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What are the natural terpenes

What are the natural terpenes

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The terpens form a group of compounds the majority of which occur in the plant kingdom; a few terpenes have been obtain from other sources. The simpler mono- and sesquiterpenes are the chief constituents of the essential oils; there are the volatile oils obtained from the sap and tissues of certain plants and trees, the essential oils have been used in perfumery from the earliest times. The di- and tri-terpenes, which are not steam volatile, are obtained from plant and tree gums and resins.

Most natural terpene hydrocarbons have the molecular formula (C5H8)n, such as:

  1. Monoterpenes, C10H16
  2. Sesquiterpenes, C15H24
  3. Diterpenes, C20H32
  4. Triterpenes, C30H48
  5. Tetraterpenes, C40H64 (carotenoids)
  6. Polyterpenes, (C5H8)n

Monocyclic terpenes contain a six-membered ring, the p-cymene structure, all-natural monocyclic monoterpenes are derivatives of p-cymene.

In general, there are four methods of extraction of the terpenes; (i) expression; (ii) steam distillation; (iii) extraction by means of volatile solvents; (iv) adsorption in purified fats. The essential oils so obtained usually contain a number of terpenes, and these are separated by fractional distillation.

MONOCYCLIC MONOTERPENES

  • Myrcene, C10H16, is an acyclic monoterpene hydrocarbon that occurs in verbena and bay oils.
  • Ocimene, C10H16, us and acyclic compound which contains three double bonds.
  • Citral, C10H16O, is widely distributed and occurs to an extent of 60-80% in lemongrass oil. Citral is liquid which has the smell of lemons.
  • Ionones, the ionones are related to irone, C14H22O, this occurs in the oil obtained from the orris root.
  • Geraniol, C10H18O, is found in many essential oils, particularly rose oil.
  • Linalool, C10H18O, is an optically active compound, the (-)-form occurs in rose oil and the (+)-form in orange oil.
  • Citronellal, C10H18O, is an optically active compound which occurs in citronella oil
  • Citronellol and Rhodinol, C10H20O, (-)-Citronellol occurs in rose and geranium oils, and is a mixture of the two forms: the (+)-form of citronellol is made commercially by reduction of citronellal with sodium or aluminum amalgam; it also occurs in Java citronella oil.
  • Alpha terpineol, is an optically active monoterpene that occurs naturally in the (+), (-)- and (+-)-forms; when heated with sulphuric acid, alpha terpineol forms some p-cymene. There are two other terpineols, beta terpineol, and gamma terpineol, both occur naturally.
  • Carvone, G10H14O, occurs in various essential oils, spearmint, and caraway oils, in optically active forms and also as the racemic modification.
  • Limonene, C10H16, is optically active, the (+)-form occurs in lemon and orange oils, the (-)-form in peppermint oil, and the (+-)-form in turpentine oil, the racemic modification is also known as dipentene.
  • Terpinolene, C10H16, occurs naturally, is not an optically active, and it may be prepared by dehydrating alpha terpineol with oxalic acid.
  • Phellandrenes, C10H16, there are two phellandrenes, alpha- and beta-, both of which are optically active.
  • 1.8 Cineole, C10H18O, occurs in eucalyptus oils, it is isomeric with alpha terpineol, but contains neither a hydroxyl group nor a double bond.
  • Menthol and menthone, Menthol, C10H20O, is an optically active compound, but only the (-)-form occurs naturally in peppermint oils.
    Menthone, C10H18O, (-)-menthone occurs in peppermint oil, and it may readily be prepared by the oxidation of (-)-menthol with chromic acid.

to be continued