Menthol determination

Assay for Total Menthol Determine as directed under Total Alcohols, Appendix VI, using 2.5 g of acetylated sample. Calculate the percentage of total menthol by the formula... 

Human perception creates difficulty ia the characterization of flavor people often, if not always, perceive flavors differently due to both psychological and physiological factors. For example, certain aryl thiocarbamates, eg, phenylthiocarbamide, taste exceedingly bitter to some people and are almost tasteless to others (5). This difference is genetically determined, and the frequency of its occurrence differs from one population to another 40% of U.S. Caucasians are nontasters, whereas only 3% of the Korean population caimot perceive the strong bitter taste of the aryl thiocarbamates (6). Similar differences were found ia the sense of smell for compounds such as menthol, carvone, and ethyl butyrate (7). 

CO2 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (/ )-"y-decalactone, they were able to determine the correct ratios, with relatively little sample preparation. The technical... 

The interest in asymmetric synthesis that began at the end of the 1970s did not ignore the dihydroxylation reaction. The stoichiometric osmylation had always been more reliable than the catalytic version, and it was clear that this should be the appropriate starting point. Criegee had shown that amines, pyridine in particular, accelerated the rate of the stoichiometric dihydroxylation, so it was understandable that the first attempt at nonenzymatic asymmetric dihydroxylation was to utilize a chiral, enantiomerically pure pyridine and determine if this induced asymmetry in the diol. This principle was verified by Sharpless (Scheme 7).20 The pyridine 25, derived from menthol, induced ee s of 3-18% in the dihydroxylation of /rcms-stilbene (23). Nonetheless, the ee s were too low and clearly had to be improved. 

IR spectroscopy of two supports was used for the determination of their surface acidity. The presence of Lewis acid sites on the surface of sepiolite allowed the preparation of a catalyst able to transform citral into menthol in fairly good yield under veiy mild conditions (90°C, 1 barH2). 

Determination of the acidic sites through IR spectroscopy of adsorbed CO is a valuable tool for the choice of the support when selective or multifunctional processes are to be set up. This technique allowed to identify a particular kind of silica as the support of choice for the selective hydrogenation of citral to citronellal and sepiolite as a Lewis acid support able to promote the one-step transformation of citral into menthol. 

By this method, for example, the absolute configurations of the following compounds were established (-)-2-phenylbutyric acid,[48] (-)-hydratropic acid,[48] (+)-0-acetyl-mandelic acid,t48] (-)-2-(7/-carbazolyl)propionic acid,t48] (+)-1 -phenylethanol,[48] (-)-menthol,t48] (+)-1 -phenylethylamine,[48] and 1-alanine ethylester.[48] The determination of the absolute configuration of bacteriochlorophylles c, d and e was made possible by the esterification of the phaeophorbides by CDI to imidazolides.[49]... 

Brimble and coworkers172 reported the asymmetric Diels-Alder reactions between quinones 265 bearing a menthol chiral auxiliary and cyclopentadiene (equation 73). When zinc dichloride or zinc dibromide was employed as the Lewis acid catalyst, the reaction proceeded with complete endo selectivity, but with only moderate diastereofacial selectivity affording 3 1 and 2 1 mixtures of 266 and 267 (dominant diastereomer unknown), respectively. The use of stronger Lewis acids, such as titanium tetrachloride, led to the formation of fragmentation products. Due to the inseparability of the two diastereomeric adducts, it proved impossible to determine which one had been formed in excess. 

In order to determine whether trans elimination may occur also in the removal of elements of water from alcohols, the dehydration of menthol... 

An early example of an MIP-QCM sensor was a glucose monitoring system by Malitesta et al. (1999). A glucose imprinted poly(o-phenylenediamine) polymer was electrosynthesized on the sensor surface. This QCM sensor showed selectivity for glucose over other compounds such as ascorbic acid, paracetamol, cysteine, and fructose at physiologically relevant millimolar concentrations. A unique QCM sensor for detection of yeast was reported by Dickert and coworkers (Dickert et al. 2001 Dickert and Hayden 2002). Yeast cells were imprinted in a sol-gel matrix on the surface of the transducer. The MIP-coated sensor was able to measure yeast cell concentrations in situ and in complex media. A QCM sensor coated with a thin permeable MIP film was developed for the determination of L-menthol in the liquid phase (Percival et al. 2001). The MIP-QCM sensor displayed good selectivity and good sensitivity with a detection limit of 200 ppb (Fig. 15.7). The sensor also displayed excellent enantioselectivity and was able to easily differentiate the l- and D-enantiomers of menthol. 

Determine the absolute configurations of the chiral centres in menthol and phenbutrazate. List the configurations of the pairs of enantiomeric diastereoisomers of menthol (Fig. 2.24). 

Besides thymol, other terpenes have been tested for their toxicity against Varroa jacobsoni. Imdorf et al. determined in vitro the effective miticidal air concentrations, but with minimal effects on the bees as follows 5-15 pg/litre air for thymol, 50-150 pg/litre for camphor and 20-60 pg/litre for menthol 1,8-cineole was too toxic for honey bees [86], Another interesting paper considered the efficacy of different isomers of menthol on Acarapis woodi [87]. The natural crystals obtained from the plant, synthetic crystals and the L-form gave more than 96% mite mortality, while the D-form crystals only a 37% mortality. 

Many essential oils contain esters (mostly acetates) of alcohols of the formulae C10HlsO (borneol, geraniol, terpineol, linalool), C H O (menthol, citronellol), C1SH240 (santalol). When boiled with alcoholic potash, these esters are hydrolysed (saponified) and yield the free alcohol and the potassium salt corresponding with the acid of the ester. Thus, the volatile oils containing esters have saponification numbers, which may be determined in a manner analogous to that used for fatty matters. 

Free Alcohols alone.—In this case the content in free alcohols (borneol, geraniol, terpineol, linalool, menthol, citronellol, santalol, thujyl alcohol) is determined by transforming the alcohols into the corresponding acetates by boiling with acetic anhydride and then determining the saponification number of the acetylated product acetyl saponification number). 

Fontes et al. (1998b) studied the enantioselectivity of cutinase and found that it was very selective toward one enantiomer with an enantiomeric excess of almost 100%. They found that the enantioselectivity was very sensitive to changes in water content. Bornscheuer et al. (1992) studied hydrolysis, esterification, and transesterification in carbon dioxide to try to find the best method for producing enantiomerically pure substances in carbon dioxide. They found that the thermodynamically favored hydrolysis led to higher enantiomeric excess with less enzyme in the shortest time. Michor et al. (1996b) also examined more than one system to determine a better route to product and found that while the transesterification of -menthol was fast and resulted in high enantiomeric excess, resolution of -citronellol was not feasible. The reaction rate for the reaction of -citronellol was 10-20 times of that of -menthol, but was not selective. 

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the 13C/12C ratio of the analyte is measured versus a C02 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (R)-y-decalactone, they were able to determine the correct 12C/13C ratios, with relatively little sample preparation. The technical details of multidimensional GC-isotope ratio MS have been described fully by Nitz et al. (29). A MDGC-IRMS separation of a natural ds-3-hexen-l-ol fraction is... 

Combined thermoanalytical (TA,TGA and DSC) investigations of DBTA complexes of chiral alcohols may serve valuable data on the composition and stabilities of these solid supramolecular compounds. DSC monitoring of menthol resolution with DBTA in melt has already discussed in point 3.4. Thermal stability of further ten complexes of DBTA with alcohols 26, 29-31, 35-37 and 39-41 was also determined. [47] The melting points of the DBTA complexes (Table 11) increase in the 2-alkanol, 2-alkoxycyclohexanol, 2-halogenocyclohexanol order. 

Ligor, M. and B. Buszewski. 1999. Determination of menthol and menthone and pharmaceutical products by solid-phase microextraction-gas-chromatography. J. Chromatogr. A 847 161-169. 

S. K. Pant, P. N. Gupta, K. M. Thomas, B. K. Maitin, and C. L. Jain, Simultaneous determination of camphor, menthol, methyl salicylate, and thymol in analgesic ointments by gas-liquid chromatography, LC-GC, 8 322. 

K. Nakajima and T. Yasuda, Simultaneous determination of 1-menthol, dl-camphor and methyl salicylate in pharmaceutical preparations for external application using headspace gas chromatography, Chiba-Ken Eisei Kenkyusho Kenkyu Haboku, 5 14-18 (1984). 

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