Phellandrene

Phellandrenes
α-Phellandrene α-Phellandrene	β-Phellandrene β-Phellandrene
Names
	IUPAC names α: 2-Methyl-5-(1-methylethyl)-1,3-cyclohexadiene; β: 3-Methylene-6-(1-methylethyl)cyclohexene
Identifiers
CAS Number	99-83-2 (α) ; 555-10-2 (β) ;
3D model (JSmol)	(α): Interactive image; (β): Interactive image;
ChemSpider	7180 (α) ; 10669 (β) ;
ECHA InfoCard	100.014.121
UNII	49JV13XE39 (α) ; 2KK225M001 (β) ;
CompTox Dashboard (EPA)	DTXSID8051673 ;
	InChI (α): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4-6,8,10H,7H2,1-3H3 Key: OGLDWXZKYODSOB-UHFFFAOYSA-N; (β): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4,6,8,10H,3,5,7H2,1-2H3 Key: LFJQCDVYDGGFCH-UHFFFAOYSA-N;
	SMILES (α): CC1=CCC(C=C1)C(C)C; (β): CC(C)C1CCC(=C)C=C1;
Properties[1]
Chemical formula	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	α: 171-172 °C; β: 171-172 °C
Solubility in water	Insoluble (α and β)
	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

Phellandrenes are a pair of organic compounds that 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 ether.

α-Phellandrene was named after Eucalyptus phellandra, now called Eucalyptus radiata, from which it can be isolated.[2] It is also a constituent of the essential oil of Eucalyptus dives.[3] β-Phellandrene has been isolated from the oil of water fennel and Canada balsam oil.

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.

The α-phellandrene isomer can form hazardous and explosive peroxides on contact with air at elevated temperatures.[4]

Biosynthesis

The biosynthesis of phellandrene begins with dimethylallyl pyrophosphate and isopentenyl pyrophosphate condensing in an S_N1 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.[5]

References

The Merck Index, 12th Edition, 7340, 7341
Jacobs, S.W.L., Pickard, J., Plants of New South Wales, 1981, ISBN 0-7240-1978-2.
Boland, D.J., Brophy, J.J., and A.P.N. House, Eucalyptus Leaf Oils, 1991, ISBN 0-909605-69-6.
Urben, Peter (2007). Bretherick's Handobook of Reactive Chemical Hazards. 1 (7 ed.). Butterworth-Heinemann. p. 1154.
Dewick, Paul M. Medicinal natural products : a biosynthetic approach (3rd ed.). Chichester, West Sussex, United Kingdom. ISBN 9780470741689. OCLC 259265604.

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[1] The Merck Index, 12th Edition, 7340, 7341

[2] Jacobs, S.W.L., Pickard, J., Plants of New South Wales, 1981, ISBN 0-7240-1978-2.

[3] Boland, D.J., Brophy, J.J., and A.P.N. House, Eucalyptus Leaf Oils, 1991, ISBN 0-909605-69-6.

[4] Urben, Peter (2007). Bretherick's Handobook of Reactive Chemical Hazards. 1 (7 ed.). Butterworth-Heinemann. p. 1154.

[5] Dewick, Paul M. Medicinal natural products : a biosynthetic approach (3rd ed.). Chichester, West Sussex, United Kingdom. ISBN 9780470741689. OCLC 259265604.