Chemistry of Volatile Oils

• Ways to separate compounds in volatile oil mixtures

  • Low temperature
  • Fractional Distillation
  • Fractional Distillation from poor solvents
  • Different forms of chromatography
  • Removal by chemical action
• Low temperature crystallization

  Method used to separate out stereoptenes from volatile oils
• Forms of chromatography used in analysis of volatile oils

  • Capillary-column gas chromatography
  • High-pressure liquid chromatography
  • Gas chromatography with mass spectrometry
• Compounds removed from volatile oils using chemical action

  • Compounds with free acidic groups (by sodium carbonate)
  • Basic compounds (by HCl)
  • Phenolic groups (by sodium hydroxide)
  • Aldehydes (by sodium bisulfite)
• Terpenes

  Natural products found in most volatile oils, whose structures are composed of isoprene units (C5H8)
• Isoprene units arise from acetate via mevalonic acid
• Terpene formation

  Formed by linking isoprene units in a head-to-tail fashion
• Common classifications of terpenes based on number of isoprene units

  • Monoterpenes
  • Sesquiterpenes
  • Diterpenes
  • Triterpenes
• Monoterpenes

  Composed of 2 isoprene units (C10H16)
• Sesquiterpenes

  Composed of 3 isoprene units (C15H24)
• Diterpenes

  Composed of 4 isoprene units (C20H32)
• Triterpenes

  Composed of 6 isoprene units (C30H48)
• Phenylpropanoid

  Contains a C6 phenyl ring with an attached C3 propane side chain
• Phenylpropanoids are present in compounds like methyl salicylate and vanillin
• Various constituents of volatile oils are responsible for their characteristic odor, flavor, and therapeutic properties
• Stereochemistry, including geometric isomers and enantiomers, determines the type, quality, and strength of the odor in volatile oils
• Enantiomers are optically active isomers, and plant species may produce either one or both enantiomers. The physiological properties of enantiomers may differ
• (+)-carvone

  Odor of caraway
• (-)-carvone

  Odor of spearmint