Volatile Oils

17.1. INTRODUCTION

  • Definition of Volatile Oils:

    • Volatile oils are odorous volatile principles derived from plant and animal sources.

    • They evaporate when exposed to air at ordinary temperature, hence termed volatile or ethereal oils.

    • Known as essential oils because they represent the essence of active constituents of the plant.

    • These oils typically preexist in the plant and are contained in special secretory tissues (e.g., oil ducts in umbelliferous fruits, oil cells in lemon/orange peel, mesophyll of eucalyptus leaves).

    • In some cases, volatile oils are formed from the decomposition of glycosides.

    • Example: Whole black mustard seeds are odourless, but crushing them and adding water releases allyl isothiocyanate (essential oil of mustard) formed by the enzyme myrosin acting on the glycoside sinigrin.

    • Volatile oils are soluble in ether and chloroform, fairly soluble in alcohol, and insoluble in water.

    • They can dissolve many proximate principles in plant and animal tissues, including fixed oils, fats, resins, and some alkaloids.

  • Chemical Composition:

    • Derived from terpenes, primarily mono and sesquiterpenes and their oxygenated derivatives.

    • Characteristics:

    • Solubility: Soluble in alcohol and other organic solvents, insoluble in water.

    • Physical properties: Typically lighter than water, high refraction index, and most are optically active.

    • Color: Colorless liquids that darken upon exposure to air and sunlight due to oxidation.

    • Unlike fixed oils, volatile oils do not leave permanent grease spots on filter paper or saponify with alkalis.

17.2. CLASSIFICATION OF VOLATILE OILS

  • Classification Basis: Functional groups present.

  • Groups and Examples:

    • Hydrocarbons: Turpentine oil

    • Alcohols: Peppermint oil, Sandalwood oil

    • Aldehydes: Cymbopogon sp., Lemongrass oil, Cinnamon, Cassia, Saffron

    • Ketones: Camphor, Caraway, Dill, Jatamansi, Fennel

    • Phenols: Clove, Ajowan, Tulsi

    • Phenolic ethers: Nutmeg, Calamus

    • Oxides: Eucalyptus, Cardamom, Chenopodium oil

    • Esters: Valerian, Rosemary oil, Garlic, Gaultheria oil

17.3. EXTRACTION OF VOLATILE OILS

  • Methods of Extraction:

    • Extraction by Distillation:

    • Hydrodistillation: For fresh materials.

    • Steam Distillation: For air-dried parts.

    • Extraction by Scarification:

    • Used for lemon, orange, bergamot oils.

    • Methods:

      • (a) Sponge Process:

      • Make cuts in fruit peel and immerse in water.

      • Use a sponge to press against the peel, absorbing the oil.

      • Allow the mixture to settle to separate oil from water.

      • (b) Ecuelle Process:

      • Mechanically rupture rinds using rotary movement with pointed projections.

    • Extraction by Non-Volatile Solvent:

    • Use lard or olive oil as solvent.

    • Processes:

      • (a) Enfleurage:

      • A fatty layer is prepared with lard; flower petals placed on it.

      • Replace petals as saturation occurs, then extract with alcohol for triple extract.

      • (b) Maceration:

      • Heat lard/oil and mix with flowers, continuing until defined weights used.

      • Extract perfumed lard/oil with alcohol for triple extract.

      • (c) Spraying:

      • Warm air sprayed through flowers, capturing oil or fat which is extracted with alcohol.

    • Extraction by Volatile Solvent:

    • Use light petroleum, distilled off at low temperature, leaving volatile oil.

17.4. TERPENOIDS

  • Definition:

    • Group of naturally occurring volatile compounds primarily from plants, some from other sources.

    • Responsible for fragrance in plants and flowers.

    • Common in leaves and fruits of higher plants, conifers, citrus, eucalyptus.

  • Origin of the Term:

    • The term 'terpene' derives from turpentine, isolated from pine trees.

  • Classification:

    • Simpler mono and sesquiterpenes: Chief constituents of essential oils.

    • Di- and triterpenoids: Non-steam volatile, from gums and resins.

    • Tetraterpenoids: Known as carotenoids.

  • Chemical Composition:

    • General formula: C<em>nH</em>2nC<em>nH</em>{2n} for terpenoids and oxygenated, hydrogenated, dehydrogenated derivatives.

  • Isoprene Rule:

  • Definition:

    • Terpenoids are constructed from isoprene units (C₅H₈).

  • Special Isoprene Rule:

    • Asserts that terpenoid molecules are assembled 'head to tail.'

  • Examples:

    • Myrcene (monoterpene) and Farnesol (sesquiterpene).

    • Exceptions exist such as carotenoids exhibiting tail-to-tail connections.

17.5. CLASSIFICATION OF TERPENOIDS

  • Classification by Carbon Atoms:


    • | Carbon Atoms | Value of n | Class |
      |-------|-----------|----------------------|
      | 10 | 2 | Monoterpenoids (C₁₀H₁₆) |
      | 15 | 3 | Sesquiterpenoids (C₁₅H₂₄) |
      | 20 | 4 | Diterpenoids (C₂₀H₃₂) |
      | 25 | 5 | Sesterpenoids (C₂₅H₄₀) |
      | 30 | 6 | Triterpenoids (C₃₀H₄₈) |
      | >40 | >8 | Tetraterpenoids (C₄₀H₆₄), Polyterpenoids (CₓHₓₙ) |

  • Subclassification by Rings:

    • Acyclic: Open structure.

    • Monocyclic: One ring present.

    • Bicyclic: Two rings present.

    • Tricyclic: Three rings present.

    • Tetracyclic: Four rings present.

17.6. EVALUATION OF VOLATILE OILS

  • Variability of Products:

    • Essential oil quality varies due to environmental conditions (sunlight, rainfall) and manufacturing processes.

  • Evaluation Procedures:

    • Preliminary examinations: Odour, taste, colour.

    • Physical measurements: Optical rotation, relative density, refractive index.

    • Chromatography to determine proportions of components.

    • Aldehyde and ketone content analyzed through hydroxylamine hydrochloride reaction and acid titration.

17.7. CHEMICAL TESTS

  • Testing Methods:

    1. Treatment with alcoholic solution of Sudan III produces red color, indicating presence of volatile oils.

    2. Tincture of alkana treatment yields red color, supportive of volatile oils presence in natural drugs.

17.8. STORAGE OF VOLATILE OILS

  • Risks of Oxidation:

    • Volatile oils oxidize in the presence of air, moisture, and light, causing color change, viscosity increase, and odour alteration.

  • Storage Recommendations:

    • Store in well-closed, completely filled containers, away from light, in cool places.

17.9. PHARMACEUTICAL APPLICATIONS

  • Uses of Volatile Oils:

    • Flavoring and perfuming agents in pharmaceutical formulations, food, beverages, cosmetics.

    • Therapeutic purposes include:

    1. Carminative (e.g., Umbelliferous fruits)

    2. Anthelminitic (e.g., Chenopodium oil)

    3. Diuretics (e.g., Juniper)

    4. Antiseptic (e.g., Eucalyptus)

    5. Counter irritant (e.g., Oil of wintergreen)

    6. Local anesthetic (e.g., Clove)

    7. Sedative (e.g., Jatamansi)

    8. Local irritant (e.g., Turpentine)

    9. Insect repellent (e.g., Citronella)

    10. Source of vitamin A (e.g., Lemongrass)

17.10. VOLATILE OILS CONTAINING HYDROCARBONS

  • Hydrocarbon Types:

    • Limonene: Widely distributed monocyclic terpene in various oils (Citrus, Mint, etc.).

    • p-Cymene: Monocyclic hydrocarbon in various oils (Coriander, Thyme, etc.).

    • Pinene: Dicyclic monoterpene, found in conifers and various oils (Eucalyptus, Lemon, etc.).

    • Sabinene: Present in cardamom and lemon oils.

    • Acyclic monoterpene: Myrcene in Myricia, Lemon, Myristica.

    • Cadinene in juniper tar, and β-Caryophyllene in Wormwood oils.

  • Example of Volatile Oil Drug: Turpentine oil.

TURPENTINE OIL

  • Synonyms: Oleum terbinthae, rectified oil of turpentine.

  • Botanical Source: Distillation of oleoresin from Pinus longifolia and various Pinus species (family Pinaceae).

  • Geographical Source: Cultivated in India, Pakistan, and the USA, France, Europe, Russia.

  • Collection and Preparation:

    • Collect oleoresin, transfer to copper stills, add water, heat.

    • Remove impurities, clarify resin, distill to obtain oil, treat with sodium hydroxide to remove phenols and acid traces; results in rectified turpentine oil.

  • Characteristics:

    • Colorless/slightly yellowish, strong odour, pungent taste, soluble in alcohol, miscible with ether and fixed oils, insoluble in water.

  • Chemical Constituents:

    • Contains >40 terpenes, primarily α- and β-pinene; also camphene, limonene.

  • Uses:

    • Counterirritant, rubefacient, antiseptic, expectorant, and diuretic.

    • Industrial purposes: disinfectants, insecticides, paints.

  • Adulterants:

    • Common adulterants include resin oil, wood turpentine, petroleum jelly; tested via low weight per ml and staining characteristics.

  • Marketed Products:

    • Used in Rumalaya gel, Pain balm (Himalaya Drug Company).

17.11. VOLATILE OILS CONTAINING ALCOHOLS

  • Classification of Alcohols in Volatile Oils:

    • Acyclic Alcohols:

    • Monocyclic Alcohols:

    • Dicyclic Alcohols:

    • Examples include methyl, ethyl, isobutyl, isoamyl etc.

  • Solubility:

    • Alcohols are soluble in water and may be washed away during steam distillation.

  • Key Alcohols:

    • Acyclic alcohols include geraniol, linalool and citronellol; monocyclic alcohols include menthol and α-terpineol; dicyclic alcohols include borneol.

  • Example Oils:

    • Peppermint, Cardamom, Coriander, Rose, Orange flower, Juniper, Pine oils.