Menthyl benzoate

C10H20O 2276-57-5) see Paroxetine (+)-menthyl benzoate (C17H24O2 38649-18-2) see (-)-Menthol ( )-mepromazine... 

The enantioselective hydrolysis of racemic menthyl benzoate (industrially key compound) by recombinant Candida rugosa lipase LIPl leads to optically pure l-(-)-menthol ee>99% [21]. This pathway is part of a menthol synthesis developed by the flavour industry. 

The effects of polar substituents on the alkaline hydrolysis of esters are well-established. Since the rate of the reaction is determined largely by the rate of addition of hydroxide ion to the carbonyl group of the ester, any substituent which withdraws electrons from the carbonyl group will increase the reactivity of the ester. The most accessible quantitative measure of the effect is the Hammett or Taft reaction constant, and a large number of measurements are available. Taft et al.2i0 found p = 2.53 for the base-catalyzed methanolysis of meta- and para-substituted (/)-menthyl benzoates, closely similar to the known value of p = 2.37 for the alkaline hydrolysis of substituted ethyl benzoates. Jones and Sloane s value239, obtained with five esters, of p = 2.41 for the methoxyl exchange reaction of substituted methyl benzoates in methanol, is almost identical. 

J. Fleischer, K. Bauer, and R. Hopp, Resolution of DL-menthyl benzoates,... 

Fig. 1. The relationship between log (k/k ) for the methanolysis of J-menthyl benzoates with methoxide in methanol and the Hammett a-constants.

Figure 25 Lipase-catalyzed enantioselective hydrolysis of dZ-menthyl benzoate (dl-41).

Vorlova, S. Bomscheuer, U. T. Gatfield, I. Hilmer, J-M. Bertram, H-J. Schmid, R. D. Enantioselective hydrolysis of d,l-menthyl benzoate to /-(-)-menthol by recombinant Candida rugosa lipase LIP1. Adv. Synth. Catal. 2002, 10, 344. 

Photoisomerization of (Z)-l-methylcyclo-octene 59aZ sensitized by chiral benzene(poly)carboxylates suffers significantly from steric effects. The photosensitization of 59aZ with bulky sensitizers leads to photostationary E/Z ratios and product ee s much lower than those obtained for less-hindered (Z)-cyclo-octene 38Z [158]. Enantiodifferentiating photoisomeri-zations of (Z,Z)-l,3-cyclo-octadiene and (Z,Z)-l,5-cyclo-octadiene (71Z and 78Z) have also been studied by using chiral benzene(poly)carboxylates at various temperatures [159]. Photosensitization of 71Z with hexa-(—)-menthyl benzenehexacarboxylate affords the (E,Z)-product 71E in 18% ee in pentane at —40 °C. In the photoisomerization of 78Z in pentane sensitized by (—)-menthyl benzoate, the (—j- Zj-isomer 78E is only slightly favored giving a 2% ee [126]. 

Figure 6.17.2 Symrise process for menthol production Hydrogenation of thymol leads to a mixture of ( )-menthol, ( )-isomenthol, and ( )-neomenthol. Thereafter, ( )-menthol is separated by rectification and converted by esterification with methyl benzoate C6H5COOCH3) into ( )-menthyl benzoate and methanol.

Finally, —)-menthyl benzoate is separated by crystallization, and the final product (—)-menthol is obtained by the reverse reaction, that is, by hydrolysis with methanol. The (-F)-menthol benzoate is also hydrolyzed, and the resulting (+)-menthol is converted into a racemic mixture of all menthol isomers. This mixture is combined with the iso- and neomenthol separated by rectification and used as feed for the epimerization. 

Taft, R., Newman, M. and Verhoek, R (1950). The Kinetics of the Base-Catalyzed Methanoly-sis of Ortho-Substituted, Meta-Substituted and Para-Substituted L-Menthyl Benzoates, J. Am. Chem. Soc., 72, pp. 4511-4519. 

Biochemical methods for the resolution of menthol are now being developed. Symrise have patented a method for the selective hydrolysis of Candida rugosa, will hydrolyze the benzoate of /-menthol, but not that of separated without recourse to fractional crystallization. Takasago developed a similar process somewhat earlier (200). 

Enantiodifferentiating photoisomerization of (Z,Z)-l,3-cyclooctadiene (60ZZ) is sensitized by chiral benzene(poly)carboxylates." Upon sensitization with hexa-(-)-menthylbenzenehexacarboxylate in pentane at -40°C, the ( ,Z)-isomer (60EZ) is obtained in 18% ee. Photoisomerization of (Z,Z)-l,5-cyclooc-tadiene (69ZZ) sensitized by (-)-menthyl benzoate affords (-)-( ,Z)-isomer (69EZ) in only 1.6% eei ... 

Menthyl benzoate (-)-Menthyl benzoate Di- (-) -menthyl phthalate Di-(-)-menthyl phthalate Di- (-) -menthyl terephthalate... 

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