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 func ...

s. Two geometric

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

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. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as ...

. 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 e ...

. Pinenes are also found in many non-coniferous

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

s such as camphorweed (''

Heterotheca ''Heterotheca'' (common names goldenasters, camphorweed, and telegraph weed) is a genus of North American plants in the family Asteraceae. Etymology ''Heterotheca'' (heterothe'ca:) comes from Ancient Greek "other, different" and "case, chest ...

'') 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 simply sagebrush (one of several related species of this name), is an aromatic shrub from the ...

'').

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 thousands of natural product, natural products. Occurrence GPP is an int ...

, 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, Greek tea and shepherd's tea, is a genus of flowering plants known for their use as herbal medicine, commonly as a herbal tea. They are abundant in Mediterranean regions, the Balkans, the Iberi ...

'' spp. (ironwort) and ''

Salvia ''Salvia'' () is the largest genus of plants in the sage family Lamiaceae, with just under 1,000 species of shrubs, Herbaceous plant, herbaceous Perennial plant, perennials, and Annual plant, annuals. Within the Lamiaceae, ''Salvia'' is part o ...

'' spp. (sage). ''

Cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...

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

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

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

Pine nuts Pine nuts, also called piñón (), pinoli (), or pignoli, 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 traded locall ...

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. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...

trees contain pinene.

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

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

α-Pinene

Selective oxidation of α-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 pheromon ...

, along with pinene oxide, as well as verbenol and its hydroperoxide. α-Pinene can be converted to

camphor Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (''Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapu ...

by way of

isobornyl acetate Isobornyl acetate is an organic compound consisting of the acetate ester or the terpenoid isoborneol. It is a colorless liquid with a pleasant pine-like scent, and it is produced on a multi-ton scale for this purpose. The compound is prepared by ...

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 redox, reduce or Saturated ...

of pinene gives

pinane Pinane describes a pair of isomeric hydrocarbons. The isomers, actually diastereomers, are both chiral. They are the cis and trans isomers arising from the hydrogenation of the terpenes pinene. Both isomers undergo reaction with air (autoxidati ...

, precursor to a useful pinane

hydroperoxide Hydroperoxides or peroxols are Chemical compound, compounds of the form ROOH, where R stands for any group, typically Organic compound, organic, which contain the hydroperoxy functional group (). Hydroperoxide also refers to the hydroperoxide anio ...

. 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. 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 substra ...

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 language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

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 o ...

ly reduce aldehydes in what is known as the

Midland Alpine borane reduction Midland may refer to: Places Australia * Midland, Western Australia Canada * Midland, Albert County, New Brunswick * Midland, Kings County, New Brunswick * Midland, Newfoundland and Labrador * Midland, Ontario India * Midland Ward, Kohima, Nag ...

β-Pinene

β-Pinene can be converted to α-pinene in the presence of strong bases, or pyrolysed to produce

myrcene Myrcene, or β-myrcene, is a terpene, monoterpene. A colorless oil, it occurs widely in essential oils. It is produced mainly semi-synthetically from ''Myrcia'', from which it gets its name. It is an intermediate in the production of several frag ...

at 400 °C.

Use

Pinenes, especially α, are the primary constituents of

turpentine Turpentine (which is also called spirit of turpentine, oil of turpentine, terebenthine, terebenthene, terebinthine and, colloquially, turps) is a fluid obtainable by the distillation of resin harvested from living trees, mainly pines. Principall ...

, 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 Wood extracts