Myrcene
Encyclopedia
Myrcene, or β-myrcene, is an olefinic
natural organic compound
. It is classified as a hydrocarbon
, more precisely as a monoterpene
. Terpenes are dimers of isoprene
and myrcene is one of the most important. It is a component of the essential oil
of several plants including bay
, ylang-ylang
, wild thyme
, and hops
. It is produced mainly semi-synthetically from myrcia
, from which it gets its name. It is a key intermediate in the production of several fragrances. α-Myrcene is the name for the structural isomer 2-methyl-6-methylene-1,7-octadiene, which is not found in nature and is little used.
. It could in principle be extracted from any number of plants, for example wild thyme
, the leaves of which contain up to 40% by weight of myrcene. The current route to commercial samples is by the pyrolysis
(400 °C) of pinene
, which is obtained from turpentine
.
ize. Samples are stabilized by the addition of alkylphenols or tocopherol
. It is thus more highly valued as an intermediate for the preparation of flavor and fragrance chemicals such as menthol
, citral
, citronellol
, citronellal
, geraniol
, nerol
, and linalool. Treatment of myrcene with hydrogen chloride
gives geranyl chloride, neryl chloride, and linalyl chloride. Treatment of these compounds with acetate
gives geranyl acetate, neryl acetate, and linalyl acetate, respectively. These esters are then hydrolyzed
to the corresponding alcohols. Myrcene is also converted to myrcenol
, another fragrance found in lavender
, via uncatalyzed hydroamination
of the 1,3-diene followed by hydrolysis and Pd
-catalyzed removal of the amine
.
As 1,3-dienes, both myrcene and mycenol undergo Diels-Alder reaction
s with several dienophiles such as acrolein
to give cyclohexene
derivatives that are also useful fragrances.
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
natural organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
. It is classified as a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
, more precisely as a monoterpene
Terpene
Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium. They are often strong smelling and thus may have had a protective...
. Terpenes are dimers of isoprene
Isoprene
Isoprene , or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=CCH=CH2. Under standard conditions it is a colorless liquid...
and myrcene is one of the most important. It is a component of the essential oil
Essential oil
An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...
of several plants including bay
Bay leaf
Bay leaf refers to the aromatic leaf of the bay laurel . Fresh or dried bay leaves are used in cooking for their distinctive flavor and fragrance. The leaves are often used to flavor soups, stews, braises and pâtés in Mediterranean cuisine...
, ylang-ylang
Ylang-ylang
Cananga odorata, commonly called Ylang-ylang , cananga tree, ilang-ilang, kenanga , fragrant cananga, Macassar-oil plant or perfume tree),is a tree valued for its perfume...
, wild thyme
Wild thyme
Thymus serpyllum, known by the common names of Breckland Thyme, Wild Thyme or Creeping Thyme is a species of thyme native to most of Europe and North Africa. It is a low, usually prostrate subshrub growing to 2 cm tall with creeping stems up to 10 cm long, with oval evergreen leaves...
, and hops
Hops
Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...
. It is produced mainly semi-synthetically from myrcia
Myrcia
Myrcia is a genus of the flowering plant family Myrtaceae.Selected species* Myrcia albobrunnea* Myrcia albo-tomentosa DC.* Myrcia almasensis* Myrcia bella Cambess.* Myrcia calcicola...
, from which it gets its name. It is a key intermediate in the production of several fragrances. α-Myrcene is the name for the structural isomer 2-methyl-6-methylene-1,7-octadiene, which is not found in nature and is little used.
Biosynthesis and production
Terpenes arise naturally from dehydration of terpenol geraniolGeraniol
Geraniol is a monoterpenoid and an alcohol. It is the primary part of rose oil, palmarosa oil, and citronella oil . It also occurs in small quantities in geranium, lemon, and many other essential oils. It appears as a clear to pale-yellow oil that is insoluble in water, but soluble in most common...
. It could in principle be extracted from any number of plants, for example wild thyme
Wild thyme
Thymus serpyllum, known by the common names of Breckland Thyme, Wild Thyme or Creeping Thyme is a species of thyme native to most of Europe and North Africa. It is a low, usually prostrate subshrub growing to 2 cm tall with creeping stems up to 10 cm long, with oval evergreen leaves...
, the leaves of which contain up to 40% by weight of myrcene. The current route to commercial samples is by the pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
(400 °C) of pinene
Pinene
Pinene is a bicyclic monoterpene chemical compound. There are two structural isomers of pinene found in nature: α-pinene and β-pinene. As the name suggests, both forms are important constituents of pine resin; they are also found in the resins of many other conifers, as well as in non-coniferous...
, which is obtained from turpentine
Turpentine
Turpentine is a fluid obtained by the distillation of resin obtained from trees, mainly pine trees. It is composed of terpenes, mainly the monoterpenes alpha-pinene and beta-pinene...
.
Use in fragrance industry
Myrcene is an important intermediate used in the perfumery industry. It has pleasant odor, but is rarely used directly. It is also unstable in air, tending to polymerPolymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ize. Samples are stabilized by the addition of alkylphenols or tocopherol
Tocopherol
Tocopherols are a class of chemical compounds of which many have vitamin E activity. It is a series of organic compounds consisting of various methylated phenols...
. It is thus more highly valued as an intermediate for the preparation of flavor and fragrance chemicals such as menthol
Menthol
Menthol is an organic compound made synthetically or obtained from peppermint or other mint oils. It is a waxy, crystalline substance, clear or white in color, which is solid at room temperature and melts slightly above. The main form of menthol occurring in nature is -menthol, which is assigned...
, citral
Citral
Citral, or 3,7-dimethyl-2,6-octadienal or lemonal, is either of, or a mixture of, a pair of terpenoids with the molecular formula C10H16O. The two compounds are double bond isomers. The E-isomer is known as geranial or citral A...
, citronellol
Citronellol
Citronellol, or dihydrogeraniol, is a natural acyclic monoterpenoid. Both enantiomers occur in nature. -Citronellol, which is found in citronella oils, including Cymbopogon nardus , is the more common isomer. -Citronellol is found in the oils of rose and Pelargonium geraniums.Citronellol is...
, citronellal
Citronellal
Citronellal or rhodinal or 3,7-dimethyloct-6-en-1-al is a monoterpenoid, the main component in the mixture of terpenoid chemical compounds that give citronella oil its distinctive lemon scent....
, geraniol
Geraniol
Geraniol is a monoterpenoid and an alcohol. It is the primary part of rose oil, palmarosa oil, and citronella oil . It also occurs in small quantities in geranium, lemon, and many other essential oils. It appears as a clear to pale-yellow oil that is insoluble in water, but soluble in most common...
, nerol
Nerol
Nerol is a monoterpene found in many essential oils such as lemongrass and hops. It was originally isolated from neroli oil, hence its name. This colourless liquid is used in perfumery. Like geraniol, nerol has a sweet rose odor but it is considered to be fresher.Isomeric with nerol is geraniol,...
, and linalool. Treatment of myrcene with hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
gives geranyl chloride, neryl chloride, and linalyl chloride. Treatment of these compounds with acetate
Acetate
An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...
gives geranyl acetate, neryl acetate, and linalyl acetate, respectively. These esters are then hydrolyzed
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
to the corresponding alcohols. Myrcene is also converted to myrcenol
Myrcenol
Myrcenol is an organic compound, specificially a terpenoid. It is most notable as one of the fragrant components of lavender oil.-Role in fragrance industry:...
, another fragrance found in lavender
Lavender
The lavenders are a genus of 39 species of flowering plants in the mint family, Lamiaceae. An Old World genus, distributed from Macaronesia across Africa, the Mediterranean, South-West Asia, Arabia, Western Iran and South-East India...
, via uncatalyzed hydroamination
Hydroamination
The hydroamination reaction is the addition of an N-H bond across the C=C or C≡C bonds of an alkene or alkyne. This is a highly atom economical method of preparing substituted amines that are attractive targets for organic synthesis and the pharmaceutical industry.The hydroamination reaction is...
of the 1,3-diene followed by hydrolysis and Pd
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
-catalyzed removal of the amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
.
As 1,3-dienes, both myrcene and mycenol undergo Diels-Alder reaction
Diels-Alder reaction
The Diels–Alder reaction is an organic chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. The reaction can proceed even if some of the atoms in the newly formed ring are not carbon...
s with several dienophiles such as acrolein
Acrolein
Acrolein is the simplest unsaturated aldehyde. It is produced widely but is most often immediately reacted with other products due to its instability and toxicity...
to give cyclohexene
Cyclohexene
Cyclohexene is a hydrocarbon with the formula C6H10. This cycloalkene is a colorless liquid with a sharp smell. It is an intermediate in various industrial processes...
derivatives that are also useful fragrances.
Partial list of the plants that contain myrcene
As mentioned above, many plants contain myrcene, sometimes in very large amounts.- HouttuyniaHouttuyniaHouttuynia cordata in Lao; ; English lizard tail and chameleon plant; ), In English, it is known as Lizard tail, chameleon plant, heartleaf, fishwort and Bishop's weed...
- Mangoes
- CannabisCannabisCannabis is a genus of flowering plants that includes three putative species, Cannabis sativa, Cannabis indica, and Cannabis ruderalis. These three taxa are indigenous to Central Asia, and South Asia. Cannabis has long been used for fibre , for seed and seed oils, for medicinal purposes, and as a...
spp. - HopsHopsHops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...
- Lemon grass
- West Indian Bay TreeWest Indian Bay treeThe West Indian bay tree , also known as the bay rum tree, is a plant in the myrtle family native to the Caribbean region...
- VerbenaVerbenaVerbena , verbenas or vervains, is a genus in the family Verbenaceae. It contains about 250 species of annual and perennial herbaceous or semi-woody flowering plants. The majority of the species are native to the New World from Canada south to southern Chile, but some are also native in the Old...
- MerciaMerciaMercia was one of the kingdoms of the Anglo-Saxon Heptarchy. It was centred on the valley of the River Trent and its tributaries in the region now known as the English Midlands...