Анісовий альдегід

Structure and identity

The molecule consists of a benzene ring with a formyl and a methoxy group. Its preferred IUPAC name is 4-methoxybenzaldehyde. It is structurally related to vanillin. Two isomers of anisaldehyde are known, ortho-anisaldehyde and meta-anisaldehyde, and they are less commonly encountered. The related ortho isomer has a scent of liquorice.

Natural occurrence

Anisaldehyde is present in star anise, anise and Ceylon cinnamon essential oils, from which it can be extracted. It also occurs in some natural ingredients, among them anise seed oil, star anise oil, cassie absolute and mimosa absolute.

Occurrence in plant materials

Anise fruits contain anethole in large amounts, together with anisaldehyde, anisic acid and eugenol.

Chemistry

Anisaldehyde is the precursor for the synthesis of anisic alcohol by hydrogenation and of anisic acid by oxidation. It can also react with methyl anthranilate or indole to form a Schiff base.

Production routes

In a liquid-phase route, p-methoxytoluene is added to a manganic alum in sulfuric acid of about 8 percent by weight. The acidity is kept between 2.5 and 8.5 percent and the temperature must not rise much beyond 30 °C. A large excess of p-methoxytoluene is kept in the system, which gives a high yield with only a minimum of tars and aromatic acids. In a vapor-phase route, p-methoxytoluene is oxidised over a catalyst of vanadium oxide, phosphorus oxide and potassium sulfate, and copper oxide in the catalyst extends its useful life.

Other uses

Anisaldehyde is used as an intermediate in the synthesis of other compounds important in pharmaceuticals and perfumery. It also serves as a key intermediate in the synthesis of the antibiotic amoxicillin.

Industrial applications

Anisaldehyde is used in perfuming, soap additives, food additives, chemical intermediates and electroplating. In electroplating it is added to zinc plating solutions, where it brightens the deposits.

Physical behaviour

Anisaldehyde is poorly soluble in water, glycols and glycerol, and soluble in organic solvents and oils. It is miscible with ethanol at room temperature. Aldehydes may form diethylacetals in alcoholic perfumes, with no real impact on their smell.

Taste

In flavour its taste is sweet powdery, spicy creamy, with spice anise, nutty, cherry pit and almond-like nuances. The taste turns bitter above 30 to 40 ppm.

Regulation

The IFRA restriction on anisaldehyde is based on dermal sensitization and systemic toxicity. Its allergen entry states that it is not an allergen.

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