Extraction of Essential Oils
Essential oils are extracted from plants by several methods as below:
1. Steam distillation.
2. Direct solvent extraction
3. The Enfleurage process
The plant material prepared suitably is steam distilled. The oil if any is collected separately. The steam distillate is saturated with salt and extracted with purified solvents (petroleum and benzene). The combination and solvent extracts are dried and the solvent evaporated some-time through a fractionating column under reduced pressure to give the essential oils.
2.Direct Solvent Extraction:
The plant material is extracted directly with solvents (ether and light petroleum) at room temperature. The filtered extract is evaporated under reduced pressure to yield the essential oils.
3. The Enfleurage Process:
This method consists in leaving flower petals in contact with a fat preparation (an odourless mixture of lard and tallow) for several days. The fat is freed from the petals and stirred with absolute alcohol. The alcohol extract is evaporated in vacuum at 0° to give the essential oil.
The terpene alcohols (eg menthol) extracted by this method separation of aldehyde or ketone terpenes may make use of their reaction with carbonyl reagents such as sodium bisulphite, semicarbazide hydrochloride etc.
Important Essential Oils:
1. Peppermint: From axial portion of mentha plant chief constituent terpene e.g. menthol
2. Eucalyptus: From eucalyptus tree terpene.
3. Terpentine oil: From camphor Terpene, pinene.
4. Oil of Winter Green: Winter plant i.e. lower leaves of winter green plant and chief constituent is methyl salicylate.