Laevo-menthol

Natural menthol is laevo-rotatory. The reduction of both laevo-menthone and dextro-menthone yields a mixture in which laevo-menthol predominates. The constitution of menthol is as follows —... 

Four isomeric menthones may exist, with eight corresponding isomeric menthols (vide supra). But whichever menthone is converted into menthol, natural laevo-menthol is the predominating resulting compound. 

LefSngwell, J-C. Shakelford, R-E. Laevo menthol synthesis and organoleptric properties. Cosmetic and perfumery 1974, 89 (6), 69-89. 

Menthol is natural laevo-menthol, obtained from the volatile oils of various species of Mentha (Labiatae), or synthetic laevo-menthol, or racemic menthol. 

Leffingwell, J.C. and Shackelford, R.E. (1974) Laevo-menthol. Syntheses and organoleptic properties. Cosmetics Perfumery, 89, 69-78. 

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 —... 

Japanese.—Specific gravity at 25° C., 0 895-0 900 optical rotation, laevo-rotatory up to 43° solidifies at 17 to 27° 0. total menthol, 70-90 per cent., of which 65-85 per cent, is free soluble in 3-5 volumes of 70 per cent, alcohol. 

Muckiger and Power isolated two laevo-rotatory terpenes from English peppermint oil, but their purity is doubtful. It is probable that they were mixtures of pinene, phellai rene, and limonene. A dextrorotatory sesquiterpene.(cadinene ) is also psresent, as well as menthone,. and menthol, both in the free state and as acetate and isovalerianate. 

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