Monoterpenoid hydrocarbons

Monosodium L-glutamate (MSG), 12 49 Monosodium phosphate (MSP), 18 833 manufacture of, 18 853, 857-858 thermal dehydration of, 18 846 Monostatic optical arrangement, 23 139 Monosubstituted boranes, 13 635-636 Monoterpenoid alcohols, 24 500-528 bicyclic, 24 527-528 monocyclic, 24 509-527 Monoterpenoid aldehydes, 24 529-536 Monoterpenoid ethers, 24 528-529 Monoterpenoid hydrocarbons,... 

G.l.c. papers of interest include the classification of 22 acyclic monoterpenoid alcohols according to retention indexes, resolution of cyclic ketones [e.g. ( )-menthone, ( )-isomenthone] as diethyl (+)-tartrate acetals, and the use of lanthanide shift reagents to resolve non-terpenoid racemic epoxides.The occurrence and prevention of monoterpenoid hydrocarbon isomerization during silica gel chromatography has been examined and the separation of monoterpenoids and sesquiterpenoids by gel permeation chromatography is reported. Monoterpenoid hydrocarbons have been selectively extracted from essential oils using dimethylsilicone. ... 

Monoterpenoids are responsible for fragrances and flavors of many plants and thus their products are used in perfumery and as spices. To date over 1,500 monoterpenoids are known, and these constitute acyclic, monocyclic, and bicyclic monoterpenoids (32), which occur in nature as hydrocarbons, alcohols, aldehydes, and carboxylic acids and their esters. Several acyclic monoterpenoid hydrocarbons are known, and these include trienes such as 3-myrcene (Cl), a-myrcene (C2), (Z)-a-ocimene (C3), ( )-a-ocimene (C4), (Z)-3-ocimene (C5), and ( )-P-ocimene (C6). 3-Myrcene and 3-ocimene are constituents of basil (Oci-mum basilicum, Labiatae) and bay (Pimenta acris, Myrtaceae), pettitgrain (Citrus vulgaris, Rutaceae) leaves, strobiles of hops (Humulus lupulus, Cannabaceae), and several other essential oils. Unsaturated acyclic monoterpene alcohol constituents of plants and their derived aldehydes play a signihcant role in the perfume industry. Some common acyclic monoterpene alcohols and aldehydes include geraniol (C7), linalool (C8) (a... 

Mass spectral papers include another compilation of monoterpenoid alcohol spectra, a comparison of fragmentation patterns for camphor and menthone with their oxime, semicarbazone, and nitrophenylhydrazone derivatives, and a comparison of collisional activation mass spectra of ten related acyclic, monocyclic, and bicyclic monoterpenoid hydrocarbons together with derived 7119 ions. ... 

Chromatography of radiochemically homogeneous terpenoids has been reviewed useful gas-chromatographic techniques reported include the use of polyphenyl ether in g.c.-m.s. of 23 monoterpenoid hydrocarbons,the use of 3,4,5-trimethoxybenzylhydrazine for pre-column removal of aldehydes and ketones, and the resolution of some bicyclic alcohols and ketones by co-injection with a volatile chiral resolving agent. 

Perfume materials obtained by distillation are referred to as essential oils. Thus, for example, the oil obtained by steam distillation of lavender is known as the essential oil of lavender or lavender oil. Sometimes, the monoterpenoid hydrocarbons are removed from the oils by distillation or solvent extraction to give a finer odour in the product. The process is known as deterpenation and the product is referred to as a terpeneless oil or folded oil. 

Chromatography.—G.l.c. papers of interest include the separation of monoterpenoid hydrocarbons on modified graphitized carbon black, the separation of... 

Some other common monoterpenoid hydrocarbons are shown in Figure 3.4. Citronellene is also known as dihydromyrcene. It does not occur in nature but is prepared by pyrolytic cracking of pinane. Hydration of the trisubstituted bond of citronellene produces dihydro-myrcenol which is used to provide fresh notes in perfumery. Further details of both of these processes are given in Chapter 9. a-Ocimene occurs in various essential oils such as those of basil, catnip and magnolia, while the P-isomer occurs in the leaf oils of lemon, orange and grapefruit and also in narcissus flowers. Allo-ocimene occurs in the leaves of sequoia trees and is the thermodynamically most stable of the three ocimenes since the double bonds are all in conjugation and as heavily substituted as possible. Double bonds can be isomerised under... 

Bicyclo[3,14]heptanes.— The structure of paeoniflorin (338), a monoterpenoid glucoside that is the major principle from Chinese paeony root Paeonia albiflora), has been confirmed by X-ray analysis of a bromo-derivative. It is accompanied in the plant by albiflorin (339). ° The crystal structure of bis-(7r-pinenyl)nickel has been given as an example of the use of automated X-ray structural determination as an analytical method. The conversion of the pinenes into other monoterpenoid hydrocarbons continues to produce many publications e.g. conversion... 

Green plants also release substantial quantities of isoprene (2) as well as monoterpenoid hydrocarbons such as a-pinene (3), myrcene (4), and limonene (5). These compounds contribute significantly to atmospheric organic concentrations in remote or forested areas (Altshuller, 1983 Hutte et al., 1984). It has been estimated that the global output of these substances may equal about 28% of the annual output of methane (Rasmussen and Went, 1965). 

Bark beetles oxidise toxic monoterpenoid hydrocarbons in their respiratory air, which originate from the resin of the tree they colonise, and thereby circumvent this defense barrier of the tree. Converting these compounds into less toxic secondary metabolites serves another purpose, by providing pheromones to attract insects of the same species, of both sexes. Therefore, an oxygen function is often introduced species-specifically and stereoselectively. European spruce bark beetles oxidise (-)-a-pinene to (S)-cis-verbenol, whereas pine beetles produce (R)-trans-verheno. In the California fivespined engraver Ips paraconfu-sus), myrcene is converted into (S)-ipsdienol and (S)-ipsenol. But Ips pint and Ips paraconfusus are also able to synthesise their pheromones de novo via the classical mevalonate biosynthetic pathway. 

Some of the more commonly encountered monoterpenoid hydrocarbons (Arctander, 1960 Essential Oils Database, 2006 Gildemeister and Hoffmann, 1956 Gunther, 1948 Sell, 2007) are shown in Figure 6.16. Many of these can be formed by dehydration of alcohols, and so their presence in essential oils could be as artifacts arising from the extraction process. Similarly, p-cymene (83) is one of the most stable materials of this class and can be formed from many of the others by appropriate cyclization and/or isomerization and/or oxidation reactions and so its presence in any essential oil could be as an artifact. 

The term terpene was originally applied to the hydrocarbons found in turpentine and is sometimes applied more generally to any unsaturated terpenoid hydrocarbon. Usually, it will indicate an unsaturated monoterpenoid hydrocarbon, the higher nonoxygenated homologues being referred to as sesquiterpenes, diterpenes, etc. 

Dipentene The terms dipentene or />-menthadienes are used to indicate a mixture of monoterpenoid hydrocarbons and ethers usually produced as by-products from processes for the manufacture of other terpenoids. The major source is as a by-product from the... 

Another process of major importance is the acid catalysed hydration of a-pinene to give a-terpineol as is described in section Monocyclic Monoterpenoid Hydrocarbons under a-terpineol. 

Pure a-terpineol has a delicate sweet floral, lilac-type odor (though only present at very low levels, if at all, in lilac). Its odor qualities are greatly affected by impurities, and many fragrance houses buy cheap grades and redistill it to their perfumery quality. The monoterpenoid hydrocarbons tend to give a pine character, the other alcohols and the phenols give a medicinal quality. Low-cost, ready availability and stability to air, soap and household products make it a very useful ingredient. 

---