2.1.2 Eucalyptol
Synonyms Cineole; Cajeputol.
Biological Source It is obtained from the leaves of Eucalyptyus globulus Labill, belonging to family Myrtaceae.
Geographical Source The eucalyptus tree is a native of Australia and Tasmania. It is largely cultivated in Calfornia, Spain, Portugal and India. In India it is abundantly found in the Himalayan region, Nilgiri district, Kumaon Hills and Assam.
Preparation A number of volatile oils from certain Eucalyptus species invariably contain eucalyptol as high as 30 to 70%. It also occurs in cajuput oil (40%) and in laurel leaf oil (50%). However, eucalyptol may be isolated from these oils by adopting one of the following methods:
Method 1 By subjecting the volatile oil to fractional distillation and collecting the fractions between 170-180oC to obatin crystals of cineole at –10oC (m.p. + 1.5oC)
Method-2 Cineole forms addition compounds with halogen acids, e.g., C10H18O HCl and C10H18O. HBr; with phosphoric acid as C10H18O.H3PO4which also serve as a means of its purification, and
Method 3 Eucalyptol yields an addition product with a 50% (w/v) alcoholic solution eg; C10H18O. C6H6O2 (mp 82-85oC), from which the former may be generated.
Note: This method is mostly applicable to such volatile oils that have a higher cineole content.
Synthetic Method Eucalyptol may be prepared synthetically by the dehydration of terpin hydrate as given below:
Description
Colour : Colurless or pale yellow liquid.
Odour : Camphoraceous and aromatic.
Taste : Pungent and leaves a cold sensation.
Solubility : Water insoluble; soluble in paraffin, fixed oils and ethanol 90%.
Chemical Structure
Eucalyptol is an epoxy or oxido derivative of p-menthane. and is also known as 1,8-epoxy-pmethane or 1,8-oxido-p-menthane. It is found to be quite stable and hence may be distilled over metallic sodium safely without undergoing any change whatsoever. It is not affected by the action of reducing agents.
Chemical Tests
1. When a drop of eucalyptol is carefully treated with a drop of 5% (w/v) solution of hydroquinone in alcohol on a slide, it forms either colourless prisms or rhomboids; but with a 50% (w/v) solution of resorcinol in alcohol leaf-like crystals are obtained.
2. It forms characteristic addition compounds with HCl, HBr and H3PO4 with well defined melting points.
Uses
1. It is used internally as a stimulating expectorant to relieve severe cough and in bronchitis in the form of inhalatious.
2. It is abundantly employed externally as a mild anaesthetic and antiseptic for the treatment of various inflammatory conditions.
