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A method for preparing optically pure L-menthol

A technology of menthol and isopulegol, which is applied in the field of preparing optically pure L-menthol, can solve the problems of low space-time efficiency, limited raw materials, high energy consumption, etc., and achieve high stability, high activity and stability, The effect of increasing lifespan

Active Publication Date: 2021-02-02
WANHUA CHEM GRP CO LTD +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The stereoselectivity of the asymmetric hydrogenation step of this method is not high, and the L-isopulegol with a certain optical purity needs to be purified by melting crystallization. The melting crystallization of this step has the disadvantages of high equipment investment, high energy consumption, and low space-time efficiency.
[0006] The existing technology of artificially synthesizing optically pure L-menthol has the disadvantages of limited raw materials, low stereoselectivity of the reaction, the need for melting crystallization to improve optical purity, high equipment investment, high energy consumption, and low space-time efficiency, making it difficult to achieve artificial synthesis Large-scale, low-cost, continuous and stable supply of L-menthol

Method used

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  • A method for preparing optically pure L-menthol
  • A method for preparing optically pure L-menthol
  • A method for preparing optically pure L-menthol

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0039]In an argon atmosphere, 31.2mg of bisphosphine ligand (1), 24.7mg [Rh(cod)Cl]2Dissolve in 15mL toluene, and transfer to a 50mL autoclave, add 15.22g racemic isopulegol (ee=0%, L-isopulegol / D-isopulegol=1:1 (mol)) Inject into the autoclave, pass hydrogen to replace the gas in the autoclave three times, and adjust the pressure to 50 bar. Turn on the stirring and react at 80°C for 10 hours. The conversion rate of L-isopulegol measured by gas chromatography is 99.9%. The product is L-menthol with an optical purity of 99ee%. The raw material is L-isopulegol. The yield of L-menthol based on alcohol was 99.8%.

Embodiment 2

[0041]In an argon atmosphere, 61.9mg bisphosphine ligand (1), 48.8mg[Rh(cod)Cl]2Dissolve in 15 mL of toluene, and transfer to a 50 mL autoclave, inject 15.22 g of L-isopulegol (ee=98%) into the autoclave, pass hydrogen to replace the gas in the autoclave for three times, and adjust the pressure to 50 bar. Turn on the stirring and react at 80°C for 10 hours. The conversion rate of L-isopulegol measured by gas chromatography is 99.9%. The product is L-menthol with an optical purity of 99ee%. The raw material is L-isopulegol. The yield of L-menthol based on alcohol was 99.8%.

Embodiment 3-9

[0043]In an argon atmosphere, 0.05mmol and 24.7mg [Rh(cod)Cl] of bisphosphine ligands of structural formulas (2)-(8) are used respectively2Dissolve in 15mL toluene, and transfer to a 50mL autoclave, add 15.22g racemic isopulegol (ee=0%, L-isopulegol / D-isopulegol=1:1 (mol)) Inject into the autoclave, pass hydrogen to replace the gas in the autoclave three times, and adjust the pressure to 50 bar. Turn on the stirring, and after reacting at 60°C for 15 hours, use gas chromatography to determine the conversion rate of L-isopulegol in the raw material and the yield of L-menthol based on the L-isopulegol in the raw material, and the product L-menthol The optical purity of the alcohol is shown in Table 1.

[0044]Table 1 Reaction conditions and results

[0045] Example Bisphosphine ligand Conversion rate Yield ee value 3(2)92.5％92.0％96％ 4(3)86.5％85.8％98％ 5(4)83.2％82.7％94％ 6(5)91.4％90.6％95％ 7(6)84.6％83.2％92％ 8(7)81.3％79.8％96％ 9(8)79.5％78.7％91％

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Abstract

The invention provides a method for preparing optically pure L-menthol. Under the action of a transition metal catalyst, L-isopulegol in isopulegol is selectively hydrogenated to prepare optically pure L-menthol. The transition metal catalyst includes a transition metal compound and a chiral phosphine ligand. The high stereoselective synthesis of L-menthol is realized, and the optical purity of the product can be as high as 99ee%.

Description

Technical field[0001]The invention relates to a method for preparing optically pure L-menthol, in particular to a method for preparing optically pure L-menthol by selectively hydrogenating L-isopulegol.Background technique[0002]Menthol has a characteristic mint aroma and can produce a cooling sensation. It is widely used in the fields of food, daily chemicals and medicine. There are two enantiomers of menthol, D-menthol and L-menthol. The naturally extracted menthol is L-menthol, which has a pure smell and cooling feeling; D-menthol has a moldy smell and obvious It’s spicy, so pure L-menthol has a higher value.[0003]At present, L-menthol on the market is mainly derived from the cultivation and extraction of natural mint plants. Affected by unpredictable factors such as climatic conditions, its output, quality, and product prices often fluctuate drastically, which adversely affects the use of downstream users. The large-scale industrial synthesis of L-menthol overcomes the above-ment...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C07C29/17C07C35/12B01J31/24
CPCB01J31/2409B01J2231/645B01J2531/0225B01J2531/822B01J2531/842C07B2200/07C07C29/172C07C35/12
Inventor 董菁于磊王亚新王联防朱洪亮胡展张永振黎源
Owner WANHUA CHEM GRP CO LTD
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