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.
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'') and big sagebrush (''
Artemisia tridentata'').
Isomers
Biosynthesis
α-Pinene and β-pinene are both produced from
geranyl pyrophosphate, 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
conifers 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 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'' (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.
''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...
trees contain pinene.
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, along with pinene oxide, as well as verbenol and its hydroperoxide.
α-Pinene can be converted to
camphor by way of
isobornyl acetate.
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, precursor to a useful pinane
hydroperoxide.
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 gives the reagent called
alpine borane. This sterically crowded
chiral trialkylborane can
stereoselectively reduce aldehydes in what is known as the
Midland Alpine borane reduction.
β-Pinene
β-Pinene can be converted to α-pinene in the presence of strong bases, or pyrolysed to produce
myrcene 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.]
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