Terpineol

Terpineol is a monoterpene alcohol that has been isolated from a variety of sources such as cajuput oil, pine oil, and petitgrain oil.[2] There are four isomers: alpha-, beta-, gamma-terpineol, and terpinen-4-ol. Beta- and gamma-terpineol differ only by the location of the double bond. Terpineol is usually a mixture of these isomers with alpha-terpineol as the major constituent.

Terpineols: alpha-, beta-, gamma-, and the 4-terpineol isomer
alpha-terpineol
Skeletal formula
Ball-and-stick model
Names
Preferred IUPAC name
2-(4-Methylcyclohex-3-en-1-yl)propan-2-ol
Other names
2-(4-Methyl-1-cyclohex-3-enyl)propan-2-ol
alpha-terpineol
α-terpineol
p-menth-1-en-8-ol
α,α,4-Trimethylcyclohex-3-ene-1-methanol
Terpene alcohol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
UNII
Properties
C10H18O
Molar mass 154.253 g·mol−1
Appearance Colorless liquid[1]
Density 0.93 g/cm3[1]
Melting point −35.9 to −28.2 °C (−32.6 to −18.8 °F; 237.2 to 245.0 K)[1] (mixture of isomers)
Boiling point 214–217 °C (417–423 °F; 487–490 K)[1] (mixture of isomers)
2.42 g/L[1]
−111.9·10−6 cm3/mol
Hazards
Safety data sheet External MSDS
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
2
0
Flash point 88 °C (190 °F; 361 K)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Terpineol has a pleasant odor similar to lilac and is a common ingredient in perfumes, cosmetics, and flavors. α-terpineol is one of the two most abundant aroma constituents of lapsang souchong tea; the α-terpineol originates in the pine smoke used to dry the tea.[3] (+)-α-terpineol is a chemical constituent of skullcap.

Synthesis

Although it is naturally occurring, terpineol is commonly manufactured from the more readily available alpha-pinene.

In one study, an alternative route starting from limonene was demonstrated:[4]

Terpineol synthesis from limonene

Limonene is reacted with trifluoroacetic acid in a Markovnikov addition to a trifluoroacetate intermediate, which is easily hydrolyzed with sodium hydroxide to α-terpineol with 7% selectivity. Side-products are β-terpineol in a mixture of the cis-isomer, the trans-isomer, and 4-terpineol.

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References
  1. Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  2. Merck Index, 11th Edition, 9103
  3. Shan-Shan Yao; Wen-Fei Guo; Yi Lu; Yuan-Xun Jiang (2005). "Flavor Characteristics of Lapsang Souchong and Smoked Lapsang Souchong, a Special Chinese Black Tea with Pine Smoking Process". Journal of Agricultural and Food Chemistry. 53 (22): 8688–93. doi:10.1021/jf058059i. PMID 16248572.
  4. Yuasa, Yoshifumi; Yuasa, Yoko (2006). "A Practical Synthesis of d-α-Terpineol via Markovnikov Addition of d-limonene Using Trifluoroacetic Acid". Organic Process Research & Development. 10 (6): 1231–1232. doi:10.1021/op068012d.
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