A process for the preparation of menthane and anethane bifunctional perfume derivatives

Abstract

The present application relates to the field of preparation of perfume derivatives, and particularly relates to a preparation method of bifunctional perfume derivatives of menthol and anethole. The present application uses natural menthol and trans-anethole from anise oil as raw materials, and uses solid acid as catalyst to synthesize the target bifunctional perfume derivatives through ester exchange and condensation reaction. In the preparation method provided by the present application, no organic solvent is used, which is green and environmentally friendly, the catalyst can be recycled and used, and the method is suitable for industrial production. The product prepared has both menthol cooling and anise pungency, and the antibacterial rate of the product on escherichia coli, staphylococcus aureus and candida albicans is greater than or equal to 98%, the product has excellent thermal stability, and can be widely applied to various fields such as food, daily chemical, tobacco and medicine.

Description

Technical Field

[0001] This invention relates to the field of flavor derivative preparation, specifically to a method for preparing a bifunctional flavor derivative of menthol and anethole. Background Technology

[0002] Menthol is a naturally derived cooling agent widely used in food, daily chemicals, pharmaceuticals, and tobacco industries. It provides a strong cooling sensation, but suffers from drawbacks such as short-lasting cooling effect, high volatility, a high cooling threshold, and poor stability under high-temperature processing conditions. Trans-anetraloids, the main active ingredient in fennel oil, possess a characteristic fennel-like spicy aroma and are commonly used natural flavorings in the food and daily chemical industries. However, they suffer from aroma loss, lack of cooling function, and lack of biological activity. Current technologies often employ direct physical blending of menthol and fennel-based flavorings to achieve both cooling and aroma effects. However, the polarity difference between the two leads to poor compatibility in the blended system, resulting in issues like layering and precipitation. Furthermore, these methods fail to address the volatilization, limited functionality, and lack of antibacterial activity of both, thus restricting their application scope. In existing technologies, the synthesis of peppermint-based flavor derivatives mostly employs multi-step reaction processes and requires the use of organic solvents such as toluene, xylene, and dichloromethane. This not only results in long process flows and low production efficiency but also causes environmental pollution from solvent volatilization and solvent residues in the products. Furthermore, existing synthetic products primarily focus on optimizing cooling properties and cannot simultaneously achieve the integration of cooling sensation, characteristic aroma, and broad-spectrum antibacterial activity, making it difficult to apply them to various fields.

[0003] Therefore, inventing a simple, environmentally friendly method for preparing a dual-functional fragrance derivative that possesses cooling, fragrance, and antibacterial activity is very promising. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention aims to provide a method for preparing a bifunctional flavor derivative of menthol and anethole. This invention uses natural menthol and trans-anethole derived from fennel oil as raw materials, and a solid acid as a catalyst, to synthesize the target bifunctional flavor derivative through transesterification and condensation reactions. The preparation method provided by this invention uses no organic solvents, making it environmentally friendly. The catalyst is recyclable and suitable for industrial production. The obtained product possesses both a mentholic cooling sensation and aniseed spiciness, and exhibits an antibacterial rate of ≥98% against Escherichia coli, Staphylococcus aureus, and Candida albicans. It also demonstrates excellent thermal stability and can be widely applied in various fields such as food, daily chemicals, tobacco, and pharmaceuticals.

[0005] This invention discloses a method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following preparation steps:

[0006] S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are subjected to vacuum drying and dehydration treatment, and the moisture content is controlled to be ≤0.05wt% for later use. S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and solid acid catalyst treated in step S1 are added to the reactor, stirring is started, the temperature is raised to the first reaction temperature, and the transesterification reaction is carried out to generate monomenthyl carbonate intermediate; then, trans-anetinoside treated in step S1 is added to the reaction system, the temperature is raised to the second reaction temperature, and the in-situ condensation reaction is carried out to obtain the crude product. S3 Post-processing: The crude product obtained in step S2 is filtered to recover the solid acid catalyst. The filtrate is collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives.

[0007] Preferably, in step S2, the molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinoside is 1:(1~2):(0.7~1.2).

[0008] Preferably, in step S2, the solid acid catalyst is a heteropolyacid solid catalyst, and its mass ratio with the treated menthol is 1:(5~10).

[0009] Preferably, the heteropolyacid solid catalyst is a silicotungstic acid solid catalyst supported on activated carbon.

[0010] Preferably, in step S2, the first reaction temperature is 110~120℃, and the holding time for the transesterification reaction is 3~4h.

[0011] Preferably, in step S2, the second reaction temperature is 150~160℃, and the in-situ condensation reaction is kept at a temperature of 5~6h.

[0012] Preferably, in step S2, the stirring rate is 600~700 rpm; the pressure during the reaction process is 0.01~0.06 MPa.

[0013] Preferably, in step S3, the vacuum degree of the reduced pressure distillation is -0.1 to -0.2 MPa, and the temperature is 100 to 110°C.

[0014] Preferably, in step S3, the recrystallization uses a mixed solvent composed of anhydrous ethanol and n-hexane, wherein the volume ratio of anhydrous ethanol to n-hexane in the mixed solvent is 1:4, the recrystallization temperature is -5~0℃, and the recrystallization time is 4~7h.

[0015] Preferably, in step S3, the recovered solid acid catalyst is collected and recycled after being washed with anhydrous ethanol and vacuum dried in the reaction system.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for preparing a bifunctional flavoring derivative of menthol and anethole, which has the following characteristics: (1) In this invention, dimethyl carbonate is used as a bridging group. Through the directional synthesis of asymmetric carbonate, the menthol-based cooling unit and the anethole-based fragrance unit are covalently bonded to the same molecule. While retaining the characteristic spatial conformation of isopropyl and methyl groups on menthol cyclohexane, the characteristic aroma structure of the p-propenyl benzene ring of trans-anetinoside is completely preserved, thus realizing the integration of cooling and fragrance functions.

[0017] (2) This invention uses a heteropolyacid solid catalyst supported on activated carbon with silicotungstic acid as a heterogeneous catalytic system to achieve precise matching and efficient advancement of transesterification and condensation tandem reactions. Silicotungstic acid itself has strong and uniform Brønsted acidic sites, which can simultaneously and efficiently catalyze the transesterification reaction of menthol and dimethyl carbonate, and the in-situ condensation reaction of monomenthyl carbonate and anethole hydroxyl derivatives. The two-step reaction can be carried out continuously without replacing the catalyst. By supporting silicotungstic acid on activated carbon with a high specific surface area, the inherent defects of pure heteropolyacids, such as small specific surface area, insufficient exposure of active sites, and easy solubility in the reaction system leading to loss and deactivation, are solved. Furthermore, through the adsorption and enrichment effect of activated carbon, the reaction raw materials are directionally enriched around the active sites of the catalyst, which greatly improves the reaction rate and conversion efficiency, effectively avoids the occurrence of side reactions such as the self-polymerization of dimenthyl carbonate and anethole, and achieves high yield and high purity of the product.

[0018] (3) The product prepared by the method provided by this invention possesses two complementary antibacterial active structures, exhibiting broad-spectrum and highly efficient antibacterial effects. Specifically, the carbonate bonds in the molecule can insert into the phospholipid bilayer of the cell membrane of bacteria and fungi through hydrophobic interactions, disrupting the integrity and fluidity of the cell membrane, altering cell membrane permeability, and causing leakage of intracellular nutrients, electrolytes, and genetic material, directly resulting in microbial death. Meanwhile, the aromatic ring conjugated structure of the anisyl group can inhibit electron transfer in the microbial respiratory chain, hindering nucleic acid replication and protein synthesis, and blocking the proliferation process of microorganisms. The synergistic effect of the two active structures results in an antibacterial rate of ≥98% against Escherichia coli, Staphylococcus aureus, and Candida albicans, making it applicable in various fields.

[0019] (4) The present invention adopts a completely solvent-free reaction system, which avoids the use of organic solvents in traditional processes and solves the problems of environmental pollution and product solvent residue caused by solvent volatilization; it adopts a solid acid heterogeneous catalyst, which eliminates equipment corrosion problems, and the catalyst can be recycled and reused. No toxic or harmful byproducts are generated throughout the reaction process, which meets the requirements of green chemical industry and sustainable development. Detailed Implementation

[0020] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0021] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0022] Example 1: A method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following steps: S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are subjected to vacuum drying and dehydration treatment, and the moisture content is controlled to be ≤0.05wt% for later use. S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and a solid acid catalyst treated in step S1 were added to a reaction vessel. The molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinolate was 1:1:0.7. The solid acid catalyst was a heteropoly acid solid catalyst, specifically a silicotungstic acid solid catalyst supported on activated carbon, with a mass ratio of silicotungstic acid to the treated menthol of 1:5. Stirring was started at a speed of 600 rpm. The pressure during the reaction was 0.01 MPa. The temperature was raised to the first reaction temperature and maintained for 3 hours for transesterification, at 110°C, to generate a monomenthyl carbonate intermediate. Then, trans-anetinolate treated in step S1 was added to the reaction system, and the temperature was raised to the second reaction temperature and maintained for 5 hours for in-situ condensation, at 150°C, to obtain the crude product.

[0023] S3 Post-processing: The crude reaction product obtained in step S2 was filtered to recover the solid acid catalyst. The filtrate was collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives. The vacuum distillation was performed at -0.1 MPa and 100°C. Recrystallization was carried out using a mixed solvent of anhydrous ethanol and n-hexane, with a volume ratio of anhydrous ethanol to n-hexane of 1:4. The recrystallization temperature was -5°C, and the recrystallization time was 4 hours. The solid acid catalyst was recovered by washing it with anhydrous ethanol and vacuum drying before collection and recycling.

[0024] Example 2: A method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following steps: S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are subjected to vacuum drying and dehydration treatment, and the moisture content is controlled to be ≤0.05wt% for later use. S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and a solid acid catalyst treated in step S1 were added to a reaction vessel. The molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinolate was 1:1.2:0.8. The solid acid catalyst was a heteropoly acid solid catalyst, specifically a silicotungstic acid solid catalyst supported on activated carbon, with a mass ratio of silicotungstic acid to the treated menthol of 1:6. Stirring was started at a speed of 620 rpm. The pressure during the reaction was 0.02 MPa. The temperature was raised to the first reaction temperature and held for transesterification at 112°C for 3.2 h, generating a monomenthyl carbonate intermediate. Then, trans-anetinolate treated in step S1 was added to the reaction system, and the temperature was raised to the second reaction temperature and held for in-situ condensation at 152°C for 5.2 h, yielding the crude product.

[0025] S3 Post-processing: The crude reaction product obtained in step S2 was filtered to recover the solid acid catalyst. The filtrate was collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives. The vacuum distillation was performed at -0.12 MPa and a temperature of 102 °C. Recrystallization was carried out using a mixed solvent of anhydrous ethanol and n-hexane, with a volume ratio of anhydrous ethanol to n-hexane of 1:4. The recrystallization temperature was -4 °C, and the recrystallization time was 4.5 h. The solid acid catalyst was recovered by washing it with anhydrous ethanol and vacuum drying before collection and recycling.

[0026] Example 3: A method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following steps: S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are subjected to vacuum drying and dehydration treatment, and the moisture content is controlled to be ≤0.05wt% for later use. S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and a solid acid catalyst treated in step S1 were added to a reaction vessel. The molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinolate was 1:1.4:0.9. The solid acid catalyst was a heteropoly acid solid catalyst, specifically a silicotungstic acid solid catalyst supported on activated carbon, with a mass ratio of silicotungstic acid to the treated menthol of 1:7. Stirring was started at a speed of 640 rpm. The pressure during the reaction was 0.03 MPa. The temperature was raised to the first reaction temperature and held for transesterification at 114°C for 3.4 h, generating a monomenthyl carbonate intermediate. Then, trans-anetinolate treated in step S1 was added to the reaction system, and the temperature was raised to the second reaction temperature and held for in-situ condensation at 154°C for 5.4 h, yielding the crude product.

[0027] Post-processing (S3): The crude product obtained in step S2 was filtered to recover the solid acid catalyst. The filtrate was collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives. The vacuum distillation was performed at -0.14 MPa and a temperature of 104 °C. Recrystallization was carried out using a mixed solvent of anhydrous ethanol and n-hexane, with a volume ratio of anhydrous ethanol to n-hexane of 1:4. The recrystallization temperature was -3 °C, and the recrystallization time was 5 h. The solid acid catalyst was recovered by washing it with anhydrous ethanol and vacuum drying before collection and recycling.

[0028] Example 4: A method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following steps: S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are subjected to vacuum drying and dehydration treatment, and the moisture content is controlled to be ≤0.05wt% for later use. S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and a solid acid catalyst treated in step S1 were added to a reaction vessel. The molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinolate was 1:1.6:1. The solid acid catalyst was a heteropoly acid solid catalyst, specifically a silicotungstic acid solid catalyst supported on activated carbon, with a mass ratio of 1:8 to the treated menthol. Stirring was started at a rate of 660 rpm. The pressure during the reaction was 0.04 MPa. The temperature was raised to the first reaction temperature and maintained for transesterification at 116°C for 3.6 h, generating a monomenthyl carbonate intermediate. Then, trans-anetinolate treated in step S1 was added to the reaction system, and the temperature was raised to the second reaction temperature and maintained for in-situ condensation at 156°C for 5.6 h, yielding the crude reaction product.

[0029] S3 Post-processing: The crude reaction product obtained in step S2 was filtered to recover the solid acid catalyst. The filtrate was collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives. The vacuum distillation was performed at -0.16 MPa and a temperature of 106 °C. Recrystallization was carried out using a mixed solvent of anhydrous ethanol and n-hexane, with a volume ratio of anhydrous ethanol to n-hexane of 1:4. The recrystallization temperature was -2 °C, and the recrystallization time was 5.5 h. The solid acid catalyst was recovered by washing it with anhydrous ethanol and vacuum drying before collection and recycling.

[0030] Example 5: A method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following steps: S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are subjected to vacuum drying and dehydration treatment, and the moisture content is controlled to be ≤0.05wt% for later use. S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and a solid acid catalyst treated in step S1 were added to a reaction vessel. The molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinolate was 1:1.8:1.1. The solid acid catalyst was a heteropoly acid solid catalyst, specifically a silicotungstic acid solid catalyst supported on activated carbon, with a mass ratio of silicotungstic acid to the treated menthol of 1:9. Stirring was started at a speed of 680 rpm. The pressure during the reaction was 0.05 MPa. The temperature was raised to the first reaction temperature and held for transesterification at 118°C for 3.8 h, generating a monomenthyl carbonate intermediate. Then, trans-anetinolate treated in step S1 was added to the reaction system, and the temperature was raised to the second reaction temperature and held for in-situ condensation at 158°C for 5.8 h, yielding the crude product.

[0031] S3 Post-processing: The crude reaction product obtained in step S2 was filtered to recover the solid acid catalyst. The filtrate was collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives. The vacuum distillation was performed at -0.18 MPa and a temperature of 108 °C. Recrystallization was carried out using a mixed solvent of anhydrous ethanol and n-hexane, with a volume ratio of anhydrous ethanol to n-hexane of 1:4. The recrystallization temperature was -1 °C, and the recrystallization time was 6 h. The solid acid catalyst was recovered by washing it with anhydrous ethanol and vacuum drying before collection and recycling.

[0032] Example 6: A method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following steps: S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are subjected to vacuum drying and dehydration treatment, and the moisture content is controlled to be ≤0.05wt% for later use. S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and a solid acid catalyst treated in step S1 were added to a reaction vessel. The molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinolate was 1:2:1.2. The solid acid catalyst was a heteropolyacid solid catalyst, specifically a silicotungstic acid solid catalyst supported on activated carbon, with a mass ratio of silicotungstic acid to the treated menthol of 1:10. Stirring was started at a speed of 700 rpm. The pressure during the reaction was 0.06 MPa. The temperature was raised to the first reaction temperature and held for 4 hours for transesterification, producing a monomenthyl carbonate intermediate. Then, trans-anetinolate treated in step S1 was added to the reaction system, and the temperature was raised to the second reaction temperature and held for 6 hours for in-situ condensation, producing the crude product.

[0033] S3 Post-processing: The crude product obtained in step S2 was filtered to recover the solid acid catalyst. The filtrate was collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives. The vacuum distillation was performed at -0.2 MPa and a temperature of 110°C. Recrystallization was carried out using a mixed solvent of anhydrous ethanol and n-hexane, with a volume ratio of anhydrous ethanol to n-hexane of 1:4. The recrystallization temperature was 0°C, and the recrystallization time was 7 hours. The solid acid catalyst was recovered by washing it with anhydrous ethanol and vacuum drying before collection and recycling.

[0034] Example 7: Dimethyl carbonate was not added to the raw materials, and all other raw materials and step parameters were the same as in Example 4.

[0035] Example 8: No solid acid catalyst was added to the raw materials, and the other raw materials and step parameters were the same as in Example 4.

[0036] Example 9: In step S2, the two-stage temperature reaction is not carried out. The second reaction temperature is the same as the first reaction temperature, which is 116°C. All other raw materials and step parameters are the same as in Example 4.

[0037] Example 10: A method for preparing a bifunctional flavoring derivative of menthol and anethole, comprising the following steps: Menthol, dimethyl carbonate, toluene, and p-toluenesulfonic acid catalyst were heated to 110°C and refluxed for 4 hours. After the reaction, the solvent and excess raw material were removed by vacuum distillation to obtain a monomenthyl carbonate intermediate. The obtained monomenthyl carbonate intermediate, trans-anisole, dichloromethane, and 4-dimethylaminopyridine catalyst were stirred at room temperature for 5 hours. After the reaction, the mixture was washed successively with dilute hydrochloric acid and saturated brine. The organic phase was dried with anhydrous sodium sulfate, and the solvent was removed by vacuum distillation. After recrystallization and purification, and vacuum drying, a bifunctional flavor derivative of menthol and anethole was obtained.

[0038] The properties of the menthol and anethole bifunctional flavor derivatives prepared in Examples 1-10 were tested, and the results are shown in the table below: Table 1: Examples 1-6

[0039] Table 2: Examples 7-10

[0040] From the data in Tables 1 and 2 above, we can see that: (1) Examples 1-6 achieved gradual optimization of reaction efficiency and product performance by gradient control of core parameters such as raw material molar ratio, catalyst dosage, reaction temperature, time, and system pressure. Example 4 represents the optimal process combination. Dimethyl carbonate, as a bridging group, with a molar ratio of 1.6, ensured complete transesterification of menthol to generate monosubstituted monomenthyl carbonate intermediate while avoiding the disubstituted dimenthyl carbonate side reaction caused by excess dimethyl carbonate, thus ensuring high selectivity of the intermediate. The amount of silicotungstic acid-supported activated carbon catalyst was 12.5% ​​of the menthol mass, providing sufficient and uniform Brønsted acidic sites to achieve continuous catalysis of transesterification and condensation tandem reactions, while avoiding raw material adsorption loss and anethole self-polymerization side reaction caused by excess catalyst. The two-stage temperature control design ensured high selectivity of the transesterification reaction in the low-temperature stage and was suitable for the activation energy of the condensation reaction in the high-temperature stage, achieving complete in-situ conversion of the intermediate without separation and purification, ultimately achieving high yield and high purity synthesis of the target product.

[0041] (2) Example 7 shows a bifunctional flavor derivative of menthol and anethole prepared without the addition of dimethyl carbonate, and its properties are reduced across the board. This is because without the presence of dimethyl carbonate, it is impossible to construct an asymmetric carbonate covalent structure, and the menthol and anethole groups cannot be integrated. Only a small amount of random side reaction can occur, resulting in extremely low purity and yield of the target product, and therefore, the bifunctional properties cannot be achieved.

[0042] (3) Example 8 shows a bifunctional flavor derivative of menthol and anethole prepared without the addition of a solid acid catalyst. All its data showed a significant decrease. This is because both transesterification and condensation reactions require acidic active sites to lower the activation energy of the reaction. Without a catalyst, the two-step reaction cannot proceed, and only trace amounts of the target product can be generated.

[0043] (4) Example 9 is a bifunctional flavoring derivative of menthol and anethole prepared by a single-temperature reaction. The results are higher than those of Examples 7-8, but still lower than those of Examples 1-6. This is because the activation energy of the condensation reaction is higher than that of the transesterification reaction. The uniform low temperature cannot meet the energy requirements of the condensation reaction, resulting in incomplete conversion of intermediates, a significant decrease in the yield and purity of the target product, an increase in the content of by-products, and a significant degradation of various properties.

[0044] (5) Example 10 is a bifunctional flavor derivative of menthol and anethole prepared by a traditional solvent two-step method. Its properties are improved compared with those of Examples 7-9, but are still lower than those of Examples 1-6. The traditional two-step method requires the use of organic solvents and the replacement of the catalytic system. The process is long, the homogeneous catalyst has poor selectivity, and there are many by-products. The purity and yield of the products are significantly lower than those of the process of this invention. In addition, there are problems such as solvent residue and high environmental pressure.

[0045] In summary, the preparation method provided by this invention achieves three major functions—cooling sensation, fragrance, and broad-spectrum antibacterial properties—of menthol and anethole dual-function fragrance derivatives through dimethyl carbonate-bridged molecular covalent integration, a silicotungstic acid-supported activated carbon catalytic system, and solvent-free transesterification and condensation tandem processes. Example 4 represents the optimal process combination, with a product purity of 99.4%, an overall reaction yield of 89.2%, a cooling threshold 45% lower than that of natural menthol, a fragrance retention time of 75 hours, an antibacterial rate of ≥99% against all three test strains, and a thermal decomposition temperature of 230℃, demonstrating the best overall performance.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a bifunctional flavoring derivative of menthol and anethole, characterized in that, Includes the following steps: S1 Raw Material Pretreatment: Natural menthol and trans-anetinoside are dried and dehydrated to control the moisture content to ≤0.05wt% for later use; S2 Solvent-free tandem reaction: Under a nitrogen protective atmosphere, menthol, dimethyl carbonate, and solid acid catalyst treated in step S1 are added to the reactor, stirring is started, the temperature is raised to the first reaction temperature, and the transesterification reaction is carried out to generate monomenthyl carbonate intermediate; then, trans-anetinoside treated in step S1 is added to the reaction system, the temperature is raised to the second reaction temperature, and the in-situ condensation reaction is carried out to obtain the crude product. S3 Post-processing: The crude product obtained in step S2 is filtered to recover the solid acid catalyst. The filtrate is collected and subjected to depressurization distillation, recrystallization, and vacuum drying to obtain menthol and anethole bifunctional flavor derivatives.

2. The method for preparing a bifunctional flavoring derivative of menthol and anethole according to claim 1, characterized in that, In step S2, the molar ratio of the treated menthol, dimethyl carbonate, and treated trans-anetinoside is 1:(1~2):(0.7~1.2).

3. The method for preparing a bifunctional flavoring derivative of menthol and anethole according to claim 1, characterized in that, In step S2, the solid acid catalyst is a heteropoly acid solid catalyst, and its mass ratio with the treated menthol is 1:(5~10).

4. The method for preparing a bifunctional flavoring derivative of menthol and anethole according to claim 3, characterized in that, The heteropolyacid solid catalyst is a solid catalyst of silicotungstic acid supported on activated carbon.

5. The method for preparing a bifunctional flavor derivative of menthol and anethole according to claim 1, characterized in that, In step S2, the first reaction temperature is 110~120℃, and the holding time for the transesterification reaction is 3~4h.

6. The method for preparing a bifunctional flavor derivative of menthol and anethole according to claim 1, characterized in that, In step S2, the second reaction temperature is 150~160℃, and the in-situ condensation reaction is kept at this temperature for 5~6 hours.

7. The method for preparing a bifunctional flavor derivative of menthol and anethole according to claim 1, characterized in that, In step S2, the stirring rate is 600~700 rpm; the pressure during the reaction process is 0.01~0.06 MPa.

8. The method for preparing a bifunctional flavor derivative of menthol and anethole according to claim 1, characterized in that, In step S3, the vacuum degree of the reduced pressure distillation is -0.1 to -0.2 MPa, and the temperature is 100 to 110 °C.

9. The method for preparing a bifunctional flavor derivative of menthol and anethole according to claim 1, characterized in that, In step S3, the recrystallization uses a mixed solvent composed of anhydrous ethanol and n-hexane, with a volume ratio of anhydrous ethanol to n-hexane of 1:

4. The recrystallization temperature is -5 to 0°C, and the recrystallization time is 4 to 7 hours.

10. The method for preparing a bifunctional flavor derivative of menthol and anethole according to claim 1, characterized in that, In step S3, the recovery of the solid acid catalyst involves washing the solid acid catalyst in the reaction system with anhydrous ethanol and vacuum drying before collecting and recycling it.

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