Of borneol

Present in citronella and valerian oils, tur penline, ginger, rosemary and spike oils. It is produced artificially by the elimination of hydrogen chloride from bornyl chloride (artifi cial camphor) or from isobornyl chloride, by the dehydrogenation of borneol and isobor-neol and by the action of elhanoic anhydride on bornylamine. Chiral. 

The structure of the bicychc monoterpene borneol is shown in Figure 26 7 Isoborneol a stereoisomer of borneol can be prepared in the labora tory by a two step sequence In the first step borneol is oxidized to camphor by treatment with chromic acid In the second step camphor is reduced with sodium borohydride to a mixture of 85% isoborneol and 15% borneol On the basis of these transformations deduce structural formulas for isoborneol and camphor... 

Thin-Layer Chromatography TLC) The function of TLC in organic synthesis is primarily one of allowing the experimenter to follow the progress of the reaction without actually interrupting the reaction. Since successful TLC can be carried out on a minute scale, only a very small fraction of the reaction mixture need be withdrawn and subjected to analysis. The following example of the TLC analysis of the chromic acid oxidation of borneol, described by Davis (3), is a useful model. 

The acc-tie c.-tur of eraniol is more yi odounned ui the leaf oils than is that of borneol. and it couiiciai .- to meriiasii io the several tuember.a leseclion, until a maximum of OTri 00 rr ( / ni. is reached tn ibe... 

The oil was found to conlain about 6 per cent, of piuene, 60 per cent-Of euoalyptol, 9 per cent, of borneol, 19 per ceul. of linalyl acetate, with a little camphor, meth. i salicylate, and sesqnitci-pene alcohol. 

Bornyl Acetate.—The acetic acid ester is the most important of the series. It is a constituent of pine-needle and rosemary oils, and has a most fragrant and refreshing odour. It is prepared artificially by the action of acetic anhydride on borneol, in the presence of sodium acetate, or by the condensation of borneol with glacial acetic acid in the presence of a small amount of a mineral acid. It is absolutely necessary in the reproduction of any pine odour. It is a crystalline body, crystallising from peDroleum ether in rhombic hemihedric crystals melting at 29°. The optical activity depends on that of the borneol from which it has been prepared. It has the following characters —... 

Bomyl Butyrate.—The next higher ester, of borneol is the butyrate. It is a similar camphoraceous ester, having the formula... 

Bornyl Propionate.—The propionic acid ester of borneol closely resembles the acetic ester, but as is, of course, usual in homologous series, its odour is slightly different. It has the formula... 

Camphor, Cj HjgO, occurs in the wood of the camphor tree Laurus camphora) as dextro-camphor. This is the ordinary camphor of commerce, known as Japan camphor, whilst the less common laevo-camphor is found in the oil of Matricaria parthenium. Camphor can also be obtained by the oxidation of borneol or isoborneol with nitric acid. Camphor may be prepared from turpentine in numerous ways, and there are many patents existing for its artificial preparation. Artificial camphor, however, does not appear to be able to compete commercially with the natural product. Amongst the methods may be enumerated the following —... 

N-Hydroxyphthalimide A-Hydroxyphth-alimide (NHPI) was shown to be a mediator for the electrochemical oxidation of (1) to (2) (Eq. 6) [57, 58], although the yields of (2) were not always satisfactory. A large deuterium isotope effect ( h/ d = 10.6) was observed in the oxidation of benzhydrol [59]. Recently, tetrafluoro-NHPI was found to be efficient for the oxidation of borneol [60]. 

Kreis R Juchelka D, Motz C, Mosandl A, Chiral compounds in essential oils, DC Stereodifferentiation of borneol, iso-borneol and bornyl acetate, Dtsch Apoth Ztg, 131 198 1987, 1991. 

Bornyl acetate [5655-61-8] is a characteristic component of most conifer oils. It has a camphoraceous, pine-needle-like odor. Both (+)-bornyl acetate [20347-65-3] and (-)-bornyl acetate form colorless crystals the racemate [36386-52-4 ] is a colorless liquid. Bomyl acetate is prepared by esterification of borneol with acetic anhydride or via the process described under borneol (see p. 59). 

SCHEME 122. Selective oxidation of borneols and menthols with immobilized Mo catalysts and TBHP... 

A slightly modified procedure - oxidation with 100 per cent excess of chromic acid at 0 °C for a short period - is adopted for strained bicyclic alcohols (e.g. the oxidation of ( —)-borneol to ( —)-camphor, Expt 5.87) and gives excellent yields of the corresponding ketones. Cycle ketones which are susceptible to acid-catalysed epimerisation are moreover obtained by this procedure in a high degree of epimeric purity. 

Unless otherwise stated, all the conversions are quantitative. rfThe oxidation was performed on a 80/20 mixture of borneol and iso-borneol. The oxidation was effected on a 30/70 mixture of axial and equatorial isomers. The conversion amounted to 95% in this case. 

Ravid, U., Putievsky, E. and Katzir, I. (1 996) Sterochemical analysis of borneol in essential oils using permethylated P-cyclodextrin as a chiral stationary phase. Flavour and Fragrance Journal 11, 1 91-1 95. 

Tishchenko (79), using a modified form of Raney nickel, obtained a 95.7 % yield of camphor from the dehydrogenation of borneol. Rutovskii, (80) received a 93.5% yield of camphor with Raney alloy. Reeves and Adkins (81), studying the dehydrogenation of primary alcohols, removed the hydrogen with ethylene. It was found that, though Raney nickel could be used for a catalyst for the reaction, the yields were low and, in general, the Raney nickel was inferior to a catalyst composed of copper, zinc, nickel, and barium chromite. 

Metal-ammonia reduction of bicyclo[2,2,l]heptanones has been examined by Coulombeau and Rassat, who point out that the conformationally more stable forms of substituted alcohols are the exo-isomers in the case of norbornan-2-ol and the 1-methyl homologue, but the endo-isomers in the case of borneol (1,7,7-trimethyl) and fenchol (1,3,3-trimethyl). The same authors have also examined the reduction of camphorquinone [2,3-dioxo-bornane, (249)] with... 

Bicyclic cyclopropyl compounds are anodically dimethoxylated to give stereoisomeric cis and trans) cyclopropane ring-opened products, as in Eq. (48) [322]. Shono and coworkers [323] reported a different type of ring-opening reaction of a cyclobutyl compound through anodic methoxylation. They also found that anodic oxidation of borneol and isoborneol in methanol resulted in a rearrangement to provide methoxylated stereoisomeric products with the same endo-exo ratio, as in Eq. (49) [324] ... 

Meerwein, H. Pinacolin rearrangement. III. Mechanism of the transformation of borneol into camphene. Ann. 1914,405,129-175. 

Chlorohydroboration-oxidation of camphene yields a 3 1 endo exo mixture of (185 X = CH20H), and bornylene is converted into a mixture of borneols and epiborneols, the -isomers predominating in each case. ... 

An efficient route to 7-oxocamphene involved as its key step the solvolytic rearrangement of 3,3-ethylenedioxyisobomyl tosylate (derived from camphor-quinone).621 Brief (3 min 0 °C) treatment (PCl5-CaC03) of borneol gave excellent yields of camphene hydrochloride longer reaction times gave bornyl chlorides.522... 

Bomeol (12), on the other hand, undergoes exchange at a much smaller rate (of the order of about 106 times slower) (see Table 1) under identical experimental conditions but undergoes racemization and decomposition at the same time. The rate of heterolysis of borneol is about the same as that estimated for s-butyl alcohol under the same conditions. A detailed explanation of the differences in rate of exchange in bicyclic alcohols requires considerable further work. 

Amination of borneol with ammonia over an Fe-, Cu- and Al203-containing catalyst afforded bornylamines mainly as endo isomers (Scheme 4) [11]. 

H. Firouzabadi and E. Ghaderi, Tetrahedron Letters, 1978, 839 the borneols [a mixture of (+)-borneol and (—)-isoborneol was used] and camphor each lack the C-10 methyl group in this paper. 

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