A biphenyl diphenol-based aluminum catalyst for preparing thymol, a preparation method and application thereof

Abstract

The present invention provides a biphenyl diphenol-based aluminum catalyst for preparing thymol, a preparation method thereof, and a preparation method of thymol and an application method thereof. The present invention prepares a catalyst by using a biphenyl diphenol compound and an aluminum-containing compound (such as alkyl aluminum or aluminum hydride), and then uses the catalyst to catalyze an alkylation reaction of m-cresol and propylene to prepare thymol. The catalytic effect can be further improved by adding isopropyl ether or isopropyl ester. The method of the present invention has the advantages of mild reaction conditions, high product selectivity, etc., and is particularly suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis and relates to a method for preparing thymol, and specifically relates to a biphenyl diphenol-based aluminum catalyst for preparing thymol and a preparation method thereof and a method for preparing thymol. Background Art

[0002] Thymol is named after the thyme from which it is isolated. It has medicinal value and can be used in oral hygiene products. It has antifungal and antiparasitic functions. Thymol can also be used as a spice to prepare flavors. In addition, thymol is also an important raw material for the synthesis of L-menthol.

[0003] Thymol is produced by reacting m-cresol with an alkylating agent, which is mainly divided into the isopropyl halogenation method, the propylene method and the isopropanol method. The raw materials of the propylene method and the isopropanol method are easier to source, and the propylene method has lower costs and is easier to industrialize.

[0004]

[0005] Patent US1886311 reported a method for synthesizing thymol by propylene method, with a temperature of 330-350°C, a pressure of 30-40MPa, a m-cresol conversion rate of about 40%, and a thymol selectivity of 50-60%. Patent US4086283 reported that activated hydrous alumina was used as a catalyst in the presence of a nitrogenous base, the reaction temperature was 350-365°C, and the pressure was 5MPa. The crude product contained about 60% thymol, of which 25% m-cresol was not converted.

[0006] The existing processes generally have the problems of harsh reaction conditions, low conversion rate and selectivity. The main isomers produced during the reaction are as follows:

[0007]

[0008] Some existing technologies improve the technical effect by adding nitrogen-containing organic bases as additives, but this will affect the odor and quality of the product, the catalyst life is short and regeneration is difficult. Summary of the invention

[0009] In view of the above-mentioned shortcomings in the prior art, one of the objects of the present invention is to provide a biphenyl diphenol-based aluminum catalyst for preparing thymol and a preparation method thereof, wherein the catalyst is prepared by reacting a biphenyl diphenol compound with an alkyl aluminum or aluminum hydride.

[0010] The present invention also aims to provide a method for preparing thymol, wherein the alkylation reaction of m-cresol and propylene is catalyzed by the above catalyst to prepare thymol. The reaction selectivity can be improved by adding auxiliary agents such as isopropyl ether and / or isopropyl ester. The method has the advantages of mild reaction conditions and high product selectivity, and is suitable for industrial production.

[0011] In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0012] The present invention provides a biphenol-based aluminum catalyst, which is prepared from a biphenol compound represented by formula (I) and an aluminum-containing compound represented by formula (II);

[0013]

[0014] In formula (I): R1, R2, and R3 are independently selected from hydrogen, C1 to C 10 Alkyl, C6~C l4 substituted or unsubstituted aryl, preferably C1-C6 alkyl, C6-C8 substituted or unsubstituted aryl, wherein the substituents are independently selected from C1-C5 alkyl, halogen, trihalomethyl, trihalomethoxy, methoxy, acetyl, acetoxy, dimethylamino, diethylamino, trimethylsilyl, triethylsilyl, cyano or nitro; preferably, the alkyl is isopropyl or tert-butyl; preferably, the aryl is an aryl with 1 to 5 substituents, more preferably a group with large steric hindrance and electron-withdrawing substituents, most preferably 3,5-bis(trifluoromethyl)phenyl;

[0015] (R4) 3-n AlH n (II)

[0016] In formula (II): R4 is selected from C1-C5 alkyl, preferably methyl, ethyl, isobutyl; n is 0 or an integer of 1-3.

[0017] Further, in the biphenyl diphenol compound represented by formula (I), R1, R2, and R3 may be the same or different, and in each case, the two substituents R2 and R3 bonded to the biphenyl diphenol compound are preferably the same;

[0018] More preferably, the biphenyl diphenol compound represented by formula (I) is selected from one of the following structural formulas:

[0019]

[0020]

[0021] The present invention also provides a method for preparing the above-mentioned biphenyl diphenol-based aluminum catalyst, the steps comprising:

[0022] In an anhydrous and oxygen-free atmosphere, the biphenyl diphenol compound represented by formula (I) and the aluminum-containing compound represented by formula (II) are dissolved in a solvent to prepare a biphenyl diphenol compound solution and an aluminum-containing compound solution, respectively; then the aluminum-containing compound solution is added to the biphenyl diphenol compound solution, and the reaction is stirred at 5 to 35° C., preferably 15 to 25° C. for 0.5 to 6 hours, preferably 1 to 3 hours, to obtain a solution containing a biphenyl diphenol-based aluminum catalyst.

[0023] In the present invention, the molar ratio of the biphenol compound represented by formula (I) to the aluminum-containing compound represented by formula (II) is 1.5 to 10:1, preferably 2 to 3:1.

[0024] In the present invention, when preparing the biphenol compound solution and the aluminum compound solution, the solvent used is selected from at least one of alkanes, aromatic hydrocarbons, halogenated hydrocarbons, ethers and ester solvents, preferably at least one of n-hexane, toluene, tetrahydrofuran and dichloromethane;

[0025] The solvents used in preparing the biphenol compound solution and the aluminum compound solution can be the same or different, preferably the same solvent is used for both;

[0026] The prepared biphenol compound solution and aluminum compound solution have a mass concentration of 1-80%, preferably 5-25%. More preferably, the amount of the solvent used is the minimum amount required to dissolve the biphenol compound or the aluminum compound.

[0027] In the present invention, when the aluminum compound solution is added to the biphenyl diphenol compound solution, it is preferably added dropwise, and the adding time is 0.05 to 3 hours, preferably 0.5 to 2 hours.

[0028] In the present invention, the anhydrous and oxygen-free atmosphere is preferably an inert gas environment, and the inert gas is selected from nitrogen and argon.

[0029] In the present invention, the prepared product is a solution containing a biphenyldiphenol-based aluminum catalyst, which can be directly used in subsequent catalytic reactions or used after the biphenyldiphenol-based aluminum catalyst is separated. The separation can be carried out by conventional operations in the art, such as removing the solvent by rotary evaporation, distillation, etc. The specific operation can be selected by technicians according to actual needs, and the present invention has no special requirements.

[0030] The present invention also provides a method for preparing thymol, wherein the method comprises the following steps: alkylating meta-cresol with propylene under the action of the above-mentioned biphenyl diphenol-based aluminum catalyst and auxiliary agent isopropyl ether or isopropyl ester to prepare thymol.

[0031] In the preparation method of the present invention, an auxiliary agent is added to the reaction system, and the auxiliary agent is selected from at least one of isopropyl ether and isopropyl ester, which can adjust the isomer ratio in the product and improve the reaction selectivity;

[0032] The isopropyl ether is selected from at least one of vinyl isopropyl ether, diisopropyl ether, ethyl isopropyl ether, methyl isopropyl ether and tert-butyl isopropyl ether, preferably at least one of vinyl isopropyl ether and diisopropyl ether;

[0033] The isopropyl ester is selected from at least one of isopropyl acetate, isopropyl carbonate, isopropyl isobutyrate and isononanoate, preferably isopropyl carbonate;

[0034] The dosage of the auxiliary agent is 0.5-3% of the mass of m-cresol, preferably 1-2%.

[0035] In the preparation method of the present invention, the amount of the biphenyl diphenol-based aluminum catalyst is 0.1 to 10% of the molar amount of meta-cresol, preferably 0.5 to 5% based on the molar amount of aluminum atoms;

[0036] The biphenyl diphenol-based aluminum catalyst is prepared as a biphenyl diphenol-based aluminum catalyst solution with a concentration of 1 to 80 wt%, preferably 10 to 25 wt%;

[0037] The solution can be prepared directly using the solution containing the biphenyl diphenol aluminum catalyst prepared by the above method, or can be prepared by mixing the biphenyl diphenol aluminum catalyst with a solvent;

[0038] When preparing the solution, a solvent that is inert during the alkylation reaction is used, which is selected from at least one of alkanes, aromatic hydrocarbons, halogenated hydrocarbons, ethers and esters, more preferably at least one of n-hexane, toluene, tetrahydrofuran and dichloromethane; most preferably, the same solvent as that used in the above-mentioned method for preparing the biphenyldiphenol-based aluminum catalyst is used.

[0039] In the preparation method of the present invention, the biphenyldiphenol-based aluminum catalyst solution is preferably added dropwise during the alkylation reaction, and the dropping time is 0.5 to 24 hours, preferably 2 to 4 hours, and the dropping time is included in the alkylation reaction time.

[0040] In the preparation method of the present invention, the molar ratio of m-cresol to propylene is 1:1-3, preferably 1:1.5-2.5.

[0041] In the preparation method of the present invention, the alkylation reaction has a reaction temperature of 0 to 90° C., preferably 40 to 60° C., and a reaction time of 0.5 to 24 h, preferably 1 to 6 h.

[0042] Preferably, the alkylation reaction is carried out in an inert gas atmosphere, and the oxygen content in the inert gas is controlled to be less than 20 ppm, including but not limited to high-purity nitrogen and high-purity argon.

[0043] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0044] The present invention prepares a catalyst by using a biphenyl diphenol compound and an aluminum compound (alkyl aluminum or aluminum hydride) to catalyze the alkylation reaction of m-cresol and propylene to prepare thymol. The addition of isopropyl ether and / or isopropyl ester can further improve the catalytic effect. The present invention overcomes the disadvantage of low selectivity of catalyst products in the prior art, has mild reaction conditions, high product selectivity, and low process safety risk, and is particularly suitable for industrial production. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with embodiments, but the present invention is not limited to the listed embodiments, and should also include equivalent improvements and modifications of the technical solutions defined in the claims attached to the present application.

[0046] In the embodiment of the present invention, gas chromatography analysis was performed according to the following method: 30mDB-WAX, ID.: 0.32mm, FD.: 0.25μm; 80~230℃, 3℃ / min;

[0047] In the various embodiments and comparative examples of the present invention, the sources of the main raw materials are as follows. Unless otherwise specified, other raw materials and reagents are purchased through common commercial channels:

[0048] 3,3'-di-tert-butyl-5,5',6,6'-tetramethylbiphenyl-2,2'-diol, i.e. biphenol compound (4): 98 wt%, Daicel Pharmaceutical Chiral Technology (Shanghai) Co., Ltd.;

[0049] 4',5',5",6"-tetramethyl-[1,1':3',1":3",1"'-quadrphenyl]-2',2"-diphenol, i.e. biphenol compound (5): 98wt%, Daicel Pharmaceutical Chiral Technology (Shanghai) Co., Ltd.;

[0050] 3,3'-di(9-anthracenyl)-5,5',6,6'-tetramethylbiphenyl-2,2'-diphenol, i.e. biphenol compound (8): 98wt%, Daicel Pharmaceutical Chiral Technology (Shanghai) Co., Ltd.;

[0051] 3,3'-Bis[3,5-bis(trifluoromethyl)phenyl]-5,5',6,6'-tetramethylbiphenyl-2,2'-diphenol, i.e. biphenol compound (10): 98wt%, Daicel Pharmaceutical Chiral Technology (Shanghai) Co., Ltd.;

[0052] tert-Butyl lithium 1.3 M hexane solution, J&K Technology Co., Ltd.;

[0053] Triethylaluminum, trimethylaluminum, triisobutylaluminum: 98wt%, Bailingwei Technology Co., Ltd.

[0054] Example 1

[0055] Thymol is prepared from m-cresol and propylene under high-purity nitrogen protection by the following steps:

[0056] 1) Preparation of catalyst solution:

[0057] 6.61 g (10 mmol) of 3,3'-bis[3,5-bis(trifluoromethyl)phenyl]-5,5',6,6'-tetramethylbiphenyl-2,2'-diphenol (ie, biphenyl diphenol compound 10) and 20 g of anhydrous n-hexane were mixed to prepare a biphenyl diphenol compound transparent solution with a concentration of 25.0 wt%.

[0058] 0.57 g (5 mmoL) of triethylaluminum and 10 g of anhydrous n-hexane were mixed to prepare a triethylaluminum solution with a concentration of 5.4 wt%.

[0059] At room temperature, the triethylaluminum solution was added dropwise to the transparent solution of the biphenyl diphenol compound for 0.5 h, and then stirred and reacted at 25° C. for 1 h to obtain a biphenyl diphenol-based aluminum catalyst solution with a concentration of 19.4 wt%.

[0060] 2) Preparation of thymol:

[0061] 108.06 g (1.0 mol) of m-cresol was mixed with 84.10 g (2.0 mol) of propylene and 2.16 g of vinyl isopropyl ether, and then the temperature was raised to 50°C. The catalyst solution of step 1) (the amount of catalyst was 5 mmol based on aluminum atoms) was added dropwise thereto, and the mixture was mixed and stirred to start the alkylation reaction. The reaction was carried out for 5 h (the catalyst solution was added dropwise for 0.5 h) to obtain thymol.

[0062] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 98.6%, the selectivity of thymol was 93.7%, the total selectivity of other isomers was 4.2% (of which isomer I accounted for 0.1%), and the selectivity of other impurities was 2.1%.

[0063] Example 2

[0064] Thymol is prepared from m-cresol and propylene under high-purity nitrogen protection by the following steps:

[0065] 1) Preparation of catalyst solution:

[0066] 19.98 g (30 mmol) of 3,3'-bis[3,5-bis(trifluoromethyl)phenyl]-5,5',6,6'-tetramethylbiphenyl-2,2'-diphenol (ie, biphenyl diphenol compound 10) and 100 g of anhydrous toluene were mixed to prepare a biphenyl diphenol compound transparent solution with a concentration of 16.65 wt%.

[0067] 1.14 g (10 mmol) of triethylaluminum and 10 g of anhydrous toluene were mixed to prepare a triethylaluminum solution with a concentration of 10.2 wt%.

[0068] At room temperature, the triethylaluminum solution was added dropwise to the transparent solution of the biphenyl diphenol compound for 1 hour, and then stirred and reacted at 15° C. for 2 hours to obtain a biphenyl diphenol-based aluminum catalyst solution with a concentration of 16.1 wt%.

[0069] 2) Preparation of thymol:

[0070] 108.06 g (1.0 mol) of m-cresol was mixed with 63.08 g (1.5 mol) of propylene and 1.08 g of diisopropyl ether, and then the temperature was raised to 60°C. The catalyst solution of step 1) (the amount of catalyst was 10 mmol based on aluminum atoms) was added dropwise thereto, and the mixture was mixed and stirred to start the alkylation reaction. The reaction was carried out for 4 h (the catalyst solution was added dropwise for 1 h) to obtain thymol.

[0071] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 98.3%, the selectivity of thymol was 93.4%, the total selectivity of other isomers was 4.3% (of which isomer I accounted for 0.2%), and the selectivity of other impurities was 2.3%.

[0072] Example 3

[0073] Thymol is prepared from m-cresol and propylene under high-purity nitrogen protection by the following steps:

[0074] 1) Preparation of catalyst solution:

[0075] 17.73 g (50 mmol) of 3,3'-di-tert-butyl-5,5',6,6'-tetramethylbiphenyl-2,2'-diol (ie, biphenyl diphenol compound 4) and 150 g of anhydrous toluene were mixed to prepare a biphenyl diphenol compound transparent solution with a concentration of 10.57 wt%.

[0076] 1.44 g (20 mmoL) of trimethylaluminum and 10 g of anhydrous toluene were mixed to prepare a trimethylaluminum solution with a concentration of 12.6 wt%.

[0077] At room temperature, the trimethylaluminum solution was added dropwise to the transparent solution of the biphenyl diphenol compound for 1.5 hours, and then stirred and reacted at 20° C. for 1.5 hours to obtain a biphenyl diphenol-containing aluminum catalyst solution with a concentration of 10.7 wt%.

[0078] 2) Preparation of thymol:

[0079] 108.06 g (1.0 mol) of m-cresol was mixed with 105.13 g (2.5 mol) of propylene and 1.62 g of isopropyl carbonate, and then the temperature was raised to 90°C. The catalyst solution of step 1) (the amount of catalyst was 20 mmol based on aluminum atoms) was added dropwise thereto, and the mixture was mixed and stirred to start the alkylation reaction. The reaction was carried out for 2.5 h (the catalyst solution was added dropwise for 2 h) to obtain thymol.

[0080] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 98.9%, the selectivity of thymol was 93.2%, the total selectivity of other isomers was 4.6% (of which isomer I accounted for 0.3%), and the selectivity of other impurities was 2.2%.

[0081] Example 4

[0082] Thymol is prepared from m-cresol and propylene under high-purity nitrogen protection by the following steps:

[0083] 1) Preparation of catalyst solution:

[0084] 98.63 g (250 mmoL) of 4',5',5",6"-tetramethyl-[1,1':3',1":3",1"'-tetraphenyl]-2',2"-diphenol (i.e., biphenyldiphenol compound 5) and 200 g of anhydrous n-hexane were mixed to prepare a biphenyldiphenol compound transparent solution with a concentration of 33.0 wt%.

[0085] 9.92 g (50 mmoL) of triisopropylaluminum and 30 g of anhydrous n-hexane were mixed to prepare a triisopropylaluminum solution with a concentration of 24.8 wt%.

[0086] At room temperature, the triisopropylaluminum solution was added dropwise to the transparent solution of the biphenyl diphenol compound for 2 hours, and then stirred at 5° C. for 3 hours to obtain a biphenyl diphenol aluminum catalyst solution with a concentration of 32.1 wt%.

[0087] 2) Preparation of thymol:

[0088] 108.06 g (1.0 mol) of m-cresol was mixed with 126.15 g (3.0 mol) of propylene and 1.62 g of tert-butyl isopropyl ether, and then the temperature was raised to 40°C. The catalyst solution of step 1) (the amount of catalyst was 50 mmol based on aluminum atoms) was added dropwise thereto, and the mixture was mixed and stirred to start the alkylation reaction. The reaction was carried out for 3 h (the catalyst solution was added dropwise for 2 h) to obtain thymol.

[0089] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 99.1%, the selectivity of thymol was 92.5%, the total selectivity of other isomers was 5.1% (of which isomer I accounted for 0.6%), and the selectivity of other impurities was 2.4%.

[0090] Example 5

[0091] Thymol is prepared from m-cresol and propylene under high-purity nitrogen protection by the following steps:

[0092] 1) Preparation of catalyst solution:

[0093] 89.21 g (150 mmol) of 3,3'-di(9-anthryl)-5,5',6,6'-tetramethylbiphenyl-2,2'-diphenol (ie, biphenyl diphenol compound 8) and 300 g of anhydrous n-hexane were mixed to prepare a biphenyl diphenol compound transparent solution with a concentration of 22.9 wt%.

[0094] 19.83 g (100 mmoL) of triisopropylaluminum and 50 g of anhydrous n-hexane were mixed to prepare a triisopropylaluminum solution with a concentration of 28.4 wt%.

[0095] At room temperature, the triisopropylaluminum solution was added dropwise to the transparent solution of the biphenyl diphenol compound for 3 hours, and then stirred and reacted at 30° C. for 0.5 hours to obtain a biphenyl diphenol aluminum catalyst solution with a concentration of 23.8 wt%.

[0096] 2) Preparation of thymol:

[0097] 108.06 g (1.0 mol) of m-cresol was mixed with 42.05 g (1.0 mol) of propylene and 3.24 g of isopropyl isononanoate, and then the temperature was raised to 30°C. The catalyst solution of step 1) (the amount of catalyst was 100 mmol based on aluminum atoms) was added dropwise thereto, and the mixture was mixed and stirred to start the alkylation reaction. The reaction was carried out for 4 h (the catalyst solution was added dropwise for 3 h) to obtain thymol.

[0098] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 99.4%, the selectivity of thymol was 92.8%, the total selectivity of other isomers was 4.9% (of which isomer I accounted for 0.4%), and the selectivity of other impurities was 2.3%.

[0099] Comparative Example 1

[0100] The catalyst solution was prepared by referring to the method in Example 1, except that: no biphenyl diphenol compound was added, and the prepared triethylaluminum solution was directly used as the catalyst solution;

[0101] The catalyst solution containing biphenyl aluminum in Example 1 was replaced by the catalyst solution, and other parameters and operations remained unchanged to prepare thymol.

[0102] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was >99.9%, but thymol was not detected.

[0103] Comparative Example 2

[0104] The catalyst solution was prepared by referring to the method in Example 1, except that triethylaluminum was not added, and the prepared biphenyl diphenol compound transparent solution was directly used as the catalyst solution;

[0105] The aluminum-biphenol-containing catalyst solution in Example 1 was replaced with an equal mass thereof, and other parameters and operations remained unchanged to prepare thymol.

[0106] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was <1%, but thymol was not detected.

[0107] Comparative Example 3

[0108] The catalyst solution was prepared by referring to the method in Example 1 and used for preparing thymol, except that vinyl isopropyl ether was not added in the preparation of thymol, and other parameters and operations remained unchanged to prepare the catalyst solution;

[0109] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 94.9%, and the selectivity of thymol was 31.6%.

[0110] Comparative Example 4

[0111] The catalyst solution was prepared by referring to the method in Example 1 and used for preparing thymol, except that vinyl isopropyl ether was replaced by vinyl isoamyl ether, and other parameters and operations remained unchanged to prepare the catalyst solution;

[0112] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 97.1%, and the selectivity of thymol was 65.2%.

[0113] Comparative Example 5

[0114] The catalyst solution was prepared by referring to the method in Example 1 and used for preparing thymol, except that vinyl isopropyl ether was replaced by isooctyl carbonate, and other parameters and operations remained unchanged to prepare the catalyst solution;

[0115] The content of each component was detected by sampling gas chromatography: the conversion rate of m-cresol was 95.3%, and the selectivity of thymol was 57.1%.

Claims

1. A biphenyl diphenol-based aluminum catalyst for preparing thymol, characterized in that: The catalyst is used to catalyze the alkylation reaction of m-cresol and propylene to prepare thymol; The catalyst is prepared from a biphenol compound represented by formula (I) and an aluminum-containing compound represented by formula (II); In formula (I): R1 is independently selected from C6 to C 14 substituted or unsubstituted aryl, R2, R3 are independently selected from hydrogen, C1~C 10 The alkyl group is independently selected from halogen and trihalomethyl; (R4) 3-n AlH n (II) In formula (II): R4 is selected from C1-C5 alkyl; n is 0.

2. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 1, characterized in that: In formula (I), R1 is independently selected from C6 to C8 substituted or unsubstituted aryl groups, and R2 and R3 are independently selected from C1 to C6 alkyl groups.

3. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 1, characterized in that: In formula (I): the aryl group is an aryl group having 1 to 5 substituents.

4. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 3, characterized in that: The aryl group is a group having a large steric hindrance and having an electron-withdrawing substituent.

5. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 4, characterized in that: The aryl group is 3,5-bis(trifluoromethyl)phenyl.

6. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 1, characterized in that: In formula (II): R4 is selected from methyl, ethyl and isobutyl.

7. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 1, characterized in that: In the biphenol compound represented by formula (I), R2 and R3 may be the same or different.

8. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 7, characterized in that: The R2 and R3 are the same.

9. The biphenyl diphenol-based aluminum catalyst for preparing thymol according to claim 1, characterized in that: The biphenyl diphenol compound represented by formula (I) is selected from one of the following structural formulas:

10. A method for preparing the biphenyl diphenol-based aluminum catalyst for preparing thymol according to any one of claims 1 to 9, characterized in that: The steps include: In an anhydrous and oxygen-free atmosphere, dissolving the biphenyl diphenol compound represented by formula (I) and the aluminum-containing compound represented by formula (II) in a solvent to prepare a biphenyl diphenol compound solution and an aluminum-containing compound solution, respectively; Then, the aluminum compound solution is added to the biphenyl diphenol compound solution, and the mixture is stirred and reacted at 5 to 35° C. for 0.5 to 6 hours to obtain a solution containing a biphenyl diphenol-based aluminum catalyst.

11. The preparation method according to claim 10, characterized in that: The reaction temperature is 15-25°C, and the reaction time is 1-3h.

12. The preparation method according to claim 10, characterized in that: The molar ratio of the biphenyl diphenol compound represented by formula (I) to the aluminum-containing compound represented by formula (II) is 1.5 to 10:

1.

13. The preparation method according to claim 12, characterized in that: The molar ratio of the biphenyl diphenol compound represented by formula (I) to the aluminum-containing compound represented by formula (II) is 2 to 3:

1.

14. The preparation method according to claim 10, characterized in that: When preparing the biphenol compound solution and the aluminum compound solution, the solvent used is selected from at least one of alkane, aromatic hydrocarbon, halogenated hydrocarbon, ether and ester solvents; The solvents used in preparing the biphenol compound solution and the aluminum compound solution may be the same or different; The mass concentration of the prepared biphenol compound solution and aluminum compound solution is 1-80%.

15. The preparation method according to claim 14, characterized in that: The solvent is selected from at least one of n-hexane, toluene, tetrahydrofuran and dichloromethane.

16. The preparation method according to claim 14, characterized in that: When preparing the biphenyl diphenol compound solution and the aluminum compound solution, the same solvent is used for both.

17. The preparation method according to claim 14, characterized in that: The mass concentrations of the prepared biphenol compound solution and aluminum compound solution are both 5-25%.

18. The preparation method according to claim 10, characterized in that: The prepared biphenol compound solution and aluminum-containing compound solution have a solvent dosage that is the minimum amount required to dissolve the biphenol compound or the aluminum-containing compound.

19. The preparation method according to claim 10, characterized in that: When adding the aluminum compound solution to the biphenyl diphenol compound solution, the method of dropwise addition is adopted, and the dropwise addition time is 0.05 to 3 hours; The anhydrous and oxygen-free atmosphere is an inert gas environment.

20. The preparation method according to claim 19, characterized in that: The dropping time is 0.5 to 2 hours.

21. The preparation method according to claim 19, characterized in that: The inert gas is selected from nitrogen and argon.

22. A method for preparing thymol, characterized in that: The method comprises the following steps: alkylating meta-cresol with propylene under the action of the biphenylene-based aluminum catalyst for preparing thymol as described in any one of claims 1 to 9 or the biphenylene-based aluminum catalyst for preparing thymol prepared by the preparation method as described in any one of claims 10 to 21, and auxiliary agents isopropyl ether and / or isopropyl ester to prepare thymol.

23. The method according to claim 22, characterized in that The auxiliary agent is selected from at least one of isopropyl ether and / or isopropyl ester; The isopropyl ether is selected from at least one of vinyl isopropyl ether, diisopropyl ether, ethyl isopropyl ether, methyl isopropyl ether and tert-butyl isopropyl ether; The isopropyl ester is selected from at least one of isopropyl acetate, isopropyl carbonate, isopropyl isobutyrate and isononanoate; The dosage of the auxiliary agent is 0.5-3% of the mass of m-cresol.

24. The method according to claim 23, characterized in that The dosage of the auxiliary agent is 1-2% of the mass of m-cresol.

25. The method according to claim 22, characterized in that The amount of the biphenyl diphenol-based aluminum catalyst used is 0.1 to 10% of the molar amount of meta-cresol based on the molar amount of aluminum atoms; The biphenol-based aluminum catalyst is prepared as a biphenol-based aluminum catalyst solution with a concentration of 1 to 80 wt%; The solution may be a solution containing a biphenyldiphenol-based aluminum catalyst prepared by the preparation method according to any one of claims 10 to 21, or may be prepared by mixing a biphenyldiphenol-based aluminum catalyst with a solvent; When preparing the solution, a solvent showing inertness during the alkylation reaction is used, which is selected from at least one of alkane, aromatic hydrocarbon, halogenated hydrocarbon, ether and ester solvents.

26. The method according to claim 25, characterized in that The amount of the biphenyl diphenol-based aluminum catalyst used is 0.5 to 5% of the molar amount of meta-cresol based on the molar amount of aluminum atoms.

27. The method according to claim 25, characterized in that The biphenyl bisphenol-based aluminum catalyst is prepared into a biphenyl bisphenol-based aluminum catalyst solution with a concentration of 10 to 25 wt %.

28. The method according to claim 25, characterized in that The solvent is selected from at least one of n-hexane, toluene, tetrahydrofuran and dichloromethane.

29. The method according to claim 25, characterized in that The solvent is the same solvent as that used in preparing the biphenyl diphenol-based aluminum catalyst by the preparation method according to any one of claims 10-21.

30. The method according to claim 25, characterized in that The biphenyldiphenol-based aluminum catalyst solution is added dropwise during the alkylation reaction, and the dropwise addition time is 0.5 to 24 hours, and the dropwise addition time is included in the alkylation reaction time.

31. The method according to claim 30, characterized in that The dropping time is 2 to 4 hours.

32. The method according to claim 22, characterized in that The molar ratio of m-cresol to propylene is 1:1-3; The alkylation reaction has a reaction temperature of 0 to 90° C. and a reaction time of 0.5 to 24 h.

33. The method according to claim 32, characterized in that The molar ratio of m-cresol to propylene is 1:1.5-2.

5.

34. The method according to claim 32, characterized in that The alkylation reaction has a reaction temperature of 40 to 60° C. and a reaction time of 1 to 6 hours.

35. The method according to claim 22, characterized in that The alkylation reaction is carried out in an inert gas atmosphere, wherein the oxygen content in the inert gas is controlled to be less than 20 ppm and the inert gas is selected from high-purity nitrogen and high-purity argon.

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