Patents

The invention related to the synthesis of menthol from citronellal rich essential oils. The common citronellal rich essential oils such as citronella oil and eucalyptus oil fetched low price due to their limited application in the house-hold products. Now, the invention claim is related to an eco-friendly process for the selective conversion of citronellal compound of these essential oils to menthol without affecting the other major compounds in a two step reaction. In this process, the high value menthol is obtained and further it can purify using column chromatography or fractional distillation. Alternatively, the menthol rich essential oil is slowly freezing to obtain menthol crystal. Besides, we claim new catalysts such as -zeolite-Boric acid-AlCl3 or -zeolite-Boric acid-Al or -zeolite-Boric acid-AlCl3 or -Na-zeolite-Boric acid-AlCl3 or Ag-zeolite-Boric acid-AlCl3 or -zeolite-Boric acid-SnCl2 or -zeolite-Boric acid-SnCl2 or -Na-zeolite-Boric acid-SnCl2 or Ag-zeolite-Boric acid-SnCl2. All these catalysts are prepared easily through impregnation method, and these are effective in the conversion of the citronellal to isopulegol. Similarly, the syntheses of reduced metals (1%Pd or 1%Ru) in activated charcoal or graphene re prepared. These synthesized metal catalysts are effective for conversion of isopulegol to menthol under external hydrogen ressure (~10 psi). This reduction is equally efficient using metal catalysts with catalytic amounts of alkali or alkaline earth etal hydrides without external hydrogen pressure. Finally, L-menthol is enriched through esterification of menthol nantiomers followed by hydrolysis.