1. VOLATILE OILS & RELATED TERPENES
PHARMACOGNOSY-II
PHR 205

2. Definition
Volatile or essential oils, as their name implies, are volatile in steam. 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 are frequently associated with other substances such as gums and resins and themselves tend to resinify on exposure to air.

3. Volatile oil
Fixed Oil
Also called as an essential oil.
Also called as natural non-volatile oil.
Volatile oil can evaporate when placed under room temperature
Fixed oils do not evaporate at room temperature
They can be extracted easily by the distillation process
They require some specific techniques for extraction.
There is no spot (no permanent stain) left after evaporation
Some type of spot (permanent stain) left after evaporation
They are unable to undergo saponification
Fixed oils can be easily sponified.
Mixtures of cleoptenes & stearoptenes are termed as volatile oils
Esters of higher fatty acids & glycerin are called as fixed oils.
Posses high refractive index
Posses low refractive index
These are optically active.
These are optically inactive.
Their primary source is leaves,roots,in petals and bark.
Their major source is seeds of the plant.

4. Preparation of volatile oils
The principal methods used in the preparation of volatile oils from plants depend on: Distillation in water or steam. Scarification. Extraction with solvents. Enzymatic hydrolysis (for glycosidic volatile oils e.g. mustard oil). Enfleurage (extraction of oils used in perfumery).

5. Production and uses of volatile oils
The total annual production of volatile oils is estimated to be in the region of 45,000 tones, worth approximately US$700 million. There are about 100 commercially valuable volatile oils directly derived from plants. Volatile oils are used for their therapeutic action , for flavoring (e.g. oil of lemon), in perfumery (e.g. oil of rose) or as starting materials for the synthesis of other compounds (e.g. oil of turpentine).

6. Therapeutic uses of volatile oils
For therapeutic purposes they are administered as inhalations (e.g. eucalyptus oil), orally (e.g. peppermint oil), as gargles and mouthwashes (e.g. thymol) and transdermally (many essential oils including those of lavender, rosemary and bergamot are employed in the practice of aromatherapy). Those oils with a high phenol content, e.g. clove and thyme have antiseptic properties, whereas others are used as carminatives. Oils showing antispasmodic activity, and much used in popular medicine

7. Composition of volatile oils
Volatile oils are generally mixtures of hydrocarbons and oxygenated compounds derived from these hydrocarbons. The odour and taste of volatile oils is mainly determined by these oxygenated constituents, which are to some extent soluble in water but more soluble in alcohol. Practically all volatile oils consist of chemical mixtures that are often quite complex; they vary widely in chemical composition. Almost any type of organic compound may be found in volatile oils (hydrocarbons, alcohols, ketones, aldehydes, ethers, oxides, esters, and others). “usually volatile oils are classified according to the type of organic compounds”. It is not uncommon for a volatile oil to contain over 200 components, and often the trace constituents are essential to the odor and flavor. The absence of even one component may change the aroma.

8. Biosynthesis and chemical composition
Biosynthesis and chemical composition Chemical constituents of volatile oils may be divided into 2 broad classes, based on their biosynthetic origin: Terpene derivatives formed via the acetate-mevalonic acid pathway. Aromatic compounds formed via the shikimic acid-phenylpropanoid route. 1. Terpene derivatives: 2. Aromatic compounds:

9. Classification of Volatile Oils
Example
Source
Hydro-carbon
α-pinine
Turpentine oil
2. Alcohol-volatile oil
Linalool
Peppermint oil
3. Aldehyde-volatile oil
Cinnamaldehyde
Cinnamon oil
4. Ketone-volatile oil
Carvone
Spearmint oil
5. Phenol-volatile oil
Eugenol
Clove oil

10. α-Pinine
Cinnamaldehyde
Linalool
Carvone
Eugenol

11. Classification of Volatile Oils
Example
Source
6. Phenolic-ether-volatile oil
Safrole
Nutmeg oil
7. Oxide-volatile oil
Cineol
Eucalyptus oil
8.Ester-volatile oil
Menthyl acetate
Oil of wintergreen
9.Peroxide-volatile oil
Ascardiol
Chenopodium oil
10. others
Methyl salicylate

12. Safrole
Cineol
Menthyl acetate
Methyl salicylate
Ascardiol

13. Physical properties
Although volatile oils differ greatly in their chemical constitution, they have a number of physical properties in common: They possess characteristic odors. They are characterized by high refractive indices (Refractive index measures the speed at which light passing through an essential oil is refracted). Most of them are optically active. Their density is generally lower than that of water (the essential oils of sassafras, clove, or cinnamon are the exceptions). As a rule, volatile oils are immiscible with water, but they are sufficiently soluble to impart their odor to water. The aromatic waters are dependent on this slight solubility.

14. Chemistry of volatile oil:
Volatile oil consists of the following compounds:
Terpene type compounds
Aromatic type compounds
Terpene type compounds: Terpenes are defined as natural products whose structure may be divided into isoprene units. These units arise from acetate-mevalonate pathway and are branched chain of 5-carbon units containing two unsaturation in head and tail fusion.

15. Follwing types of isoprenes are usually found-
Monoterpene(C10H16): composed of 2 isoprene units
Sesquiterpene(C15H24): composed of 3 isoprene units
Diterpene(C20H32): composed of 4 isoprene units
Triterpene(C30H48): composed of 6 isoprene units
Tetraterpene(C40H64): composed of 8 isoprene units
 Most of the volatile oil are composed of monoterpenes are classified into two groups.
Acyclic; e.g. Geraniol

16. Cyclic monoterpenes are classified into-
i.Monocyclic; e.g. Limonene
ii.Dicyclic; e.g. α-pinine

17. Aromatic type compounds: Volatile oils having benzene ring with a propane side chain belong to these group of compounds. These type of compounds are generally biosynthesized by a Shikimic acid pathway; e.g. Cinnamaldehyde,
Anethole

18. Turpentine oil
Common names: Turpentine , gum turpentine, gum thus, turpentine oil , turpentine balsam
Biological name: Turpentine oil or spirits of turpentine is the volatile oil obtained by distillation of Oleoresin present in Pinus palustris and other species of Pinus Family: Pinaceae
Habitat: Portugal, Greece, Poland, France
Constituents: It contains-(65%)α-pinine, (30%) β -pinine and 5% other including α-terpenene, β-terpenene
Uses:
Carminative; Stimulant; Tonic; Expectorant; Diuretic; Antiseptic;
Counter irritant; Flavouring agent, as wax solvent.

19. Functions of volatile oil
Functions in plants:
They sometimes protect plants from harmful effects of animals and insects.
Sometimes helps in pollination through insects
Therapeutic function:
Carminative; e.g. clove oil
Antispasmodic; Bitter almond oil
Antibacterial; e.g. Pine tar oil
Aromatic stimulant; e.g. peppermint oil
Anthelmintic; e.g. thymol
Expectorant e.g. turpentine oil
Antiseptic; e.g. Eucalyptus oil
Diuretic; e.g. Juniper oil
Antipruritic (used to relieve itching.); e.g. Camphor
Pharmaceutical use
As a flavoring agent
As a preservative

20. Uses of drugs containing essential oils
Uses of drugs containing essential oils Pharmacy Perfumery Food technology Miscellaneous industries (as starting materials for the synthesis of the active principles of medicines, vitamins, and fragrances).

21. Definition
Terpenes - class of >20,000 compounds containing carbon atoms in multiples of five
Terpenoids - oxygen-containing terpenes or oxygenated derivatives, e.g. alcohols, aldehydes, ketones, phenols, oxides & esters.
Terpenoids contain only the most volatile terpenes (i.e. molecular weight is not too high)- mono and sesquiterpenes
The name "terpene" is derived from the word "turpentine"
Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers.

22. Different types of Terpenes

23. “Head” - branched end of isoprene “Tail” - unbranched end of isoprene
The basic molecular formulae of terpenes are multiples of that, (C5H8)n where n is the number of linked isoprene -Isoprene-2-methyl-1,3-butadiene- units. This is called the isoprene rule or the C5 rule. Compounds containing carbon atoms in multiples of 5 suggest a C5 building block - isoprene units linked in a “head-to-tail” fashion
2-methyl-1,3-butadiene
“Head” - branched end of isoprene
“Tail” - unbranched end of isoprene

24. Finding the isoprene building block - cyclic compounds
Finding the isoprene building block - sesquiterpenes (C15)

25. Finding the isoprene building block - triterpenes (C30)
Squalene has a natural and vital part in the synthesis of all plant and animal sterols, including cholesterol, steroid hormones, and vitamin D in the human body

26. Finding the isoprene building block - tetraterpenes (C40)
Lycopene's eleven conjugated double bonds give it its deep red color and are responsible for its antioxidant activity.
Lycopene is responsible for the red color in tomatoes and watermelon
-carotene is the compound that causes carrots and apricots to be orange

27. Classification of Terpenes
Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only hemiterpene, but oxygen-containing derivatives  are hemiterpenoids such as prenol (found in citrus fruits, cranberry, grapes, raspberry, blackberry, tomato, white bread…)  and isovaleric acid (found in in essential oils).
Monoterpenes consist of two isoprene units and have the molecular formula C10H16. Examples of monoterpenes are: geraniol, limonene and terpineol.
Sesquiterpenes consist of three isoprene units and have the molecular formula C15H24. Examples of sesquiterpenes are: humulene, farnesenes, farnesol.

28. found in the essential oils of Humulus lupulus
 humulene
Prenol
 found in the essential oils of Humulus lupulus 
isovaleric acid
limonene
terpineol
a strong smell of oranges
found in pine oil

29. Diterpenes are composed of four isoprene units and have the molecular formula C20H32. Examples are cafestol, kahweol, cembrene and taxadiene (precursor of taxol). Diterpenes also form the basis for biologically important compounds such as retinol, retinal, and phytol. They are known to be antimicrobial and antiinflammatory.
Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the other sizes. An example of a sesterterpene is geranylfarnesol.
Triterpenes consist of six isoprene units and have the molecular formula C30H48. The linear triterpene squalene, the major constituent of shark liver oil.
Tetraterpenes contain eight isoprene units and have the molecular formula C40H64. Biologically important tetraterpenes include the acyclic lycopene, the monocyclic gamma-carotene, and the bicyclic alpha- and beta-carotenes.
Polyterpenes consist of long chains of many isoprene units. Natural rubber consists of polyisoprene in which the double bonds are cis.

30. Taxadiene from enzymes
Retinol is one of the forms of vitamin A
taxol used in cancer chemotherapy

31. EXAMPLES OF TERPENES
LIMONENE
MENTHOL
BORNEOL
SESQUITERPENES

32. i. LIMONENE Structural classification: Monocyclic terpene
Functional Classification: Unsaturated HC
Occurrence: Citrus fruit

33. ii. MENTHOL Structural classification: Monocyclic with hydroxyl group
Functional classification: Alcohol
Occurrence: Peppermint

34. iii. BORNEOL
Functional Classification: ////
Occurrence: Cinnamon

35. iv. SESQUITERPENES (Contain 3 isoprene units) Acyclic – E.g. Farnesol
Monocyclic – E.g. Bisobolol
Bicyclic e.g. Chamezulene (Chamomile)