All official volatile oils are of vegetable origin. All official volatile oils are of vegetable origin



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Synthesis & accumulation of essential oils are generally associated with the presence of specialized histological structures, often located on or near the surface of the plant:

  • - Oil cells of Zingiberaceae

  • - Glandular trichomes of Lamiaceae

  • - Secretory cavities of Myrtaceae or Rutaceae

  • - Secretory canals of Apiaceae or Astereraceae (Compositeae)



  • Mixtures of HC’s and oxygenated compounds derived from these HC’s.

    • Mixtures of HC’s and oxygenated compounds derived from these HC’s.

      • Oil of turpentine – mainly HC’s
      • Oil of Clove – mainly oxygenated compounds
    • EXCEPTION: Oils derived from glycosides (e.g. bitter almond oil & mustard oil).

    • Oxygenated compounds – responsible for the odour/smell of the oil. They are slightly water soluble – Rose water & Orange Water; more alcohol soluble.

    • Most volatile oils are terpenoid. Some are aromatic (benzene) derivatives mixed with terpenes.

    • Some compounds are aromatic, but terpenoid in origin (e.g. Thymol – Thyme)



    Volatile oils are divided into 2 main classes based on their biosynthetic origin

    • Volatile oils are divided into 2 main classes based on their biosynthetic origin

    • Terpene derivatives (formed via the acetate mevalonic acid pathway)

    • Aromatic compounds (formed via the shikimic acid-phenylpropanoid route)

    • Miscellaneous Origin



    Terpenes, or terpenoids, are the largest group of secondary products (metabolites).

    • Terpenes, or terpenoids, are the largest group of secondary products (metabolites).

    • They are all formed from acetyl CoA or glycolytic intermediates.



    All terpenes are formed from 5-C elements

    • All terpenes are formed from 5-C elements

    • Isoprene is the basic structural element.



    Terpenes are classified by the number of 5-C atoms they contain

    • Terpenes are classified by the number of 5-C atoms they contain

    • 10-Carbon terpenes (contain 2 C-5 units) – monoterpenes

    • 15- Carbon terpenes (3 C-5 units) are called sesquiterpenes.

    • 20-carbon terpenes (4 C-5 units) are diterpenes.

    • Larger terpenes (30 Carbons) are called triterpenes (triterpenoids), 40 Carbons – called tetraterpenes and polyterpenoids.



    Terpenoids contain only the most volatile terpenes (i.e. molecular weight is not too high)  mono and sesquiterpenes

    • Terpenoids contain only the most volatile terpenes (i.e. molecular weight is not too high)  mono and sesquiterpenes

    • May occur as oxygenated derivatives, e.g. alcohols, aldehydes, ketones, phenols, oxides & esters.



    LIMONENE

    • LIMONENE

    • MENTHOL

    • BORNEOL

    • SESQUITERPENES



    Structural classification: Monocyclic terpene

    • Structural classification: Monocyclic terpene

    • Functional Classification: Unsaturated HC

    • Occurrence: Citrus fruit



    Structural classification:

    • Structural classification:

    • Monocyclic with hydroxyl group

    • Functional classification: Alcohol

    • Occurrence: Peppermint



    • Functional Classification: ////

    • Occurrence: Cinnamon



    (Contain 3 isoprene units)

    • (Contain 3 isoprene units)

    • Acyclic – E.g. Farnesol

    • Monocyclic – E.g. Bisobolol

    • Bicyclic e.g. Chamezulene (Chamomile)



    Many are phenols are phenol esters

    • Many are phenols are phenol esters

    • E.g. Vanillin



    Almost entirely volatile without decomposition.

    • Almost entirely volatile without decomposition.

    • Density: Most are less than 1g/ml.

      • 2 are heavier – Oil of Cinnamon and Clove oil.
    • Soluble in ether, chloroform & alcohol.

    • Slightly soluble in water: give it a characteristic odour & taste.

    • Leaves a temporary translucent stain on paper which disappears as the oil volatilizes.

    • Most are colourless. Oxidize on exposure to air and resinify  colour becomes darker (odour changes slightly).

    • All are characteristic odours.

    • Most are optically active.



    Essential oils may be produced

    • Essential oils may be produced

    • By steam

    • - Simple steam distillation

    • - Saturated steam distillation

    • - Hydrodiffusion

    • By expression

    • Other Methods

    • Concretes & Resinoids may be produced

    • By solvent extraction

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