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. Iso ...

s of pinene are found in nature, α-pinene 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 accep ...

. 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 extan ...

. 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 exclud ...

s such as camphorweed ('' Heterotheca'') and big sagebrush ('' Artemisia tridentata'').

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 isoprenoid ...

, 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 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 ''Sideritis'', also known as ironwort, mountain tea, and shepherd's tea, is a genus of flowering plants known for their use as herbal medicine, commonly as an herbal tea. They are abundant in Mediterranean regions, the Balkans, the Iberian Penins ...

'' spp. (ironwort) and ''

Salvia ''Salvia'' () is the largest genus of plants in the sage family Lamiaceae, with nearly 1000 species of shrubs, herbaceous plant, herbaceous perennial plant, perennials, and annual plant, annuals. Within the Lamiaceae, ''Salvia'' is part of the ...

'' 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''. Alternatively ...

'' also contains alpha-pinene and beta-pinene. Resin from '' Pistacia terebinthus'' (commonly known as terebinth or turpentine tree) is rich in pinene. Pine nuts produced by

pine 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 accep ...

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 leave ...

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 pheromo ...

, 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 Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...

of pinene gives

pinane Pinane is a set of isomeric terpenes. Existing as chiral cis and trans isomers, they arise from the hydrogenation of pinene Pinene is a collection of unsaturated bicyclic monoterpenes. Two geometric isomers of pinene are found in nature, α-pi ...

, precursor to a useful pinane

hydroperoxide Hydroperoxides or peroxols are Chemical compound, 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 t ...

. The hydroboration of α-pinene has been extensively examined. With borane-dimethylsulfide, two equivalents of α-pinene react to give (diisopinocampheyl)borane. Reaction with

9-BBN 9-Borabicyclo .3.1onane or 9-BBN is an organoborane compound. This colourless solid is used in organic chemistry as a hydroboration reagent. The compound exists as a hydride-bridged dimer, which easily cleaves in the presence of reducible substr ...

gives the reagent called

alpine borane Alpine borane is the commercial name for an organoboron compound that is used in organic synthesis. It is a colorless liquid, although it is usually encountered as a solution. Preparation and reactions This reagent is generated by treating 9-BB ...

. This sterically crowded chiral trialkylborane can stereoselectively 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