Terpinene

The terpinenes are a group of isomeric hydrocarbons that are classified as monoterpenes. They each have the same molecular formula and carbon framework, but they differ in the position of carbon-carbon double bonds. α-Terpinene has been isolated from cardamom and marjoram oils, and from other natural sources. β-Terpinene has no known natural source but has been prepared from sabinene. γ-Terpinene and δ-terpinene (also known as terpinolene) have been isolated from a variety of plant sources. They are all colorless liquids with a turpentine-like odor.^[1]

Terpinenes

α-Terpinene β-Terpinene
γ-Terpinene δ-Terpinene (terpinolene)
Names
IUPAC names α: 4-Methyl-1-(1-methylethyl)-1,3-cyclohexadiene β: 4-Methylene-1-(1-methylethyl)cyclohexene γ: 4-Methyl-1-(1-methylethyl)-1,4-cyclohexadiene δ: 1-Methyl-4-(propan-2-ylidene)cyclohex-1-ene
Identifiers
CAS Number	(α): 99-86-5 Y (β): 99-84-3 Y (γ): 99-85-4 Y (δ): 586-62-9 Y
3D model (JSmol)	(α): Interactive image (β): Interactive image (γ): Interactive image (δ): Interactive image
ChEBI	(α): CHEBI:10334 Y (β): CHEBI:59159 (γ): CHEBI:10577 (δ): CHEBI:9457
ChemSpider	(α): 7182 N (β): 60205 (γ): 7181
ECHA InfoCard	100.029.440
EC Number	(α): 202-795-1 (β): 202-793-0 (γ): 202-794-6 (δ): 209-578-0
KEGG	(α): C09898 (γ): C09900 (δ): C06075
PubChem CID	(α): 7462 (β): 66841 (γ): 7461 (δ): 11463
UNII	(α): I24X278AP1 Y (β): DV74J5RW4Y Y (γ): 4YGF4PQP49 Y (δ): N9830X5KSL Y
InChI InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h6,8H,3-5,7H2,1-2H3 Y Key: SCWPFSIZUZUCCE-UHFFFAOYSA-N Y (β): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h6,8H,3-5,7H2,1-2H3 Key: SCWPFSIZUZUCCE-UHFFFAOYSA-N (γ): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4,7-8H,5-6H2,1-3H3 Key: YKFLAYDHMOASIY-UHFFFAOYSA-N (δ): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4H,5-7H2,1-3H3 Key: MOYAFQVGZZPNRA-UHFFFAOYSA-N
SMILES (α): CC1=CC=C(C(C)C)CC1 (β): C=C1CC=C(C(C)C)CC1 (γ): CC1=CCC(C(C)C)=CC1 (δ): C/C(C)=C1CCC(C)=CC/1
Properties
Chemical formula	C10H16
Molar mass	136.238 g·mol−1
Density	α: 0.8375 g/cm3 β: 0.838 g/cm3 γ: 0.853 g/cm3
Melting point	α: 60-61 °C
Boiling point	α: 173.5-174.8 °C β: 173-174 °C γ: 183 °C
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Production and uses

α-Terpinene is produced industrially by acid-catalyzed rearrangement of α-pinene. It has perfume and flavoring properties but is mainly used to confer pleasant odor to industrial fluids. Hydrogenation gives the saturated derivative p-menthane.^[1]

Biosynthesis of α-terpinene

Biosynthetic pathway to alpha-terpinene from geranyl pyrophosphate.^[2]

The biosynthesis of α-terpinene and other terpenoids starts with the isomerization of geranyl pyrophosphate to linalyl pyrophosphate (LPP). LPP then forms a resonance-stabilized cation by loss of the pyrophosphate group. Cyclization is then completed thanks to this more favorable stereochemistry of the LPP cation, yielding a terpinyl cation.^[3] Finally, a 1,2-hydride shift via a Wagner-Meerwein rearrangement produces the terpinen-4-yl cation. It is the loss of a hydrogen from this cation that generates α-terpinene.

Plants that produce terpinene

• Cuminum cyminum^[4][5][6]
• Melaleuca alternifolia
• Cannabis ^[7]
• Origanum syriacum
• Coriandrum sativum^[8]
• Monarda fistulosa