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Method for preparing optical 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: 2018-05-29
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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  • Method for preparing optical pure L-menthol
  • Method for preparing optical pure L-menthol
  • Method for preparing optical pure L-menthol

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

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

Embodiment 2

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

Embodiment 3-9

[0043] Under an argon atmosphere, 0.05 mmol and 24.7 mg of [Rh(cod)Cl] bisphosphine ligands of structural formulas (2)-(8) were used respectively 2 Dissolved in 15 mL of toluene, and transferred to a 50 mL autoclave, 15.22 g of racemic isopulegol (ee=0%, L-isopulegol / D-isopulegol=1:1 (mol)) Inject into the autoclave, and adjust the pressure to 50 bar after passing through hydrogen to replace the gas in the autoclave three times. Start stirring, and react at 60°C for 15 hours, use gas chromatography to measure 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 alcohols is detailed in Table 1.

[0044] Table 1 Reaction conditions and results

[0045] Example

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Abstract

The invention provides a method for preparing optical pure L-menthol. Under the action of a transition metal catalyst, L-isopulegol in isopulegol is selectively hydrogenated, and the optical pure L-menthol is prepared. The transition metal catalyst comprises a transition metal compound and a chiral phosphine ligand. High stereo-selective synthesis of the L-menthol is realized, and the optical purity of a product can reach up to 99ee%.

Description

technical field [0001] The invention relates to a method for preparing optically pure L-menthol, in particular to a method for selectively hydrogenating L-isopulegol to prepare optically pure L-menthol. Background technique [0002] Menthol has a characteristic mint aroma and can produce a cooling sensation, and is widely used in the fields of food, daily chemicals, and medicine. There are two enantiomers of menthol, D-menthol and L-menthol, and the naturally extracted menthol is L-menthol, which has a pure smell and cool feeling; D-menthol has a musty smell and obvious Spicy feeling, so pure L-menthol has a higher value. [0003] At present, L-menthol in the market mainly comes from the planting and extraction of natural mint plants. Affected by unpredictable factors such as climatic conditions, its output, quality and product price often fluctuate violently, which has a negative impact on the use of downstream users. The large-scale industrial synthesis of L-menthol over...

Claims

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Application Information

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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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