Pinene is a collection of unsaturated bicyclic

monoterpene Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear (acyclic) or contain rings (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen funct ...

s. Two geometric

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. I ...

s of pinene are found in nature,

α-pinene 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 a ...

and β-pinene. Both are chiral. As the name suggests, pinenes are found in

pines A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanical Garden accepts ...

. Specifically, pinene is the major component of the liquid extracts of

conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ext ...

. Pinenes are also found in many non-coniferous

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae ex ...

s such as camphorweed ('' Heterotheca'') and big sagebrush (''

Artemisia tridentata ''Artemisia tridentata'', commonly called big sagebrush,MacKay, Pam (2013), ''Mojave Desert Wildflowers'', 2nd ed., , p. 264. Great Basin sagebrush or (locally) simply sagebrush, is an aromatic shrub from the family Asteraceae, which grows in ar ...

'').

Isomers

Biosynthesis

α-Pinene and β-pinene are both produced from

geranyl pyrophosphate Geranyl pyrophosphate (GPP), also known as geranyl diphosphate (GDP), is the pyrophosphate ester of the terpenoid geraniol. Its salts are colorless. It is a precursor to many natural products. Occurrence GPP is an intermediate in the isopreno ...

, via cyclisation of linaloyl pyrophosphate followed by loss of a proton from the carbocation equivalent. Researchers at the Georgia Institute of Technology and the Joint BioEnergy Institute have been able to synthetically produce pinene with a bacterium.

Plants

Alpha-pinene 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 a ...

is the most widely encountered terpenoid in nature and is highly repellent to insects. Alpha-pinene appears in

and numerous other plants. Pinene is a major component of the essential oils of '' Sideritis'' spp. (ironwort) and ''

Salvia ''Salvia'' () is the largest genus of plants in the sage family Lamiaceae, with nearly 1000 species of shrubs, herbaceous perennials, and annuals. Within the Lamiaceae, ''Salvia'' is part of the tribe Mentheae within the subfamily Nepetoide ...

'' spp. (sage). ''

Cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae. The number of species within the genus is disputed. Three species may be recognized: ''Cannabis sativa'', '' C. indica'', and '' C. ruderalis''. Alternative ...

'' also contains alpha-pinene and beta-pinene. Resin from ''

Pistacia terebinthus ''Pistacia terebinthus'' also called the terebinth and the turpentine tree, is a deciduous tree species of the genus ''Pistacia'', native to the Mediterranean region from the western regions of Morocco and Portugal to Greece and western and ...

'' (commonly known as terebinth or turpentine tree) is rich in pinene.

Pine nuts Pine nuts, also called piñón (), pinoli (), pignoli or chilgoza (), are the edible seeds of pines (family Pinaceae, genus ''Pinus''). According to the Food and Agriculture Organization, only 29 species provide edible nuts, while 20 are tr ...

produced by

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family (biology), family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanic ...

trees contain pinene.

Makrut lime ''Citrus hystrix'', called the kaffir lime or makrut lime, (, ) is a citrus fruit native to tropical Southeast Asia. Its fruit and leaves are used in Southeast Asian cuisine, and its essential oil is used in perfumery. Its rind and crushed lea ...

fruit peel contains an essential oil comparable to lime fruit peel oil; its main components are limonene and β-pinene. The racemic mixture of the two forms of pinene is found in some oils like eucalyptus oil.

Reactions

β-Pinene can be converted to α-pinene in the presence of strong bases. Selective oxidation of pinene occurs at the allylic position to give

verbenone Verbenone is a natural organic compound classified as a terpene that is found naturally in a variety of plants. The chemical has a pleasant characteristic odor. Besides being a natural constituent of plants, it and its analogs are insect pherom ...

, along with pinene oxide, as well as verbenol and its hydroperoxide.

Hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate orga ...

of pinene gives pinane, precursor to a useful pinane

hydroperoxide Hydroperoxides or peroxols are compounds containing the hydroperoxide functional group (ROOH). If the R is organic, the compounds are called organic hydroperoxides. Such compounds are a subset of organic peroxides, which have the formula ROOR. ...

. The

hydroboration In organic chemistry, hydroboration refers to the addition of a hydrogen-boron bond to certain double and triple bonds involving carbon (, , , and ). This chemical reaction is useful in the organic synthesis of organic compounds. Hydrobora ...

of α-pinene has been extensively examined. With borane-dimethylsulfide, two equivalents of α-pinene react to give (diisopinocampheyl)borane. Reaction with 9-BBN gives the reagent called alpine borane. This sterically crowded

chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from ...

trialkylborane can

stereoselective In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during a non- stereospecific creation of a new stereocenter or during a non-stereospecific transformation ...

ly reduce aldehydes in what is known as the Midland Alpine borane reduction.

Use

Pinenes, especially α, are the primary constituents of

turpentine Turpentine (which is also called spirit of turpentine, oil of turpentine, terebenthene, terebinthine and (colloquially) turps) is a fluid obtained by the distillation of resin harvested from living trees, mainly pines. Mainly used as a special ...

, a nature-derived solvent and fuel. The use of pinene as a biofuel in spark ignition engines has been explored. Pinene dimers have been shown to have heating values comparable to the jet fuel JP-10.

References

Bibliography

* {{cite book, first1=J., last1=Mann, first2=R. S., last2=Davidson, first3=J. B., last3=Hobbs, first4=D. V., last4=Banthorpe, first5=J. B., last5=Harborne, title=Natural Products, page
309–311
publisher=Addison Wesley Longman Ltd., location=Harlow, UK, year=1994, isbn=978-0-582-06009-8, url-access=registration, url=https://archive.org/details/isbn_9780582060098/page/309 Monoterpenes Cyclobutanes Cyclohexenes