Camphene, from pinene

Ordinary commercial camphor is (-i-)-cam phor, from the wood of the camphor tree. Cinnamonum camphora. Camphor is of great technical importance, being used in the manufacture of celluloid and explosives, and for medical purposes, /t is manufactured from pinene through bornyl chloride to camphene, which is either directly oxidized to camphor or is hydrated to isoborneol, which is then oxidized to camphor. A large number of camphor derivatives have been prepared, including halogen, nitro and hydroxy derivatives and sulphonic acids. 

Camphene is extremely difficult to separate in the solid condition from essential oils, and it may therefore be taken for granted that natural camphene is rarely prepared in the pure condition. The figure given above for the specific rotation is for a sample artificially prepared from pinene hydrochloride. 

Camphene is prepared artificially by the isomerisation of pinene with sulphuric acid or by the withdrawal of HCl from pinene monohydrochloride, or by the action of heat in the presence of acetic anhydride on bornylamine, CjjHj7NH2, which causes the withdrawal of ammonia and leaves camphene, as follows —... 

Approximately 45 constituents have been determined from fennel seed oil (Fig. 12.1), the main constituents being transanethole (60-65%, but up to 90%), fen-chone (2-20%), estragol (methyl chavicol), limonene, camphene, a-pinene and other monoterpenes, fenchyl alcohol and anisalde-hyde. The major compounds in supercritical... 

In summary, Foeniculum is stated to have three species, F. vulgare (fennel), F. azoricum Mill. (Florence fennel) and F. dulce (sweet fennel). Fennel is widely cultivated, both in its native habitat and elsewhere, for its edible, strongly flavoured leaves and seeds. The flavour is similar to, but milder than, that of anise and star anise. Anethole and fenchone are the major constituents of the solvent extract of seed phenols, free fatty acids, carbohydrates, proteins, vitamins and minerals have been reported in varying proportions. In the mature fruit, up to 95% of the essential oil is located in the fruit, greater amounts being found in the fully ripe fruit. Approximately 45 constituents have been determined from fennel seed oil, the main constituents being frans-anethole, fenchone, estragol (methyl chavicol), limonene, camphene, a-pinene and other monoterpenes, fenchyl alcohol and... 

The essential oil, which ranges from 2.5 to 5.0%, includes the following chemical compounds tt-pinene, camphene, /i-pinene, linalool, cis-anethole, trans-anethole, safrole,... 

Camphene is a solid terpene. The dextro variety d-camphene is found in camphor, ginger and spike oils, and the levo variety, 1-camphene is in citrondla and valerian oil and in French and American turpentine. Bornylene does not occur in nature but has been prepared from the alcohol corresponding to it known as Borneol or Borneo camphor. This, as previously stated, may be prepared from pinene so that Bornylene itself may be made from pinene. Fenchene, also, is not found in nature but is obtained by reduction of fenchone a terpene ketone found in fennel oil and in Thuja oil. 

Derivation Steam distillation of camphor-tree wood and crystallization. This product is called natural camphor and is dextrorotatory. Synthetic camphor, most of which is optically inactive, may be made from pinene, which is converted into camphene by treatment with acetic acid and nitrobenzene it becomes camphor, turpentine oil is also used. 

Berthelot s researches on the terpenes and camphor were important from the point of view of classification and he discovered some new compounds. He distinguished d- and /-pinene, calling them australene and terebentene, and d-, /-, and rf/-camphene, the last obtained by removing hydrogen chloride from pinene hydrochloride (bornyl chloride his camphene is now called bornylene). Berthelot used only the hydrochlorides to characterise the various pinenes. He... 

Tricyclene is a minor component of many terpene oils from which it is purified. It is made industrially by isomerization of pinenes. It is a waxy solid that sublimes at room temperature. However, it usually occurs with camphene, from which it is separated with difficulty. 

The volatile oil from the leaves and twigs of Liquidambar Formoscma has been examined by Kafuku. A yield of about 0-05 per cent, was obtained. It was greenish-yellow in colour, having a specific gravity of 0-8655 at 20 C., optical rotation - 3-3 , refractive index 1-4755 at 20 C., acid value nil, ester value 5-9, ester value after acetylation 25-2. It consisted principally of terpenes camphene, a-pinene, and dipentene were identified with certainty, nopinene and phellandrene being also indicated. Traces of aldehydes and ketones were found to be present. 

The preparation and uses of isobomeol (119) and its esters are described above in section Bicyclic Monoterpeniod Hydrocarbons under camphene. Optically pure (—)-bomeol can also be prepared from (—)-pinenes (277). Bomeol, isobomeol, and their acetates occur in a wide variety of herbs and other plants. They are used in perfumes for soaps and detergents for woody, camphor, and pine notes with a relatively low cost. Two monoethers of... 

Bomeol is oxidized to camphor with chromic or nitric acid dehydration with dilute acids yields camphene. Bomeol is readily esterified with acids, but on an industrial scale bornyl esters are prepared by other routes. For example, levorotatory bomeol is synthesized industrially from levorotatory pinenes by Wagner Meerwein rearrangement with dilute acid, followed by hydrolysis of the resulting esters [86]. 

Commercially camphene is obtained by acid-catalyzed rearrangement of pinene, recognized many years prior to the isolation from natural sources. 

Most synthetic camphor (43) is produced from camphene (13) made from a-pinene. The conversion to isobomyl acetate followed by saponification produces isobomeol (42) in good yield. Although chemical oxidations of isobomeol with sulfuric/nitric acid mixtures, chromic acid, and others have been developed, catalytic dehydrogenation methods are more suitable on an industrial scale. A copper chromite catalyst is usually used to dehydrogenate isobomeol to camphor (171). Dehydrogenation has also been performed over catalysts such as zinc, indium, gallium, and thallium (172). 

Sorensen and co-workers799-801 have studied the fate of observable camphene hydrocation 190 prepared from isoborneol 187, camphene 188, or tricyclene 189 in HSO3F acid medium (Scheme 5.74). The intermediate cycloalkenyl cation 191 can also be prepared by protonation of a-terpineol (192), sabine (193), and /3-pinene (194) (Scheme 5.75). 

Terpenes are a class of naturally occurring olefins found in many plants. They are biosynthetically derived from isoprene, CsHg, and therefore consist of Cs-building blocks and are found in both cyclic and acyclic forms. An important subgroup is the monoterpenes, which consist of two isoprene units and are of the molecular formula Ci0H16. Of the monocyclic monoterpenes, by far the most industrially relevant is limonene, which is abundantly present as a fragrance in various household products. From the bicyclic monoterpenes, a-pinene, p-pinene, camphene, and carene are of industrial relevance and are also mostly used in the fragrance industry [44]. 

Borneol, camphene, and a-pinene are made in nature from geranyl pyrophosphate. The biosynthesis of a-pinene and the related camphor is described in the chapter. In the laboratory bornyl chloride and camphene can be made from a-pinene by the reactions described below. Give mechanisms for these reactions and say whether you consider them to be biomimetic. 

Manganese(m) acetate oxidation (cf. Vol. 3, p. 34) of camphene gives (186) as a 95 5 mixture by carboxymethyl radical insertion no rearranged products were obtained, in contrast to /3-pinene which gave Wagner-Meerwein products only, and no free-radical insertion.279 The E- and Z-isomers of (187) probably result from a non-concerted biradical intermediate formed by benzyne addition to camphene.280 Benzyl-lithium adds to the aminocamphor (188) exclusively from the exo-side whereas only the competing enolization reaction occurs with more sterically hindered organometallics.281... 

Fig. II Selected experimental and calculated results for the temperature dependence of the optical rotation at 365 nm. Top-. Fenchone. Center a-Pinene. Bottom Camphene. Data to prepare the plots were taken from [125] (experimental data were from Wiberg et al., J. Phys. Chem. A (2005), 109 3405)...

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