Process for the preparation of 2,6-di-tert-butyl-p-cresol

Abstract

The application provides a preparation method of 2,6-di-tert-butyl-p-cresol, which comprises the following steps: adding p-cresol and a catalyst into a reactor, heating in a constant-temperature water bath to mix the p-cresol and the catalyst sufficiently, and introducing isobutene into the system to prepare 2,6-di-tert-butyl-p-cresol through catalytic alkylation; wherein the catalyst is an ionic liquid complex composed of an ionic liquid ligand and a metal salt ligand. The method of the application uses the ionic liquid complex composed of the ionic liquid ligand and the metal salt ligand as the catalyst, so that the process reaction condition is more moderate, the process complexity and the production cost are reduced, and meanwhile, the p-cresol has a high conversion rate, the reaction has a high yield, and the demand of industrial production is met.

Description

Technical Field

[0001] This invention relates to the field of antioxidant technology, and more specifically to a method for preparing 2,6-di-tert-butyl-p-cresol. Background Technology

[0002] 2,6-Di-tert-butyl-p-cresol is an important class of phenolic antioxidants, widely used in the food, cosmetics, pharmaceutical, agricultural, plastics manufacturing, bio-fermentation, and petroleum processing industries. It is one of the earliest and most widely used phenolic antioxidants. In the food industry, 2,6-di-tert-butyl-p-cresol is widely used in low-fat foods, fish products, packaging materials, paraffin wax, and mineral oils. In the cosmetics industry, 2,6-di-tert-butyl-p-cresol is also a commonly used antioxidant, appearing in 1709 cosmetic formulations. In the pharmaceutical industry, 2,6-di-tert-butyl-p-cresol can be used in the preparation of various drugs and can also act as a stabilizer, protecting drugs from oxidation and deterioration. In the agricultural industry, 2,6-di-tert-butyl-p-cresol can be used as a fungicide and preservative, for seed treatment and crop protection.

[0003] Currently, the main methods for synthesizing 2,6-di-tert-butyl-p-cresol include the mixed-cresol method, the phenol method, and the p-cresol method. The mixed-cresol method uses a mixture of p-cresol and m-cresol as raw materials, isobutylene as the alkylating agent, and concentrated sulfuric acid as a catalyst to carry out the alkylation reaction at 65°C. The main products of the alkylation reaction are 2,6-di-tert-butyl-p-cresol and 4,6-di-tert-butyl-m-cresol. The alkylation solution is then separated by distillation, and finally crystallization yields the product 2,6-di-tert-butyl-p-cresol. Although this method has low raw material costs, the quality of the produced 2,6-di-tert-butyl-p-cresol is relatively poor.

[0004] The phenol method uses phenol as a raw material, isobutylene as an alkylating agent, and aluminum phenolate as a catalyst to carry out an alkylation reaction to produce 2,6-di-tert-butylphenol. Subsequently, 2,6-di-tert-butylphenol undergoes a Mannich reaction with formaldehyde and dimethylamine to produce a Mannich base. Finally, the Mannich base is subjected to high-temperature and high-pressure catalytic hydrogenation to obtain 2,6-di-tert-butyl-p-cresol. This method uses phenol as the main raw material and has a low cost, but the reaction process requires hydrogenation reduction, which has high process requirements.

[0005] The p-cresol method uses p-cresol as a raw material and isobutylene as an alkylating agent, carrying out a Friedel-Crafts alkylation reaction under acid catalysis. This method has mild reaction conditions, and when gaseous isobutylene is insufficient, tert-butanol can be used as an alkylating agent to react with p-cresol and dehydrate to obtain 2,6-di-tert-butyl-p-cresol. Therefore, the synthesis method using p-cresol as a raw material has high economic feasibility and is widely used in industrial production.

[0006] In the synthetic route for the alkylation of p-cresol to prepare 2,6-di-tert-butyl-p-cresol, the catalyst is crucial. For example, Chinese patent CN111099967A discloses a method for preparing 2,6-di-tert-butyl-p-cresol using a solid superacid catalyst. Silver nitrate, nickel nitrate, and cobalt nitrate are supported on zirconium dioxide and titanium dioxide to prepare a solid superacid catalyst, which is used for the alkylation of p-cresol to prepare 2,6-di-tert-butyl-p-cresol. Another example is Chinese patent CN106631706A, which discloses a method for preparing 2,6-di-tert-butyl-p-cresol using silica gel as a catalyst. A solid acid catalyst is prepared by impregnation using silica gel as a support and p-toluenesulfonic acid as the active component, which is used for the alkylation of p-cresol to prepare 2,6-di-tert-butyl-p-cresol. The catalysts used in the above-mentioned prior art face multiple challenges, including complex preparation methods, high cost, numerous byproducts, and poor cycle stability. Furthermore, the reaction temperatures are high and the preparation process conditions are demanding.

[0007] Ionic liquid catalysts possess advantages such as relatively high solubility, high activity, strong catalytic effect, easy adjustment of polarity and pH, good thermal stability, and good antioxidant capacity. They have gradually become the main force in the development of green chemical industry, replacing traditional homogeneous acid-base catalysts. Chinese patent CN112225643A discloses a method for the alkylation of cresol using an acidic ionic liquid in a microreactor. This method first liquefies the alkylating agent, then uses the ionic liquid as a catalyst, and carries out the alkylation reaction under medium pressure in a microchannel reactor, achieving a cresol conversion rate of up to 93.2%. However, this method requires relatively high reaction conditions, and the yield of the target product, 2,6-di-tert-butylphenol, is low. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing 2,6-di-tert-butyl-p-cresol. This method uses an ionic liquid complex composed of an ionic liquid ligand and a metal salt ligand as a catalyst, which makes the process reaction conditions milder, reduces process complexity and production costs, while ensuring a high conversion rate of p-cresol and a high yield, thus meeting the needs of industrial production.

[0009] According to the present invention, a method for preparing 2,6-di-tert-butyl-p-cresol is provided. The method includes: adding p-cresol and a catalyst into a reactor, heating in a constant temperature water bath to fully mix the p-cresol and the catalyst, introducing isobutylene into the system, and catalytically alkylating to obtain 2,6-di-tert-butyl-p-cresol; wherein the catalyst is an ionic liquid complex composed of an ionic liquid ligand and a metal salt ligand.

[0010] As an optional implementation, the catalyst is prepared as follows:

[0011] Weigh the ionic liquid ligand and the metal salt ligand according to their molar ratio, and dissolve them separately in ethanol to prepare ionic liquid solution and metal salt solution, respectively.

[0012] The ionic liquid solution is heated to a first temperature, and the metal salt solution is heated to a second temperature. Then, the ionic liquid solution is added to the metal salt solution for mixing, and the mixture is heated under reflux with stirring. After the reaction is completed, the mixture is cooled and then collected by vacuum filtration.

[0013] As an optional implementation, the molar ratio of the ionic liquid ligand to the metal salt ligand is (1:1) to (4:1).

[0014] As an optional implementation, the first temperature range is 30°C to 80°C, and the second temperature range is 30°C to 80°C.

[0015] As an optional implementation method, the reflux reaction conditions are: heating and refluxing at 70°C to 80°C for 1 hour.

[0016] As an optional embodiment, the ionic liquid ligand includes any one or more of 1,3-dimethylimidazolium sulfate, 1,3-dimethylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium phosphate, 1-ethyl-2,3-dimethylimidazolium phosphate, and 1,3-dimethylimidazolium p-toluenesulfonate.

[0017] As an optional implementation, the metal salt ligand is any one or more of copper sulfate, copper chloride, zinc sulfate, zinc chloride, cobalt sulfate, cobalt chloride, nickel sulfate, and aluminum chloride.

[0018] As an optional implementation method, the mass ratio of catalyst to p-cresol is (2-5):100, and the water bath heating temperature is 60℃-120℃.

[0019] As an optional implementation, the isobutylene ventilation rate is 50 mL / min to 100 mL / min.

[0020] As an optional implementation method, the catalytic conditions are: reaction under a slightly positive pressure for 1 to 5 hours.

[0021] Compared with the prior art, the significant advantages of the present invention are as follows:

[0022] The method for preparing 2,6-di-tert-butyl-p-cresol of the present invention uses an ionic liquid complex composed of an ionic liquid ligand and a metal salt ligand as a catalyst. The complex is generated by a coordination complexation reaction between the metal complex and the ionic liquid ligand through the inherent coordination bond structure of the metal complex itself. The catalytic reaction is carried out under synergistic effect, thereby achieving a high conversion rate of p-cresol and a high yield. At the same time, the process reaction conditions are milder.

[0023] In the method of this invention, the ionic liquid complex can reduce interfacial tension and increase the contact area at the phase interface, thereby promoting the contact and interaction between raw material molecules and accelerating the reaction rate. Simultaneously, thorough stirring of the reaction system ensures more uniform mixing of the ionic liquid complex and the raw materials, increasing the opportunities for interaction and further improving reaction efficiency. A high yield of 2,6-di-tert-butyl-p-cresol can be obtained within 1-2 hours, exhibiting high catalytic activity approaching that of a sulfuric acid catalyst.

[0024] The ionic liquid complex used in this invention has a very low vapor pressure at room temperature. Therefore, the ionic liquid complex is not easily volatilized at room temperature or higher temperatures, which reduces catalyst loss during the reaction process and improves production efficiency.

[0025] The ionic liquid complex used in this invention settles at the bottom of the reactor after the reaction, making the catalyst easier to separate. Furthermore, the catalytic effect of the ionic liquid complex does not decrease after multiple uses, indicating that the ionic liquid complex catalyst has good cycle stability. Detailed Implementation

[0026] To better understand the technical content of this invention, specific embodiments are described below.

[0027] The embodiments disclosed herein are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of a number of ways.

[0028] This invention provides a method for preparing 2,6-di-tert-butyl-p-cresol, which uses an ionic liquid complex as a catalyst, and solves the technical problems of harsh process conditions, high process complexity, difficulty in catalyst preparation, need to improve catalyst activity, and poor cycle stability in the prior art.

[0029] In an exemplary embodiment of the present invention, a method for preparing 2,6-di-tert-butyl-p-cresol is provided. The method includes: adding p-cresol and a catalyst into a reactor, heating in a constant temperature water bath to fully mix the p-cresol and the catalyst, introducing isobutylene into the system, and catalytically alkylating to obtain 2,6-di-tert-butyl-p-cresol; wherein the catalyst is an ionic liquid complex composed of an ionic liquid ligand and a metal salt ligand.

[0030] As an optional implementation, the catalyst is prepared as follows:

[0031] Weigh the ionic liquid ligand and the metal salt ligand according to their molar ratio, and dissolve them separately in ethanol to prepare ionic liquid solution and metal salt solution, respectively.

[0032] The ionic liquid solution is heated to a first temperature, and the metal salt solution is heated to a second temperature. Then, the ionic liquid solution is added to the metal salt solution for mixing, and the mixture is heated under reflux with stirring. After the reaction is completed, the mixture is cooled and then collected by vacuum filtration.

[0033] As an optional implementation, the molar ratio of the ionic liquid ligand to the metal salt ligand is (1:1) to (4:1).

[0034] As an optional implementation, the first temperature range is 30°C to 80°C, and the second temperature range is 30°C to 80°C.

[0035] As an optional implementation method, the reflux reaction conditions are: heating and refluxing at 70°C to 80°C for 1 hour.

[0036] As an optional embodiment, the ionic liquid ligand includes any one or more of 1,3-dimethylimidazolium sulfate, 1,3-dimethylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium phosphate, 1-ethyl-2,3-dimethylimidazolium phosphate, and 1,3-dimethylimidazolium p-toluenesulfonate.

[0037] As an optional implementation, the metal salt ligand is any one or more of copper sulfate, copper chloride, zinc sulfate, zinc chloride, cobalt sulfate, cobalt chloride, nickel sulfate, and aluminum chloride.

[0038] As an optional implementation method, the mass ratio of catalyst to p-cresol is (2-5):100, and the water bath heating temperature is 60℃-120℃.

[0039] As an optional implementation, the isobutylene ventilation rate is 50 mL / min to 100 mL / min.

[0040] As an optional implementation method, the catalytic conditions are: reaction under a slightly positive pressure for 1 h to 5 h; it is understood that the slightly positive pressure is generally 0.1 MPa to 0.3 MPa.

[0041] To facilitate better understanding, the present invention will be further illustrated below with several specific examples, but the preparation process is not limited to these examples, and the content of the present invention is not limited to these examples.

[0042] Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0043] Preparation of ionic liquid complexes

[0044] Example 1

[0045] First, weigh 1,3-dimethylimidazolium sulfate and copper sulfate at a molar ratio of 1:1 and dissolve them separately in ethanol to prepare ethanol solutions. Then, add the metal salt ligand solution to a three-necked flask and heat it, while heating the ionic liquid ligand solution in a constant temperature bath. Once both solutions reach the set temperature (40°C), add the ionic liquid ligand solution to the three-necked flask and mix it with the metal salt solution. Then, turn on the stir and heat under reflux at 70–80°C for 1 hour. After cooling, filter, and recover the solution, the ionic liquid complex catalyst sample can be obtained.

[0046] Example 2

[0047] First, weigh 1-butyl-3-methylimidazolium methanesulfonate and zinc chloride at a molar ratio of 1:1, and dissolve them separately in ethanol to prepare ethanol solutions. Then, add the metal salt ligand solution to a three-necked flask and heat it, while placing the ionic liquid ligand solution in a constant temperature bath and heating it. After both solutions reach the set temperature (40℃), add the ionic liquid ligand solution to the three-necked flask and mix it with the metal salt solution. Then, turn on the stir and heat the mixture under reflux at 70-80℃ for 1 hour. After cooling, filter, and recover the solution, the ionic liquid complex catalyst sample can be obtained.

[0048] Example 3

[0049] First, weigh 1-butyl-3-methylimidazolium methanesulfonate and zinc chloride at a molar ratio of 1:2, and dissolve them separately in ethanol to prepare ethanol solutions. Then, add the metal salt ligand solution to a three-necked flask and heat it, while placing the ionic liquid ligand solution in a constant temperature bath and heating it. Once both solutions reach the set temperature (40℃), add the ionic liquid ligand solution to the three-necked flask and mix it with the metal salt solution. Then, turn on the stir and heat the mixture under reflux at 70-80℃ for 1 hour. After cooling, filter, and recover the solution, the ionic liquid complex catalyst sample can be obtained.

[0050] Example 4

[0051] First, weigh 1-ethyl-2,3-dimethylimidazolium phosphate and cobalt sulfate in a molar ratio of 1:2, and dissolve them separately in ethanol to prepare ethanol solutions. Then, add the metal salt ligand solution to a three-necked flask and heat it, while placing the ionic liquid ligand solution in a constant temperature bath and heating it. Once both solutions reach the set temperature (40℃), add the ionic liquid ligand solution to the three-necked flask and mix it with the metal salt solution. Then, turn on the stir and heat the mixture under reflux at 70-80℃ for 1 hour. After cooling, filter, and recover the solution, the ionic liquid complex catalyst sample can be obtained.

[0052] [Preparation of 2,6-di-tert-butyl-p-cresol]

[0053] Example 5

[0054] 82.2 g of p-cresol and 2.8 g of ionic liquid complex catalyst (obtained according to the method of Example 1) were weighed and added to the reactor. The system was heated to 80 °C to ensure that the p-cresol and the catalyst were fully mixed. Isobutylene was introduced into the system to carry out the reaction at a flow rate of 80 mL / min. Under slightly positive pressure, the catalytic alkylation reaction was carried out for 2 h to obtain 2,6-di-tert-butyl-p-cresol.

[0055] Experimental calculations show that the conversion rate of p-cresol in this example is 99.3%, the yield of 2,6-di-tert-butyl-p-cresol is 78.9%, and the selectivity of 2,6-di-tert-butyl-p-cresol is 79.5%.

[0056] Example 6

[0057] 82.2 g of p-cresol and 2.8 g of ionic liquid complex catalyst (obtained according to the method of Example 2) were weighed and added to the reactor. The system was heated to 80 °C to ensure that the p-cresol and the catalyst were fully mixed. Isobutylene was introduced into the system to carry out the reaction at a flow rate of 80 mL / min. Under slightly positive pressure, the catalytic alkylation reaction was carried out for 4 h to obtain 2,6-di-tert-butyl-p-cresol.

[0058] Experimental calculations show that the conversion rate of p-cresol in this example is 99.8%, the yield of 2,6-di-tert-butyl-p-cresol is 84.8%, and the selectivity of 2,6-di-tert-butyl-p-cresol is 85.0%.

[0059] Example 7

[0060] A recycling experiment was conducted on the catalyst used in Example 6, keeping the ratio of raw materials to catalyst, the isobutylene gas flow rate, the reaction time, and the reaction temperature constant. Seven experiments were performed (the catalyst for each of the seven experiments was recovered by filtration of the reaction product after the previous experiment), and the results are as follows:

[0061] (1) The conversion rate of p-cresol was 99.8%, the yield of 2,6-di-tert-butyl-p-cresol was 84.8%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 85.0%.

[0062] (2) The conversion rate of p-cresol was 99.7%, the yield of 2,6-di-tert-butyl-p-cresol was 84.9%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 85.2%.

[0063] (3) The conversion rate of p-cresol was 99.7%, the yield of 2,6-di-tert-butyl-p-cresol was 84.7%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 85.0%.

[0064] (4) The conversion rate of p-cresol was 99.8%, the yield of 2,6-di-tert-butyl-p-cresol was 87.3%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 87.5%.

[0065] (5) p-Cresol conversion rate 99.6%, 2,6-di-tert-butyl-p-cresol yield 84.0%, and 2,6-di-tert-butyl-p-cresol selectivity 84.3%.

[0066] (6) p-Cresol conversion rate 99.8%, 2,6-di-tert-butyl-p-cresol yield 87.8%, and 2,6-di-tert-butyl-p-cresol selectivity 87.9%.

[0067] (7) p-Cresol conversion rate 99.7%, 2,6-di-tert-butyl-p-cresol yield 84.2%, and 2,6-di-tert-butyl-p-cresol selectivity 84.5%.

[0068] Example 8

[0069] 82.2 g of p-cresol and 2.8 g of ionic liquid complex catalyst (obtained according to the method of Example 3) were weighed and added to the reactor. The system was heated to 80 °C to ensure that the p-cresol and the catalyst were fully mixed. Isobutylene was introduced into the system to carry out the reaction at a flow rate of 80 mL / min. Under slightly positive pressure, the catalytic alkylation reaction was carried out for 2 h to obtain 2,6-di-tert-butyl-p-cresol.

[0070] Experimental calculations show that the conversion rate of p-cresol in this example is 99.1%, the yield of 2,6-di-tert-butyl-p-cresol is 84.3%, and the selectivity of 2,6-di-tert-butyl-p-cresol is 83.5%.

[0071] Example 9

[0072] 82.2 g of p-cresol and 2.8 g of ionic liquid complex catalyst (obtained according to the method of Example 4) were weighed and added to the reactor. The system was heated to 80 °C to ensure that the p-cresol and the catalyst were fully mixed. Isobutylene was introduced into the system to carry out the reaction at a flow rate of 80 mL / min. Under slightly positive pressure, the catalytic alkylation reaction was carried out for 2 h to obtain 2,6-di-tert-butyl-p-cresol.

[0073] Experimental calculations show that the conversion rate of p-cresol in this example is 99.3%, the yield of 2,6-di-tert-butyl-p-cresol is 79.4%, and the selectivity of 2,6-di-tert-butyl-p-cresol is 78.9%.

[0074] Comparative Example 1

[0075] 80.3 g of p-cresol and 1.2 g of sulfuric acid catalyst were weighed and added to the reactor. The system was heated to 80 °C to ensure that the p-cresol and catalyst were fully mixed. Isobutylene was introduced into the system to carry out the reaction. The isobutylene gas flow rate was 80 mL / min. Under slightly positive pressure, the catalytic alkylation reaction was carried out for 3 h to obtain 2,6-di-tert-butyl-p-cresol.

[0076] Experimental calculations show that the conversion rate of p-cresol in this example is 99.9%, the yield of 2,6-di-tert-butyl-p-cresol is 93.6%, and the selectivity of 2,6-di-tert-butyl-p-cresol is 93.7%.

[0077] Comparative Example 2

[0078] 30g of p-cresol and 3g of CuSO4-Ce(SO4)2 / SiO2 solid acid catalyst were weighed and added to the reactor. The system was heated to 80℃, and the p-cresol and catalyst were stirred thoroughly. Isobutylene was introduced into the system to carry out the reaction. The isobutylene gas flow rate was 80mL / min. Under slightly positive pressure, the catalytic alkylation reaction was carried out for 4h to obtain 2,6-di-tert-butyl-p-cresol.

[0079] Experimental calculations show that the conversion rate of p-cresol in this example is 96.1%, the yield of 2,6-di-tert-butyl-p-cresol is 83.2%, and the selectivity of 2,6-di-tert-butyl-p-cresol is 86.6%.

[0080] Comparative Example 3

[0081] A recycling experiment was conducted on the catalyst used in Example 2, keeping the ratio of raw materials to catalyst, the isobutylene gas flow rate, the reaction time, and the reaction temperature constant. The results of the three experiments are as follows:

[0082] (1) The conversion rate of p-cresol was 96.1%, the yield of 2,6-di-tert-butyl-p-cresol was 83.2%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 86.6%.

[0083] (2) The conversion rate of p-cresol was 96.4%, the yield of 2,6-di-tert-butyl-p-cresol was 60.4%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 62.7%.

[0084] (3) p-Cresol conversion rate 90.2%, 2,6-di-tert-butyl-p-cresol yield 60.1%, 2,6-di-tert-butyl-p-cresol selectivity 66.6%.

[0085] Comparative Example 4

[0086] 30g of p-cresol and 3g of Ce(SO4)2 / SiO2 solid acid catalyst were weighed and added to the reactor. The system was heated to 80℃, and the p-cresol and catalyst were stirred thoroughly. Isobutylene was introduced into the system to carry out the reaction. The isobutylene gas flow rate was 80mL / min. Under slightly positive pressure, the catalytic alkylation reaction was carried out for 4h to obtain 2,6-di-tert-butyl-p-cresol.

[0087] Experimental calculations show that the conversion rate of p-cresol in this comparative example is 94.2%, the yield of 2,6-di-tert-butyl-p-cresol is 88.6%, and the selectivity of 2,6-di-tert-butyl-p-cresol is 94.1%.

[0088] Comparative Example 5

[0089] A recycling experiment was conducted on the catalyst used in Comparative Example 4, keeping the feed-catalyst ratio, isobutylene gas flow rate, reaction time, and reaction temperature constant. The results of the three experiments are as follows:

[0090] (1) The conversion rate of p-cresol was 94.2%, the yield of 2,6-di-tert-butyl-p-cresol was 88.6%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 94.1%.

[0091] (2) The conversion rate of p-cresol was 93.6%, the yield of 2,6-di-tert-butyl-p-cresol was 53.5%, and the selectivity of 2,6-di-tert-butyl-p-cresol was 57.1%.

[0092] (3) p-Cresol conversion rate was 64.0%, 2,6-di-tert-butyl-p-cresol yield was 31.0%, and 2,6-di-tert-butyl-p-cresol selectivity was 48.4%.

[0093] The experimental results of the above embodiments and comparative examples were statistically analyzed, and the results are shown in the table below.

[0094]

[0095]

[0096] As can be seen from the above, the method of the present invention achieves a high conversion rate of p-cresol and a high yield of the reaction. Furthermore, the catalyst of the present invention does not show a decrease in catalytic effect after multiple uses, indicating that the ionic liquid complex catalyst has good cycle stability.

[0097] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for preparing 2,6-di-tert-butyl-p-cresol, characterized in that, The preparation method includes: adding p-cresol and a catalyst into a reactor, heating in a constant temperature water bath to fully mix the p-cresol and the catalyst, introducing isobutylene into the system, and catalytically alkylating to obtain 2,6-di-tert-butyl-p-cresol; wherein the catalyst is an ionic liquid complex composed of an ionic liquid ligand and a metal salt ligand. The ionic liquid ligands include any one or more of 1,3-dimethylimidazolium sulfate, 1,3-dimethylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium phosphate, 1-ethyl-2,3-dimethylimidazolium phosphate, and 1,3-dimethylimidazolium p-toluenesulfonate. The metal salt ligand is any one or more of copper sulfate, copper chloride, zinc sulfate, zinc chloride, cobalt sulfate, cobalt chloride, nickel sulfate, and aluminum chloride. The catalyst is prepared as follows: Weigh the ionic liquid ligand and the metal salt ligand according to their molar ratio, and dissolve them separately in ethanol to prepare ionic liquid solution and metal salt solution, respectively. The ionic liquid solution is heated to a first temperature, and the metal salt solution is heated to a second temperature. Then, the ionic liquid solution is added to the metal salt solution for mixing, and the mixture is heated under reflux with stirring. After the reaction is completed, the mixture is cooled and then collected by vacuum filtration.

2. The method for preparing 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The molar ratio of the ionic liquid ligand to the metal salt ligand is (1:1) to (4:1).

3. The method for preparing 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The first temperature range is 30 ℃ to 80 ℃, and the second temperature range is 30 ℃ to 80 ℃.

4. The method for preparing 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The reflux reaction conditions were: heating and refluxing at 70 ℃~80 ℃ for 1 h.

5. The method for preparing 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The mass ratio of catalyst to p-cresol is (2~5):100, and the water bath heating temperature is 60 ℃~120 ℃.

6. The method for preparing 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The isobutylene ventilation rate is 50 mL / min to 100 mL / min.

7. The method for preparing 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The catalytic conditions were: reaction under a slightly positive pressure for 1 h to 5 h.

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