Phellandrene
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| Template:Longitem | C10H16 |
| Molar mass | 136.24 g/mol |
| Appearance | Colorless oil (α and β) |
| Density | α: 0.846 g/cm3 β: 0.85 g/cm3 |
| Boiling point | Template:Chembox CalcTemperatures |
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Phellandrenes are organic compounds with the formula Template:Chem2. They have a similar molecular structure and similar chemical properties. α-Phellandrene and β-phellandrene are cyclic monoterpenes and are double-bond isomers. In α-phellandrene, both double bonds are endocyclic, and in β-phellandrene, one of them is exocyclic. Both are insoluble in water, but miscible with organic solvents.
Etymology and occurrence
α-Phellandrene was named after Eucalyptus phellandra, now called Eucalyptus radiata, from which it can be isolated.[1] It is also a constituent of the essential oil of Eucalyptus dives.[2] β-Phellandrene has been isolated from the oil of water fennel and Canada balsam oil. The main source of β-phellandrene is terpentine.[3]
β-pinene is a source of β-phellandrene.[3]
Reactions and uses
α-Phellandrene undergoes hydrochlorination to give phellandrene hydrochloride (a cyclohexenyl chloride). Base hydrolysis of this hydrochloride gives piperitol.[3]
The phellandrenes are used in fragrances because of their pleasing aromas. The odor of β-phellandrene has been described as peppery-minty and slightly citrusy.
Like other cyclohexadienes, α-phellandrene reacts with ruthenium trichloride to give (cymene)ruthenium chloride dimer.
Biosynthesis
The biosynthesis of phellandrene begins with dimethylallyl pyrophosphate and isopentenyl pyrophosphate condensing in an SN1 reaction to form geranyl pyrophosphate. The resultant monoterpene undergoes cyclization to form a menthyl cationic species. A hydride shift then forms an allylic carbocation. Finally, an elimination reaction occurs at one of two positions, yielding either α-phellandrene or β-phellandrene.[4]
File:Phellandrene mechanism.jpg
Safety
The α-phellandrene isomer can form hazardous and explosive peroxides on contact with air at elevated temperatures.[5]
References
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- ↑ Jacobs, S.W.L., Pickard, J., Plants of New South Wales, 1981, Template:ISBN.
- ↑ Boland, D. J., Brophy, J. J., and A. P. N. House, Eucalyptus Leaf Oils, 1991, Template:ISBN.
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