Dementholized oils, menthone from

Menthol from Dementholized Cornmint Oil. Dementholized cornmint oil, from which (-)-menthol has been removed by crystallization and which still contains 40-50% free menthol, can be reused for producing (-)-menthol. The fairly large quantity of (-)-menthone in the oil (30-50%) is hydrogenated to form a mixture of mainly (-)-menthol and (+)-neomenthol the (-)-menthyl esters present (chiefly (-)-menthyl acetate) are saponified. Additional (—)-menthol is then separated from other components by crystallization, distillation, or via the boric acid esters. 

Natural menthol is obtained by freezing the essential oil, eg, Mentha arvensis, and the menthol crystals are separated by centrifuging the supernatant liquid away from the crystals. The supernatant oil is then called dementholized commint oil. Impurities in the crystals come from the essential oil and usually give a slight peppermint aroma to the crystallized menthol. The commint oil, rich in (—)-menthone ( 28%) and (—)-menthol ( - 32%), can be further... 

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