Method for preparing p-alkylbenzaldehyde

Abstract

The invention provides a method for preparing p-alkyl benzaldehyde. The method comprises the following steps: under the catalysis of a hexafluorophosphoric acid solution, carbon monoxide and alkylbenzene are subjected to a formylation reaction to obtain p-alkylbenzaldehyde, and the hexafluorophosphoric acid solution contains hexafluorophosphoric acid and hydrogen fluoride. According to the method disclosed by the invention, disproportionation reaction of the raw material alkylbenzene can be effectively avoided, so that a post-treatment process is simplified, and the yield and the purity of the p-alkylbenzaldehyde are improved.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and more specifically, to a method for preparing p-alkylbenzaldehyde. Background Technology

[0002] Alkylbenzaldehyde is a common chemical product or raw material widely used in perfumes, pharmaceuticals, and agrochemicals. Currently, the formylation reaction of alkylbenzenes is the main challenge in its preparation. Two main methods have been reported: one using hydrochloric acid-aluminum chloride as a catalyst, and the other using hydrogen fluoride-boron trifluoride as a catalyst. However, both methods have certain drawbacks. The former method involves difficult catalyst recovery and generates a large amount of waste during post-processing, increasing costs. The latter method's catalyst induces disproportionation reactions in the raw materials, increasing post-processing difficulty and resulting in low product yields.

[0003] Therefore, finding more effective and environmentally friendly preparation methods is particularly important. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art, to at least some extent.

[0005] In a first aspect, this application discloses a method for preparing p-alkylbenzaldehyde. According to embodiments of this application, the method includes: a formylation reaction of carbon monoxide with an alkylbenzene under the catalysis of a hexafluorophosphate solution to obtain the p-alkylbenzaldehyde, wherein the hexafluorophosphate solution contains hexafluorophosphate and hydrogen fluoride. The formylation reaction is catalyzed by the formation of a complex between hexafluorophosphate and the alkylbenzene, thus avoiding disproportionation reactions that would occur due to contact between the alkylbenzene and Lewis acids (such as PF5 or BF3). Therefore, the method of this application effectively suppresses disproportionation reactions, simplifies post-processing, and improves the yield and purity of p-alkylbenzaldehyde.

[0006] According to embodiments of this application, the method may further include at least one of the following additional technical features:

[0007] According to embodiments of this application, the hexafluorophosphoric acid is obtained by reacting hydrogen fluoride (HF) with phosphorus pentafluoride (PF5) to obtain hexafluorophosphoric acid (HPF6). Since alkylbenzenes readily undergo disproportionation reactions under the action of Lewis acids (such as BF3 or PF5), boron trifluoride and hydrogen fluoride cannot form stable tetrafluoroboric acid. However, phosphorus pentafluoride and hydrogen fluoride can form stable hexafluorophosphoric acid under certain conditions, thereby avoiding contact between alkylbenzenes and Lewis acids. Therefore, by using phosphorus pentafluoride instead of boron trifluoride, the occurrence of disproportionation reactions is successfully reduced. This substitution not only optimizes the reaction process and simplifies the post-processing, but also improves the yield and purity of alkylbenzaldehyde.

[0008] According to embodiments of this application, the molar ratio of hydrogen fluoride to phosphorus pentafluoride is not less than 5:1. Therefore, by maintaining the molar ratio of hydrogen fluoride to phosphorus pentafluoride within the above range, complete conversion of phosphorus pentafluoride to hexafluorophosphoric acid can be ensured, avoiding contact between alkylbenzene and Lewis acid, thereby preventing the occurrence of alkylbenzene disproportionation reaction.

[0009] According to an embodiment of this application, the temperature of the first reaction is -30°C to 0°C. By keeping the first reaction temperature within the above range, it is possible to ensure that phosphorus pentafluoride is completely converted into hexafluorophosphoric acid without the risk of pressure runaway due to intense exothermic reaction (pressure ≤ 5 MPa).

[0010] According to embodiments of this application, the formylation reaction and the first reaction are carried out in the same container. Conducting the formylation reaction and the first reaction in the same container simplifies the process and avoids the decomposition of hexafluorophosphate into hydrogen fluoride and phosphorus pentafluoride during the transfer process. This method helps to utilize the generated hexafluorophosphate to form a stable complex with the raw material alkylbenzene in a timely manner during the reaction, thereby improving product yield and reaction efficiency.

[0011] According to embodiments of this application, the molar ratio of the alkylbenzene to the phosphorus pentafluoride is (0.5-1.5):1. By using a feeding ratio within the above range, it is possible to ensure that the alkylbenzene and hexafluorophosphoric acid form a stable complex, reducing the possibility of hexafluorophosphoric acid decomposing to produce phosphorus pentafluoride and thus inducing a disproportionation reaction.

[0012] According to embodiments of this application, the pressure of the formylation reaction is 1 MPa-10 MPa. Therefore, by keeping the pressure of the formylation reaction within this range, effective contact between the carbon monoxide gas and the reaction liquid can be ensured.

[0013] According to embodiments of this application, the temperature of the formylation reaction is -30°C to 0°C. Therefore, by keeping the temperature of the formylation reaction within the above range, the decomposition of hexafluorophosphoric acid to produce phosphorus pentafluoride can be effectively avoided, while ensuring that the alkylbenzene reacts with carbon monoxide to form the p-alkylbenzaldehyde product.

[0014] According to embodiments of this application, the alkylbenzene has at least one primary alkyl group on its benzene ring. This allows the formation of p-alkylbenzaldehyde.

[0015] According to embodiments of this application, the primary alkyl group is as follows:

[0016] -CH2R, where R includes H or a straight-chain, branched, or cyclic saturated hydrocarbon group having 1-10 carbon atoms.

[0017] According to embodiments of this application, the formylation reaction further includes: distilling the solution obtained after the formylation reaction to obtain a first gas and a first liquid; and subjecting the first liquid to a first distillation process to obtain the p-alkylbenzaldehyde. This removes impurities and byproducts, thereby obtaining high-purity p-alkylbenzaldehyde.

[0018] According to an embodiment of this application, the first gas comprises hydrogen fluoride and phosphorus pentafluoride. Therefore, the hydrogen fluoride and phosphorus pentafluoride can be used in the first reaction to generate hexafluorophosphoric acid, saving costs.

[0019] According to an embodiment of this application, the pressure of the distillation process is -0.10 MPa to 0 MPa. Therefore, by keeping the distillation pressure within this range, the recovery of hydrogen fluoride and phosphorus pentafluoride can be effectively promoted, raw material loss can be reduced, and the treatment of hazardous waste gases can be avoided.

[0020] According to an embodiment of this application, the distillation process is carried out at a temperature of 50°C to 150°C. Therefore, by keeping the distillation process within this range, the decomposition of hexafluorophosphoric acid into phosphorus pentafluoride and hydrogen fluoride can be effectively promoted, thereby enabling catalyst recovery.

[0021] According to an embodiment of this application, the pressure of the first distillation process is -0.05 MPa to -0.1 MPa. Therefore, by keeping the pressure of the first distillation process within the above range, the purity and yield of p-alkylbenzaldehyde can be improved.

[0022] According to an embodiment of this application, the temperature of the first distillation process is 100°C to 200°C. Therefore, by keeping the temperature of the first distillation process within the above range, p-alkylbenzaldehyde can be effectively separated.

[0023] According to an embodiment of this application, the formylation reaction further includes: washing the solution obtained after the formylation reaction to obtain an organic layer; and subjecting the organic layer to a second distillation process to obtain the p-alkylbenzaldehyde. Thus, high-purity p-alkylbenzaldehyde can be obtained.

[0024] According to an embodiment of this application, the washing process is carried out using ice water. This allows for simple and effective removal of the complex, reduces the diffusion of hazardous gases HF and PF5, and rapidly yields crude p-alkylbenzaldehyde.

[0025] According to an embodiment of this application, the pressure of the second distillation process is -0.05 MPa to -0.1 MPa. Therefore, by keeping the pressure of the second distillation process within the above range, the purity and yield of p-alkylbenzaldehyde can be improved.

[0026] According to an embodiment of this application, the temperature of the second distillation process is 100°C to 200°C. Therefore, by keeping the temperature of the first distillation process within the above range, p-alkylbenzaldehyde can be effectively separated.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 This is an experimental flowchart for the preparation of p-alkylbenzaldehyde according to embodiments of this application. Detailed Implementation

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value, or with other lower or upper limits, to form an unspecified range.

[0032] Unless otherwise defined, 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; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0033] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this application but do not exclude other contents.

[0034] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] In alkylbenzoylation reactions, the main challenges of existing technologies are how to effectively suppress disproportionation and improve catalyst recovery efficiency. Suppression of disproportionation typically involves adding disproportionation inhibitors, but this method has several shortcomings in practice. First, adding inhibitors significantly increases raw material costs. Second, after using inhibitors, the reaction process requires additional purification steps to remove them, which increases the complexity and operational difficulty of the process. Furthermore, the recovery of inhibitors also requires more resources and time, further increasing the production cost of alkylbenzaldehyde.

[0037] In light of this, based on the mechanism of disproportionation, which typically occurs when alkylbenzenes contact Lewis acids, leading to electron rearrangement in the benzene ring and triggering the disproportionation reaction, the applicant explored a novel catalyst system to effectively suppress this reaction by reducing the direct contact between the Lewis acid and the alkylbenzene. The applicant discovered that using hexafluorophosphoric acid solution as a catalyst can rapidly form a stable complex with alkylbenzenes. In the presence of carbon monoxide, the formation of this complex not only accelerates the formylation reaction but also, due to the strong acidity of hexafluorophosphoric acid, more effectively promotes the formylation of alkylbenzenes while reducing the occurrence of disproportionation. This strategy significantly improves the yield and purity of alkylbenzaldehyde.

[0038] Method for preparing p-alkylbenzaldehyde

[0039] Therefore, this application proposes a method for preparing p-alkylbenzaldehyde. According to embodiments of this application, refer to... Figure 1 The method of this application includes:

[0040] S100: Formylation reaction

[0041] In this step, carbon monoxide reacts with alkylbenzene in a formylation reaction under the catalysis of a hexafluorophosphate solution to obtain the p-alkylbenzaldehyde, wherein the hexafluorophosphate solution contains hexafluorophosphate and hydrogen fluoride. According to an embodiment of this application, taking isopropylbenzene as an example, the specific reaction formula is as follows:

[0042]

[0043] Hexafluorophosphate exhibits higher stability and stronger acidity compared to the complex formed by boron trifluoride and hydrogen fluoride, enabling it to form complexes with alkylbenzenes more effectively. In the presence of carbon monoxide, this complex rapidly converts to p-alkylbenzaldehyde, significantly reducing unnecessary contact between Lewis acids and alkylbenzenes, thereby effectively suppressing the disproportionation reaction. Therefore, the method described in this application helps improve the rate and selectivity of the formylation reaction, promotes the main reaction, increases the purity and yield of p-alkylbenzaldehyde, simplifies post-processing, and makes the entire preparation process more efficient and economical.

[0044] In some embodiments of this application, the pressure of the formylation reaction is 1 MPa-10 MPa. For example, it can be 1 MPa, 2 MPa, 4 MPa, 6 MPa, 8 MPa, 10 MPa, or any range of the above values. Therefore, by keeping the pressure of the formylation reaction within the above range, the reaction rate can be accelerated, ensuring effective contact between carbon monoxide gas and the reaction liquid, making the formylation reaction more rapid and complete, thereby improving the efficiency and quality of p-alkylbenzaldehyde formation.

[0045] It should be noted that the pressure of this formylation reaction is maintained by carbon monoxide regulation.

[0046] In some embodiments of this application, the temperature of the formylation reaction is -30°C to 0°C. For example, it can be -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, or any range of the above values. Therefore, by keeping the formylation reaction temperature within the above range, the decomposition of hexafluorophosphate to produce phosphorus pentafluoride can be effectively avoided, side reactions can be suppressed, the selectivity of formylate can be improved, and the formylation reaction of alkylbenzene with carbon monoxide to generate p-alkylbenzaldehyde can be ensured, thereby ensuring the selectivity of the reaction and the high purity of p-alkylbenzaldehyde.

[0047] In some embodiments of this application, the formylation reaction time is 1 h to 10 h. For example, it can be 1 h, 2 h, 4 h, 6 h, 10 h, or any range of the above values. Therefore, by keeping the formylation reaction time within the above range, sufficient time can be ensured for the reaction to proceed to achieve complete conversion of alkylbenzene to p-alkylbenzaldehyde, thereby improving the yield and purity of the product.

[0048] In some embodiments of this application, the alkylbenzene has at least one primary alkyl group on its benzene ring. The primary alkyl group, acting as an electron-donating group, increases the electron density of the benzene ring through a resonance effect, thereby enhancing the reactivity of the benzene ring with electrophilic reagents. Furthermore, the presence of the primary alkyl group helps guide the electrophilic reagent to selectively attack the para-position of the benzene ring, because para-substitution maximizes spatial distance and reduces steric hindrance, thus improving the regioselectivity of the reaction.

[0049] In some embodiments of this application, the primary alkyl group is represented by the formula -CH2R, where R includes H or a straight-chain, branched, or cyclic saturated hydrocarbon group having 1-10 carbon atoms. The alkylbenzene preferably has 1-3 primary alkyl groups and may also have one or more methyl groups in addition to the primary alkyl groups.

[0050] Examples of alkylbenzenes that can be used in this application include monoalkylbenzenes such as toluene, ethylbenzene, n-propylbenzene, isopropylbenzene, n-butylbenzene, and isobutylbenzene; dialkylbenzenes such as o-ethyltoluene, m-ethyltoluene, p-ethyltoluene, o-diethylbenzene, m-diethylbenzene, and p-diethylbenzene; and trialkylbenzenes such as 1,2,3-triethylbenzene, 1,2,4-triethylbenzene, and 1,2,5-triethylbenzene.

[0051] S200: First reaction

[0052] In this step, hydrogen fluoride is reacted with phosphorus pentafluoride to obtain the above-mentioned hexafluorophosphoric acid, specifically the reaction formula: HF + PF5 → HPF6.

[0053] Because alkylbenzenes readily undergo disproportionation reactions under Lewis acids (such as BF3 or PF5), boron trifluoride and hydrogen fluoride cannot form stable tetrafluoroboric acid. However, phosphorus pentafluoride and hydrogen fluoride can form hexafluorophosphoric acid under certain conditions. Compared to tetrafluoroboric acid, hexafluorophosphoric acid has higher stability and stronger acidity, making it more effective in forming p-alkylbenzaldehyde with alkylbenzenes. This method avoids the use of boron trifluoride (BF3), reduces the occurrence of disproportionation reactions, facilitates the formation of p-alkylbenzaldehyde in the formylation reaction, and improves the yield and purity of the product.

[0054] In some embodiments of this application, the molar ratio of hydrogen fluoride to phosphorus pentafluoride is not less than 5:1. For example, it can be 5:1, 8:1, 10:1, 12:1, 15:1, 20:1, or any range of the above values. By keeping the molar ratio of hydrogen fluoride to phosphorus pentafluoride within the above range, it is possible to ensure that phosphorus pentafluoride is completely converted to hexafluorophosphoric acid, avoiding contact between alkylbenzene and Lewis acid, thereby preventing the disproportionation reaction of alkylbenzene and improving the yield of hexafluorophosphoric acid.

[0055] In some embodiments of this application, the molar ratio of hydrogen fluoride to phosphorus pentafluoride is (5-15):1. This improves the yield of hexafluorophosphoric acid while avoiding unnecessary waste.

[0056] In some embodiments of this application, the temperature of the first reaction is -30°C to 0°C. For example, it can be -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, or any range of the above values. Therefore, by keeping the temperature of the first reaction within the above range, complete conversion of phosphorus pentafluoride to hexafluorophosphoric acid can be ensured, guaranteeing the purity and yield of hexafluorophosphoric acid, and preventing the risk of pressure runaway due to intense exothermic reactions (pressure ≤ 5 MPa).

[0057] In some embodiments of this application, the pressure of the first reaction is 0.2 MPa to 5 MPa. For example, it can be 0.2 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, or any range of the above values. Therefore, by keeping the pressure of the first reaction within the above range, pressure runaway will not occur, making the first reaction more rapid and complete, and ensuring the complete conversion of phosphorus pentafluoride to hexafluorophosphoric acid, thereby improving the production efficiency and quality of hexafluorophosphoric acid.

[0058] In some embodiments of this application, the time for the first reaction is 0.5 h to 2 h. For example, it can be 0.5 h, 0.8 h, 1 h, 1.2 h, 1.5 h, 2 h, or any range of the above values. Therefore, by keeping the time of the first reaction within the above range, sufficient time can be ensured for the reaction to proceed to achieve complete conversion of phosphorus pentafluoride to hexafluorophosphoric acid, thereby improving the yield and purity of the product.

[0059] In some embodiments of this application, the formylation reaction and the first reaction are carried out in the same container, namely a reaction vessel. That is, after the first reaction in the reaction vessel is completed, alkylbenzene is directly added to the reaction vessel to carry out the formylation reaction. By continuously carrying out the reaction in the reaction vessel, the process can be simplified, the reaction time shortened, intermediate stagnation reduced, the overall reaction efficiency improved, and the decomposition of hexafluorophosphoric acid into hydrogen fluoride and phosphorus pentafluoride during the transfer process can be avoided. At the same time, product loss during multiple transfers and operations can be reduced, thereby increasing the yield of the final product.

[0060] In some embodiments of this application, the molar ratio of alkylbenzene to phosphorus pentafluoride is (0.5-1.5):1. For example, it can be 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, or any range of the above values. Therefore, by keeping the molar ratio of alkylbenzene to phosphorus pentafluoride within the above range, it is possible to ensure that alkylbenzene and hexafluorophosphoric acid form a stable complex, reducing the possibility of hexafluorophosphoric acid decomposing to produce phosphorus pentafluoride and thus inducing a disproportionation reaction, ensuring the efficient generation of the final product.

[0061] S300: Post-processing

[0062] According to embodiments of this application, the formylation reaction further includes a post-treatment stage, which includes two methods: one is to perform distillation and a first rectification treatment on the solution obtained after the formylation reaction, and the other is to perform washing and a second rectification treatment on the solution obtained after the formylation reaction. Both methods can effectively improve the purity and yield of p-alkylbenzaldehyde. Those skilled in the art can choose the post-treatment method according to the specific circumstances, and they will be described in detail below.

[0063] In some embodiments of this application, the solution obtained after the formylation reaction is distilled to obtain a first gas and a first liquid; the first liquid is then subjected to a first distillation to obtain the p-alkylbenzaldehyde. Through distillation and the first distillation, p-alkylbenzaldehyde can be separated from the reaction mixture, improving its purity, removing byproducts and impurities, while also allowing for the recovery and reuse of hydrogen fluoride and phosphorus pentafluoride, reducing production costs, and minimizing waste generation.

[0064] In some embodiments of this application, the first gas includes hydrogen fluoride and phosphorus pentafluoride. This allows for the recovery and reuse of hydrogen fluoride and phosphorus pentafluoride for the first reaction to produce hexafluorophosphoric acid, reducing production costs and waste generation.

[0065] In some embodiments of this application, the pressure of the distillation process is -0.1 MPa to 0 MPa. For example, it can be -0.1 MPa, -0.08 MPa, -0.06 MPa, -0.04 MPa, -0.02 MPa, 0 MPa, or any range of the above values. Therefore, by keeping the distillation pressure within the above range, it helps to more easily separate hydrogen fluoride and phosphorus pentafluoride from the reaction mixture, effectively promoting the recovery of hydrogen fluoride and phosphorus pentafluoride, reducing raw material loss, and avoiding the treatment of hazardous waste gases.

[0066] In some embodiments of this application, the distillation temperature is 50°C-150°C. For example, it can be 50°C, 80°C, 100°C, 120°C, 150°C, or any range of the above values. Therefore, by keeping the distillation temperature within the above range, the decomposition of hexafluorophosphoric acid into phosphorus pentafluoride and hydrogen fluoride can be effectively promoted, thereby enabling catalyst recovery.

[0067] In some embodiments of this application, the distillation process takes 1-5 hours. For example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or any range of the above values. Therefore, by keeping the distillation time within the above range, hydrogen fluoride and phosphorus pentafluoride can be effectively recovered, reducing raw material loss and facilitating subsequent separation and purification.

[0068] In some embodiments of this application, the pressure of the first distillation process is -0.05 MPa to -0.1 MPa. For example, it can be -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, -0.09 MPa, -0.1 MPa, or any range of the above values. Therefore, by keeping the pressure of the first distillation process within the above range, it helps to more easily separate p-alkylbenzaldehyde from the reaction mixture, while the lower operating pressure reduces the energy required for heating and lowers energy consumption.

[0069] In some embodiments of this application, the temperature of the first distillation process is 100°C to 200°C. For example, it can be 100°C, 120°C, 150°C, 180°C, 200°C, or any range of the above values. Therefore, by keeping the temperature of the first distillation process within the above range, the evaporation rate of p-alkylbenzaldehyde can be increased, its separation efficiency from the reaction mixture can be improved, and the purity and yield of the product can be ensured.

[0070] In some embodiments of this application, the time for the first distillation process is 1-5 hours. For example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or any range of the above values. Therefore, by keeping the time of the first distillation process within the above range, sufficient separation of alkylbenzaldehyde can be ensured, thereby improving the purity and yield of alkylbenzaldehyde.

[0071] In some embodiments of this application, the solution obtained after the formylation reaction is washed to obtain an organic layer; the organic layer is then subjected to a second distillation to obtain the p-alkylbenzaldehyde. Specifically, the washing process utilizes the characteristic that acidic substances such as HPF6 / HF / PF5 are readily soluble in water, while p-alkylbenzaldehyde is insoluble in water, to wash away residual catalyst from the reaction solution, resulting in a neutral eluent. The organic layer in the eluent is then distilled to obtain p-alkylbenzaldehyde. Therefore, this post-processing method can also yield p-alkylbenzaldehyde with high purity.

[0072] In some embodiments of this application, the washing process is carried out using ice water. This avoids the danger posed by the large amount of heat released during acid dissolution.

[0073] In some embodiments of this application, the pressure of the second distillation process is -0.05 MPa to -0.1 MPa. For example, it can be -0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, -0.09 MPa, -0.1 MPa, or any range of the above values. Therefore, by keeping the pressure of the second distillation process within the above range, it helps to more easily separate p-alkylbenzaldehyde from the reaction mixture, while the lower operating pressure reduces the energy required for heating and lowers energy consumption.

[0074] In some embodiments of this application, the temperature of the second distillation process is 100°C to 200°C. For example, it can be 100°C, 120°C, 150°C, 180°C, 200°C, or any range of the above values. Therefore, by keeping the temperature of the second distillation process within the above range, the evaporation rate of p-alkylbenzaldehyde can be increased, its separation efficiency from the reaction mixture can be improved, and the purity and yield of the product can be ensured.

[0075] In some embodiments of this application, the time for the second distillation process is 1-5 hours. For example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or any range of the above values. Therefore, by keeping the time of the second distillation process within the above range, sufficient separation of alkylbenzaldehyde can be ensured, thereby improving the purity and yield of alkylbenzaldehyde.

[0076] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0077] Example 1

[0078] 1. Catalyst Preparation (First Reaction)

[0079] Hydrogen fluoride was added to a sealed high-pressure reactor at a low temperature (-20℃), and phosphorus pentafluoride was added under high pressure with stirring. The molar ratio of hydrogen fluoride to phosphorus pentafluoride was 5:1. The first reaction was carried out at a temperature of -20℃ for about 1 hour until the pressure dropped to zero, thus preparing the catalyst hexafluorophosphoric acid solution.

[0080] 2. Formylation reaction

[0081] The internal pressure of the reactor was maintained at 2 MPa using carbon monoxide. Alkylbenzene (selected from toluene) was introduced into the reactor under high pressure, with a molar ratio of alkylbenzene to phosphorus pentafluoride of 0.5:1. The reaction was carried out at a low temperature (-20℃). The pressure inside the high-pressure reactor was maintained at 2 MPa for 2 hours, at which point the reaction was complete.

[0082] 3. Post-processing

[0083] The reaction liquid in the high-pressure reactor was squeezed out, and then hydrogen fluoride and phosphorus pentafluoride were distilled out of the reaction liquid under normal pressure, at a temperature of 150°C, and for 2 hours. The distilled gas (HF / PF5) can be used to prepare the catalyst in step 1. The remaining liquid was cooled to room temperature and then distilled again under negative pressure (-0.1MPa) with a slow temperature increase to 100°C and a distillation time of 2 hours. Specific fractions were collected and identified by NMR and GC to obtain the product p-alkylbenzaldehyde (p-methylbenzaldehyde).

[0084] Example 2

[0085] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of hydrogen fluoride to phosphorus pentafluoride was 10:1.

[0086] Example 3

[0087] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of hydrogen fluoride to phosphorus pentafluoride was 15:1.

[0088] Example 4

[0089] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of hydrogen fluoride to phosphorus pentafluoride was 20:1.

[0090] Example 5

[0091] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of hydrogen fluoride to phosphorus pentafluoride was 1:1.

[0092] Example 6

[0093] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of toluene to phosphorus pentafluoride was 1:1.

[0094] Example 7

[0095] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of toluene to phosphorus pentafluoride was 1.5:1.

[0096] Example 8

[0097] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of toluene to phosphorus pentafluoride was 0.1:1.

[0098] Example 9

[0099] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the molar ratio of toluene to phosphorus pentafluoride was 2:1.

[0100] Example 10

[0101] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the alkylbenzene was selected from isopropylbenzene.

[0102] Example 11

[0103] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the alkylbenzene was selected from ethylbenzene.

[0104] Example 12

[0105] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the alkylbenzene was selected from n-propylbenzene.

[0106] Example 13

[0107] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the alkylbenzene was selected from o-ethyltoluene.

[0108] Example 14

[0109] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the alkylbenzene was selected from 1,2,3-triethylbenzene.

[0110] Example 15

[0111] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the first reaction temperature in the preparation of the catalyst in step 1 was -10°C.

[0112] Example 16

[0113] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the first reaction temperature was 0°C in the preparation of the catalyst in step 1.

[0114] Example 17

[0115] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the temperature in the formylation reaction in step 2 was -10°C.

[0116] Example 18

[0117] p-alkylbenzaldehyde was prepared according to the method described in Example 1, except that the temperature was 0°C in the formylation reaction in step 2.

[0118] Comparative Example 1

[0119] The p-alkylbenzaldehyde (p-methylbenzaldehyde) product was prepared according to the method of Example 1, except that boron trifluoride was used instead of phosphorus pentafluoride. The specific process is as follows:

[0120] 1. Catalyst Preparation (First Reaction)

[0121] Hydrogen fluoride was added to a closed high-pressure reactor at a low temperature (-20℃), and boron trifluoride was added under high pressure with stirring. The molar ratio of hydrogen fluoride to boron trifluoride was 5:1. The first reaction was carried out at a temperature of -20℃ for about 1 hour until the pressure dropped to zero, thus obtaining the catalyst.

[0122] 2. Formylation reaction

[0123] The internal pressure of the reactor was maintained at 2 MPa using carbon monoxide. Alkylbenzene (selected from toluene) was introduced into the reactor under high pressure, with a molar ratio of alkylbenzene to boron trifluoride of 0.5:1. The reaction was carried out at a low temperature (-20℃). The pressure inside the high-pressure reactor was maintained at 2 MPa for 2 hours, at which point the reaction was complete.

[0124] 3. Post-processing

[0125] The reaction liquid in the high-pressure reactor was squeezed out, and then hydrogen fluoride and boron trifluoride were distilled out of the reaction liquid under normal pressure, at a temperature of 150°C, and for 2 hours. The distilled gas (HF / BF3) can be used to prepare the catalyst in step 1. The remaining liquid was cooled to room temperature and then distilled again under negative pressure (-0.1MPa) with a slow temperature increase to 100°C and a distillation time of 2 hours. Specific fractions were collected and identified by NMR and GC to obtain the product p-alkylbenzaldehyde (p-methylbenzaldehyde).

[0126] The differences between Examples 1-18 are shown in Table 1.

[0127] Table 1

[0128]

[0129]

[0130] The p-alkylbenzaldehydes prepared in Examples 1-18 and Comparative Example 1 were collected, and their purity and yield were determined. The purity was determined by gas chromatography, and the yield was the ratio of the actual p-alkylbenzaldehyde obtained to the theoretical value.

[0131] The results are shown in Table 2. Compared with Comparative Example 1, which used boron trifluoride to prepare p-alkylbenzaldehyde, the method of this application using phosphorus pentafluoride instead of boron trifluoride can effectively improve the yield of p-alkylbenzaldehyde while ensuring high purity and avoiding the occurrence of disproportionation reaction.

[0132] Compared to Example 5, Examples 1-4 show that only when the molar ratio of hydrogen fluoride to phosphorus pentafluoride reaches 5:1 or higher can the yield of alkylbenzaldehyde be effectively improved. This is because when the amount of hydrogen fluoride added is low, phosphorus pentafluoride is not completely converted to hexafluorophosphoric acid, resulting in a higher concentration of phosphorus pentafluoride, which induces the disproportionation reaction of alkylbenzene, thus leading to a lower yield of alkylbenzaldehyde.

[0133] Compared to Examples 8 and 9, Examples 6 and 7 show that the yield of alkylbenzene formaldehyde can only be effectively improved when the molar ratio of alkylbenzene to phosphorus pentafluoride is within a certain range. Specifically, when the molar ratio of alkylbenzene to phosphorus pentafluoride is 0.1:1, meaning the amount of phosphorus pentafluoride is much higher than that of alkylbenzene, contact between alkylbenzene and phosphorus pentafluoride is inevitable, leading to a disproportionation reaction and an increase in disproportionation products, resulting in a lower yield of alkylbenzene formaldehyde. When the molar ratio of alkylbenzene to phosphorus pentafluoride is 2:1, some alkylbenzene cannot complex with hexafluorophosphoric acid, resulting in the inactivation of the para-hydrogen alkyl group on the benzene ring, making it difficult to undergo formylation with carbon monoxide. This leads to a decrease in the conversion efficiency of the alkylbenzene feedstock, resulting in a lower yield of alkylbenzene formaldehyde.

[0134] The results of Examples 10-14 show that when the type of alkylbenzene is changed, the prepared p-alkylbenzaldehyde has a high yield and purity, and the disproportionation reaction can be avoided, indicating that the method of this application is applicable to different alkylbenzenes.

[0135] The results of Examples 15-18 show that changing the first reaction temperature or the formylation reaction temperature can result in high yields and purity of the prepared p-alkylbenzaldehyde, while avoiding disproportionation reactions. This indicates that the method of this application can be used to prepare p-alkylbenzaldehyde over a wide temperature range.

[0136] Table 2

[0137] Yield (%) purity(%) Content of disproportionation products in the first liquid (%) Example 1 94 99.5 0.15 Example 2 94 99.5 0.1 Example 3 95 99.5 0.1 Example 4 95 99.5 0.1 Example 5 78 98.9 5.0 Example 6 93 99.5 0.2 Example 7 92 99.5 0.15 Example 8 76 98.4 6.8 Example 9 65 99.5 0.1 Example 10 94 99.5 0.15 Example 11 94 99.5 0.15 Example 12 94 99.5 0.15 Example 13 94 99.5 0.15 Example 14 93 99.5 0.15 Example 15 93 99.5 0.15 Example 16 94 99.5 0.15 Example 17 93 99.5 0.15 Example 18 93 99.5 0.15 Comparative Example 1 57 98.1 31

[0138] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0139] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing p-alkylbenzaldehyde, characterized in that, include: In the presence of a hexafluorophosphate solution as a catalyst, carbon monoxide reacts with alkylbenzene to formylate, yielding p-alkylbenzaldehyde, wherein the hexafluorophosphate solution contains hexafluorophosphate and hydrogen fluoride.

2. The method according to claim 1, characterized in that, The hexafluorophosphate is obtained by the following method: Hydrogen fluoride is reacted with phosphorus pentafluoride in a first reaction to obtain hexafluorophosphoric acid.

3. The method according to claim 2, characterized in that, The molar ratio of hydrogen fluoride to phosphorus pentafluoride is not less than 5:1; And / or, the temperature of the first reaction is -30℃ to 0℃.

4. The method according to claim 2, characterized in that, The formylation reaction and the first reaction are carried out in the same container.

5. The method according to claim 4, characterized in that, The molar ratio of the alkylbenzene to the phosphorus pentafluoride is (0.5-1.5):

1.

6. The method according to claim 5, characterized in that, The pressure of the formylation reaction is 1 MPa-10 MPa; And / or, the temperature of the formylation reaction is -30°C to 0°C.

7. The method according to claim 6, characterized in that, The alkylbenzene has at least one primary alkyl group on its benzene ring.

8. The method according to claim 7, characterized in that, The primary alkyl group is shown in the following formula: -CH2R, R includes H or a straight-chain, branched, or cyclic saturated hydrocarbon group having 1-10 carbon atoms.

9. The method according to claim 1, characterized in that, The formylation reaction further includes: The solution obtained after the formylation reaction is distilled to obtain a first gas and a first liquid. The first liquid was subjected to a first distillation process to obtain the p-alkylbenzaldehyde.

10. The method according to claim 9, characterized in that, The first gas includes hydrogen fluoride and phosphorus pentafluoride; And / or, the pressure of the distillation treatment is -0.1 MPa to 0 MPa; And / or, the distillation treatment is performed at a temperature of 50°C-150°C; And / or, the pressure of the first distillation treatment is -0.05 MPa to -0.1 MPa; And / or, the temperature of the first distillation treatment is 100℃~200℃.

11. The method according to claim 1, characterized in that, The formylation reaction further includes: The solution obtained after the formylation reaction is washed to obtain an organic layer; The organic layer is subjected to a second distillation process to obtain the p-alkylbenzaldehyde.

12. The method according to claim 11, characterized in that, The washing process is carried out using ice water; And / or, the pressure of the second distillation treatment is -0.05 MPa to -0.1 MPa; And / or, the temperature of the second distillation treatment is 100℃~200℃.

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