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α-Pinene

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α-Pinene
Names
IUPAC names
(1S,5S)-2,6,6-Trimethyl
bicyclo[3.1.1]hept-2-ene
((−)-α-Pinene)
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.161 Edit this at Wikidata
RTECS number
  • DT7000000 (unspec. isomer)
  • InChI=1/C10H16/c1-7-4-5-8-6-9(7)10(8,2)3/h4,8-9H,5-6H2,1-3H3/t8-,9-/m0/s1
    Key: GRWFGVWFFZKLTI-IUCAKERBBG
  • C\1=C(\[C@@H]2C[C@H](C/1)C2(C)C)C
Properties
C10H16
Molar mass 136.23 g/mol
Appearance Clear, colourless liquid
Density 0.858 g/mL (liquid at 20°C)
Melting point −64 °C (−83 °F; 209 K)
Boiling point 155 °C (311 °F; 428 K)
Very low
−50.7° (1S,5S-Pinene)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 flammable
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 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 33 °C
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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α-Pinene is an organic compound of the terpene class, one of two isomers of pinene.[1] It is an alkene and it contains a reactive four-membered ring. It is found in the oils of many species of many coniferous trees, notably the pine. It is also found in the essential oil of rosemary (Rosmarinus officinalis).[2] Both enantiomers are known in nature; 1S,5S- or (−)-α-pinene is more common in European pines, whereas the 1R,5R- or (+)-α-isomer is more common in North America. The racemic mixture is present in some oils such as eucalyptus oil.

Reactivity

The four-membered ring in α-pinene 1 makes it a reactive hydrocarbon, prone to skeletal rearrangements such as the Wagner-Meerwein rearrangement. For example, attempts to perform hydration or hydrogen halide addition with the alkene functionality typically lead to rearranged products. With concentrated sulfuric acid and ethanol the major products are terpineol 2 and its ethyl ether 3, while glacial acetic acid gives the corresponding acetate ester 4. With dilute acids, terpin hydrate 5 becomes the major product.

With one molar equivalent of anhydrous HCl, the simple addition product 6a can be formed at low temperature in the presence of ether, but it is very unstable. At normal temperatures, or if no ether is present, the major product is bornyl chloride 6b, along with a small amount of fenchyl chloride 6c.[3] For many years 6b (also called "artificial camphor") was referred to as "pinene hydrochloride", until it was confirmed as identical with bornyl chloride made from camphene. If more HCl is used, achiral 7 (dipentene hydrochloride) is the major product along with some 6b. Nitrosyl chloride followed by base leads to the oxime 8 which can be reduced to "pinylamine" 9. Both 8 and 9 are stable compounds containing an intact four-membered ring, and these compounds helped greatly in identifying this important component of the pinene skeleton.[4]

A variety of reagents such as iodine or PCl3 cause aromatisation, leading to p-cymene 10.

Under aerobic oxidation conditions, the main oxidation products are pinene oxide, verbenyl hydroperoxide, verbenol and verbenone.[5]

Some general reactions of alpha-pinene


Atmospheric Role

Monoterpenes, of which alpha-pinene is one of the principal species, are emitted in substantial amounts by vegetation, and these emissions are affected by temperature and light intensity. In the atmosphere alpha-pinene undergoes reactions with ozone, the OH radical or the NO3 radical (IUPAC Subcommittee on Gas Kinetic Data Evaluation), leading to low-volatility species which partly condense on existing aerosols, thereby generating Secondary Organic Aerosols. This has been shown in numerous laboratory experiments for the mono- and sesquiterpenes [6]. Products of alpha-pinene which have been identified explicitly are pinonaldehyde, norpinonaldehyde, pinic acid, pinonic acid and pinalic acid.

References

  1. ^ Simonsen, J. L. (1957) The Terpenes (2nd edition) Vol. 2 Cambridge:Cambridge University Press, pp 105-191.
  2. ^ PDR for Herbal Medicine. Montvale, NJ: Medical Economics Company. p. 1100
  3. ^ Richter, G. H. (1945) Textbook of Organic Chemistry, 2nd ed., John Wiley & Sons., New York, PP 663-666.
  4. ^ Ruzicka, L. (1921). "Zur Kenntnis des Pinens III Konstitution des Nitrosopinens und seiner Umwandlungsprodukte". Helvetica Chimica Acta. 4: 566. doi:10.1002/hlca.19210040161.
  5. ^ U. Neuenschwander (2010), "Mechanism of the Aerobic Oxidation of α-Pinene", ChemSusChem, vol. 3, no. 1, pp. 75–84, doi:10.1002/cssc.200900228
  6. ^ Odum, J. R., Hoffmann, T., Bowman, F., Collins, D., Flagan, R.C., Seinfeld, J. H., (1996) Gas/particle partitioning and secondary organic aerosol yields , Environmental Science and Technology, 30, pp 2580-2585.

See also

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