A method for the continuous production of L-menthol-2-substituted glycol ethers

Abstract

The present application relates to the field of chemical synthesis, and relates to a method for continuously preparing L-menthol-2-substituted glycol ether, comprising loading a mixed solution A of L-menthol and aluminum chloride and an ethylene oxide solution B into a pipeline reaction device to perform reaction, so as to obtain the L-menthol-2-substituted glycol ether, wherein the pipeline reaction device comprises a pipeline reactor, and a mixed solution A raw material bottle and a solution B raw material bottle which are connected in parallel to an inlet end of the pipeline reactor. Compared with the prior art, the present application has the advantages of continuous production, precise reaction control, high product yield and the like.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis, and in particular to a method for the continuous preparation of L-menthol-2-substituted glycol ethers. Background Technology

[0002] L-Menthol, also known as menthol, is a cyclic monoterpenoid compound, originally extracted from peppermint. It possesses a distinctly pleasant, slightly sweet, and cool aroma and is widely used in fragrances, daily chemicals, medical products, food and beverages, and tobacco industries. However, menthol readily sublimates or volatilizes upon exposure to air, and its cooling effect is short-lived yet intensely immediate, thus affecting its effectiveness in food and personal care products. To overcome these drawbacks, a series of menthol derivative cooling agents have been developed in recent decades. Among them, L-menthol 2-substituted glycol ethers are a typical example of L-menthol ether derivative cooling agents. They provide the icy, refreshing sensation of L-menthol while avoiding its short duration and intensely immediate cooling effect, thus finding widespread application in food, cosmetics, tobacco, and pharmaceuticals.

[0003] Chinese patent application CN1764622A discloses a method for preparing L-menthol-2-substituted ethylene glycol ethers. In a batch reactor, L-menthol and anhydrous aluminum chloride are used as raw materials, and substituted ethylene oxides are reacted with solvents such as toluene. During the reaction, the epoxide solution is added dropwise to the reaction system, followed by a reheating reaction to obtain the product. However, the selectivity of the product generally does not exceed 90%, with the highest yield based on L-menthol being only 47.4%. Japanese patent JP2012-224600A describes a method for preparing L-menthol ethylene glycol ethers. First, sodium is added to a mixed solution of L-menthol and toluene, and after heating and stirring, a mixed solution of chloroacetic acid and toluene is added dropwise. After the reaction, the intermediate L-propoxyacetic acid is obtained by vacuum distillation. Subsequently, concentrated sulfuric acid is added to a mixed solution of L-propoxyacetic acid and methanol, and after heating and stirring, sodium carbonate is added. After washing, vacuum distillation yields the intermediate L-propoxyacetic acid methyl ester. Then, L-propoxyacetic acid methyl ester, methanol, and sodium methoxide are placed in an autoclave for hydrogenation. Finally, L-menthoxyethanol was obtained by vacuum distillation with a yield of 87%. This method is complex to operate, requires harsh reaction conditions, and produces inconsistent product quality, making it unsuitable for large-scale production. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art by providing a continuous method for preparing L-menthol-2-substituted glycol ethers, which enables continuous production, precise reaction control, and high product yield.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for the continuous preparation of L-menthol-2-substituted glycol ethers, comprising:

[0007] Solution A is obtained by mixing L-menthol as shown in Formula 1 with aluminum chloride. Solution B is obtained by dissolving ethylene oxide compound as shown in Formula 2 in an organic solvent. Solutions A and B are then placed in a tubular reaction apparatus to react and obtain L-menthol-2-substituted ethylene glycol ether as shown in Formula 3. The reaction equation is as follows:

[0008]

[0009] In Formula 2, R is H, methyl, ethyl, n-propyl, or n-butyl, etc.

[0010] The pipeline reaction device includes a pipeline reactor and solution A raw material bottle and solution B raw material bottle connected in parallel to the inlet end of the pipeline reactor.

[0011] Furthermore, when preparing solution A of L-menthol and anhydrous aluminum chloride, L-menthol is first dissolved in an organic solvent, and then anhydrous aluminum chloride is added under N2 protection to obtain solution A.

[0012] Furthermore, the organic solvent includes one or more of n-heptane, n-hexane, cyclohexane, toluene, xylene, tetrahydrofuran, or ethylene glycol dimethyl ether.

[0013] Furthermore, the temperature at which solutions A and B are reacted in the tubular reaction apparatus is 5-50℃.

[0014] Furthermore, the molar ratio of L-menthol to aluminum chloride is 1:0.1-1:1.

[0015] Furthermore, the molar ratio of L-menthol to the ethylene oxide compound is 1:1 to 1:8.

[0016] Furthermore, the reactants reside in the pipeline reactor for 100-600 seconds.

[0017] Furthermore, the inner diameter of the pipeline reactor is 1-7 mm.

[0018] Furthermore, the length of the pipeline reactor is 1-20m.

[0019] Furthermore, the flow rate of solution A is 1-2 mL / min, and the flow rate of solution B is 0.5-4 mL / min.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] This invention provides a continuous synthesis method for L-menthol-2-substituted ethylene glycol ethers. By controlling the residence time of the reaction solution in a tubular reactor, the materials in the reactor are fully mixed and reacted. This includes changing the flow rate of the reaction solution pumped into the tubular reactor, the length of the tubular reactor, and the diameter of the tubular reactor, while maintaining continuous feeding and discharging. This continuous production method reduces losses during material transfer and has advantages such as precise reaction control, high product yield, high purity, simple operation, and low cost, providing a more efficient and environmentally friendly technology for production. Attached Figure Description

[0022] Figure 1 This is a diagram of the pipeline reaction apparatus of the present invention;

[0023] Figure 2 This is a gas chromatogram of the reaction solution in the receiving bottle of the product of this invention;

[0024] Figure 3 This is a gas chromatogram of the purified reaction solution in the receiving bottle of the product of this invention.

[0025] Figure reference numerals:

[0026] 1-Epoxy compound solution mixing bottle; 2-Menthol mixing bottle; 3-Epoxy compound feed pump; 4-Menthol mixture feed pump; 5-Pipeline reactor; 6-Product receiving bottle; 7-Nitrogen gas. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. The scope of protection of the present invention includes, but is not limited to, the following embodiments.

[0028] A pipeline reaction device, such as Figure 1 As shown, the pipeline reaction apparatus includes: a nitrogen protective gas, a menthol preparation bottle 2 for containing a mixed solution A of L-menthol and anhydrous aluminum chloride, an epoxy compound preparation bottle 1 for containing an ethylene oxide solution B, a pipeline reactor 5, a menthol mixture feed pump 4 and an epoxy compound feed pump 3 for pumping the reactants into the pipeline reactor 5, and a product receiving bottle 6 for collecting the product mixture.

[0029] Example 1

[0030] (1) Take 15.6 g (0.10 mol, 1.00 eq) of L-menthol and add it to 100 mL of n-heptane. Stir to dissolve it, and control the temperature at 15 ± 2 °C during the dissolution process. Then, under N2 protection, add 9.32 g (0.07 mol, 0.70 eq) of anhydrous aluminum chloride in four batches (2.3 g per batch) to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride. Dissolve 8.80 g (0.2 mol, 2.00 eq) of ethylene oxide in 100 mL of n-heptane at 15 °C to obtain ethylene oxide solution B. Load the reaction solution into a tubular reaction apparatus, as shown in the figure. Figure 1 As shown, a mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol preparation bottle 2, and a n-heptane solution B of ethylene oxide is placed in epoxide compound preparation bottle 1.

[0031] (2) In this embodiment, mixed solution A and solution B are pumped into the transparent polytetrafluoroethylene pipeline reactor 5 at rates of 1 mL / min and 1 mL / min, respectively, through menthol mixture feed pump 4 and epoxy compound feed pump 3.

[0032] In this embodiment, the pipe is 10 meters long, the pipe has an inner diameter of 1 mm, the reaction temperature is controlled at 15°C, and the residence time of the reaction liquid in the pipe is 240 seconds.

[0033] (3) The product mixture received in product receiving bottle 6 was quenched with 10% wt NaOH solution, and the solid and liquid were separated. The organic phase was dried with anhydrous MgSO4, the solvent was recovered, and the product was concentrated to obtain 18.95 g of crude product. Gas chromatography analysis showed that the crude product contained 31.56% L-menthol, 67.01% L-menthol glycol ether, and 1.03% by-products.

[0034] (4) The crude product was purified and distilled to recover 6.06 g of L-menthol, 10.7 g of the target product L-menthol glycol ether, and 1.70 g of the residue (high-boiling matter left at the bottom of the vessel after distillation).

[0035] The obtained products were characterized and analyzed. Taking the L-menthol-ethylene glycol ether prepared in Example 1 as an example, for instance... Figure 2 , 3 As shown, a retention time of approximately 8.6 min corresponds to the target product L-menthol-ethylene glycol ether, and approximately 6.7 min corresponds to the raw material L-menthol.

[0036] Using the area normalization method (the same below), the product purity is 99.85%, the yield is 87.50%, and the theoretical yield is 53.41% based on L-menthol. The calculation method is as follows:

[0037] Yield calculation: Theoretically, the menthol consumed in the reaction, m1, can produce a product with a mass of m2. The product obtained by distillation has a mass of m3. Yield = m3 / m2 × 100%.

[0038] The theoretical yield is calculated based on the L-menthol yield: the theoretical product amount m4 generated from the total input menthol is calculated based on the L-menthol yield = m3 / m4 × 100%.

[0039] Example 2

[0040] (1) Take 15.6 g (0.10 mol, 1.00 eq) of L-menthol and add it to 100 mL of organic solvent (hexane in this example). Stir to dissolve and control the temperature at 10 ± 2 °C. Then, under N2 protection, add 3.99 g (0.03 mol, 0.30 eq) of anhydrous aluminum chloride in batches to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride. Dissolve 17.40 g (0.3 mol, 3.00 eq) of propylene oxide in 200 mL of hexane at 10 ± 2 °C to obtain a hexane solution B of propylene oxide. Load the reaction solution into a tubular reaction apparatus, as shown in the figure. Figure 1 As shown, a mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol preparation bottle 2, and a n-heptane solution B of ethylene oxide is placed in epoxide compound preparation bottle 1.

[0041] (2) In this embodiment, mixed solutions A and B are pumped into a transparent polytetrafluoroethylene pipe reactor with an inner diameter of 3 mm at a speed of 1.5 mL / min and 3 mL / min, respectively, through a menthol mixture feed pump 4 and an epoxy compound feed pump 3. The pipe is 3 meters long, the reaction temperature is controlled at 35±2℃, and the residence time of the reaction liquid in the pipe is 300s.

[0042] (3) The product liquid received by the product receiving bottle 6 at the outlet of the pipeline reactor 5 was quenched with 15% NaOH solution, and the solid and liquid were separated. The organic phase was dried with anhydrous MgSO4, the solvent was recovered, and the product was concentrated to obtain 21.33g of crude product. Gas chromatography analysis showed that the crude product contained 73.17% L-menthol, 24.7% L-menthol-2-methyl ethylene glycol ether, and 2.13% by-products.

[0043] (4) The crude product was distilled to recover 10.20 g of L-menthol, and 6.12 g of the target product and 2.60 g of the residue were obtained. The product purity was 99.03% and the yield was 88.41%. The theoretical yield was based on L-menthol of 30.55%, and the calculation method was the same as in Example 1.

[0044] Example 3

[0045] (1) Add 15.6 g (0.10 mol, 1.00 eq) of L-menthol to 100 mL of cyclohexane, stir to dissolve, and add 13.34 g (0.10 mol, 0.30 eq) of anhydrous aluminum chloride in portions under N2 protection at a controlled temperature of 20±2℃ to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride; dissolve 36.02 g (0.50 mol, 5.00 eq) of epoxide in 200 mL of cyclohexane at 20±2℃ to obtain a cyclohexane solution B of epoxide. Load the reaction solution into a tubular reaction apparatus, as shown in the diagram. Figure 1 As shown, a mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol preparation bottle 2, and a n-heptane solution B of epoxide butane is placed in epoxide compound solution preparation bottle 1.

[0046] (2) In this embodiment, mixed solution A and solution B are pumped into a transparent polytetrafluoroethylene pipe reactor with an inner diameter of 4 mm at a speed of 2 mL / min and 4 mL / min respectively through menthol mixed solution feed pump 4 and epoxy compound feed pump 3. The pipe length is 3 meters, the reaction temperature is controlled at 20±2℃, and the residence time of the reaction liquid in the pipe is 360s.

[0047] (3) The received liquid was quenched with 20% NaOH solution, and the solid and liquid phases were separated. The organic phase was dried with anhydrous MgSO4, and the solvent was recovered. After concentration, 23.16 g of crude product was obtained. Gas chromatography analysis showed that the crude product contained 38.61% L-menthol, 57.26% L-menthol-2-ethylhexyl glycol ether, and 3.39% byproducts.

[0048] (4) The product liquid received by the product receiving bottle 6 at the outlet of the pipeline reactor 5 is distilled to recover 7.01g of L-menthol, yielding 9.43g of the target product and 2.90g of residue. The product purity is 98.63%, the yield is 85.64%, and the theoretical yield is based on L-menthol of 47.05%, calculated in the same way as in Example 1.

[0049] Example 4

[0050] (1) Add 15.6 g (0.10 mol, 1.00 eq) of L-menthol to 200 mL of n-heptane, stir to dissolve, and add 5.33 g (0.04 mol, 0.40 eq) of anhydrous aluminum chloride in portions under N2 protection at a temperature controlled at 15±2℃ to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride; dissolve 14.42 g (0.20 mol, 2.00 eq) of isobutane oxide in 300 mL of n-heptane at 15±2℃ to obtain a n-heptane solution B of isobutane oxide. Load the reaction solution into a tubular reaction apparatus, as shown in the diagram. Figure 1As shown, a mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol preparation bottle 2, and a n-heptane solution B of isobutane epoxide is placed in epoxy compound solution preparation bottle 1.

[0051] (2) In this embodiment, mixed solution A and solution B are pumped into a transparent polytetrafluoroethylene pipe reactor with an inner diameter of 2 mm at a rate of 1 mL / min and 1.5 mL / min, respectively, through menthol mixture feed pump 4 and epoxy compound feed pump 3. The pipe length is 4 meters, the reaction temperature is controlled at 25±2℃, and the residence time of the reaction liquid in the pipe is 200s.

[0052] (3) The product liquid received in product receiving bottle 6 at the outlet of pipeline reactor 5 was quenched with 8% NaOH solution, and the solid and liquid phases were separated. The organic phase was dried with anhydrous MgSO4, and the solvent was recovered. After concentration, 19.79 g of crude product was obtained. Gas chromatography analysis showed that the crude product contained 57.86% L-menthol, 39.21% L-menthol-2,2-diethylethylene glycol ether, and 1.53% byproducts.

[0053] (4) The crude product was distilled to recover 10.75 g of L-menthol, yielding 5.04 g of the target product and 2.30 g of the residue. The product purity was 98.96%, the yield was 81.07%, and the theoretical yield was based on 25.16% L-menthol, calculated using the same method as in Example 1.

[0054] Example 5

[0055] (1) Add 15.6 g (0.10 mol, 1.00 eq) of L-menthol to 200 mL of tetrahydrofuran, stir to dissolve, and add 6.67 g (0.05 mol, 0.50 eq) of anhydrous aluminum chloride in portions under N2 protection at a temperature controlled at 10±2℃ to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride; dissolve 25.8 g (0.30 mol, 3.00 eq) of 1,2-epoxypentane in 300 mL of tetrahydrofuran at 10±2℃ to obtain a tetrahydrofuran solution B of 1,2-epoxypentane. Load the reaction solution into a tubular reaction apparatus, as shown in the figure. Figure 1 As shown, the mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol preparation bottle 2, and the n-heptane solution B of 1,2-epoxypentane is placed in epoxy compound solution preparation bottle 1.

[0056] (2) In this embodiment, mixed solutions A and B are pumped into a transparent polytetrafluoroethylene pipe reactor with an inner diameter of 4 mm at a rate of 2.5 mL / min and 4 mL / min, respectively, through a menthol mixture feed pump 4 and an epoxy compound feed pump 3. The pipe is 4 meters long, the reaction temperature is controlled at 20±2℃, and the residence time of the reaction liquid in the pipe is 420 s.

[0057] (3) The product liquid received in product receiving bottle 6 at the outlet of pipeline reactor 5 was quenched with 8% NaOH solution, and the solid and liquid phases were separated. The organic phase was dried with anhydrous MgSO4, and the solvent was recovered. After concentration, 17.43 g of crude product was obtained. Gas chromatography analysis showed that the crude product contained 56.43% L-menthol, 39.58% L-menthol-2-propyl glycol ether, and 2.88% byproducts.

[0058] (4) The crude product was distilled to recover 8.83 g of L-menthol, yielding 4.96 g of the target product and 2.64 g of the residue. The product purity was 99.01%, the yield was 57.15%, and the theoretical yield was based on 24.76% L-menthol, calculated using the same method as in Example 1.

[0059] Example 6

[0060] (1) Take 15.6 g (0.10 mol, 1.00 eq) of L-menthol and add it to 200 mL of ethylene glycol dimethyl ether. Stir to dissolve. Under the condition of 10±2℃ and N2 protection, add 6.67 g (0.05 mol, 0.50 eq) of anhydrous aluminum chloride in portions to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride. Under the condition of 10±2℃, dissolve 45.6 g (0.40 mol, 4.00 eq) of 1,2-epoxyheptane in 400 mL of ethylene glycol dimethyl ether to obtain a ethylene glycol dimethyl ether solution B of 1,2-epoxyheptane. Put the reaction solution into a tubular reaction apparatus, the apparatus as follows. Figure 1 As shown, a mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol preparation bottle 2, and a n-heptane solution B of ethylene oxide is placed in epoxide compound preparation bottle 1.

[0061] (2) In this embodiment, mixed solutions A and B are pumped into a transparent polytetrafluoroethylene pipe reactor with an inner diameter of 4 mm at a rate of 2.5 mL / min and 5 mL / min, respectively, through a menthol mixture feed pump 4 and an epoxy compound feed pump 3. The pipe is 5 meters long, the reaction temperature is controlled at 35±2℃, and the residence time of the reaction liquid in the pipe is 480s.

[0062] (3) The product liquid received in the product receiving bottle 6 at the outlet of the pipeline reactor 5 was quenched with 10% NaOH solution, and the solid and liquid phases were separated. The organic phase was dried with anhydrous MgSO4, and the solvent was recovered. After concentration, 17.81 g of crude product was obtained. Gas chromatography analysis showed that the crude product contained 53.27% L-menthol, 41.20% L-menthol-2-pentyl ethylene glycol ether, and 3.06% byproducts.

[0063] (4) The crude product was distilled to recover 8.49 g of L-menthol, yielding 5.73 g of the target product and 1.83 g of the residue. The product purity was 99.22%, the yield was 62.87%, and the theoretical yield was based on L-menthol of 28.60%, calculated in the same way as in Example 1.

[0064] Example 7

[0065] (1) Add 15.6 g (0.10 mol, 1.00 eq) of L-menthol to 250 mL of toluene, stir to dissolve, and add 8.00 g (0.06 mol, 0.60 eq) of anhydrous aluminum chloride in portions under N2 protection at a temperature controlled at 20±2℃ to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride; dissolve 60.1 g (0.60 mol, 6.00 eq) of 2-isobutylethylene oxide in 400 mL of toluene at 20±2℃ to obtain a toluene solution B of propylene oxide. Load the reaction solution into a tubular reaction apparatus, as shown in the diagram. Figure 1 As shown, the mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol mixing bottle 2, and the n-heptane solution B of 2-isobutyl ethylene oxide is placed in epoxy compound solution mixing bottle 1.

[0066] (2) In this embodiment, mixed solutions A and B are pumped into a transparent polytetrafluoroethylene pipe reactor with an inner diameter of 5 mm at a rate of 1.5 mL / min and 2.5 mL / min, respectively, through a menthol mixture feed pump 4 and an epoxy compound feed pump 3. The pipe is 2 meters long, the reaction temperature is controlled at 30±2℃, and the residence time of the reaction liquid in the pipe is 500 s.

[0067] (3) The product liquid received in the product receiving bottle 6 at the outlet of the pipeline reactor 5 was quenched with 15% NaOH solution, and the solid and liquid phases were separated. The organic phase was dried with anhydrous MgSO4, and the solvent was recovered. After concentration, 18.02 g of crude product was obtained. Gas chromatography analysis showed that the crude product contained 47.20% L-menthol, 47.39% L-menthol-2-isobutyl glycol ether, and 4.07% byproducts.

[0068] (4) The crude product was distilled to recover 8.02 g of L-menthol, yielding 7.63 g of the target product and 1.42 g of the residue. The product purity was 99.72%, the yield was 78.52%, and the theoretical yield was based on L-menthol of 38.09%, calculated using the same method as in Example 1.

[0069] Example 8

[0070] (1) Add 15.6 g (0.10 mol, 1.00 eq) of L-menthol to 200 mL of cyclohexane, stir to dissolve, and add 9.33 g (0.07 mol, 0.70 eq) of anhydrous aluminum chloride in portions under N2 protection at a temperature controlled at 30±2℃ to obtain a mixed solution A of L-menthol and anhydrous aluminum chloride; dissolve 35.24 g (0.80 mol, 8.00 eq) of ethylene oxide in 400 mL of cyclohexane at 30±2℃ to obtain a cyclohexane solution B of ethylene oxide. Load the reaction solution into a tubular reaction apparatus, as shown in the diagram. Figure 1 As shown, a mixed solution A of L-menthol and anhydrous aluminum chloride is placed in menthol preparation bottle 2, and a n-heptane solution B of ethylene oxide is placed in epoxide compound preparation bottle 1.

[0071] (2) In this embodiment, mixed solutions A and B are pumped into a transparent polytetrafluoroethylene pipe reactor with an inner diameter of 5 mm at a rate of 1.5 mL / min and 2.5 mL / min, respectively, through a menthol mixture feed pump 4 and an epoxy compound feed pump 3. The pipe is 5 meters long, the reaction temperature is controlled at 40±2℃, and the residence time of the reaction liquid in the pipe is 600 s.

[0072] (3) The product liquid received in the product receiving bottle 6 at the outlet of the pipeline reactor 5 was quenched with 20% NaOH solution, and the solid and liquid phases were separated. The organic phase was dried with anhydrous MgSO4, and the solvent was recovered. After concentration, 16.43 g of crude product was obtained. Gas chromatography analysis showed that the crude product contained 32.56% L-menthol, 61.76% L-menthol-2-methylethylene glycol ether, and 4.38% byproducts.

[0073] (4) The crude product was distilled to recover 5.04 g of L-menthol, yielding 8.74 g of the target product and 2.41 g of the residue. The product purity was 99.61%, the yield was 64.57%, and the theoretical yield was based on 43.63% of L-menthol, calculated using the same method as in Example 1.

[0074] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for the continuous preparation of L-menthol-2-substituted glycol ethers, characterized in that, include: L-menthol as shown in Formula 1 is mixed with aluminum chloride in batches to obtain solution A. Ethylene oxide compound as shown in Formula 2 is dissolved in an organic solvent to obtain solution B. Solutions A and B are then placed in a tubular reaction apparatus to react and yield L-menthol-2-substituted glycol ether as shown in Formula 3. The pipeline reaction device includes: a pipeline reactor (5) and solution A raw material bottle and solution B raw material bottle connected in parallel to the inlet end of the pipeline reactor (5). ， In Formula 2, R is H, methyl, ethyl, n-propyl, or n-butyl; The inner diameter of the pipeline reactor (5) is 1-7 mm, the length of the pipeline reactor (5) is 1-20 m, and during the preparation process, the molar ratio of L-menthol and ethylene oxide compound is 1:1-1:8, the reaction temperature is 5-50℃, the reaction residence time is 100-600 s, the flow rate of solution A is 1-2 mL / min, and the flow rate of solution B is 0.5-4 mL / min. L-menthol is first dissolved in an organic solvent, and then mixed with aluminum chloride to obtain solution A. The organic solvent includes one or more of n-heptane, n-hexane, cyclohexane, toluene, xylene, tetrahydrofuran, or ethylene glycol dimethyl ether. The molar ratio of L-menthol to aluminum chloride is 1:0.1-1:1.

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