Menthol - and

Piperitone is of considerable technical im portance. It is a colourless oil of a pleasant peppermint-like smell. (-)-Piperilone has b.p. 109-5-110-5 C/I5mm. Piperitone yields thymol on oxidation with FeCl. On reduction with hydrogen in presence of a nickel catalyst it yields menthone. On reduction with sodium in alcoholic solution all forms of piperitone yield racemic menthols and womenthols together with some racemic a-phel)andrene. 

AH (A)-menthol is made by synthetic methods. One method involves the cyclization of (+)-citroneIlal (68). Using a mild acid catalyst, (+)-citroneIlal [2385-77-5] undergoes an ene-reaction to produce a mixture of isopulegols (142). Catalytic hydrogenation of the isopulegol mixture gives a mixture of menthol and its isomers. The (A)-menthol is obtained after efficient fractional distillation and the remaining isomers can be equilibrated, usually with sodium menthol ate or aluminum isopropoxide. An equilibrium mixture is obtained, comprised of 62 wt % (A)-menthol, 23 wt % (+)-neomenthol, 12 wt % (+)-isomenthol, and 3 wt % (+)-neoisomenthol. The equilibrium mixture can be distilled to recover additional (+)-mentbol. 

Active agents vary according to use. For controlling bad breath, 2iac salts, sodium lauryl sulfate, and flavors are used. To destroy oral microorganisms, chlorhexidine, cetylpyridinium chloride [123-03-5] and ben2alkonium chloride [68391-01-5] are valuable. Essential oils, such as thymol [89-83-8] eucalyptol [470-82-6] menthol, and methyl salicylate [119-36-8] reduce plaque-related gingivitis (see Oils, essential). Sodium fluoride aids ia caries coatrol. 

Fig 33 Differentiation of primary (citronellol), secondary (menthol) and tertiary alcohols (linalool) by in situ prechromatographic acetylation citronellol reacts completely, menthol partially and linalool not at all. 

Reduction of l-methyl-2-alkyl-.d -pyrroline and l-methyl-2-alkyl-.d -piperideine perchlorates with complex hydrides prepared in situ by partial decomposition of lithium aluminum hydride with the optically active alcohols (—)-menthol and (—)-borneol affords partially optically active l-methyl-2-alkyl pyrrolidines (153, n = 1) and 1-methy 1-2-alkyl piperideines (153, n = 2), respectively (241,242). 

Examine the two chair conformers of menthol, and label each substituent in each conformer as equatorial or axial. 

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 etfect of shade upon the pcppcrminl plant is to decreaae esterilieation and the Lormation of menthol, and i.s due possibly to the leasened activilv of the elimination of water by the plant. 

French oil of peppermint eontains. in addition to menthol and iia, isovaleric aldehyde, isoamyl alcohol, i-pinenc. A -p-monthcne aed... 

The principal conatiluent of the oil ia the ketone puloaonr, which, in very fine apecimena, may be present to the estent of over 90 per cent. Acoofdiiig to Tclry there ate aUo present Mimooene. dipentene, menthol, and iiicuthoiie. 

Comparing the undissolved essential oil with that which was dissolved in the waters, it is seen that the former is richer in esters, poorer in free menthol and total menthol, and richer in menthone than the second. In other words the relatively sparingly soluble constituents are esters and menthone, whilst menthol is particularly soluble. 

Isobutyl, isoamyl, and cinnamic alcohols, menthol and geraniol gave (-nitrobenzyl phthalates which were oily liquids and could not be ciystallised. 

It forms a characteristic benzoic ester, Cj HjgO. CO. CgH, melting at 54°. This is a useful compound for identifying menthol and may be obtained by heating menthol with the theoretical amount of benzoic acid, in a sealed tube to 170° excess of acid is removed by shaking with a boiling solution of sodium carbonate, and the ester is crystallised from alcohol. Menthol forms a phenylurethane, melting at 111° to 112°. 

The same menthol and neomenthol have also been obtained by the reduction of inactive menthone by means of hydrogen, in presence of uickel at 180° C. 

Draw the two chair conformations of menthol, and tell which is more stable. 

A similar but asymmetric variant of the reaction, involving the radical addition of alkyl iodides and trialkylboranes to chiral azirine esters derived from 8-phenyl-menthol and camphorsultam, in the presence of a Cu(i) catalyst, has subsequently been reported [64]. The diastereoselectivity of the addition is variable (0-92% de)... 

Explain how this enzyme may be used to resolve a racemic mixture of DL-menthol. Assume you want to prepare both D-menthol and L-menthol. 

Chiral alcohols have also been used in an asymmetric synthesis of sulphoxides based on halogenation of sulphides. Johnson and coworkers have found319 that the reaction of benzyl p-tolyl sulphide with JV-chlorobenzotriazole (NCBT) followed by addition of (—) menthol and silver tetrafluoroborate afforded diastereoisomeric menthoxysulphonium salts 267 which, upon recrystallization and hydrolysis, gave benzyl p-tolyl sulphoxide with 87% optical purity (equation 145). More recently, Oae and coworkers reported320 that optically active diaryl sulphoxides (e.e. up to 20%) were formed either by hydrolysis or thermolysis of the corresponding diaryl menthoxysulphonium salts prepared in situ from diaryl sulphides using ( —) menthol and t-butyl hypochlorite. 

A chiral version of this [4+3] heterocyclisation was achieved using chiral, non-racemic carbene complexes derived from menthol and oximes as depicted... 

Liquids with high vapor pressures at ordinary temperatures are said to be volatile. Methanol (vapor pressure 98 Torr at 20°C) is highly volatile mercury (1.4 mTorr) is not. Solids also exert a vapor pressure, but their vapor pressures are usually much lower than those of liquids because the molecules arc gripped more tightly in a solid than they are in a liquid. Nevertheless, solids vaporize in the process called sublimation (Section 6.11), which we can observe in the presence of some pungent solids—such as menthol and mothballs. 

Foss S, J Harder (1998) Thauera linaloolentis sp. nov. and Thauera terpenica sp. nov., isolated on oxygen-containing monoterpenes (linalool, menthol, and eucalyptol) and nitrate. System Appl Microbiol 21 365-373. 

Menthol and camphor have caused respiratory distress in infants and should not be used in children under 2 years of age. Despite limits on the concentration of available products, camphor can be toxic to children even in small amounts.45 Patients should be advised to keep the products out of the reach of children. 

When the reaction is complete, the flask is removed from the oil bath and the cooled reaction mixture is transferred to a 5-1. separatory funnel and extracted with three 1-1. portions of water (Note 6). The water extract is carefully acidified with 20 per cent hydrochloric add, and the crude menthoxyacetic acid, which collects on top as a brown oil, is extracted with three 200-cc. portions of benzene. The benzene extracts aip combined, and the solvent is removed by distillation on a steam cone. The residue is then fractionally distilled under reduced pressure. The fraction boiling bdow 100°/20 mm. is mainly water and toluene. The second fraction boiling at 100-115°/8-10 mm. is impure /-menthol and may be saved for redistillation (Note 6). The yield of /-menthoxyacetic acid, boiling at 134-137°/2 mm. (150-155°/4 nun-)) Md = —92.4°, amounts to 166-180 g. (78-84 per cent of the theoretical amount). 

Spectrophotometry has been used in the measurement of the dissociation constants of some weak acids using the color of the ion as an indicator. The dissociation constant of tris-(/>-nitrophenyl)-methane in ethanolic sodium ethoxide at 25° is 3.66 X 10-18.848 Another method makes use of the difference in optical rotation between menthol and sodium mentholate to find the position of the equilibrium 844... 

The peppermint oil gland secretory cell cDNA library has proven to provide a highly enriched source of candidate genes involved in essential oil biosynthesis. A functional genomics approach has successfully been employed to clone genes involved in the mevalonate-independent pathway of isoprenoid biosynthesis and in the peppermint-specific steps producing (-)-menthol and (-)-menthone. The optimization of LC-MS technology to profile phosphoiylated carbohydrates and... 

The degree of enantioselective bias was improved shortly after this time. In 1971, Morrison et al. reported that the rhodium(I) complex [RhCl(NMDPP)3] (NMDPP= neomethyldiphenylphosphine) reduces ( )-/ -methylcinnamic and ( )-a-methylcinnamic acids with 61 and 52% ee, respectively (Scheme 1.9) [41]. NMDPP is a monodentate phosphine derived from (-)-menthol, and its asymmetry lies at carbon atoms. 

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