Анетол

Anethole is an aromatic, unsaturated ether related to lignols. It is a derivative of the aromatic compound allylbenzene and occurs widely in the essential oils of plants. Its IUPAC name is 1-methoxy-4-[(E)-prop-1-enyl]benzene. It exists as cis and trans isomers, which involve the double bond outside the ring. The more abundant isomer, and the one preferred for use, is the trans or E isomer, which carries CAS number 4180-23-8. The Z isomer has CAS number 25679-28-1. Anethole that is produced synthetically, or has been exposed to UV light, can contain substantial cis-anethole, which is toxic. The presence of cis-anethole in natural anethole is used as a measure of spoilage. For industrial purposes only trans-anethole is of use, as the cis isomer has a higher toxicity and unpleasant organoleptic properties. The cis isomer melts at -22.5 °C and boils at 79 to 79.5 °C at 23 mm Hg.

Estragole is an isomer of anethole, differing with respect to the location of the double bond. Estragole converts to anethole upon treatment with potassium hydroxide.

Anethole contributes a large component of the odor and flavor of anise and fennel (both in the botanical family Apiaceae), anise myrtle, liquorice, magnolia blossoms, and star anise. Star anise contains anethole, the same compound that gives anise, an unrelated plant, its flavor. The aniseed or licorice flavor of fennel comes from anethole, an aromatic compound also found in anise and star anise. The taste and aroma of fennel are similar to those of anise and star anise, though usually not as strong. The trans-anethole content of the essential oil is given as 95% for anise, 87% for star anise and 70% for fennel. In 1999 world production was 8 tonnes for anise, 400 tonnes for star anise, mostly from China, and 25 tonnes for fennel, mostly from Spain. Anise oil also holds minor components, among them 4-anisaldehyde and estragole. Star anise is considerably less expensive to produce and has gradually displaced anise in Western markets.

Anethole is only slightly soluble in water but exhibits high solubility in ethanol. It is also miscible with chloroform and ether. Historically, its poor solubility in water was used to detect adulteration in samples. Anethole is distinctly sweet, measuring 13 times sweeter than sugar. Many people find it pleasant to the taste even at higher concentrations. In the ouzo effect, a strongly hydrophobic essential oil such as trans-anethole is dissolved in a water-miscible solvent such as ethanol, which itself forms a solution with water. When more water lowers the concentration of ethanol, the hydrophobic substance precipitates and forms an emulsion. The tiny droplets in the emulsion scatter light and so make the mixture appear white.

Analyses of anise oil give anethole as its main component, at 80 to 90 percent. Star anise comes from an evergreen tree native to South China and northeast Vietnam, and China is its main producing country, followed by Vietnam and other Southeast Asian countries. In fennel fruits, trans-anethole and estragole give a licorice-like aroma, alongside fenchone (mint and camphor), limonene and 1-octen-3-ol (mushroom).

In water at 25 °C anethole dissolves to about 0.11 g/l, and 1 ml of it dissolves in 2 ml of 96% ethanol. As a flavoring it goes into alcoholic drinks such as ouzo, rakı, anisette and absinthe, into seasoning and confectionery applications such as German Lebkuchen, and in small quantities into natural berry flavors. Anethole also acts as an insecticide, more strongly as a fumigant than as a contact agent; it is highly effective as a fumigant against the cockroach Blattella germanica and is an effective repellent against mosquitoes.

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