alpha-Pinene

Template:Chembox/Top Template:Chembox/Image Template:Chembox/SectGeneral Template:Chembox/IUPACName Template:Chembox/OtherNames Template:Chembox/Formula Template:Chembox/SMILES Template:Chembox/MolarMass Template:Chembox/Appearance | CAS number |[80-56-8] (unspecified)
[7785-70-8] (+)-α-Pinene
[7785-26-4] (−)-α-Pinene) |- Template:Chembox/SectProperties Template:Chembox/Density | Solubility in water | Very low |- Template:Chembox/Solubility Template:Chembox/Solubility Template:Chembox/Solubility Template:Chembox/MeltingPt Template:Chembox/BoilingPt Template:Chembox/SpecificRotation Template:Chembox/SectHazards Template:Chembox/MainHazards Template:Chembox/NFPA Template:Chembox/RPhrases Template:Chembox/SPhrases Template:Chembox/RTECSNo Template:Chembox/SectDataPage Template:Chembox/SectRelated Template:Chembox/RelatedX Template:Chembox/RelatedCpds Template:Chembox/Bottom α-Pinene is an organic compound of the terpene class, one of two isomers of pinene. 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). 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.

Chemical properties

General 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. 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.

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

Some general reactions of alpha-pinene