Method for preparing phenyl acetate with high selectivity

Abstract

The invention discloses a method for preparing phenyl acetate with high selectivity. A phosphoric acid solution is added into a magnesium chloride solution, stirring and heating are performed to obtain a suspension, the suspension is dried to constant weight to obtain a white solid, the white solid is ground to obtain powder, and the powder is calcined to obtain the catalyst. Then mixing phenol and a catalyst, placing the mixture in an oil bath for reflux reaction, dropwise adding acetic anhydride, distilling after the reaction is finished, and collecting a fraction at 190-195 DEG C, namely phenyl acetate. According to the magnesium chloride loaded phosphoric acid type catalyst (MgCl2-H3PO4) prepared by the method disclosed by the invention, phenol and acetic anhydride react without a solvent, MgCl2-H3PO4 is a solid catalyst, can be recycled only by filtering and can be repeatedly used after being washed, and MgCl2-H3PO4 also improves the selectivity of phenyl acetate and reduces the production cost.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for the highly selective preparation of phenyl acetate. Background Technology

[0002] Phenylacetate is an important organic compound with wide applications in fragrances, food additives, solvents, and pharmaceutical synthesis. Its aromatic properties and suitable solubility make it widely used in perfume manufacturing and the food industry. Furthermore, phenyl acetate is a key raw material for the synthesis of important chemical intermediates such as benzylamine and benzyl alcohol, holding a significant position in the pharmaceutical and fine chemical industries. Therefore, developing efficient and low-cost methods for the synthesis of phenyl acetate has significant industrial application value.

[0003] Currently, there are two main methods for preparing phenyl acetate: one is the acetyl chloride method, using phenol and acetyl chloride as reactants; the other is the acetic anhydride method, using phenol and acetic anhydride as reactants. The preparation of phenyl acetate using phenol and acetic anhydride requires a catalyst; otherwise, the conversion rate is low. Currently, the most commonly used catalyst is anhydrous aluminum chloride, but other catalytic systems exist, such as homogeneous acids, solid superacids, and ionic liquids. However, the synthesis of phenyl acetate using anhydrous aluminum chloride (AlCl3) is problematic. The strong Lewis acid AlCl3 is hygroscopic and releases corrosive HCl, requiring expensive and corrosion-resistant equipment (such as glass-lined / Hastelloy alloy). The reaction terminates, producing highly acidic wastewater (pH 1-2) containing aluminum salts and organic acids, resulting in high treatment costs. The strong acidity of AlCl3 leads to excessive acylation of phenol, increasing byproducts and reducing selectivity to 80%–92%. Furthermore, the high cost of AlCl3 itself increases the overall production cost. In homogeneous acid catalysis systems under strong acid conditions, the aromatic ring of phenol is prone to sulfonation, nitration, or oxidation reactions. For example, with sulfuric acid catalysis, sulfonation byproducts (such as benzenesulfonic acid) can account for 5%–10% of the product, leading to reduced product purity. This necessitates multiple purification steps (such as alkali washing and distillation), increasing process complexity. Furthermore, large amounts of water or alkali are required to neutralize the acidic waste liquid after the reaction, increasing treatment costs. Solid superacids catalyze esterification reactions through their surface strongly acidic sites, avoiding the corrosion problems associated with liquid acids. However, the synthesis of this catalyst requires multiple steps, including sol-gel, sulfuric acid impregnation, and high-temperature calcination. During calcination, SO42-... 2- Partial decomposition leads to significant batch-to-batch variations in acid strength. Catalysts in ionic liquid catalytic systems are difficult to recover, ionic liquid preparation is costly (due to multi-step synthesis), some types (such as imidazoles) pose environmental accumulation risks, and high viscosity requires vigorous stirring or microreactors, increasing equipment costs. Therefore, it is necessary to develop a catalyst that can improve the selectivity of phenyl acetate, solve the solvent dependence problem in phenyl acetate preparation, reduce the difficulty of catalyst recovery, and enable repeated use, thereby reducing the synthesis cost of phenyl acetate. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for the highly selective preparation of phenyl acetate. This invention first prepares a magnesium chloride-supported phosphoric acid catalyst (MgCl2-H3PO4) by supporting phosphoric acid with magnesium chloride. In this catalyst system, the reaction of phenol and acetic anhydride does not require a solvent, and MgCl2-H3PO4 is a solid catalyst that can be recovered simply by filtration and reused after washing. MgCl2-H3PO4 also improves the selectivity of phenyl acetate and reduces production costs.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a catalyst for improving the selectivity of phenyl acetate, prepared by the following method: Phosphoric acid solution was added to magnesium chloride solution, stirred and heated to obtain a suspension. The suspension was dried until constant weight to obtain a white solid. The white solid was ground to obtain a powder, and the powder was calcined to obtain a catalyst.

[0006] Preferably, the concentration of the phosphoric acid solution is 2-3 mol / L; the concentration of the magnesium chloride solution is 1-3 mol / L; and the molar ratio of phosphoric acid to magnesium chloride is 1:2.

[0007] Preferably, the heating temperature is 60~80℃ and the time is 5h; the drying temperature is 120℃.

[0008] Preferably, the calcination heating rate is 5℃ / min, the temperature is 300~600℃, and the time is 3~5h.

[0009] In a second aspect, the present invention provides the application of the above-described catalyst in the preparation of phenyl acetate, wherein the catalyst improves the selectivity of phenyl acetate and can be reused after recovery.

[0010] Preferably, the application includes purity and yield.

[0011] Selectivity refers to the fact that during the formation of phenyl acetate from phenol, a small amount of p-hydroxyacetophenone may be further reacted to produce phenyl acetate, or that phenyl acetate may be hydrolyzed to produce phenol under acidic conditions.

[0012] A third aspect of the present invention provides a method for the highly selective preparation of phenyl acetate using the above-mentioned catalyst, the method comprising: Phenol and catalyst are mixed and refluxed in an oil bath while acetic anhydride is added dropwise. After the reaction is complete, distillation is performed, and the fraction collected at 190-195℃ is phenyl acetate.

[0013] Preferably, the molar ratio of phenol to acetic anhydride is 1:1.10~1.15; and the amount of catalyst added accounts for 0.45~1.4% of the total molar amount of phenol and acetic anhydride.

[0014] Preferably, the acetic anhydride is added over a period of 1 hour.

[0015] Preferably, the temperature of the oil bath is 80~140℃; the reflux reaction time is 1h.

[0016] The beneficial effects of this invention are: (1) The magnesium chloride-supported phosphoric acid used in this invention as a reaction catalyst not only simplifies the post-processing procedure, but also addresses the complex and time-consuming process of removing residual acid after traditional liquid acid catalytic reactions, which requires neutralization, separation, and multiple washing steps. Solid catalysts only require filtration, and the filtrate can be directly washed and distilled to obtain the product. Furthermore, the catalyst can be reused repeatedly after simple washing and drying, making the post-processing method simple. Magnesium chloride and phosphoric acid are both common chemical raw materials, inexpensive, and their catalyst preparation process is simple, requiring no complex equipment, making them suitable for large-scale production. Compared with traditional production methods, this invention shortens the reaction steps and offers advantages such as simple operation and low synthesis cost.

[0017] (2) The composite catalyst prepared in this invention has high raw material conversion rate and excellent product selectivity, specifically: the yield can reach 98.59%, the conversion rate can reach 99.78%, and the selectivity is 98.81%. This catalyst system is particularly suitable for the continuous production process of phenyl acetate.

[0018] (3) This invention aims to improve resource utilization by developing a magnesium chloride-supported phosphoric acid catalyst (MgCl2-H3PO4) suitable for industrial production. This solid acid catalyst is insoluble in the reaction system and can be efficiently separated by simple filtration, producing virtually no acidic waste liquid and solving the wastewater treatment problem at its source. Compared with traditional liquid acids and anhydrous aluminum chloride catalysts that are highly corrosive and require expensive special materials such as glass-lined or Hastelloy, this catalyst has significantly reduced corrosivity and can be used directly with conventional glass or stainless steel equipment, greatly reducing equipment investment costs and maintenance difficulty. Attached Figure Description

[0019] Figure 1 XRD pattern of the catalyst prepared in Example 1; Figure 2 Image of the catalyst prepared in Example 1; Figure 3 Infrared spectra of the catalyst prepared in Example 1; where curve a is the infrared spectrum of pure silica and curve b is the infrared spectrum of the catalyst prepared in Example 1. Figure 4Example 2: Phenyl acetate prepared 1 H-NMR spectrum. Detailed Implementation

[0020] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] As described in the background section, in the synthesis of phenyl acetate, in addition to the main reaction, side reactions such as hydrolysis and Fries rearrangement of phenyl acetate often occur, resulting in the possible presence of impurities such as phenol, p-hydroxyacetophenone, and o-hydroxyacetophenone in the product. These side reactions not only reduce the effective utilization rate of raw materials but also cause a decrease in the selectivity of the target product. In the existing technology, the industrial production of phenyl acetate uses traditional liquid acids (such as sulfuric acid), which requires neutralization and water washing to remove residual acid after the reaction, generating a large amount of acidic wastewater that is costly to treat and pollutes the environment.

[0022] Therefore, the purpose of this invention is to provide a method for the highly selective preparation of phenyl acetate. This invention first prepares a magnesium chloride-supported phosphoric acid catalyst. Phosphoric acid is chosen as the support (acidic active component) because its acidic characteristics create a synergistic effect with the support, while overcoming the inherent defects of pure magnesium chloride as a catalyst. Its advantages are reflected in several aspects, including catalytic performance regulation, improved stability, and practical application value.

[0023] The supported catalyst of this invention exhibits significantly weaker Lewis acid strength than anhydrous aluminum chloride and a lower tendency for hydrolysis (requiring high temperature and humidity conditions to occur). The loading amount is only 0.45–1.4% mol of the substrate (far lower than the 80%–120% mol required for anhydrous aluminum chloride), significantly reducing the total amount of waste and decreasing the E factor from >5 to <1, conforming to green chemistry principles. Anhydrous aluminum chloride, as a strong Lewis acid, has strong and unevenly distributed acidity, easily initiating side reactions such as multiple substitutions, carbocation rearrangements (e.g., isomerization in alkylation reactions), and excessive electrophilic substitution of aromatic rings. In contrast, the supported catalyst of this invention regulates the acidic sites through the support (Lewis acid Mg...). 2+ With Brønsted acid H +The synergistic effect results in a mild and uniformly distributed acidity, which can precisely activate reactant molecules and avoid over-reaction. The active component of this heterogeneous catalytic system is supported on a solid support, and the catalyst can be recovered by simple filtration or centrifugation after the reaction, without the need for complex post-treatment. Experiments show that the magnesium chloride-supported phosphoric acid catalyst retains more than 80% of its activity after recycling, and the cost per use is only about 1 / 3 to 1 / 2 of that of anhydrous AlCl3. At the same time, since excessive use is not required, raw material consumption is reduced; no large amount of waste liquid or residue is generated after the reaction, and the spent catalyst can be regenerated by calcination (removing surface carbon), realizing a "recycling-regeneration" closed loop, reducing the environmental impact by more than 80% compared with traditional methods.

[0024] The synthesis principle of this invention is as follows: .

[0025] Phosphoric acid is anchored to the magnesium chloride surface via Mg-OP bonds, forming a stable supported structure. The Lewis acid sites (Mg...) of magnesium chloride... 2+ ) and the Brønsted acidic site of phosphate (H + A dual-acid synergistic network is formed on the support surface, with both enhancing each other through electronic effects. Compared to homogeneous acid catalysis systems, the mild acidity of the supported catalyst reduces the activation of phenolic hydroxyl groups, selectively inhibits the formation of diacetylation byproducts (o- / p-acetoxyacetophenone), improves the selectivity of the target product to 98.5%, and achieves a product purity of over 99% (GC analysis). Furthermore, no large amounts of water or alkali are required to neutralize the acidic waste liquid after the reaction. Compared to solid superacid catalysis systems, it requires no complex preparation processes, consumes less energy, and has a relatively fast reaction rate. Compared to ionic liquid catalysis systems, the supported catalyst has lower cost, faster reaction rate, shorter reaction time, and higher yield.

[0026] In the preparation of phenyl acetate, acetic anhydride must be added dropwise. Although the direct impact of dropwise addition on the reaction selectivity is relatively limited, its core advantage lies in the gradual introduction of reactants, promoting a gradual release of heat and effectively preventing safety risks such as bumping or runaway reaction. More importantly, the slow addition of acetic anhydride avoids excessively high local concentrations in the reaction system, thereby significantly suppressing polyacetylation side reactions (such as the diacetylation of phenol) and increasing the selectivity of the target product (phenyl acetate) to ≥95% (significantly higher than the 85%~90% of the single-addition method). Furthermore, single-addition is prone to a sudden increase in system pressure due to vigorous reaction and the instantaneous release of large amounts of heat and gas; while dropwise addition combined with effective stirring can achieve stable control of system pressure.

[0027] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0028] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0029] Example 1: Preparation of a catalyst to improve the selectivity of phenyl acetate Magnesium chloride was dissolved in deionized water to prepare a 2.0 mol / L magnesium chloride solution. 50 ml of a 2 mol / L phosphoric acid solution was added to 100 ml of the magnesium chloride solution. The mixture was placed on a magnetic stirrer and heated at 80°C with vigorous stirring for 5 hours to obtain a suspension. The suspension was transferred to a constant-temperature drying oven and dried at 120°C until constant weight was obtained, yielding a white solid. The white solid was ground for 10 min, primarily to grind the dried, blocky or large-particle precursor into a uniform and fine powder. The ground powder was placed in a crucible and calcined at 500°C for 5 hours with a heating rate of 5°C / min to obtain a white powdered catalyst. Its XRD pattern is shown below. Figure 1 See actual product photos Figure 2 Infrared spectrum (see) Figure 3 .

[0030] Example 2: Preparation of phenyl acetate 19.01 g of phenol (0.2 mol) and 0.19 g of the catalyst prepared in Example 1 (0.002 mol) were added to a dry, clean three-necked flask. Then, 22.69 g of acetic anhydride (0.22 mol) was weighed and placed in a constant-pressure dropping funnel. A mechanical stirrer was added, and the mixture was transferred to an oil bath heating device set to 100°C. After the temperature reached 100°C, acetic anhydride was added dropwise. At this point, the phenol was in a liquid state. After adding the phenol dropwise through the constant-pressure dropping funnel for 1 hour, the oil bath temperature was adjusted to 195°C for atmospheric distillation. The fraction of phenyl acetate obtained from the 190°C to 195°C was collected. The distilled phenyl acetate was analyzed by liquid chromatography, and the purity was 99.3%, the yield was 96.53%, and the selectivity was 96.88%. 1 See H-NMR image Figure 4 .

[0031] Selectivity = (Amount of phenyl acetate actually produced / Amount of phenyl acetate theoretically to be produced based on the amount of phenol consumed) × 100%.

[0032] Example 3 The remaining reaction solution after collecting phenyl acetate in Example 2 was filtered to recover the catalyst. The catalyst was then washed 2-3 times with anhydrous ethyl acetate and dried at 100-120°C for 1-2 hours. The recovered catalyst was used to continue preparing phenyl acetate according to the method in Example 2. This was recorded as one cycle, and five cycles were performed. The yield of phenyl acetate is shown in Table 1.

[0033] Table 1. Yield and other indicators of phenyl acetate As shown in Table 1, after 5 cycles, the selectivity of phenyl acetate remained almost unchanged, while the purity, conversion, and yield decreased slightly. This indicates that the catalyst prepared in this invention has good selectivity, can be reused, and reduces synthesis costs.

[0034] Comparative Example 1 The difference from Example 1 is that magnesium chloride was replaced with an equimolar amount of aluminum chloride. The final product was an aluminum chloride-supported phosphoric acid catalyst.

[0035] Comparative Example 2 The difference from Example 1 is that phosphoric acid was replaced with an equimolar amount of alumina. The final product was a magnesium oxide-supported alumina catalyst.

[0036] Comparative Example 3 The difference from Example 2 is that the catalyst was replaced with an equimolar amount of the catalyst prepared in Comparative Example 1. Phenyl acetate was finally prepared, with a purity of 98.67%, a yield of 92.53%, and a selectivity of 93.16%.

[0037] Comparative Example 4 The difference from Example 2 is that the catalyst was replaced with an equimolar amount of the catalyst prepared in Comparative Example 2. Phenyl acetate was finally prepared, with a purity of 98.55%, a yield of 90.69%, and a selectivity of 90.99%.

[0038] Comparative Example 5 The difference from Example 1 is that calcination was not performed, and magnesium chloride and phosphoric acid were used directly in the reaction. Phenyl acetate was finally prepared, with a purity of 98.32%, a yield of 86.39%, and a selectivity of 87.73%.

[0039] Comparative Example 6 The difference from Example 2 is that the catalyst was replaced with an equimolar amount of magnesium chloride. Phenyl acetate was finally prepared, with a purity of 98.76%, a yield of 82.31%, and a selectivity of 84.91%.

[0040] Comparative Example 7 The difference from Example 2 is that the catalyst was replaced with an equimolar amount of phosphoric acid solution. Phenyl acetate was finally prepared, with a purity of 97.99%, a yield of 82.78%, and a selectivity of 85.02%.

[0041] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A catalyst for improving selectivity of phenyl acetate, characterized by, Prepared by the following method: A phosphoric acid solution is added to a magnesium chloride solution, stirred and heated to obtain a suspension, the suspension is dried until constant weight to obtain a white solid, the white solid is ground to obtain a powder, and the powder is calcined to obtain a catalyst.

2. The catalyst according to claim 1, characterized in that, The concentration of the phosphoric acid solution is 2-3 mol / L; the concentration of the magnesium chloride solution is 1-3 mol / L; the molar ratio of phosphoric acid to magnesium chloride is 1:

2.

3. The catalyst of claim 1, wherein The heating temperature is 60-80℃, and the time is 5h; the drying temperature is 120℃.

4. The catalyst of claim 1, wherein The temperature rising rate of the calcination is 5℃ / min, the temperature is 300-600℃, and the time is 3-5h.

5. Use of the catalyst according to any one of claims 1 to 4 for the preparation of phenyl acetate, characterized in that, The catalyst improves the selectivity of phenyl acetate, and can be reused after recovery.

6. Use according to claim 5, characterized in that, The application includes purity and yield.

7. A process for the highly selective preparation of phenyl acetate using the catalyst according to any one of claims 1 to 4, characterized in that, The method is: Phenol and the catalyst according to any one of claims 1-4 are mixed, placed in an oil bath for reflux reaction, and acetic anhydride is added dropwise, distillation is performed after the reaction is completed, and the fraction of 190-195℃ collected is phenyl acetate.

8. The method of claim 7, wherein, The molar ratio of phenol to acetic anhydride is 1:1.10-1.15; the addition amount of the catalyst accounts for 0.45-1.4% of the total molar amount of phenol and acetic anhydride.

9. The method of claim 7, wherein, The dropwise addition time of acetic anhydride is 1h.

10. The method of claim 7, wherein, The temperature of the oil bath is 80-140℃; the reflux reaction time is 1h.

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