Method for preparing hydroxyanisole with high p-o ratio

Abstract

This application provides a method for preparing hydroxyanisole, the method comprising reacting anisole with an oxidant in the presence of a catalyst and an organic solvent to generate hydroxyanisole; wherein the organic solvent is a mixture of ethanol and isopropanol. The method achieves extremely high product yields and selectivity using simple catalysts and process steps, and the proportion of para- and ortho-isomers in the product hydroxyanisole is at an unprecedentedly high level.

Description

Technical Field

[0001] This application relates to the field of fine chemicals, and more specifically to a method for synthesizing hydroxyanisoles that can achieve extremely high molar ratios of p-hydroxyanisole / o-hydroxyanisole. Background Technology

[0002] p-Hydroxyanisole, also known as p-methoxyphenol, hydroquinone monomethyl ether, or hydroquinone monomethyl ether, has the molecular structure shown below. As an essential and highly efficient polymerization inhibitor in the production, storage, and transportation of acrylic acid, methacrylic acid, and their esters, it possesses extremely high commercial value and market importance. Furthermore, p-hydroxyanisole is also an important intermediate in the processing of pharmaceuticals, fragrances, pesticides, and other fine chemical products, with a very wide range of applications.

[0003]

[0004] p-hydroxyanisole and o-hydroxyanisole

[0005] However, contrary to the enormous and ever-growing demand for p-hydroxyanisole, its various production processes have always suffered from extremely serious problems that have remained unresolved for a long time, thus greatly limiting the application of p-hydroxyanisole.

[0006] Specifically, there are currently four main reported methods for synthesizing p-hydroxyanisole. These are the dimethyl sulfate method and methanol method using hydroquinone as the starting material, the p-aminoanisole method using p-aminoanisole as the starting material, and the anisole hydroxylation method using anisole as the starting material. The first two methods, the dimethyl sulfate method and the methanol method, based on hydroquinone, are the most widely used. However, the dimethyl sulfate method requires dimethyl sulfate as the methylating agent, and dimethyl sulfate is a highly toxic substance. The reaction conditions are harsh, the reaction selectivity is poor, and it readily produces tar, severely limiting the application of this process. While the methanol method uses methanol as the methylating agent, avoiding the toxicity of dimethyl sulfate, it requires a series of complex post-processing steps after the reaction, including extraction, neutralization, washing, distillation, and recrystallization, to obtain a qualified product, significantly reducing the industrial applicability and development of this process. The p-aminoanisole method uses p-aminoanisole as a raw material and obtains the target product p-hydroxyanisole through diazotization-hydrolysis steps. However, this process is relatively complex, has high production costs, and inevitably uses other highly toxic reagents, which increases the process risk.

[0007] To address the shortcomings of the aforementioned processes, engineers have been actively researching a new process that uses anisole as a raw material, reacting it with an oxidant to produce hydroxyanisole. However, the raw material conversion rate, product yield, and selectivity of this process have consistently fallen short of expectations. Even after various optimization experiments on catalysts and process conditions, these issues remain unresolved. Furthermore, modifications to the catalyst not only increase process complexity and cost but may also introduce new impurities and complications. More importantly, existing anisole oxidation processes can only achieve a very low p-hydroxyanisole / o-hydroxyanisole ratio, necessitating cumbersome post-processing to separate these two isomers and resulting in significant raw material waste.

[0008] Therefore, there is an urgent need in the art to develop a novel process suitable for the simple and efficient synthesis of p-hydroxyanisole, which can avoid complex and costly catalyst modification steps, achieve the required high conversion, yield and selectivity in a simple step, and maximize the p-hydroxyanisole / o-hydroxyanisole ratio in the hydroxyanisole product. Summary of the Invention

[0009] To address the aforementioned problems, a first aspect of this application provides a method for preparing hydroxyanisole, the method comprising reacting anisole with an oxidant in the presence of a catalyst and an organic solvent to generate hydroxyanisole; wherein the organic solvent is a mixture of ethanol and isopropanol.

[0010] According to one embodiment of the first aspect of this application, in the organic solvent, the volume ratio of ethanol to isopropanol is 5:1 to 10:1.

[0011] According to another embodiment of the first aspect of this application, in the organic solvent, the volume ratio of ethanol to isopropanol is 7:1 to 9:1.

[0012] According to another embodiment of the first aspect of this application, the oxidant is selected from one or more of the following: hydrogen peroxide, tert-butyl hydrogen peroxide, and ozone.

[0013] According to another embodiment of the first aspect of this application, the molar ratio of the anisole to the oxidant is 2:1 to 1:3.

[0014] According to another embodiment of the first aspect of this application, the molar ratio of benzyl alcohol to ethanol contained in the solvent is 1:1 to 1:10.

[0015] According to another embodiment of the first aspect of this application, the catalyst is a titanium-silicon molecular sieve catalyst, a transition metal modified titanium-silicon molecular sieve, or a combination of the two.

[0016] According to another embodiment of the first aspect of this application, the mass ratio of the catalyst to anisole is 2:1 to 1:20.

[0017] According to another embodiment of the first aspect of this application, the reaction temperature is 30-100°C, and the reaction pressure is atmospheric pressure to 0.5 MPa.

[0018] According to another embodiment of the first aspect of this application, the reaction is carried out in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere has a volume content of 1-12%.

[0019] According to another embodiment of the first aspect of this application, after the anisole reacts with the oxidant, the method further includes the following steps: The material obtained from the reaction is subjected to solid-liquid separation; The liquid phase obtained from the solid-liquid separation is purified to obtain o-hydroxyanisole and p-hydroxyanisole, respectively.

[0020] According to another embodiment of the first aspect of this application, the solid-liquid separation is performed using one or more of the following devices: centrifugal filter, candle filter, precision filter, plate and frame filter.

[0021] According to another embodiment of the first aspect of this application, the purification is carried out using a vacuum distillation column, and the bottom temperature of the vacuum distillation column is 50-200°C, and the pressure in the vacuum distillation column is 0.1-5 kPa.

[0022] The second aspect of this application provides a hydroxyanisole product prepared by a method defined in any embodiment of the first aspect of this application, the hydroxyanisole product comprising p-hydroxyanisole and o-hydroxyanisole, wherein the molar ratio of p-hydroxyanisole to o-hydroxyanisole is greater than 5:1.

[0023] In the detailed description section below, the methods and products of this application will be further described with reference to the accompanying drawings. Attached Figure Description

[0024] Figure 1 A schematic diagram of the reaction of this application is shown.

[0025] Figure 2 The liquid chromatogram of the reaction solution prepared in Example 1 of this application is shown.

[0026] Figure 3 The liquid chromatogram of the reaction solution prepared in Example 2 of this application is shown.

[0027] Figure 4 The liquid chromatogram of the reaction solution prepared in Example 3 of this application is shown.

[0028] Figure 5 The o-hydroxyanisole prepared in Example 3 of this application is shown.

[0029] Figure 6 The p-hydroxyanisole prepared in Example 3 of this application is shown.

[0030] Figure 7 The XRD pattern of the catalyst used in the embodiments of this application is shown. Detailed Implementation

[0031] The “range” disclosed in this document takes the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0032] In this application, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is simply a shortened representation of these numerical combinations.

[0033] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0034] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0035] In this application, unless otherwise specified, the term "comprising" as used herein can be either open-ended or closed-ended. For example, "comprising" may mean that it may also include other components not listed, or it may only include the listed components.

[0036] In this application, "min" means "minute".

[0037] In this application, the terms "para / ortho ratio", "para / ortho ratio", "para / ortho molar ratio" and "para / ortho isomer molar ratio" are used interchangeably to represent the molar ratio between p-hydroxyanisole and ortho-hydroxyanisole in the hydroxyanisole prepared by the reaction of the present invention.

[0038] The reaction employed in this application uses anisole as a starting material, reacting it with an oxidizing agent to generate the target compound, hydroxyanisole. A key inventive aspect of this application lies in the unexpected discovery that by using an ethanol / isopropanol mixture as the reaction solvent, extremely high ortho-parameter ratios can be achieved simply and efficiently before any purification / separation steps. This is a result that has long been desired but unattainable in previously studied processes. In other words, the method of this invention can directly obtain hydroxyanisole material with extremely high ortho-parameter ratios through the anisole oxidation reaction alone, before any separation / purification steps, resulting in significantly improved process efficiency. Existing methods, however, can only achieve this effect after complex, cumbersome, and costly separation and purification processes.

[0039] More specifically, the organic solvent used in the reaction of the present invention is a mixture of ethanol and isopropanol, wherein the volume ratio of ethanol to isopropanol is 5:1 to 10:1, or 7:1 to 9:1, or 7.5:1 to 8.5:1, and most preferably 7.8:1 to 8.2:1. For example, the volume ratio of ethanol to isopropanol can be within the range of values ​​obtained by combining any two of the following endpoints: 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 7.9:1, 8:1, 8.1:1, 8.5:1, 9:1, 9.5:1, 10:1.

[0040] The inventors of this application, through extensive research, discovered that only the specially designed mixed organic solvent system of this application can achieve this superior high para / ortho ratio effect. Using a single organic alcohol, ketone, or nitrile solvent in a non-mixture form cannot achieve this effect, nor can using mixtures of other organic solvents different from the "ethanol / isopropanol" mixed system of this application. Furthermore, the applicants also noted through experiments that when the molar ratio of ethanol to isopropanol in the ethanol / isopropanol mixed solvent system is within the range of 7:1 to 9:1, or 7.5:1 to 8.5:1, and most preferably 7.8:1 to 8.2:1, the para / ortho ratio of hydroxyanisole can be significantly increased to a level far superior to the prior art. Outside this optimal range, regardless of whether the above ratio is increased or decreased, a rapid decrease in the para / ortho ratio of hydroxyanisole is observed.

[0041] According to another embodiment of this application, in the reaction, the molar ratio of the anisole raw material to the ethanol contained in the solvent is 1:1 to 1:10. For example, the molar ratio of anisole to ethanol can be within the range of values ​​obtained by combining any two of the following endpoints: 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5, 1:10.

[0042] Another inventive aspect of this application is that the present invention can use a simply prepared titanium-silicon molecular sieve as a catalyst to achieve the high para / ortho ratio, high anisole feed conversion rate, and excellent yield of the target product, p-hydroxyanisole, as described above. The titanium-silicon molecular sieve catalyst used in this invention can be unmodified or simply modified with a very small amount of transition metal elements. In contrast, previously reported processes, in order to maximize reaction efficiency and product quality, have had to modify the titanium-silicon molecular sieve in various ways (including but not limited to: depositing a large number of complex combinations of various metal elements on the titanium-silicon molecular sieve, attaching various organic or inorganic groups to the titanium-silicon molecular sieve, and incorporating organic or inorganic modifying compounds into the titanium-silicon molecular sieve during its synthesis, etc., which inevitably leads to increased process costs and complexity). However, even with these modifications, only a mediocre feed conversion rate and hydroxyanisole product yield can be achieved, and these prior technologies have consistently failed to achieve a satisfactory para / ortho ratio.

[0043] The titanium-silicon molecular sieve is a material known in the art, and its synthesis process is also known in the art. Specifically, the titanium-silicon molecular sieve is a microporous material composed of an interconnected framework of titanium oxide and silicon oxide, and its pore structure includes independent ten-membered ring sinusoidal channels and a twelve-membered ring supercage system.

[0044] According to one embodiment of this application, the molar ratio of titanium to silicon in the titanium-silicon molecular sieve can be from 0.01:100 to 12:100, for example from 0.5:100 to 8:100, preferably from 1:100 to 5:100, for example from 1.5:100 to 3:100.

[0045] According to one embodiment of this application, the titanium-silicon molecular sieve can be prepared by mixing a silicon source, a titanium source, and a template agent, followed by hydrolysis and crystallization under heating conditions. According to an exemplary embodiment of this application, the silicon source includes silica sol, tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, and tetrabutyl silicate. According to an exemplary embodiment of this application, the titanate includes tetrabutyl titanate, tetrapropyl titanate, tetraethyl titanate, tetramethyl titanate, titanium tetrachloride, and titanium oxychloride. According to another embodiment of this application, the template agent can be an organic amine or ammonium salt, such as trimethylamine, triethylamine, tripropylamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide.

[0046] According to another embodiment of this application, the titanium-silicon ratio in the titanium-silicon molecular sieve can be controlled by the ratio of the added silicon source and titanium source.

[0047] According to another embodiment of this application, the heating for synthesizing titanium-silicon molecular sieves can be carried out under hydrothermal treatment. The heating temperature can be 100-220°C, for example, 120-200°C, and the heating time can be 4 hours to 30 days, for example, 1-30 days, or 6-20 days. According to another embodiment of this application, after crystallization is completed under the hydrothermal conditions, the generated crystals can be heated at high temperatures (e.g., 300-600°C, or 400-550°C) for 1-72 hours to remove the template agent and other organic components, thereby obtaining the desired titanium-silicon molecular sieve.

[0048] According to an exemplary embodiment of this application, the titanium-silicon molecular sieve is a TS-1 type titanium-silicon molecular sieve.

[0049] According to one embodiment of this application, the transition metal in the transition metal-modified titanium-silicon molecular sieve may be selected from one or more of the following: copper, cadmium, nickel, magnesium, zinc, manganese, iron, molybdenum, rare earth elements, zirconium, hafnium, chromium, silver, and rhenium. According to another embodiment of this application, based on the total mass of the transition metal-modified titanium-silicon molecular sieve, the content of the transition metal used for modification may be 0.001-5% by mass, for example, 0.01-3% by mass, or 0.1-1.5% by mass.

[0050] The method for modifying titanium-silicon molecular sieves with transition metals is known in the art. For example, after synthesizing the titanium-silicon molecular sieve, it can be impregnated with a solution, suspension, slurry, or other material containing a transition metal, followed by heat treatment. If necessary, different degrees of reduction can also be performed to obtain the transition metal-modified titanium-silicon molecular sieve catalyst. Alternatively, during the preparation of titanium-silicon molecular sieves as described above, a small amount of the desired transition metal can be incorporated into the raw materials, thereby generating the transition metal-modified titanium-silicon molecular sieve catalyst in situ.

[0051] According to another embodiment of this application, in the reaction of anisole with an oxidant of the present invention, the mass ratio of the catalyst to anisole is 2:1 to 1:20, for example 1:1 to 1:15, preferably 1:5 to 1:10.

[0052] According to another embodiment of this application, the oxidant is selected from one or more of the following: ozone, hydrogen peroxide, tert-butyl hydrogen peroxide, with hydrogen peroxide being preferred. The hydrogen peroxide may be added in the form of hydrogen peroxide solution.

[0053] According to another embodiment of this application, the molar ratio of the anisole to the oxidant is 2:1 to 1:3, for example, within the range of any combination of the following two values: 2:1, 1.5:1, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3. The above ratios are calculated based on the molar amount of pure oxidant. For example, when using hydrogen peroxide of a certain concentration, the above molar ratio should be calculated based on the molar amount of pure hydrogen peroxide in the hydrogen peroxide.

[0054] According to another embodiment of this application, the reaction temperature of the anisole with the oxidant is 30-100°C, for example 50-90°C, or 70-80°C. According to another embodiment of this application, the reaction pressure of the anisole with the oxidant is atmospheric pressure (i.e., one atmosphere) to 0.5 MPa, preferably atmospheric pressure to 0.3 MPa.

[0055] According to another embodiment of this application, the reaction of the anisole with the oxidant is carried out in a closed reactor, and the atmosphere in the reactor contains 1-12% by volume of oxygen, for example, the oxygen content in the reaction atmosphere can be 2-10% by volume, or 3-8% by volume, or 4-6% by volume. The remaining gas in the reaction atmosphere can be a gas that is inert to the reaction, such as nitrogen or argon.

[0056] Figure 1 The diagram illustrates the reaction of this application, in which anisole reacts with an oxidant in the presence of a catalyst and a mixed organic solvent to generate the high-value target product p-hydroxyanisole and the less valuable o-hydroxyanisole. In the hydroxyanisole product obtained by the reaction of this invention, the molar ratio of p-hydroxyanisole to o-hydroxyanisole is significantly higher than that of the prior art, for example, higher than 5:1, or higher than 8:1, or higher than 10:1, or higher than 11:1, or higher than 12:1, or higher than 16:1, preferably 11:1-20:1.

[0057] According to an exemplary embodiment of this application, the method of the present invention includes the following steps: Step 1: In the presence of a catalyst and an organic solvent (a mixture of ethanol and isopropanol), anisole is reacted with an oxidant to generate a reaction mixture containing hydroxyanisole; the reaction mixture also contains a solvent, unreacted raw materials, a solid catalyst, etc. Step 2: Perform solid-liquid separation on the reaction mixture obtained from the reaction; Step 3: Purify the liquid phase obtained from the solid-liquid separation to obtain o-hydroxyanisole and p-hydroxyanisole, respectively.

[0058] According to one embodiment of this application, the solid-liquid separation in step two can be performed using one or more of the following devices: a centrifugal filter, a candle filter, a precision filter, or a plate and frame filter. Step two removes solid components from the reaction mixture, such as solid titanium-silicon catalyst.

[0059] According to another embodiment of this application, the purification in step three is carried out in a vacuum distillation column, and the bottom temperature of the vacuum distillation column is 50-200°C, and the pressure in the vacuum distillation column is 0.1-5 kPa. According to another embodiment of this application, vacuum distillation is carried out under a vacuum condition of less than 1 kPa, and the fraction collected at 70-80°C is o-hydroxyanisole, and the fraction collected at 100-110°C is p-hydroxyanisole.

[0060] A further inventive point of this invention is that, through the process design, catalyst selection, and solvent design described above, the generation of byproducts (such as tar) can be effectively reduced. High-quality target products can be obtained with only simple separation and purification techniques, and the utilization rate of the oxidant is also effectively improved. The method of this invention is simple in design and can be easily scaled up, which is beneficial for industrial application and has excellent application prospects.

[0061] The following embodiments illustrate the methods of this application in detail, with the aim of providing a better understanding of the content of this application. It should be understood that these embodiments are merely illustrative and not restrictive. Unless otherwise stated, the reagents used in the embodiments are commercially available analytical grade reagents. Unless otherwise specified, the methods and conditions used in the embodiments are conventional methods and conditions.

[0062] Example

[0063] All reagents used in the following examples are commercially available analytical grade reagents, and the water used is deionized water.

[0064] Preparation Examples

[0065] In this preparation example, TS-1 titanium-silicon molecular sieve was prepared by hydrothermal synthesis.

[0066] The atmosphere in the dry flask was replaced with carbon dioxide-free air. Then, 455 g of tetraethyl orthosilicate was added to the flask, followed by 15 g of tetraethyl titanate. Next, 800 g of a 25% (w / w) aqueous solution of tetrapropylammonium hydroxide was slowly added dropwise while continuously stirring. After the addition was complete, the temperature of the flask was carefully raised to approximately 85°C while continuing to stir. This temperature was maintained for 5 hours, during which the material underwent hydrolysis and released ethanol. Deionized water was then added to the flask to bring the total volume of the reaction mixture to 1.5 liters. The contents of the flask were then transferred to a high-pressure reactor made of titanium alloy and equipped with a stirrer. The reactor was sealed, and the reaction temperature was raised to 175°C. Crystallization was carried out for 30 days under continuous stirring and spontaneous pressure.

[0067] After crystallization, stirring was stopped and the mixture was allowed to cool naturally to room temperature. The material in the reactor was then poured out, and the solid material was collected and washed several times with hot deionized water. The solid product was dried overnight in an infrared oven and then heated in a muffle furnace at 550°C for 6 hours.

[0068] The solid product after heating was characterized by XRD, and the obtained XRD pattern is shown below. Figure 7 As shown, this preparation example confirms the yield of TS-1 titanium-silicon molecular sieve. The average particle size of the TS-1 titanium-silicon molecular sieve was measured to be approximately 250 nanometers using laser diffraction particle size analysis.

[0069] Example 1

[0070] 26.5 g of anisole, 53 mL of ethanol, 5.3 mL of isopropanol, and 2.7 g of the TS-1 titanium-silicon molecular sieve prepared in the above preparation examples were added to a high-pressure reactor. Then, 28.3 g of 30% hydrogen peroxide was added. The reactor was sealed, and the atmosphere was replaced with a mixture of 5% oxygen / 95% nitrogen. Stirring was started, and the reactor was heated to 80°C. The pressure inside the reactor was maintained at 0.3 MPa, and the reaction was carried out under these conditions for 4 hours.

[0071] After the reaction was complete, the reactor was cooled to room temperature. The resulting reaction solution was a solid suspension, which was subjected to solid-liquid separation in a centrifugal filter. The separated liquid phase was called the initial reaction solution. The initial reaction solution was characterized using a Shimadzu LC-20AD high-performance liquid chromatograph (with an octadecylsilane-bonded column and a methanol-water solution as the mobile phase) to obtain... Figure 2 The liquid chromatogram shown is presented. Tests determined that the selectivity of hydroxyanisole was 90.91%, with a para-to-ortho ratio of 11.02.

[0072] The initial reaction solution was subjected to vacuum distillation in a distillation column at a vacuum level below 1 kPa, and the fraction collected at 70-80°C was o-hydroxyanisole (e.g., hydroxyanisole). Figure 6 As shown), the purity of the fraction was determined to be 99.51% by liquid chromatography; the fraction collected at 100-110℃ was p-hydroxyanisole (e.g. Figure 5 As shown in the figure, the purity of its fraction was determined to be 99.65% by liquid chromatography.

[0073] Example 2

[0074] 26.5 g of anisole, 106.0 mL of ethanol, 21.2 mL of isopropanol, and 5.3 g of the TS-1 titanium-silicon molecular sieve prepared in the above preparation examples were added to a high-pressure reactor. Then, 56.7 g of 30% hydrogen peroxide was added. The reactor was sealed, and the atmosphere was replaced with a mixture of 5% oxygen / 95% nitrogen. Stirring was started, and the reactor was heated to 80°C. The pressure inside the reactor was maintained at 0.3 MPa, and the reaction was carried out under these conditions for 4 hours.

[0075] After the reaction was complete, the reactor was cooled to room temperature. The resulting reaction solution was a solid suspension, which was subjected to solid-liquid separation in a centrifugal filter. The separated liquid phase was called the initial reaction solution. The initial reaction solution was characterized using liquid chromatography to obtain… Figure 3 The liquid chromatogram shown is presented. Tests determined that the selectivity of hydroxyanisole was 92.63%, and the ortho-to-para ratio was 12.93.

[0076] The initial reaction solution was subjected to vacuum distillation in a distillation column at a vacuum level below 1 kPa. The fraction collected at 70-80℃ was o-hydroxyanisole, and its purity was determined to be 99.72% by liquid chromatography. The fraction collected at 100-110℃ was p-hydroxyanisole, and its purity was determined to be 99.42% by liquid chromatography.

[0077] Example 3

[0078] 53.0 g of anisole, 265.0 mL of ethanol, 33.1 mL of isopropanol, and 10.6 g of the TS-1 titanium-silicon molecular sieve prepared in the above preparation examples were added to a high-pressure reactor. Then, 85.0 g of 30% hydrogen peroxide was added. The reactor was sealed, and the atmosphere was replaced with a mixture of 5% oxygen / 95% nitrogen. Stirring was started, and the reactor was heated to 80°C. The pressure inside the reactor was maintained at 0.3 MPa, and the reaction was carried out under these conditions for 4 hours.

[0079] After the reaction was complete, the reactor was cooled to room temperature. The resulting reaction solution was a solid suspension, which was subjected to solid-liquid separation in a centrifugal filter. The separated liquid phase was called the initial reaction solution. The initial reaction solution was characterized using liquid chromatography to obtain… Figure 3 The liquid chromatogram shown is presented. Tests determined that the selectivity of hydroxyanisole was 93.68%, with a 16.81 ortho-para ratio.

[0080] The initial reaction solution was subjected to vacuum distillation in a distillation column at a vacuum level below 1 kPa. The fraction collected at 70-80℃ was o-hydroxyanisole, and its purity was determined to be 99.62% by liquid chromatography. The fraction collected at 100-110℃ was p-hydroxyanisole, and its purity was determined to be 99.84% by liquid chromatography.

[0081] Comparative Example 1

[0082] 26.5 g of anisole, 58.3 mL of ethanol, and 2.7 g of the TS-1 titanium-silicon molecular sieve prepared in the above preparation examples were added to a high-pressure reactor, followed by the addition of 28.3 g of 30% hydrogen peroxide. The reactor was then sealed, and the atmosphere was replaced with a mixture of 5% oxygen / 95% nitrogen. Stirring was initiated, and the reactor was heated to 80°C while maintaining a pressure of 0.3 MPa. The reaction was carried out under these conditions for 4 hours.

[0083] After the reaction was complete, the reactor was cooled to room temperature. The resulting reaction solution was a solid suspension, which was subjected to solid-liquid separation in a centrifugal filter. The separated liquid phase was called the initial reaction solution. The initial reaction solution was characterized using liquid chromatography, and the selectivity for hydroxyanisole was determined to be 70.68%, with a relative proportion of 9.37 (ortho / ortho).

[0084] Comparative Example 2

[0085] 26.5 g of anisole, 58.3 mL of isopropanol, and 2.7 g of the TS-1 titanium-silicon molecular sieve prepared in the above preparation examples were added to a high-pressure reactor, followed by the addition of 28.3 g of 30% hydrogen peroxide. The reactor was then sealed, and the atmosphere was replaced with a mixture of 5% oxygen / 95% nitrogen. Stirring was initiated, and the reactor was heated to 80°C while maintaining a pressure of 0.3 MPa. The reaction was carried out under these conditions for 4 hours.

[0086] After the reaction was complete, the reactor was cooled to room temperature. The resulting reaction solution was a solid suspension, which was subjected to solid-liquid separation in a centrifugal filter. The separated liquid phase was called the initial reaction solution. The initial reaction solution was characterized using liquid chromatography, and the selectivity for hydroxyanisole was determined to be 69.16%, with a relative order of 6.22 (ortho- or tho-).

[0087] Comparative Example 3

[0088] 26.5 g of anisole, 30.0 mL of ethanol, 28.3 mL of acetonitrile, and 2.7 g of the TS-1 titanium-silicon molecular sieve prepared in the above preparation examples were added to a high-pressure reactor. Then, 28.3 g of 30% hydrogen peroxide was added. The reactor was sealed, and the atmosphere was replaced with a mixture of 5% oxygen / 95% nitrogen. Stirring was started, and the reactor was heated to 80°C. The pressure inside the reactor was maintained at 0.3 MPa, and the reaction was carried out under these conditions for 4 hours.

[0089] After the reaction was complete, the reactor was cooled to room temperature. The resulting reaction solution was a solid suspension, which was subjected to solid-liquid separation in a centrifugal filter. The separated liquid phase was called the initial reaction solution. The initial reaction solution was characterized using liquid chromatography, and the selectivity for hydroxyanisole was determined to be 92.30%, with a relative proportion of 5.79 (ortho- or tho-).

[0090] As can be seen from the above experiments, Examples 1-3 of this invention, using the method of this invention, can perform anisole oxidation very simply and efficiently, achieving high selectivity and an excellent ortho-para ratio of the target product. Furthermore, it was observed that Example 3 achieved a further significant increase in selectivity and ortho-para ratio compared to Examples 1-2. In contrast, Comparative Examples 1-3 used a single type of organic solvent or a mixed organic solvent different from that of this invention in the reaction system, resulting in significantly worse reaction efficiency and ortho-para ratio of the product.

Claims

1. A method for preparing hydroxyanisole, the method comprising reacting anisole with an oxidant in the presence of a catalyst and an organic solvent to generate hydroxyanisole; The organic solvent is a mixture of ethanol and isopropanol.

2. The method according to claim 1, characterized in that, In the organic solvent, the volume ratio of ethanol to isopropanol is 5:1 to 10:

1.

3. The method according to claim 2, characterized in that, In the organic solvent, the volume ratio of ethanol to isopropanol is 7:1 to 9:

1.

4. The method according to claim 1, characterized in that, The oxidant is selected from one or more of the following: hydrogen peroxide, tert-butyl hydrogen peroxide, and ozone; The molar ratio of the anisole to the oxidant is 2:1 to 1:

3.

5. The method according to claim 1, characterized in that, The molar ratio of benzyl alcohol to ethanol contained in the solvent is 1:1 to 1:

10.

6. The method according to claim 1, characterized in that, The catalyst is a titanium-silicon molecular sieve, a transition metal-modified titanium-silicon molecular sieve, or a combination of the two; The mass ratio of the catalyst to anisole is 2:1 to 1:

20.

7. The method according to claim 1, characterized in that, The reaction temperature is 30-100℃, and the reaction pressure is atmospheric pressure to 0.5MPa; The reaction is carried out in an oxygen-containing atmosphere, wherein the volume content of oxygen in the oxygen-containing atmosphere is 1-12 volumes.

8. The method according to claim 1, characterized in that, The method, after reacting anisole with the oxidant, further includes the following steps: The material obtained from the reaction is subjected to solid-liquid separation; The liquid phase obtained from the solid-liquid separation is purified to obtain o-hydroxyanisole and p-hydroxyanisole, respectively.

9. The method according to claim 8, characterized in that, The method satisfies one or more of the following: The solid-liquid separation is performed using one or more of the following devices: centrifugal filter, candle filter, precision filter, plate and frame filter; The purification is carried out using a vacuum distillation column, with the bottom temperature of the column being 50-200°C and the pressure being 0.1-5 kPa.

10. A hydroxyanisole product prepared by the method of any one of claims 1-9, wherein the hydroxyanisole product comprises p-hydroxyanisole and o-hydroxyanisole, and the molar ratio of p-hydroxyanisole to o-hydroxyanisole is greater than 5:1.

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