From Turpentine to (−)‐Menthol: A New Approach

Renewable 3-carene, which can be obtained from the pulp and paper industrial waste crude sulfate turpentine, is successfully transformed to the aroma compound menthol, utilizing a new, four-step synthesis route. Heterogeneous hydrogenation, solid acid catalysis, and phase transfer catalysis are utilized under organic solvent-free conditions, with hydrogen and hydrogen peroxide as the only stoichiometric reagents.

The rising popularity of (−)-menthol, as the main component of the natural mint aroma with applications in the pharmaceuticals, cosmetics, and food industries leads to a growing need for synthetic menthol production to satisfy the world demand. In this study, a novel green synthesis route for menthol is presented. The proposed method utilizes renewable starting materials and employs environmentally benign reaction conditions, making it an attractive alternative to conventional menthol synthesis methods. The starting material, 3-carene, which can be obtained by distillation from crude sulfate turpentine, is transformed via heterogeneous hydrogenation and heterogeneous acidic isomerization to a mixture of unsaturated menthenes. The catalytic epoxidation of the menthenes with hydrogen peroxide and hydrogenation of the epoxides leads to a mixture of menthol isomers, which can be separated and recycled by established methods to obtain the desired (−)-menthol.

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