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Myrcene, or β-myrcene, is an olefinic natural organic hydrocarbon. It is more precisely classified as a monoterpene. Monoterpenes are dimers of isoprenoid precursors, and myrcene is a significant component of the essential oil of several plants, including bay, cannabis, ylang-ylang, wild thyme, parsley, cardamom, and hops.[3][4] 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.[3]

Myrcene[1]
Beta-myrcene, skeletal formula
Ball-and-stick model of the beta-myrcene molecule
Names
IUPAC name
7-Methyl-3-methylene-1,6-octadiene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.004.203
KEGG
Properties
C10H16
Molar mass 136.24 g·mol−1
Density 0.794 g/cm3
Melting point < −10 °C (14 °F; 263 K)
Boiling point 166 to 168 °C (331 to 334 °F; 439 to 441 K)[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Figure 1. Biosynthesis of myrcene. A is Dimethylallyl pyrophosphate (DMAPP), B is Isopentyl pytophosphate (IPP), C is Geranyl pyrophosphate (GPP), D is Linalyl (LPP), E is myrcene.

Several terpenes can be extracted from the essential oils of Humulus lupulus (hops) used in beer manufacturing. The largest fraction of monoterpenes extracted from hops is β-myrcene, composing 29.4% to 65.8% of the chemical composition of Cannabis sativa strains.[5] Myrcene adds a peppery and balsam aroma in the beer.[6][7]

Contents

Industrial productionEdit

Myrcene is produced by the pyrolysis (400 °C) of β-pinene, which is obtained from turpentine.[3] It is rarely obtained directly from plants.[8]

BiosynthesisEdit

Terpenes arise naturally from dehydration of terpenol geraniol. 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.

Plants biosynthesize myrcene via geranyl pyrophosphate (GPP). The mevalonate pathway gives the precursors dimethylallyl pyrophosphate (Fig. 1a) and isopentenyl pyrophosphate (Fig.1b). These two precursors combine to produce GPP (Fig. 1c), which then isomerizes into linalyl pyrophosphate (Fig. 1d). The rearrangement and release of the pyrophosphate (OPP), and the double bond formation creates the product myrcene (Fig. 1e).[9]

Many plants contain myrcene, sometimes in substantial amounts.[3]

Use in fragrance industryEdit

Myrcene is an important intermediate used in the perfumery industry. It has a pleasant odor, but is rarely used directly.[3] It is also unstable in air, tending to polymerize. 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. Myrcene is converted to myrcenol, another fragrance found in lavender, via hydroamination of the 1,3-diene by diethylamine followed by hydrolysis and Pd-catalyzed removal of the amine.[11]

Both myrcene and mycenol undergo Diels-Alder reactions with several dienophiles such as acrolein to give cyclohexene derivatives that are also useful fragrances.[2]

See alsoEdit

ReferencesEdit

  1. ^ Merck Index, 11th Edition, 6243
  2. ^ a b Fahlbusch, K.-G.; Hammerschmidt, F.-J.; Panten, J.; Pickenhagen, W.; Schatkowski, D.; Bauer, K.; Garbe, D.; Surburg, H. (2002). "Flavors and Fragrances". Ullmann's Encyclopedia of Industrial Chemistry. Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. ISBN 3527306730. doi:10.1002/14356007.a11_141. 
  3. ^ a b c d e Behr, A.; Johnen, L. (2009). "Myrcene as a Natural Base Chemical in Sustainable Chemistry: A Critical Review". ChemSusChem. 2 (12): 1072–1095. PMID 20013989. doi:10.1002/cssc.200900186. 
  4. ^ Chyau, C.-C.; Mau, J.-L.; Wu, C.-M. (1996). "Characteristics of the Steam-Distilled Oil and Carbon Dioxide Extract of Zanthoxylum simulans Fruits". Journal of Agricultural and Food Chemistry. 44 (4): 1096–1099. doi:10.1021/jf950577d. 
  5. ^ "Essential oil of Cannabis sativa L. strains". druglibrary.net. Retrieved 2017-06-08. 
  6. ^ Inui, T; Tsuchiya, F; Ishimaru, M; Oka, K; Komura, H (2013). "Different beers with different hops. Relevant compounds for their aroma characteristics". Journal of Agricultural and Food Chemistry. 61 (20): 4758–64. PMID 23627300. doi:10.1021/jf3053737. 
  7. ^ Vázquez-Araújo, L; Rodríguez-Solana, R; Cortés-Diéguez, S. M.; Domínguez, J. M. (2013). "Use of hydrodistillation and headspace solid-phase microextraction to characterize the volatile composition of different hop cultivars". Journal of the Science of Food and Agriculture. 93 (10): 2568–74. PMID 23483584. doi:10.1002/jsfa.6078. 
  8. ^ M. Eggersdorfer (2005). "Terpenes". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a26_205. 
  9. ^ Dewick, Paul M. (2002). Medicinal Natural Products: A Biosynthetic Approach. New York: John Wiley and Sons, Ltd. p. 174. ISBN 0471496413. 
  10. ^ Marongiu, B; Piras, A; Porcedda, S (2004). "Comparative analysis of the oil and supercritical CO2 extract of Elettaria cardamomum (L.) Maton". Journal of Agricultural and Food Chemistry. 52 (20): 6278–82. PMID 15453700. doi:10.1021/jf034819i. 
  11. ^ Kunihiko Takabe, Takao Katagiri, Juntaro Tanaka, Tsutomu Fujita, Shoji Watanabe, And Kyoichi Suga (1989). "Addition Of Dialkylamines To Myrcene: N,n-diethylgeranylamine". Org. Synth. 67: 44. doi:10.15227/orgsyn.067.0044.