Of citronellol

The typical plant which was selected for investigation in the case of the geraniol compounds was the ordinary geranium. The principal alcohol present in this oil is geraniol, Cj HjgO, and this is accompanied by a smaller amount of citronellol, CjoH gO. A ketone, menthone, is also present. 

Up till about three years ago, there appeared to be little reason to doubt that rhodinol was in fact an impure form of citronellol, the reduction product of citroneUal being dextro-citronellol, whilst the natural alcohol, which the French chemists had termed rhodinol was considered to be laevo-citronellol. 

Further evidence of the difference between rhodinol and citronellol is forthcoming, in that the former yields on oxidation an aldehyde, rhodinal, whose oxime does not yield citronellic acid nitrile when treated with acetic anhydride, nor citronellic acid when the nitrile is treated with alkalis, wheras citronellal, the aldehyde of citronellol, does yield the nitrile and citronellic acid. 

Harries and Comberg have also supplied much evidence, which, taken with the above-mentioned researches, places the chemical isomerism of citronellol and rhodinol practically beyond dispute. By ozonisation experiments decomposition products were obtained, which proved that natural citronellal, obtained from citronella oil, is a mixture of about... 

No aldehyde or ketone has been obtained from it by oxidation. Its constitution is probably allied to those of citronellol and rhodinol, but, since it contains an asymmetric carbon atom, as shown by its optical activity, the three formulae given under bupleurol obviously cannot represent androl. 

Citronellyl Acetate.—The odour of the acetic ester of citronellol recalls to some extent that of hergamot. It is a natural constituent of geranium oil, and is useful in small amounts for blending with rose and geranium odours. It is prepared hy the action of acetic anhydride on citronellol. When pure it has the following characters —... 

It can be prepared artificially by the reduction of citronellol, CjoH jO, and the isomeric rhodinal can, according to Bouveamt, be prepared by the reduction of rhodinal from oil of rosfe. 

To 10 c.c. of the oil (otto of rose or rose-geranium oil) 10 c.c. of formic acid 100 per cent, (specific gravity 1 22) is added, and the mixture gently boiled under a reflux condenser for one hour. The mixture is cooled, 100 c.c. of water added, and the whole transferred to a separator. The aqueous layer is rejected, and the oil washed with successive quantities of water as in the acetylation process. The formylated oil is dried with anhydrous sodium sulphate, and about 2 grams neutralised and saponified with alcoholic potash in the usual manner. The percentage of citronellol is then calculated from the following formula —... 

Bioassay of alternate molecular forms supports the view that the ORs are capable of resolving isomeric distinctions in neutral (non-biological) odourants. Stereochemical pairs of odours were tested for differential sensitivities in the blind subterranean mole rat (Spalax ehrenbergi). The subjects responded to one enantiomer, but not to its stereoisomer. Both sexes were attracted to the odour of R-(-)-carvone but unresponsive to S-(+)-carvone in contrast, males and females were repelled by the odour of (+)-citronellol, but not by (-)-citronellol (Heth et al., 1992). The lack of responsiveness by mole rats could be central due to lack of salience, or peripheral due to hyposmia/anosmia for one isomer. Both carvones have distinct odours for the human nose. 

The hydrogenation of geraniol over Cu/A1203 in hydrocarbon solvents gives mixtures of citronellol 2 and menthol 3. 

It was observed that no leaching of Ti occurs during the catalytic reaction in the anhydrous medium. The acidity of the catalysts (which gave rise to many side products) was evaluated by a comparison of their reaction rates in the acid-catalyzed conversion of citronellol into isopulegol (Scheme 7). The acidity of the catalysts decreased in the following order A>C>D>B = E. The catalytic activity and epoxidation selectivities are compared in Table XIII. 

Enantioselectivity is very dependent on hydrogen pressure. Optical purities of citronellol products are 70% and 95% at 4 and 30 atm, respectively. Thus, hydrogen pressure greater than 90 atm is required for high optical yields. 

Gas chromatographic analysis indicates that this consists of 97-99% of citronellol and 1-3% of dihydrocitronellol column, SHIMADZU HiCap-CBP20, 25 m x 0.2-mm fused silica column temperature, 140°C injection temperature 160°C helium pressure as carrier gas, 1.0 kg/cm2 tR of geraniol, citronellol, and dihydrocitronellol are 16.2,13.7, and 8.6 min, respectively. 

A second nonselective synthesis involved chain extension of the tosylate of ( )-citronellol (82) with 2-methylpentyl magnesium bromide and lithium tetrachlorocuprate catalysis to give the carbon skeleton 83 (Scheme 12A) [92]. Allylic oxidation with Se02 and ferf-butylhydroperoxide, hydrogenation of the... 

Stereospecific syntheses of the eight stereoisomers [94] used a variation of the methodology developed in Mori s previous synthesis of the stereoisomers of 6,10,13-trimethyltetradecanol (see Scheme 5) [91], using chiral synthons derived from commercially available enantiomers of citronellol and methyl 3-hydroxy-2-methylpropanoate, and the iterative series of steps outlined in Scheme 13A for one of the stereoisomers [94]. A key step involved moving the... 

The unusual system franx-RulOl lTMPl/N OllO atm)/fluorobenzene epoxidised linear alkenes, cholesteryl acetate and the ferf-butyldimethylsilyl ether of citronellol [592] cholest-5-ene-3-one was oxidised to the 6a and 6p alcohols and the enedione by franx-RulOl lTMPl/OXCgH (Table 3.2) [593]. With ter-penes the 6,7-double bonds were selectively epoxidised by fran -Ru(0)2(TMP)/... 

The comparison of the olfactory properties of fluoro analogues of citronellol is a significant example (Fig. 1) [11,12]. While monofluorinated compound exhibit only minor changes in olfactory properties, this is quite different for trifluorocitro-nellol. In the absence of other factors envisioned, the important differences observed between citronellol and trifluorocitronellol are very likely due to a different recognition by the olfactory receptors, connected to the bigger size of the CF3 with respect to CH3 [10]. 

Comparison of the olfactory properties of the trifluoro analogue of citronellol is a significant example (Figure 3.1). While the mono-fluorinated analogues exhibit only... 

On the other hand, the terpene content was not consistently affected by MOX, the only differences being a higher initial level of citronellol in the Tempranillo wine, which disappeared after MLF, and more geraniol in the MOX Cabernet Sauvignon wine after 4 months, but this became lower after 8 months of aging. Some higher initial concentrations of ethyl... 

Uses. Nerol is used in perfumery not only for the same purposes as geraniol, e.g., in rose compositions, to which it lends a particular freshness, but also in other blossom compositions. In flavor work it is used for bouquetting citrus flavors. Technical-grade nerol, often in a mixture with geraniol, is used as an intermediate in the production of citronellol and citral. 

Citronellol is a colorless liquid with a sweet roselike odor. The odor of (-)-citronellol is more delicate than that of (+)-citronellol. 

Preparation of (—)-Citronellol from Optically Active Pinenes. (+)-ci5-Pinane is readily synthesized by hydrogenation of (+)-0 -pinene or (+)-/3-pinene, and is then pyrolyzed to give (+)-3,7-dimethyl-l,6-octadiene. This compound is converted into (-)-citronellol (97% purity) by reaction with triisobutylalumi-num or diisobutylaluminum hydride, followed by air oxidation and hydrolysis of the resulting aluminum alcoholate [50]. 

Synthesis from Citronellol. ( )-Citronellal can also be obtained by dehydrogenation of citronellol under reduced pressure with a copper chromite catalyst [64]. 

The composition of the Bourbon oil differs quantitatively as well as qualitatively from that of North African oil. However, they both contain an unusually high percentage of (-)-citronellol, isomenthone, formates, and tiglates, which are rarely found in essential oils. The two types of oil can be differentiated by two characteristic minor constituents the Bourbon type contains (-)-6,9-guaiadiene [36577-33-0] and the African type contains 10-e i-7-eudesmol [15051-81-7] see p. 167 [521-531b]. 

Citronellol is generally shipped in lined drums, deck tanks, or pails. U.S. production in 1993 was 1,7141 (67). The price of citronellol in drums in 1995 was 7.59/kg (45). The price varies according to quality and quantity purchased. 

Dehydrogenation of citronellol over a copper chromite catalyst produces citronellal [106-23-0] in good yield (110). If the dehydrogenation is done under distillation conditions in order to remove the lower boiling citronellal as it is formed, polymerization or cydization of citronellal is prevented. 

Synthetic methods for the production of citronellal include the catalytic dehydrogenation of citronellol (110), the telomerization of isoprene (151), and the lithium-catalyzed reaction of myrcene with secondary alkylamines (128). 

In sensitized or photocatalyzed reactions, conditions of total or constant absorbance can easily be controlled by the concentration of the sensitizer or photocatalyst added. In addition, experience has shown that the concept of spatial separation between the light source and the reaction mixture is in general not required. Dragoco uses immersion-type annular reactor geometries [2, 3, 69, 70] for the production of ( —)-rose oxide by rose bengal sensitized oxidation of (— )-citronellol (Eqs. 45-48, Figure 23). 

Figure 23. Synthesis of (—)-rose oxide by sensitized oxidation of (-)-citronellol [2, 3,81].

Fig. (4). Microbial degradation of citronellol, nerol and geraniol by Pseudomonas citronellolis (after [32])...

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