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Summary of 3 production methods of menthol - Haihang Industry

Mar. 29, 2019
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Menthol can be used as a toothpaste, perfume, beverage flavorant, can also treat headache, nose, throat and other inflammation.

Menthol can be purified from natural mint crude oil or synthesized. If you need a small amount of menthol for household use, the following manufacturing methods will help you.


Historically, there are two methods to extract menthol or menthol oil: steam distillation and organic solvent extraction.

These two methods have great drawbacks. Firstly, the extraction efficiency of steam distillation is very low, and the organic solvent extraction method will produce the toxicity of residual organic solvents.

Now the industry uses supercritical carbon dioxide to extract menthol (menthol) from the mint. Menthol produced by this method can avoid the disadvantages of the above two methods. The yield is 5 x higher than that of steam distillation.

3 x higher than organic solvent extraction.

The product has good quality, high purity, no residual toxicity of solvents, and can maintain the pure natural characteristics.


Production of menthol from citronellal


By using the properties of citronellal which is easy to cyclize to iso-peppermint alcohol, right-citronellal was cyclized to L-iso-peppermint with acid catalyst (such as silica gel). Levo-iso-peppermint was separated from citronellal and hydrogenated to L-peppermint. Its stereoisomers can be partially converted into dextrocitronellal by pyrolysis and recycled.


Production of menthol with thymol


In the presence of m-cresol aluminum, thymol was synthesized by alkylation of m-cresol.

All four pairs of stereoisomers of menthol (racemic menthol; racemic menthol; racemic isomenthol and racemic isomenthol) were obtained by catalytic hydrogenation.

Four pairs of menthol stereoisomers were distilled, racemic menthol was distilled and separated, then esterified and recrystallized repeatedly, and the isomers were separated and optically separated. Menthol was obtained from levomenthol ester after saponification.

Racementhol can be separated from the other three pairs of isomers by distillation. The remaining mixture of isomers can be balanced to racemic menthol, racemic menthol and racemic isomenthol in the ratio of 6:3:1 under thymol hydrogenation condition.

The content of new menthol is very low, but not counted. Racementhol can be separated from the mixture. Racementhol is crystallized by inoculating levo-ester with benzoate saturated solution or its supercooled mixture.

Pure L-menthol was obtained by saponification after separation.

No dextral menthol and other isomers can be converted into racemic menthol according to the equilibrium of hydrogenation conditions.


Making Menthol from Menthol Oil

The mint oil was frozen and crystallized. The crystallization obtained by centrifugation was recrystallized with low boiling solvent to obtain pure L-menthol. After removing the crystallization, the mother liquor still contains 40%-50% menthol, and a large amount of menthol, which is hydrogenated into a mixture of levomenthol and dextral neomenthol. More L-menthol can be obtained by partial saponification of esters, crystallization, distillation or preparation of borate esters and separation of other parts of menthol oil.


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