High-purity purification method of linalool essential oil

Abstract

The invention relates to the technical field of purification of natural products, in particular to a high-purity purification method of linalool essential oil. In order to solve the problems that conjugated diene impurities are difficult to efficiently remove and thermal degradation or structural damage of linalool is easily caused in the prior art, the invention adopts a three-step combined process: firstly, carrying out selective catalytic hydrogenation under a mild condition, so that only conjugated double bonds in the impurities are saturated, and non-conjugated double bonds of linalool are completely retained; then carrying out short-path molecular distillation, and realizing efficient separation at low temperature and high vacuum by utilizing the difference between the average free path of linalool and the average free path of impurity molecules; finally, further fine purification is performed through silica gel column chromatography. According to the method, the purity of the linalool can be stably improved to 99.4% or above under mild conditions, the yield reaches 90.4% or above, the optical rotation of the product is stable, the purity, the yield and the storage stability of the linalool are remarkably improved, and the method is suitable for the high-added-value fields such as medicines and high-end spices.

Description

A method for high-purity purification of linalool essential oil Technical Field

[0001] This invention relates to the field of natural product purification technology, specifically a method for high-purity purification of linalool essential oil. Background Technology

[0002] Linalool is an important monoterpene alcohol that is widely found in the essential oils of various plants such as lavender and basil. Due to its unique aroma and antibacterial and sedative biological activities, it has extremely high application value in the fields of high-end fragrances, pharmaceutical preparations and food additives.

[0003] Linalool typically constitutes only 60%-80% of natural essential oils, with the remainder containing various impurities such as monoterpenes and oxygenated compounds. Among these, the removal of conjugated diene impurities (such as ocimene) has long been a core challenge hindering technological advancements in the industry. These impurities are extremely similar to the target product linalool in molecular structure, boiling point, and molecular weight, resulting in highly similar physicochemical properties.

[0004] In existing technologies, different process routes for the removal of conjugated diene impurities all have certain limitations: when using boiling point-dependent separation methods such as distillation, in order to overcome the difficulty of the similar distillation temperatures of conjugated diene impurities and linalool, a high temperature for a long time is often required, which may cause the heat-sensitive linalool to be thermally degraded or isomerized, resulting in yield loss; if a mild separation method such as molecular distillation is used, although thermal damage can be avoided, the separation selectivity for conjugated diene impurities is insufficient, resulting in limited improvement in product purity; while conventional catalytic hydrogenation processes have the problem of lack of selectivity in reaction conditions, which can easily cause linalool itself to undergo hydrogenation side reactions to form new impurities, thereby affecting purification and final yield.

[0005] Therefore, how to efficiently remove such specific impurities while avoiding thermal or chemical damage to the target product, thereby synergistically achieving high purity and high yield, remains a pressing technical challenge. Summary of the Invention The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for high-purity purification of linalool essential oil, solving the technical problem that "in the process of linalool purification, it is difficult to efficiently remove impurities, resulting in a difficulty in achieving both product purity and yield."

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution: In the first aspect, the present invention provides a method for high-purity purification of linalool essential oil, comprising the following steps: (1) mixing linalool essential oil with an inert solvent, adding a metal catalyst, and carrying out a selective hydrogenation reaction under a hydrogen atmosphere to obtain a hydrogenated crude product; (2) subjecting the above-mentioned hydrogenated crude product to short-path molecular distillation to remove light components in sequence and collecting the linalool main fraction; (3) separating the above-mentioned linalool main fraction by silica gel column chromatography, and obtaining high-purity linalool after elution and concentration.

[0007] Specifically, the metal catalyst in step (1) is at least one of Pd / C, Raney Ni, and Pt / Al2O3.

[0008] Specifically, in step (1), the amount of metal catalyst used is 0.5 to 3.0% of the mass of linalool essential oil.

[0009] Specifically, in step (1), the inert solvent is one or more of n-hexane and cyclohexane.

[0010] Specifically, the selective hydrogenation reaction in step (1) adopts a step-by-step heating method: first react at 40-50℃ for 1 hour, and then heat to 60-80℃ for 2-3 hours.

[0011] Specifically, in step (2), short-range molecular distillation is carried out in two stages: the first stage is to remove light components at 50~100 Pa and 70~90 °C; the second stage is to collect the linalool main fraction at 0.1~1.0 Pa and 95~110 °C.

[0012] Specifically, in step (2), the evaporation surface and the condensation surface of the short-range molecular distillation apparatus are 3 to 5 cm apart.

[0013] Specifically, in step (3), the column chromatography uses gradient elution with petroleum ether and ethyl acetate as the eluent.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) The present invention uses a three-step process to steadily increase the purity of linalool from about 72% to more than 99.4%, while maintaining the yield at more than 90.4%, thus achieving a synergistic breakthrough of high purity and high yield.

[0015] (2) The present invention performs catalytic hydrogenation under mild conditions of 40~80℃, selectively saturates impurity double bonds while fully preserving the active structure of linalool; combined with high vacuum low temperature molecular distillation, the risks of thermal degradation and isomerization are avoided.

[0016] (3) The unstable impurity content in the product of this invention is less than 0.5%, which significantly enhances the storage stability; and the process is applicable to a variety of catalysts such as Pd / C and Raney Ni, with high solvent recovery rate and catalysts that can be recycled more than 5 times. The process is highly efficient and provides high-quality raw materials for pharmaceuticals, high-end fragrances and other fields. Attached Figure Description

[0017] Figure 1 is a liquid chromatogram of linalool in Example 2.

[0018] Figure 2 shows the 1H NMR spectrum of linalool in Example 2. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] The high-purity purification method for linalool essential oil proposed in this invention is based on a three-step combined process to achieve efficient and selective removal of impurities and gentle separation and purification of the product. Specifically, firstly, selective catalytic hydrogenation is employed under mild conditions, targeting only conjugated diene impurities (such as β-ocimene) in the raw material for hydrogenation saturation (C1). 10 H 16 +H2→C 10 H 18 The non-conjugated double bonds in the linalool molecule are preserved intact, avoiding unnecessary hydrogenation side reactions. Subsequently, through short-path molecular distillation, taking advantage of the significant difference in mean free path between linalool and impurity molecules (e.g., linalool approximately 0.15 mm, partially hydrogenated impurities approximately 0.08 mm / 100 Pa), efficient separation is achieved under low temperature and high vacuum conditions, greatly reducing the risk of thermal degradation or isomerization. Finally, fine purification is carried out by silica gel column chromatography to further remove residual polar impurities. This synergistic process works synergistically from both chemical transformation and physical separation dimensions, achieving highly selective removal of difficult-to-remove impurities such as conjugated dienes under mild conditions, while ensuring the structural integrity and high yield of linalool, thus effectively solving the technical problem of difficulty in achieving both purity and yield in traditional processes.

[0021] A method for high-purity purification of linalool essential oil includes the following steps: (1) Lavender essential oil and n-hexane are mixed in a volume ratio of 1:(1-3) and placed in a high-pressure reactor. 0.5-3.0% of the essential oil mass of Pd / C catalyst (palladium content 5-10%) is added. After replacing the air in the reactor three times with hydrogen, hydrogen is introduced to a pressure of 0.5-2 MPa. The stirring speed is set to 300-600 r / min. The step heating method is used to react at 40-50℃ for 1 h and at 60-80℃ for 2-3 h. After the reaction is completed, the reaction solution is cooled to room temperature, the pressure is released, and the catalyst is removed by filtration through a 0.22 μm microporous membrane to obtain the hydrogenated crude product; (2) The hydrogenated crude product is transferred to a short-path molecular distillation apparatus (the evaporation surface and the condensation surface are 3-5 cm apart). In the first stage, the system pressure is set to 50-100 Pa and the evaporation surface temperature is 70°C. ~90℃, rotation speed of 200~300r / min, distill for 20min to remove light components and discard them. In the second stage, the system pressure is reduced to 0.1~1.0Pa, the evaporation surface temperature is raised to 95~110℃, and the rotation speed is adjusted to 100~200r / min. The main fraction of this stage is collected. (3) The obtained main fraction is loaded into a chromatography column packed with 200 mesh silica gel and eluted sequentially with the following eluents: 500mL of petroleum ether; 800mL of petroleum ether / ethyl acetate (volume ratio 20:1) mixture; 500mL of petroleum ether / ethyl acetate (volume ratio 10:1) mixture. The elution fraction rich in linalool is collected by thin layer chromatography (TLC). The collected target elution fractions are combined and concentrated by rotary evaporation at 40℃ and -0.09MPa to remove all solvents and obtain colorless and transparent pure linalool.

[0022] As a preferred embodiment of the present invention, the volume ratio of lavender essential oil to n-hexane is 1:2.

[0023] As a preferred embodiment of the present invention, the palladium content of the Pd / C catalyst is 10%.

[0024] As a preferred embodiment of the present invention, the mass ratio of lavender essential oil to Pd / C catalyst is 1:2%.

[0025] As a preferred embodiment of the present invention, the stepped heating method first reacts at 45°C for 1 hour, and then the temperature is increased to 70°C to continue the reaction for 2.5 hours.

[0026] As a preferred embodiment of the present invention, the evaporation surface and the condensation surface of the short-path molecular distillation apparatus are 4 cm apart.

[0027] As a preferred embodiment of the present invention, the system pressure in the first stage is 80 Pa, the evaporation surface temperature is 90 °C, the rotation speed is 250 r / min, and the distillation time is 20 min.

[0028] As a preferred embodiment of the present invention, the system pressure in the second stage is 0.5 Pa, the evaporation surface temperature is 105 °C, and the rotation speed is adjusted to 150 r / min.

[0029] The raw material, lavender essential oil, was found to contain 72.3% linalool, as determined by LC-MS.

[0030] The gradient elution is performed by gradually increasing the proportion of ethyl acetate in the volume ratio of petroleum ether and ethyl acetate.

[0031] Example 1; (1) Take 100g of lavender essential oil, add 100mL of n-hexane as solvent and place it in a high-pressure reactor, add 0.5g of Pd / C catalyst (palladium content 5%), replace the air in the reactor with hydrogen three times, then fill with hydrogen to a pressure of 0.5MPa, set the stirring speed to 300r / min, react at 40℃ for 1h, then raise the temperature to 60℃ and continue the reaction for 2h. After the reaction is completed, cool the reaction liquid to room temperature, depressurize, filter through a 0.22μm microporous filter membrane to remove the catalyst and obtain the hydrogenated crude product; (2) Transfer the hydrogenated crude product to a short-path molecular distillation apparatus (evaporation surface and condensation surface are 3cm apart), set the system pressure to 50Pa, the evaporation surface temperature to 70℃, and the rotation speed to 200r / min in the first stage, distill for 20min to remove and discard the light components, and in the second stage, reduce the system pressure to 1.0Pa, raise the evaporation surface temperature to 95℃, adjust the rotation speed to 100r / min, and collect the main fraction in this stage.

[0032] (3) The obtained main fraction was loaded into a chromatography column packed with 200-mesh silica gel and eluted sequentially with the following eluents: 500 mL of petroleum ether; 800 mL of petroleum ether / ethyl acetate (volume ratio 20:1); 500 mL of petroleum ether / ethyl acetate (volume ratio 10:1). The elution fraction rich in linalool was collected by thin-layer chromatography (TLC). The collected target elution fractions were combined and concentrated by rotary evaporation at 40 °C and -0.09 MPa to remove all solvents, and 65.6 g of colorless and transparent pure linalool was obtained.

[0033] Example 2; (1) Take 100g of lavender essential oil, add 200mL of cyclohexane as solvent and place it in a high-pressure reactor, add 2.0g of Pd / C catalyst (palladium content 10%), replace the air in the reactor with hydrogen three times, then fill with hydrogen to a pressure of 1.0MPa, set the stirring speed to 500r / min, react at 45℃ for 1h, then raise the temperature to 70℃ and continue the reaction for 2.5h. After the reaction is completed, cool the reaction solution to room temperature, depressurize, and pass through a 0.22μm filter. (1) Filter the catalyst through a microporous membrane to obtain the crude hydrogenated product; (2) Transfer the crude hydrogenated product to a short-path molecular distillation apparatus (the evaporation surface and the condensation surface are 4 cm apart). In the first stage, set the system pressure to 80 Pa, the evaporation surface temperature to 80 °C, and the rotation speed to 250 r / min. Distill for 20 min to remove and discard the light components. In the second stage, reduce the system pressure to 0.5 Pa, raise the evaporation surface temperature to 105 °C, and adjust the rotation speed to 150 r / min. Collect the main fraction in this stage.

[0034] (3) The obtained main fraction was loaded into a chromatography column packed with 200-mesh silica gel and eluted sequentially with the following eluents: 500 mL petroleum ether; 800 mL petroleum ether / ethyl acetate (volume ratio 20:1); 500 mL petroleum ether / ethyl acetate (volume ratio 10:1). The elution fraction rich in linalool was collected by thin-layer chromatography (TLC). The collected target elution fractions were combined and concentrated by rotary evaporation at 40 °C and -0.09 MPa to remove all solvents, yielding 66.1 g of colorless and transparent pure linalool.

[0035] Example 3; (1) Take 100g of lavender essential oil, add 300mL of n-hexane as solvent and place it in a high-pressure reactor, add 3.0g of Pd / C catalyst (palladium content 10%), replace the air in the reactor with hydrogen three times, then fill with hydrogen to a pressure of 2.0MPa, set the stirring speed to 600r / min, react at 50℃ for 1h, then raise the temperature to 80℃ and continue the reaction for 3h. After the reaction is completed, cool the reaction solution to room temperature, depressurize, and pass through a 0.22μm micrometer. (1) Filter the catalyst through a pore membrane to obtain the crude hydrogenated product; (2) Transfer the crude hydrogenated product to a short-path molecular distillation apparatus (5 cm between the evaporation surface and the condensation surface). In the first stage, set the system pressure to 100 Pa, the evaporation surface temperature to 90 ° C, and the rotation speed to 300 r / min. Distill for 20 min to remove and discard the light components. In the second stage, reduce the system pressure to 0.1 Pa, raise the evaporation surface temperature to 110 ° C, and adjust the rotation speed to 200 r / min. Collect the main fraction in this stage.

[0036] (3) The obtained main fraction was loaded into a chromatography column packed with 200-mesh silica gel and eluted sequentially with the following eluents: 500 mL petroleum ether; 800 mL petroleum ether / ethyl acetate (volume ratio 20:1); 500 mL petroleum ether / ethyl acetate (volume ratio 10:1). The elution fraction rich in linalool was collected by thin-layer chromatography (TLC). The collected target elution fractions were combined and concentrated by rotary evaporation at 40 °C and -0.09 MPa to remove all solvents, yielding 65.9 g of colorless and transparent pure linalool.

[0037] Example 4; (1) Take 100g of lavender essential oil, add 200mL of cyclohexane as solvent and place it in a high-pressure reactor, add 2.0g of Raney Ni catalyst (nickel content is 90%), replace the air in the reactor with hydrogen three times, then fill with hydrogen to a pressure of 1.5MPa, set the stirring speed to 500r / min, react at 45℃ for 1h, then raise the temperature to 70℃ and continue the reaction for 2.5h. After the reaction is completed, cool the reaction solution to room temperature, depressurize, filter through a 0.22μm microporous membrane to remove the catalyst, and obtain the hydrogenated crude product; (2) Transfer the hydrogenated crude product to a short-path molecular distillation apparatus (evaporation surface and condensation surface are 4cm apart), set the system pressure to 80Pa and the evaporation surface temperature to 1.5MPa in the first stage. At 80℃ and a rotor speed of 250 r / min, distill for 20 min to remove and discard the light components. In the second stage, reduce the system pressure to 0.5 Pa, raise the evaporation surface temperature to 105℃, and adjust the rotation speed to 150 r / min. Collect the main fraction in this stage. (3) Load the obtained main fraction into a chromatography column packed with 200 mesh silica gel and elute in sequence with the following eluents: 500 mL of petroleum ether; 800 mL of a mixture of petroleum ether / ethyl acetate (volume ratio 20:1); and 500 mL of a mixture of petroleum ether / ethyl acetate (volume ratio 10:1). By monitoring with thin-layer chromatography (TLC), collect the elution fraction rich in linalool. Combine the collected target elution fractions and concentrate them by rotary evaporation at 40℃ and -0.09 MPa to remove all solvents and obtain 65.4 g of colorless and transparent pure linalool.

[0038] Comparative Example 1; The difference between Comparative Example 1 and Example 2 is that step (1) is omitted, and step (2) is modified as follows: 100g of lavender essential oil is transferred to a short-path molecular distillation apparatus (the evaporation surface and the condensation surface are 4cm apart). In the first stage, the system pressure is set to 80Pa, the evaporation surface temperature is 80℃, and the rotation speed is 250r / min. Distillation is carried out for 20min to remove and discard the light components. In the second stage, the system pressure is reduced to 0.5Pa, the evaporation surface temperature is increased to 105℃, and the rotation speed is adjusted to 150r / min. The main fraction of this stage is collected. Other steps are the same as in Example 2, and 60.9g of pure linalool is obtained.

[0039] Comparative Example 2; The difference between Comparative Example 2 and Example 2 lies in step (2). Step (2) is modified as follows: the crude hydrogenated product is transferred to a 500mL round-bottom flask, connected to a vacuum distillation apparatus with a packing height of 50cm, a theoretical plate number of 25, the system vacuum degree is maintained at 0.1kPa, the heating is slow, the top temperature of the column is controlled, the bottom temperature of the column is maintained at 180℃ throughout the distillation process, the distillation time is 6h, and the main fraction with a boiling point of 198℃ is collected; other steps are the same as in Example 2, and 55.2g of pure linalool is obtained.

[0040] Comparative Example 3; The only difference between Comparative Example 3 and Example 2 is the difference in step (1). Step (1) is modified as follows: Take 100g of lavender essential oil, add 200mL of cyclohexane as solvent and place it in a high-pressure reactor, add 2.0g of Pd / C catalyst (palladium content 10%), replace the air in the reactor with hydrogen three times, then fill with hydrogen to a pressure of 2.0MPa, set the stirring speed to 600r / min, and react at 120℃ for 3h. After the reaction is completed, cool the reaction solution to room temperature, depressurize, filter through a 0.22μm microporous membrane to remove the catalyst, and obtain the hydrogenated crude product; other steps are the same as in Example 2, and 50.7g of pure linalool is obtained.

[0041] The performance of the final products obtained from all the above examples and comparative examples was tested. The purity was determined by liquid chromatography-mass spectrometry (LCMS). The yield was calculated based on the theoretical mass of linalool in the raw material (72.3 g). The content of unsaturated impurities was estimated by the sum of the peak areas of other unsaturated components besides linalool in the LCMS analysis. The optical rotation was determined by an automatic polarimeter at 20 °C, under a sodium lamp (D line), and with chloroform as the solvent. The specific results are shown in Table 1 below.

[0042] Table 1

[0043] As shown in Table 1, Example 2 achieved the best overall effect (purity 99.7%, yield 91.42%) among all examples, indicating that within the range of process parameters, the optimal conditions of using Pd / C catalyst, step-temperature hydrogenation and two-stage molecular distillation can most effectively synergistically achieve high purity and high yield.

[0044] Example 4 also achieved excellent results using the Raney Ni catalyst (purity 99.4%, yield 90.46%), demonstrating that the core process of this invention (selective hydrogenation + molecular distillation) has a certain degree of universality in terms of catalyst type, and is not limited to a specific noble metal catalyst, thus enhancing the practicality and economic options of the solution.

[0045] The purity (91.8%) and yield (84.23%) of Comparative Example 1 without hydrogenation pretreatment were significantly lower than those of all examples, and the content of unsaturated impurities was high (4.5%). This indicates that molecular distillation and column chromatography alone cannot effectively remove conjugated diene impurities, and catalytic hydrogenation as a pretreatment step is crucial for overcoming the purity bottleneck.

[0046] The conventional vacuum distillation yield of Comparative Example 2 was only 76.35%, and the optical rotation shifted significantly (+13.5°). This indicates that the conventional high-temperature distillation process leads to severe degradation or isomerization of the thermosensitive linalool, resulting in a large loss of product and structural changes. This confirms the necessity and advantages of using mild molecular distillation in this invention.

[0047] The purity of the high-temperature non-selective hydrogenation in Comparative Example 3 was 85.3%, the yield was 70.12%, and the optical rotation deviated significantly to +9.8°. This indicates that if the hydrogenation reaction temperature is as high as 120°C, even with the same catalyst, the selectivity will be completely lost, leading to the destruction of the linalool main structure due to unnecessary hydrogenation side reactions. This proves that controlling the hydrogenation temperature within the range of 40 to 80°C is the key to achieving selectivity in this invention.

[0048] Figure 1 shows the liquid chromatogram of linalool in Example 2. As shown in Figure 1, linalool shows a characteristic main peak at 5.2 min, with a symmetrical peak shape and no obvious tailing. The impurity peak response values ​​at 3.8 min and 6.7 min are extremely low.

[0049] Figure 2 shows the 1H NMR spectrum of linalool in Example 2. As shown in Figure 2, δ=1.60ppm (6H,s,-CH3) is the characteristic peak of methyl, δ=3.85ppm (2H,t,-CH2OH) is the peak of hydroxymethyl, and δ=5.08ppm (1H,m,C=CH-) is the peak of double bond hydrogen. It is consistent with the standard 1H NMR data of linalool, and the target substance can be identified as linalool.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for high-purity extraction of linalool essential oil, characterized in that, Includes the following steps: (1) Linalool essential oil is mixed with an inert solvent, a metal catalyst is added, and selective hydrogenation is carried out in a hydrogen atmosphere to obtain a crude hydrogenated product; (2) The crude hydrogenated product is subjected to short-path molecular distillation to remove light components in sequence and collect the linalool main fraction; (3) The linalool main fraction is separated by silica gel column chromatography, and high-purity linalool is obtained after elution and concentration.

2. The method for high-purity purification of linalool essential oil according to claim 1, characterized in that, The metal catalyst in step (1) is at least one of Pd / C, Raney Ni, and Pt / Al2O3.

3. The method for high-purity purification of linalool essential oil according to claim 1, characterized in that, In step (1), the amount of metal catalyst used is 0.5 to 3.0% of the mass of linalool essential oil.

4. The method for high-purity purification of linalool essential oil according to claim 1, characterized in that, In step (1), the inert solvent is one or more of n-hexane and cyclohexane.

5. The method for high-purity purification of linalool essential oil according to claim 1, characterized in that, In step (1), the selective hydrogenation reaction adopts a step-by-step heating method: first react at 40-50℃ for 1 hour, and then heat to 60-80℃ for 2-3 hours.

6. The method for high-purity purification of linalool essential oil according to claim 1, characterized in that, In step (2), short-range molecular distillation is carried out in two stages: the first stage is to remove light components at 50~100 Pa and 70~90 °C; the second stage is to collect the linalool main fraction at 0.1~1.0 Pa and 95~110 °C.

7. The method for high-purity purification of linalool essential oil according to claim 1, characterized in that, In step (2), the evaporation surface and the condensation surface of the short-range molecular distillation apparatus are 3-5 cm apart.

8. The method for high-purity purification of linalool essential oil according to claim 1, characterized in that, In step (3), the column chromatography uses gradient elution with petroleum ether and ethyl acetate as the eluent.

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