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Aroma Chemical Profile: Menthol
By: George S. Clark (Cameron & Stuart, Inc.)
Posted: December 4, 2007, from the December 2007 issue of P&F magazine.
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Although other materials are known to display such a cooling effect, almost all of them are derivatives of l-menthol.
Organoleptically, l-menthol displays a light, minty, refreshing peppermint odor that at most practical concentrations is complicated by an intense olfactory numbing-cooling sensation. After exposure to menthol’s vapors for a while the nose becomes fatigued. The dual-sensory effect experienced makes both the odor and taste evaluation of menthol a difficult task. This decrease in one’s sharpness in smelling forces those who both QC batches of menthol production and also work in the area of flavor or fragrance creation to evaluate menthol samples at the end of their working day.
Classification: A saturated cyclic-monoterpenoid alcohol found in nature in significant concentrations mainly in the plants of the Mentha species.
Additional names: The name “menthol” commonly refers to the l isomer, which is only one of eight antipodes (chiral or optical isomers) of the molecule: 5-methyl-2-(1-methylethyl) cyclohexanol. 5-Methyl-2-isopropyl cyclohexan-1-ol, 3-p-methanol, hexahydrothymol, peppermint camphor. French = menthol; German = menthol; Portuguese = mentol; Spanish = mentol.
Physical data: Appearance: l-menthol US Pharmacopeia (USP) grade is a colorless crystal; often found as large crystals containing numerous faults which appear as cloudy-white areas. Racemic (d,l) menthol USP is an amorphous fused colorless-white mass. The USP lists both products together with their specifications, although they are two different materials with respect to usage and organoleptic properties.
- Specific gravity: 0.890 at 15°C
- Refractive index: 1,458 at 25°C
- Melting point: l-Menthol 43-44°C; the USP allows a melting range of 41°-44°C
- Racemic menthol displays a congealing point at two levels: 27-28°C and 30.5-32°C
- Boiling point: 212°C
- Flash point: 200°F/93°C
- Solubility: H2O at 20°C = 0.04%; soluble in ethanol, essential oils, esters, alcohols, chlorinated solvents, mineral and edible oils, DEP, etc.
Other topics discussed: Natural Sources, History of Menthol, The Decline of Brazil, The Emergence of India, World Consumption, Pricing, Supply of Menthol, Natural Menthol Producers and Estimated Production Capacity, Synthetic Producers, By-products, Analogs, Substitutes, Derivatives
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