Page 119 - Medicinal Plants_PharmD general

II. Volatile Oil

Volatile or essential oils, as their name implies, are volatile in steam.
They differ entirely in both chemical and physical properties from fixed
oils.

Definition:
1- Volatile oils are steam volatile
2- They are generally mixture of terpene hydrocarbons (C10H20) and

oxygenated terpenes compounds derived from these hydrocarbons.

3- They are contained as such in plants, except oil of bitter almonds and
mustard oil which are produced by hydrolysis of their corresponding
glycosides.

4- They are secreted in oil cells, secretion ducts or cavities or in glandular
hairs. They are frequently associated with other substances such as
gums and resins and they tend to resinify on exposure to air.

Properties:

- Volatile oils dissolve in alcohol, sparingly soluble in water. They
resemble fixed oils in their behaviour towards: osmic acid, Sudan III, and
alkanna tincture.
- They are not saponified when treated with caustic alkalies.
- On long standing, volatile oils tend to oxidize and resinify thus darken in
colour, therefore, they should be stored in a cool dry place, preferably in
full amber glass containers.

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