Alpha-Pinene

Template:DISPLAYTITLE:alpha-Pinene

alpha-Pinene
IUPAC name	(1S,5S-2,6,6-trimethyl bicyclo[3.1.1]hept-2-ene ((−)-Pinene)
Identifiers
CAS number	[80-56-8] (unspecified) [7785-70-8] (+)-α-Pinene [7785-26-4] (−)-α-Pinene)
RTECS number	DT7000000 (unspec. isomer)
SMILES	CC1(C)[C@H]2C(C) =CC[C@@H]1[C@]2(C)C
Properties
Molecular formula	C10H16
Molar mass	136.23 g/mol
Appearance	Clear, colourless liquid
Density	0.858 g/mL (liquid at 20°C)
Melting point	Additional recommended knowledge Daily Sensitivity Test Weighing the right way How to ensure accurate weighing results every day? −64 °C (209 K)
Boiling point	155 °C (428 K)
Solubility in water	Very low
Chiral rotation [α]D	−50.7°
Hazards
Main hazards	flammable
NFPA 704	2 1 0
R-phrases	10-20/21/22-36/37/38-43-51
S-phrases	16-26-36-37-60-61
Related Compounds
Related alkene	Beta-Pinene, Camphene 3-Carene, Bornene Limonene
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

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. of under acidic conditions. 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.

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 & Trebler, Helv. Chim. Acta. 1921, 4, 566.