stem and roots. The wood is chipped and distilled with steam. 1 pound of camphor is produced by 20-40 pounds of wood chips. Crude camphor is freed from oil by centrifugation. Specific rotation of camphor is between +41- +43. Synthetic camphor is optically inactive (racemic mixture).
Uses:
• Camphor is topically used as anti-pruritic
• Rubefacient
• Anti-infective
Spearmint:
It consists of dried leaves and flowering tops of Mentha spicata, family labiatae.
Chemical constituents:
Volatile oils, resins, tannins
Main constituent of spearmint oil is carvone.
Uses:
• Flavoring agent
• Carminative
• Febrifuge
• Diuretic
• Antiemetic
• Also used in chewing gums and mouthwashes
Buchu:
It consists of dried leaves of Barosma betulina, family rutaceae.
Chemical constituents:
Volatile oils, resins, flavonoids and calcium oxalate.
Uses:
It is used as:
• Urinary antiseptic
• Diuretic
• Carminative

4. Aldehyde V.Os:

Cinnamon oil:
It is obtained from leaves and twigs of Cinnamomum zeylanicum, family lauraceae by steam distillation.Chemical constituents:
Cinnamon oil is yellowish to brownish liquid which becomes darker and thicker upon exposure to air. Main constituent is cinnamic aldehyde. It also contains linalool and eugenol.
Uses:
• Carminative
• Flavoring agent
• Antiseptic
Bitter almond oil:
It is obtained from Prunus amygdalus, variety amara.
Chemical constituents:
Main constituent is benzaldehyde.
Uses:
• Flavoring agent
It should be used with caution as it may contain HCN (hydrocyanic acid).
Bitter orange peel:
It is a dried rind of ripe fruit of Citrus aurantium, variety amara; family rutaceae.
Chemical constituents:
It contains volatile oils, vitamin C, citral and citronellal.
Bitter taste is due to flavonoides aurantimaric acid. Main constituent of volatile oil is citronellal. It also contains hesperidin, capillary stability factor.
Uses:
• Carminative
• Flavoring agent
• Stomachache
• Bronchitis
Sweet orange peel:
It consists of fresh rind of fruit of Citrus aurantium, variety sinensis; family rutaceae.
Chemical constituents:
It contains volatile oil mainly citral. It also contains flavonoides and hesperidin.
Uses:
• Carminative
• Flavoring agent
• Aromatic
• Tonic

Lemon oil:

It is obtained from fresh rind of Citrus limon, family rutaceae.
Chemical constituents:
Flavor of lemon is due to geranial and neral, collectively known as citral. High quality is required to contain 2-4% of citral.
Uses:
• Carminative
• Flavoring agent
• Stomachache
• Stimulant
• In cosmetics e.g. in cleansers

5. Phenolic V.Os:

In volatile oil phenols are present either naturally or produced during distillation process. Important phenols usually found in V.Os include:
• Eugenol
• Thymol
• Carvacrol
The common source of eugenol is clove while thymol and carvacrol are present in thyme oil.screenshot 2021 04 11 16 04 59 886 com3186265515730930798

Clove and clove oil:

Cloves are dried flower buds of Eugenia caryophyllus, family myrtaceae.Chemical constituents:
Flower buds are collected and dried in air. A single tree can produce as much as 7 pounds of dried cloves. Large trees however can produce as much as 40 pounds. Buds are picked manually and spread on coconut mats to dry. Cloves have strong spicy odor and a pungent aromatic taste. Cloves contain 14-21% of V.O and 10-13% of tannins. Cloves are used as stimulant, aromatic, analgesic, local anesthetic (used in toothache).
Clove oil is obtained from cloves by water and steam distillation. It contains 85-95% of phenols, chiefly eugenol. Other constituents include α and β caryophyllenes.
Uses:
It is colorless to pale yellow liquid but becomes pink and thick upon exposure to air. Mainly used as:
• Carminative
• Flavoring agent
• Antiseptic
• Topically in toothache
• Counter-irritant
• Mild anesthetic
Eugenol is obtained from clove oil by shaking with 10% NaOH forming sodium eugenolate which is then washed with ether and subsequently decomposed with H2SO4. Eugenol is used as dental analgesic in dental preparations and mouthwashes.screenshot 2021 04 11 16 08 41 720 com4434769627663340449

Thyme and thyme oil:

It belongs to family labiateae. The drug thyme consists of Thymus vulgaris and/or Thymus zygis.The drug thyme consists of leaves and flowers. The minimum requirement for V.O B.P is 1.2% of thymol.
Chemical constituents:
Thyme oil consists of thymol, carvacrol, linalool and cymene.
Uses:
• Antiseptic• Antitussive
• Expectorant
• Spasmolytic
• Counter-irritant

6. Phenolic ether V.Os:

Fennel:
It is an aromatic herb also cultivated as a garden crop at all altitudes about upto 2000m. It is propagated by seeds and roots. Fennel is dried ripe fruit of Foeniculum vulgaris, family umbelliferae.
Chemical constituent:
Fennel fruit is a cremocarp. Fennel contains V.Os, fixed oils and tannins. The main constituents of V.Os are anethole and fenchone. Sweet taste of fennel is due to anethole. Other constituents of V.Os include anisic aldehyde, anisic acid and phellandrene.
Uses:
• Carminative
• Aromatic
• Stomachache
• Stimulant
• Expectorant
• Used in cough preparation
Anethole is used in
• Mouthwashes and toothpastes
• Spleen and kidney diseases
Fennel is adultrated with alcohol exhausted fennel.screenshot 2021 04 16 21 19 35 801 com1859030594073587292screenshot 2021 04 16 21 19 57 909 com7880768342905420856

Anise:

It is a dried ripe fruit of Pimpinella anisum, family umbelliferae.
Chemical constituent:
Anise oil is clear colorless/pale yellow liquid free from water with sweet aromatic taste. It crystallizes upon cooling. The main constituent is anethole, also contain anis aldehyde and anisic acid.
Uses:
• Carminative
• Diuretic
• Expectorant
• Also used in cough and sore throats.
Nutmeg (Myristica):
It is dried ripe seed of Myristica fragrans, family myrtaceae.
Chemical constituents:
It contains fixed oils and volatile oils. V.O contains myristicin(hallucinating agent), elemicin and safrole.screenshot 2021 04 16 21 22 28 685 com8925147864731240822Uses:
• Flavoring agent
• Antidiarrheal
• Condiment
• In large doses it can cause hallucination, flushing and tachycardia.
• Elemicin and myristicin are believed to be involved in toxicity.
• These compounds are metabolized to amphetamine (CNS stimulant) like compounds.

7. Oxide V.Os:

Eucalyptus oil:

Eucalyptus oil is obtained by steam distillation from the fresh leaves of Eucalyptus globulus, family myrtaceae.
Chemical constituent:
• It is colorless to pale yellow liquid having aromatic odor and pungent cooling taste.
• The chief requirements for V.O of eucalyptus are
• A high content of cineol
• Absence of appreciable quantities of phellandrene and aldehydes
Uses:
• Used for nasopharyngeal infections
• Cough
• Pain (counter-irritant or analgesic)
• Rubefacient
• Decongestant
• Expectorant
• Asthma
• Nasal inhalers (Vicks)
• External analgesics (Vicks vaporub)
• In mouth washes (Listerine)
• Febrifuge fever
Chenopodium oil:
It is obtained by steam distillation of Chenopodium ambrosioides, family chenopodiaceae.
Chemical constituents:
It contains ascaridole, limonene and methyl salicylate.
Uses:
• Used as Anthelmintic, especially for round worms and hook worms
• Also used for intestinal amoeba

8. Ester V.Os:

Rosemary oil:

The drug consists of dried leaves of Rosmarinus officinalis, family labiatae.
Chemical constituents:
Main constituent of rosemary oil is hydroxyl cinnamic acid.
Uses:
• Anti-bacterial• Carminative
• Antispasmodic

9. Miscellaneous V.Os:

Allium:
Garlic:
It is the dried bulb of Allium sativum, family liliaceae.
Chemical constituents:
It contains carbohydrates, proteins, fats and volatile oils. Chief constituent of V.Os are sulfur containing compounds like alliin and allicin. Alliin is converted into allicin by enzyme allinase. Allicin is a yellow liquid responsible for characteristic odor of garlic.
Uses:
• Allicin is the main active constituent which has antimicrobial properties.
• Garlic is an important
• Antiseptic
• Antihypertensive and anitihyperlipidemic (anticholesterolimic)
• Choliretic and cholagauge
• Expectorant
• Hypoglycemic
• Externally applied to insect bites
• Important antithrombotic factor ajoene has been isolated from garlic.
Onion:
It is an edible ground scaly bulb of Allium cepa, family liliaceae.
Chemical constituents:
It contains V.Os, minerals, vitamins and sugars
Uses:
• Antiseptic
• Expectorant
• Diuretic
• Choleretic hypotensive
• Hypoglycemic
• Can be applied to insect bites
• Also used to treat cough, bronchitis and common cold

Anethum (Dill)

Anethum consist of dried riped fruit of Anethum graveolens Family umbelliferaeConstituents
Volatile oil mainly carvone
Uses
• Carminative
• Diuretic
• Anthelmintic
• Also used in gripe waterscreenshot 2021 04 16 21 32 13 584 com1119506261378192682screenshot 2021 04 16 21 32 37 139 com2623045847505615379screenshot 2021 04 16 21 32 55 738 com918811315133528933screenshot 2021 04 16 21 33 16 411 com2664587183393923093screenshot 2021 04 16 21 33 36 245 com8957283713837816490screenshot 2021 04 16 21 33 56 123 com5110660114901270354

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