Menthol

• BPLevomenthol; Racementhol
• JPl-Menthol; dl-Menthol
• Ph. Eur.Levomenthol; Menthol, Racemic
• USP–NFMenthol

Levomenthol; L-menthol; racementhol; DL-menthol; hexahydrothymol; peppermint camphor; 2-isopropyl-5-methylcyclohexanol; mentholum

(1R,2S,5R)-2-Isopropyl-5-methylcyclohexanol (levomenthol); the racemate is (1RS,2SR,5RS) · [89-78-1]

C10H20O · 156.27

Flavouring agent

Typical concentrations: — · Dosage forms: Liquid, Semi-solid, Solid

Used as a flavour and cooling agent in oral products, toothpastes, mouthwashes, lozenges and chewable tablets, and in topical and inhaled products for its cooling, counter-irritant and mild local anaesthetic effects; it is also a skin penetration enhancer. Typical concentrations: oral suspensions and syrups about 0.003–0.015%; tablets 0.2–0.4%; topical formulations 0.05–10%.

Colourless, acicular or prismatic crystals or a crystalline powder with a strong, characteristic peppermint odour and a warm, aromatic taste followed by a cooling sensation.

Melting point

about 41–44 °C (levomenthol); about 34 °C (racemic menthol)

Boiling point

≈ 212 °C

Specific rotation

about −48° to −51° (levomenthol, in ethanol); racemate about 0°

Solubility

very slightly soluble in water; very soluble in ethanol (95%), chloroform and ether; freely soluble in fixed oils, liquid paraffin and glacial acetic acid

Stable, but volatile: it sublimes slowly at room temperature. Store in a well-closed container at a temperature not exceeding 25 °C.

Forms liquid or soft eutectic mixtures when triturated with camphor, chloral hydrate, phenol, thymol, resorcinol, β-naphthol and several other compounds. Incompatible with strong oxidising agents such as potassium permanganate and chromium trioxide.

Levomenthol is obtained from peppermint and corn mint (Mentha arvensis) oils by freezing and crystallisation, or synthetically; racemic menthol is made by hydrogenation of thymol and separation of the isomers.

Generally safe at flavouring levels. Higher concentrations can irritate skin and mucous membranes, and hypersensitivity (including contact dermatitis) has been reported. Menthol-containing products should not be applied to the nostrils or face of infants and young children, because they can cause reflex apnoea or laryngospasm. JECFA has set an ADI of 0–4 mg/kg body weight.

Observe normal precautions for the quantity handled. The vapour and dust irritate the eyes and respiratory tract; eye protection and gloves are recommended and it should be handled in a well-ventilated area.

GRAS listed as a flavouring. Included in the FDA Inactive Ingredient Database (oral capsules, solutions, suspensions, syrups and tablets; topical preparations) and in non-parenteral medicines licensed in Europe.

Peppermint oil; camphor; thymol; eucalyptol; menthyl lactate.

The isomer should be specified: levomenthol has the strongest cooling effect and the characteristic odour, while racemic menthol is cheaper and has a lower melting point. Because it sublimes, losses during drying and storage should be allowed for, and it is usually added late in processing.