Menthol, decomposition

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). 

According to Read and Smith i piperitone is, under natural conditions, optically inactive. By fractional distillation under reduced pressure, it is prepared, by means of its sodium bisulphite compound, in a laavo-rotatory form. The slight laevo-rotation is probably due to the presence of traces of cryptal. By fractional distillation alone, it is usually obtained in a laevo-rotatory form whether this is due to decomposition products or not is unknown. Piperitone has a considerable prospective economic value, as it forms thymol by treatment with formic chloride, inactive menthone by reduction when a nickel catalyst is employed, and inactive menthol by further reduction. Its char-Mters are as follows —... 

Fig. 20 MIKE/CID spectra of the substituted m/z228 ions from the enantiomers of menthol ((7/ ,25,5R)-(— )-14 (A) and (75,27 ,55)-(+)-14 (B)) formed under CE(5)-2-amino-l-butanol (As) conditions (the m/z2 0 and mlz90 daugther ions are also produced during unimolecular decomposition of the m/z228 ions) (reprinted from ref. 472, with permission from Elsevier).

CjHjCljOj Noncombustible solid. Reacts with strong bases, amines, amides, inorganic hydroxides alkalis, alkaline earth metals alkali carbonates ammoniacal silver nitrate strong oxidizers soluble barbiturates producing chloroform and formate. Incompatible with camphor, menthol, or thymol. Contact with hydroxylamine produces poisonous hydrogen cyanide gas. Attacks metals in the presence of moisture. In heat of decomposition or fire, releases hydrogen chloride and other toxic fumes. 

In 1938 Stankiewicz reproduced the asymmetric 2-butanol decomposition experiments of Schwab (1932) at a higher temperature and atmospheric pressure and extended studies to the asymmetric decomposition of racemic menthol and 3-methylheptan-3-ol. Over a Cu-r/-quartz catalyst the latter substrate produced a maximal optical rotation of -0.26° and the decomposition of 2-butanol gave a reaction mixture with a rotation of +0.25°. 

Decomposition studies of racemic menthol and 3-methylheptan-3-ol gave similar results (Scheme 2.2.). Thus dehydration of racemic menthol over Cu-/-quartz in a flowing N2-air mixture at 430-460°C results in a product with a rotation of -0.16°, which indicated preferential decomposition of the (+)-enantiomer of menthol. The same picture was obtained, but to a somewhat greater extent, for the dehydrogenation of 3-methylheptan-3-ol on Cu-/-quartz in which the (+)-enantiomer reacted and the product exhibited a rotation of -0.12°. 

Craig and coworkers have reported stereocontrolled polyol synthesis via C-H insertion reactions of silicon-tethered diazoacetates.7 Menthol was treated with diisopropylsilyl bis(trifiuoro-methanesulfonate) and the product was condensed with ethyl diazoacetate to provide the precursor 43 to the C-H insertion reaction (eq 10). The rhodium(II) octanoate-catalyzed decomposition of the diazoacetate 43 gave siloxane 44 as a single stereoisomer. Reduction of the ester, followed by oxidative cleavage of the C-Si bond, gave the desired polyol 46 in 30% yield, along with the elim-... 

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