Anethole (Synonym Anise camphor, Monasirup)

A. Anethole (Synonym Anise camphor, Monasirup)

Chemical Structure 1-Methoxy-4-(1-propenyl) benzene.

Anethole (Synonym Anise camphor, Monasirup)
It has a monohydric phenolic ether function.
Occurrence It is the chief constituent of anise (anise fruit, aniseed) i.e., the dried ripe fruits of Pimpinella anisum Linn' (Family: Umbelliferae); star anise (star anise fruit, Chinese anise i.e., the dried ripe fruits of Illicium verum Hoop (Family: Magnoliaceae); and fennel (fennel fruits finnocchio), i.e., the dried ripe fruits of Foeniculum vulgare Mill (Family: Apiaceae). It is also found in Ocimum basilicum L. (Family: Lamiaceae)-Sweet Basil, Garden Basil; Pinus elliottii Engelm. (Family: Abiataceae)-Slash Pine; Sassafras albidum (Nutt.) Nees (Family: Lauraceae)-sassafras; and Syzygium aromaticum (L.) Merr & Perry (Family: Myrtaceae)-cloves, clavos.
Isolation It may be isolated from the volatile oils by first subjecting the oil to fractionation and then cooling the corresponding fraction to a very low temperature and recrystallization. However, it may also be obtained directly from the anethole-rich oils, such as: oil of anise, oil of fennel by simply chilling it to – 30°C in a deep freezer. Commercially, anethole may be synthesized in its purest form from anisole as shown below:

Anisole
Anisole on reacting with propionaldehyde in the presence of HCl and H3PO4 yields an intermediate anisole-p-(1-chloropropane) which finally with pyridine yields anethole.
Characteristic Features It exists in two isomeric forms namely: trans-and cis-isomer, having physical parameters as stated below:

 anisole-p-(1-chloropropane)
It is a white crystalline substance with an intense sweet odour. It possesses a characteristic taste similar to anise fruit. It is practically soluble in most organic solvents but insoluble in water.
Formation of ‘Photoanethole’ (or p, p-dimethoxystilbene) Anethole on exposure to air (oxygen), light or heat undergoes structural modifications to yield photoanethole which is a viscid yellow coloured mass having a disagreeable taste and odour with a poor solubility in solvents. Perhaps the conversion of anethole to photoanethole lakes place via the formation of anisaldehyde as given below:

anisaldehyde
Identification
1. Anethole undergoes oxidation with K2Cr2O7 in two steps; first step-yields anisaldehyde (paramethoxy benzaldehyde), and second step-gives rise to para-methoxy benzoic acid (mp 184°C) as depicted below:

paramethoxy benzaldehyde
2. It gets condensed with maleic anhydride to yield a condensation product having mp 310°C as shown below:

maleic anhydride
3. It gives rise to the formation of nitroso derivative having mp 126°C.
Uses
1. It is used as a flavouring agent in perfumery particularly for soap and dentifrices.
2. It is also employed as a pharmaceutical and (flavour).
3. It finds its application as an imbedding material in microscopy.
4. It is employed as a flavouring agent in alcholic, non-aleoholic beverages and confectionaries.
5. It is used as a sensitizer in bleaching colours in colour photography.

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