Phellandrene

Phellandrenes
α-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	(α): 99-83-2 ; (β): 555-10-2 ; (−)-(α): 4221-98-1 ; (+)-(α): 2243-33-6 ;
3D model (JSmol)	(α): Interactive image; (β): Interactive image; (−)-(α): Interactive image; (+)-(α): Interactive image;
ChEBI	(β): CHEBI:48741; (−)-(α): CHEBI:301; (+)-(α): CHEBI:367; (−)-(β): CHEBI:129; (+)-(β): CHEBI:53;
ChemSpider	(α): 7180 ; (β): 10669 ;
ECHA InfoCard	100.014.121
EC Number	(α): 202-792-5; (β): 209-081-9; (−)-(α): 224-167-6;
KEGG	(−)-(α): C09875; (+)-(α): C11391; (−)-(β): C11392; (+)-(β): C09877;
PubChem CID	(α): 7460; (β): 11142; (−)-(α): 442482; (+)-(α): 443160; (−)-(β): 443161;
UNII	(α): 49JV13XE39 ; (β): 2KK225M001 ; (−)-(α): 56UV8X65K0 ; (+)-(α): E45FS72C5K ;
CompTox Dashboard (EPA)	(α): 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; (−)-(α): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4-6,8,10H,7H2,1-3H3/t10-/m1/s1 Key: OGLDWXZKYODSOB-SNVBAGLBSA-N; (+)-(α): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4-6,8,10H,7H2,1-3H3/t10-/m0/s1 Key: OGLDWXZKYODSOB-JTQLQIEISA-N;
	SMILES (α): CC1=CCC(C=C1)C(C)C; (β): CC(C)C1CCC(=C)C=C1; (−)-(α): CC1=CC[C@@H](C=C1)C(C)C; (+)-(α): CC1=CC[C@H](C=C1)C(C)C;
Properties
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)
Hazards
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H226, H304
GHS precautionary statements	P210, P233, P240, P241, P242, P243, P280, P301+310, P303+361+353, P331, P370+378, P403+235, P405, P501
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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. (9 March 2009). Medicinal natural products : a biosynthetic approach (3rd ed.). Chichester, West Sussex, United Kingdom. ISBN 9780470741689. OCLC 259265604.

[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. (9 March 2009). Medicinal natural products : a biosynthetic approach (3rd ed.). Chichester, West Sussex, United Kingdom. ISBN 9780470741689. OCLC 259265604.

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