3D model (JSmol)
|Molar mass||136.24 g·mol−1|
|Melting point||< −10 °C (14 °F; 263 K)|
|Boiling point||166 to 168 °C (331 to 334 °F; 439 to 441 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
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. 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.
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. This compound adds a peppery and balsam aroma in the beer.
Biosynthesis and production
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. The current route to commercial samples is by the pyrolysis (400 °C) of β-pinene, which is obtained from turpentine.
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).
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Many plants contain myrcene, sometimes in substantial amounts.
Use in fragrance industry
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Myrcene is an important intermediate used in the perfumery industry. It has a pleasant odor, but is rarely used directly. 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 uncatalyzed hydroamination of the 1,3-diene followed by hydrolysis and Pd-catalyzed removal of the amine.
- Merck Index, 11th Edition, 6243
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