A method for preparing 4-acetoxy-2-methyl-2-butenal

Abstract

This invention provides a method for preparing 4-acetoxy-2-methyl-2-butenal. The method includes: mixing 4-acetoxy-2-methylene-1-butenal, a stabilizer, a catalyst, and an oxygen-containing gas, and carrying out an isomerization reaction to obtain 4-acetoxy-2-methyl-2-butenal; wherein the stabilizer includes any one or more of pyridine, 3-methylpyridine, and 4-dimethylaminopyridine. This application uses 4-acetoxy-2-methylene-1-butenal as the reactant and carries out the isomerization reaction in an oxygen-containing gas atmosphere. The product, 4-acetoxy-2-methyl-2-butenal, has a high yield, and because the product does not contain the hydrogenation product of 4-acetoxy-2-methylene-1-butenal, it is easy to separate, significantly reducing the energy consumption for separation. Furthermore, no solvent is required during the reaction, making it safe and environmentally friendly, and it is a method for preparing pentacarbon aldehydes that is easy to industrialize.

Description

Technical Field

[0001] This invention relates to the field of chemical intermediate synthesis, and more specifically, to a method for preparing 4-acetoxy-2-methyl-2-butenal. Background Technology

[0002] 4-Acetoxy-2-methyl-2-butenal (abbreviated as pentacarbonal) is an important intermediate in the synthesis of vitamin A, and its yield directly affects the quality and cost of vitamin A. Therefore, research and optimization of the pentenal process have been ongoing. Among the many routes, four synthetic routes are relatively suitable for industrial production, which are classified according to their starting materials: isoprene route, dimethoxyacetone route, ethylene oxide route, and butenyl glycol route.

[0003] US Patent 5424478 discloses a method for synthesizing pentacarbonaldehyde from isoprene as the starting material. In this route, isoprene first undergoes an addition reaction with sodium hypochlorite, followed by esterification with acetate, and finally oxidation with dimethyl sulfoxide as an oxidant to obtain pentacarbonaldehyde. This method generates large amounts of wastewater and salt, causing severe pollution and failing to meet current environmental protection requirements.

[0004] Patents US4147886 and US3478060 both disclose a method for synthesizing pentacarbonaldehyde from dimethoxyacetone as the starting material. This route requires five reaction steps to obtain the product pentacarbonaldehyde, resulting in a long process, low overall yield, and the use of nitrates in the reaction, posing significant safety risks.

[0005] US Patent 4873362 discloses a route for preparing pentacarbon aldehydes from ethylene oxide. This route uses ethylene oxide as the starting material, proceeding sequentially through an addition reaction with acetic acid, a silver-catalyzed oxidation reaction, and a condensation reaction with acrolein to obtain the pentacarbon aldehyde product. The biggest problem with this route is the high safety risk, because the starting material ethylene oxide itself is very reactive, and the intermediate 2-acetoxyacetaldehyde is also extremely unstable.

[0006] Compared to the three routes mentioned above, the butenediol route has significant advantages due to its shorter synthetic route, lower safety risks, less waste, and better yield. The synthesis of pentaldehydes from butenediol is further divided into the BASF route and the Roche route.

[0007] US Patent 3732287 discloses a method for synthesizing pentacetals from butenediol. This method first esterifies the butenediol with acetic anhydride, then rearranges it in the presence of a copper catalyst, followed by hydroformylation using a rhodium catalyst, and finally decarboxylation to obtain the pentacetal product. In this method, the hydroformylation step produces a large number of byproducts due to the positional selectivity of the carbon-carbon double bond, resulting in a low yield; moreover, the rearrangement step has a low single-pass conversion rate of around 30%, requiring continuous separation and reuse of the raw material, leading to high energy consumption.

[0008] Compared to the BASF route, the Roche route involves esterification, hydroformylation, decarboxylation, and isomerization in that order. The synthetic route is as follows:

[0009]

[0010] This hydroformylation step, due to the symmetry of the carbon-carbon double bond, produces virtually no byproducts, resulting in a higher yield than the BASF hydroformylation reaction. However, the isomerization step requires a hydrogen atmosphere, generating a significant amount of hydrogenation byproducts. Patents US4124619, CN110734374, and CN103467287 have all optimized the hydroisomerization step, minimizing the amount of hydrogenation byproducts. Since the hydrogenation products have very close boiling points to the feedstock, their presence leads to higher energy consumption in subsequent separation processes. Summary of the Invention

[0011] The main objective of this invention is to provide a method for preparing 4-acetoxy-2-methyl-2-butenal, in order to solve the problem of high separation energy consumption caused by the presence of hydrogenation products with boiling points close to those of the raw materials in the isomerization reaction products in the prior art.

[0012] To achieve the above objectives, according to one aspect of the present invention, a method for preparing 4-acetoxy-2-methyl-2-butenal is provided, the method comprising: mixing 4-acetoxy-2-methylene-1-butenal, a stabilizer, a catalyst and an oxygen-containing gas, and carrying out an isomerization reaction to obtain 4-acetoxy-2-methyl-2-butenal; wherein the stabilizer comprises any one or more of pyridine, 3-methylpyridine and 4-dimethylaminopyridine.

[0013] Furthermore, the catalyst includes a support and a noble metal component;

[0014] The carrier is alumina;

[0015] The precious metal components include any one or more of palladium, platinum, and rhodium;

[0016] Preferably, the loading of the noble metal component is 0.1% to 0.8% of the catalyst mass.

[0017] Furthermore, the oxygen content of the oxygen-containing gas is 10% to 21%;

[0018] Oxygen-containing gas is air.

[0019] Furthermore, the stabilizer added is 0.01% to 0.05% of the weight of 4-acetoxy-2-methylene-1-butenal.

[0020] Furthermore, the isomerization reaction is carried out at a temperature of 50–90 °C for a time of 20–60 min.

[0021] Furthermore, the oxygen-containing gas pressure for the isomerization reaction is 0.1–0.5 MPa.

[0022] Furthermore, the liquid hourly space velocity (LHSV) of 4-acetoxy-2-methylene-1-butenal is 0.5–2.0 h⁻¹. -1 .

[0023] Furthermore, the method for preparing 4-acetoxy-2-methyl-2-butenal includes: continuously feeding 4-acetoxy-2-methylene-1-butenal, a stabilizer, and an oxygen-containing gas into a continuous reactor packed with a catalyst to carry out an isomerization reaction;

[0024] Preferably, the continuous reactor is a trickle bed reactor.

[0025] Furthermore, 4-acetoxy-2-methylene-1-butenal and the stabilizer are preheated to the reaction temperature before being introduced into a continuous reactor for isomerization reaction.

[0026] Furthermore, the product of the isomerization reaction was separated by distillation to obtain 4-acetoxy-2-methyl-2-butenal with a purity greater than 99.3%.

[0027] The present invention utilizes 4-acetoxy-2-methylene-1-butenal as a reactant, and carries out an isomerization reaction in an oxygen-containing gas atmosphere. The product, 4-acetoxy-2-methyl-2-butenal, has a high yield. Furthermore, since the product does not contain the hydrogenation product of 4-acetoxy-2-methylene-1-butenal, it is easily separated, significantly reducing energy consumption during separation. Moreover, no solvent is required during the reaction, making it safe and environmentally friendly. This method is easily scalable for industrial production of pentacarbon aldehydes. Attached Figure Description

[0028] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1The ¹H NMR spectrum of the raw material 4-acetoxy-2-methylene-1-butenal according to an embodiment of the present invention is shown.

[0030] Figure 2 The CNMR spectrum of the raw material 4-acetoxy-2-methylene-1-butenal according to an embodiment of the present invention is shown.

[0031] Figure 3 The ¹H NMR spectrum of the product 4-acetoxy-2-methyl-2-butenal according to Example 1 of the present invention is shown.

[0032] Figure 4 The CNMR spectrum of 4-acetoxy-2-methyl-2-butenal, the product of Example 1 according to the present invention, is shown. Detailed Implementation

[0033] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] As analyzed in the background section of this application, existing technologies suffer from the problem of high separation energy consumption due to the presence of hydrogenation products with boiling points close to those of the raw materials in the isomerization reaction products. To address this technical problem, this application provides a method for preparing 4-acetoxy-2-methyl-2-butenal. This method includes: mixing 4-acetoxy-2-methylene-1-butenal, a stabilizer, a catalyst, and an oxygen-containing gas, and carrying out an isomerization reaction to obtain 4-acetoxy-2-methyl-2-butenal; wherein the stabilizer includes any one or more of pyridine, 3-methylpyridine, and 4-dimethylaminopyridine (DMAP).

[0035] The above-described method for preparing 4-acetoxy-2-methyl-2-butenal uses 4-acetoxy-2-methylene-1-butenal as a reactant and carries out an isomerization reaction in an oxygen-containing gas atmosphere. The product, 4-acetoxy-2-methyl-2-butenal, has a high yield, and because it does not contain the hydrogenation product of 4-acetoxy-2-methylene-1-butenal, it is easy to separate, significantly reducing the energy consumption for separation. Furthermore, no solvent is required during the reaction, making it safe and environmentally friendly. This method is easily scalable for industrial production of pentacarbon aldehydes.

[0036] The equation for the above isomerization reaction is as follows:

[0037]

[0038] After extensive research on the isomerization reaction in the Roche route of butenyl glycol, the researchers in this application discovered that this isomerization reaction can also be carried out efficiently in the presence of oxygen-containing gas (e.g., air), thus avoiding the use of hydrogen and solving the problem of hydrogenation byproducts generated during the isomerization process. Both selectivity and overall yield are significantly improved. The probable reaction mechanism of this isomerization reaction is as follows: oxygen molecules dissociate into oxygen atoms on the catalyst surface, then attack the carbon-carbon double bond in the starting material 4-acetoxy-2-methylene-1-butenal molecule to form an epoxy intermediate. Subsequently, deoxygenation occurs, forming a new carbon-carbon double bond at a new position, completing the entire carbon-carbon double bond isomerization process. The chemical reaction equation is as follows:

[0039]

[0040] Since isomerization using oxygen-containing gas may cause the aldehyde groups in the raw materials and products to become unstable and oxidized, a stabilizer is added to prevent the yield from being affected by oxidation of the raw materials and products.

[0041] In some preferred embodiments of this application, the weight of the stabilizer added is 0.01% to 0.05% of the weight of 4-acetoxy-2-methylene-1-butenal, specifically 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, etc., or other values ​​within the above range. Adding the stabilizer within the above range can effectively prevent the oxidation of raw materials and products due to the presence of oxygen, effectively suppress side reactions, and at the same time, will not excessively affect the main reaction, ensuring the purity and yield of the product and thus improving the product yield.

[0042] In some embodiments of this application, the catalyst comprises a support and a noble metal component; wherein the support is alumina; and the noble metal component includes any one or more of palladium, platinum, and rhodium. The alumina-supported noble metal catalyst exhibits high efficiency in catalyzing isomerization reactions in the presence of oxygen, and demonstrates good stability, maintaining catalytic efficiency for extended periods. This makes it suitable for continuous production, reducing catalyst replacement frequency and saving costs. Preferably, the loading of the noble metal component is 0.1% to 0.8% of the catalyst mass, specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., or other values ​​within the aforementioned range.

[0043] The catalyst described above can be prepared using methods in the prior art or by purchasing commercially available catalysts with the above composition; this application does not impose any limitations on this. In some embodiments of this application, the catalyst is prepared according to the following method: first, the support is pretreated by calcination; then, an active metal is loaded to obtain a catalyst precursor; the catalyst precursor is dried and calcined; and finally, it is reduced with hydrogen to obtain the catalyst. The method for loading the active metal can be selected from the prior art, such as the equal-volume impregnation method. The specific process conditions for drying or calcining the support or precursor can also refer to the prior art; this application does not impose any limitations on this.

[0044] In some typical embodiments of this application, the isomerization reaction is carried out at a temperature of 50–90°C for 20–60 min, which is beneficial for further improving the selectivity and yield of the product 4-acetoxy-2-methyl-2-butenal. Specifically, the isomerization reaction temperature is 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc., or other values ​​within the above range. The mild reaction conditions reduce energy consumption, lower equipment maintenance costs, and also reduce environmental impact, making it suitable for environmentally friendly industrial production.

[0045] In some embodiments of this application, the oxygen content in the oxygen-containing gas is 10% to 21%. Preferably, the oxygen-containing gas is air. Using air as the oxygen-containing gas not only reduces production costs but also simplifies operation, ensures high safety, and is suitable for large-scale industrial production environments.

[0046] Preferably, the pressure of the oxygen-containing gas in the isomerization reaction is 0.1–0.5 MPa. Under such pressure, the reaction rate is moderate, ensuring the reaction proceeds fully while avoiding the safety hazards associated with high-pressure operation, thus meeting the safety requirements of chemical production. Specifically, the pressure of the oxygen-containing gas can be 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, or other values ​​within the above range.

[0047] In some preferred embodiments of this application, the liquid hourly space velocity (LHSV) of 4-acetoxy-2-methylene-1-butenal is 0.5–2.0 h⁻¹. -1 Optimized liquid volume hourly space velocity can improve the reactor's processing capacity and reduce its volume, thereby reducing equipment investment and making it suitable for the needs of large-scale industrial production.

[0048] In some typical embodiments of this application, the method for preparing 4-acetoxy-2-methyl-2-butenal includes: continuously feeding 4-acetoxy-2-methylene-1-butenal, a stabilizer, and oxygen-containing gas into a continuous reactor packed with a catalyst to carry out an isomerization reaction, thereby achieving continuous production of 4-acetoxy-2-methyl-2-butenal. This method allows for automated control, improves production efficiency, reduces labor costs, and is suitable for modern chemical production processes. Preferably, the continuous reactor is a trickle bed reactor.

[0049] In some preferred embodiments of this application, the isomerization reaction is carried out in a continuous reactor after the 4-acetoxy-2-methylene-1-butenal and stabilizer are preheated to the reaction temperature. This is beneficial to further improve the reaction efficiency, reduce the generation of by-products, reduce the thermal shock of the reactor, and extend the service life of the reactor. This method is suitable for stable and efficient industrial production.

[0050] The isomerization product obtained by the isomerization reaction can be separated and purified by existing techniques to obtain high-purity 4-acetoxy-2-methyl-2-butenal. In some embodiments of this application, the product of the isomerization reaction is separated by distillation to obtain 4-acetoxy-2-methyl-2-butenal product with a purity greater than 99.3%.

[0051] The researchers of this application found in their experiments that the method described in this application for preparing 4-acetoxy-2-methyl-2-butenal has good selectivity. Generally, the byproducts include 4-acetoxy-2-methylene-1-butenic acid, 4-acetoxy-2-methyl-2-butenic acid, and high-boiling polymers. The boiling points of these byproducts are significantly different from those of the product 4-acetoxy-2-methyl-2-butenal, making them easy to separate by distillation.

[0052] In some typical embodiments of this application, the method for preparing 4-acetoxy-2-methyl-2-butenal includes: (1) mixing the raw material 4-acetoxy-2-methylene-1-butenal with a stabilizer, and then conveying it to a preheater at a certain liquid volume hourly space velocity to heat it to the reaction temperature; (2) under a pressure of 0.1 to 0.5 MPa, the preheated material and air undergo a gas-liquid-solid three-phase isomerization reaction in a fixed-bed reactor filled with a shaped catalyst, the reaction retention time is 20 to 60 min, and the product 4-acetoxy-2-methyl-2-butenal is generated; (3) separating the mixture after the reaction by distillation to obtain the refined 4-acetoxy-2-methyl-2-butenal.

[0053] The main raw material for preparing 4-acetoxy-2-methyl-2-butenal, 4-acetoxy-2-methylene-1-butenal, can be prepared in-house or purchased, and this application does not impose any restrictions.

[0054] The beneficial effects that this application can achieve will be further illustrated below with reference to embodiments and comparative examples.

[0055] In the examples and comparative examples of this application, the raw material 4-acetoxy-2-methylene-1-butenal was a self-prepared intermediate, prepared as follows: 200g of trans-1,4-diacetoxy-2-butene, 1.0g of sodium acetate, and 20mg of triphenylphosphine acetylacetone carbonyl rhodium were added to a 500ml autoclave. The autoclave was then purged three times with N2 gas (0.5MPa each time), and finally pressurized to 5.0MPa with syngas (H2:CO = 1:1). The temperature was raised to 80℃ and maintained for 8 hours. GC analysis showed that the crude 4-acetoxy-2-methylene-1-butenal contained 92% purity; distillation yielded a refined product with a purity of over 99.0%. NMR analysis (see...) Figure 1 , Figure 2 ): 1 H NMR (400MHz, CDCl3) δ9.47 (s, 1H), 6.287 (tq, J = 7.2Hz, 1H), 4.105 (dd, J = 5.9, 1.0Hz, 2H), 2.519 (s, 3H), 1.956 (dd, J = 2.2, 1.0Hz, 3H); 13 C NMR (100MHz, CDCl3) δ193.8, 170.68, 145.99, 135.55, 77.00, 61.88, 43.26, 29.08, 20.65, 13.01.

[0056] The catalysts used in the examples and comparative examples were all commercially available products, and their specific sources are shown in Table 1.

[0057] Table 1

[0058] Reagent Name Reagent Specifications Manufacturer <![CDATA[Pt / Al2O3、Pd / Al2O3、Rh / Al2O3]]> CP Xinnoco trans-1,4-diacetoxy-2-butene AR Aladdin

[0059] Example 1

[0060] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with alumina-supported platinum solid catalyst (i.e., Pt / Al2O3), wherein the platinum loading was 0.3 wt%. First, the catalyst bed temperature was heated to 60 °C. Then, 0.01 wt% (by weight) of the auxiliary agent DMAP (4-acetoxy-2-methylene-1-butenal) was mixed with the raw material 4-acetoxy-2-methylene-1-butenal; subsequently, a metering pump was used to inject the mixture at a rate of 1.0 h⁻¹. -1The reactor was continuously fed at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. Air was then introduced from the top of the reactor to maintain the reactor pressure at 0.2 MPa. The feedstock 4-acetoxy-2-methylene-1-butenal underwent a gas-liquid-solid three-phase isomerization reaction in the presence of air and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor, and the composition of the reaction liquid was analyzed by gas chromatography to calculate the conversion rate and product selectivity of the feedstock 4-acetoxy-2-methylene-1-butenal. The crude product was then purified by distillation to obtain the refined pentacarbonaldehyde. The theoretical number of plates in the distillation column was 18, and the reflux ratio was 1.0. The refined pentacarbonaldehyde was detected by gas chromatography, and the pentacarbonaldehyde content was calculated using the area normalization method. The specific results are shown in Table 2.

[0061] For the structural analysis of pentacarbon aldehydes, please refer to [link / reference]. Figure 3 and Figure 4 Its NMR analysis data are as follows:

[0062] 1 H NMR (400MHz, CDCl3) δ9.45 (s, 1H), 6.67 (tq, J = 5.8, 1.3Hz, 1H), 4.91 (dd, J = 5.9, 1.0Hz, 2H), 2.08 (s, 3H), 1.70 (dd, J = 2.2, 1.0Hz, 3H);

[0063] 13 C NMR (100MHz, CDCl3) δ194.79, 170.13, 147.12, 139.32, 60.66, 40.10, 39.48, 38.85, 20.47, 8.97.

[0064] Example 2

[0065] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with alumina-supported platinum solid catalyst (i.e., Pt / Al2O3), wherein the platinum loading was 0.5 wt%. First, the catalyst bed temperature was heated to 60 °C. Then, 0.02 wt% (by weight) of the auxiliary agent DMAP (4-acetoxy-2-methylene-1-butenal) was mixed with the feedstock 4-acetoxy-2-methylene-1-butenal. Next, a metering pump was used to inject the mixture at a rate of 1.0 h⁻¹. -1The reactor was fed continuously at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. Air was then introduced from the top of the reactor to maintain a pressure of 0.2 MPa. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of air and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor, and the composition of the reaction liquid was analyzed by gas chromatography (GC), and the conversion rate and product selectivity of the feedstock 4-acetoxy-2-methylene-1-butenal were calculated. The crude product was then distilled to obtain a refined pentacarbonaldehyde. The distillation column had 18 theoretical plates, and the reflux ratio was 1.0. GC was used to detect the refined pentacarbonaldehyde, and the pentacarbonaldehyde content was calculated using the area normalization method. The specific results are shown in Table 2. The NMR results of the product pentacarbonaldehyde were consistent with those of Example 1.

[0066] Example 3

[0067] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with alumina-supported platinum solid catalyst (i.e., Pt / Al2O3), wherein the platinum loading was 0.8 wt%. First, the catalyst bed temperature was heated to 60 °C. Then, 0.02 wt% (by weight) of the auxiliary agent DMAP (4-acetoxy-2-methylene-1-butenal) was mixed with the feedstock 4-acetoxy-2-methylene-1-butenal. Next, a metering pump was used to inject the mixture at a rate of 1.0 h⁻¹. -1 The reactor was fed continuously at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. Air was then introduced from the top of the reactor to maintain a pressure of 0.2 MPa. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of air and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor, and the composition of the reaction liquid was analyzed by gas chromatography (GC), and the conversion rate and product selectivity of the feedstock 4-acetoxy-2-methylene-1-butenal were calculated. The crude product was then distilled to obtain a refined pentacarbonaldehyde. The distillation column had 18 theoretical plates, and the reflux ratio was 1.0. GC was used to detect the refined pentacarbonaldehyde, and the pentacarbonaldehyde content was calculated using the area normalization method. The specific results are shown in Table 2. The NMR results of the product pentacarbonaldehyde were consistent with those of Example 1.

[0068] Example 4

[0069] A solid catalyst (Pd / Al₂O₃) supported on alumina was packed into a fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m, wherein the palladium loading was 0.5 wt%. First, the catalyst bed temperature was heated to 60 °C. Then, 0.02 wt% (by weight) of the auxiliary agent DMAP (4-acetoxy-2-methylene-1-butenal) was mixed with the feedstock 4-acetoxy-2-methylene-1-butenal. Next, a metering pump was used to inject the mixture at a rate of 1.0 h⁻¹. -1 The reactor was fed continuously at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. Air was then introduced from the top of the reactor to maintain a pressure of 0.2 MPa. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of air and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor, and the composition of the reaction liquid was analyzed by gas chromatography (GC), and the conversion rate and product selectivity of the feedstock 4-acetoxy-2-methylene-1-butenal were calculated. The crude product was then distilled to obtain a refined pentacarbonaldehyde. The distillation column had 18 theoretical plates, and the reflux ratio was 1.0. GC was used to detect the refined pentacarbonaldehyde, and the pentacarbonaldehyde content was calculated using the area normalization method. The specific results are shown in Table 2. The NMR results of the product pentacarbonaldehyde were consistent with those of Example 1.

[0070] Example 5

[0071] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with a solid catalyst of rhodium supported on alumina (i.e., Rh / Al₂O₃), wherein the rhodium loading was 0.5 wt%. First, the catalyst bed temperature was heated to 60 °C. Then, 0.05 wt% (by weight) of the auxiliary agent DMAP (4-acetoxy-2-methylene-1-butenal) was mixed with the raw material 4-acetoxy-2-methylene-1-butenal. Next, a metering pump was used to inject the mixture at a rate of 1.0 h⁻¹. -1 The reactor was fed continuously at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. Air was then introduced from the top of the reactor to maintain a pressure of 0.2 MPa. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of air and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor, and the composition of the reaction liquid was analyzed by gas chromatography (GC), and the conversion rate and product selectivity of the feedstock 4-acetoxy-2-methylene-1-butenal were calculated. The crude product was then distilled to obtain a refined pentacarbonaldehyde. The distillation column had 18 theoretical plates, and the reflux ratio was 1.0. GC was used to detect the refined pentacarbonaldehyde, and the pentacarbonaldehyde content was calculated using the area normalization method. The specific results are shown in Table 2. The NMR results of the product pentacarbonaldehyde were consistent with those of Example 1.

[0072] Examples 6-14

[0073] Examples 6-14 compare the performance of the isomerization reaction under different process conditions. Other operations are the same as in Example 1. Specific results are shown in Table 2. The NMR results of the product pentaldehyde are consistent with those in Example 1.

[0074] Table 2

[0075]

[0076]

[0077] Note: Single-pass yield is the product of conversion and product selectivity.

[0078] Comparative Example 1

[0079] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with a solid catalyst of alumina-supported platinum (i.e., Pt / Al₂O₃), wherein the platinum loading was 0.5 wt%. The catalyst bed temperature was first heated to 60 °C; then, a metering pump was used to deliver the catalyst at a rate of 1.0 h⁻¹. -1 The reactor was continuously fed at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. A mixture of hydrogen and nitrogen, with a hydrogen volume fraction of 3%, was then introduced from the top of the reactor. The reactor pressure was maintained at atmospheric pressure. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of a hydrogen atmosphere and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor and analyzed by gas chromatography. The calculated conversion rate of the feedstock was 95.0%, the selectivity for pentacarbonaldehyde was 92.1%, and the selectivity for the hydrogenation product was 6.9%. The crude product was then purified by distillation to obtain a refined pentacarbonaldehyde with a content of 99.2%. The theoretical number of plates in the distillation column was 42, and the reflux ratio was 5.0. The refined pentacarbonaldehyde was detected by gas chromatography, and the pentacarbonaldehyde content was calculated using the area normalization method. Compared to the example, the distillation column used in this comparative example has a significantly higher theoretical plate number and a significantly higher reflux ratio during operation, resulting in higher equipment investment and energy consumption.

[0080] Comparative Example 2

[0081] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with a solid catalyst of palladium supported on alumina (i.e., Pd / Al2O3), wherein the palladium loading was 0.5 wt%. The catalyst bed temperature was first heated to 60 °C; then, a metering pump was used to deliver the catalyst at a rate of 1.0 h⁻¹. -1The reactor was continuously fed at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. A mixture of hydrogen and nitrogen, with a hydrogen volume fraction of 3%, was then introduced from the top of the reactor. The reactor pressure was maintained at atmospheric pressure. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of a hydrogen atmosphere and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor and analyzed by gas chromatography. The calculated conversion rate of the feedstock was 93.8%, the selectivity for pentacarbonaldehyde was 93.1%, and the selectivity for the hydrogenation product was 5.8%. The crude product was then purified by distillation to obtain a purified pentacarbonaldehyde with a purity of 99.4%. The distillation column had 42 theoretical plates and an operating reflux ratio of 5.0. The purified pentacarbonaldehyde was detected by gas chromatography, and the pentacarbonaldehyde content was calculated using the area normalization method.

[0082] Comparative Example 3

[0083] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with a solid catalyst of rhodium supported on alumina (i.e., Rh / Al₂O₃), wherein the rhodium loading was 0.5 wt%. The catalyst bed temperature was first heated to 60 °C; then, a metering pump was used to deliver the catalyst at a rate of 1.0 h⁻¹. -1 The reactor was continuously fed at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. A mixture of hydrogen and nitrogen, with a hydrogen volume fraction of 3%, was then introduced from the top of the reactor. The reactor pressure was maintained at atmospheric pressure. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of a hydrogen atmosphere and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor and analyzed by gas chromatography. The calculated conversion rate of the feedstock was 90.8%, the selectivity for pentacarbonaldehyde was 90.8%, and the selectivity for the hydrogenation product was 7.7%. The crude product was then purified by distillation to obtain a purified pentacarbonaldehyde with a purity of 99.3%. The distillation column had 42 theoretical plates and a reflux ratio of 5.0. The purified pentacarbonaldehyde was detected by gas chromatography, and the pentacarbonaldehyde content was calculated using the area normalization method.

[0084] Comparative Example 4

[0085] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with a solid catalyst of alumina supported on platinum (i.e., Pt / Al2O3), wherein the platinum loading was 0.5 wt%. The catalyst bed temperature was first heated to 60 °C, and the feedstock 4-acetoxy-2-methylene-1-butenal was fed at a rate of 1.0 h⁻¹ using a metering pump. -1The reactor was fed continuously at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. Air was then introduced from the top of the reactor to maintain the reactor pressure at 0.2 MPa. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of air and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor, and its composition was analyzed by gas chromatography to calculate the reaction yield. The crude product was then distilled to obtain the refined pentacarbonaldehyde. The theoretical plate number of the distillation column was 18, and the reflux ratio was 1.0. The refined pentacarbonaldehyde was detected by gas chromatography, and the pentacarbonaldehyde content was calculated using the area normalization method. The specific results are shown in Table 3.

[0086] Comparative Example 5

[0087] A fixed-bed reactor with an inner diameter of 20 mm and a height of 0.5 m was loaded with alumina-supported platinum solid catalyst (i.e., Pt / Al2O3), wherein the platinum loading was 0.5 wt%. First, the catalyst bed temperature was heated to 60 °C. Then, 0.02 wt% (by weight) of triethylamine, an auxiliary agent, was mixed with the feedstock 4-acetoxy-2-methylene-1-butenal. Next, a metering pump was used to inject the mixture at a rate of 1.0 h⁻¹. -1 The reactor was fed continuously at a liquid hourly space velocity (LHSV). The feed material was preheated to 60°C in a preheater and then entered from the top of the reactor. Air was then introduced from the top of the reactor to maintain a pressure of 0.2 MPa. The feedstock, 4-acetoxy-2-methylene-1-butenal, underwent a gas-liquid-solid three-phase isomerization reaction in the presence of air and a catalyst, with a retention time of 35 min. The crude product was collected from the bottom of the reactor, and its composition was analyzed by gas chromatography to calculate the reaction yield. The crude product was then subjected to distillation to obtain a refined pentacarbonaldehyde. The distillation column had 18 theoretical plates, and the reflux ratio was 1.0. Gas chromatography was used to detect the refined pentacarbonaldehyde, and the content was calculated using the area normalization method. The specific results are shown in Table 3. The NMR results of the product pentacarbonaldehyde were consistent with those of Example 1.

[0088] Table 3

[0089]

[0090] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: The above method for preparing 4-acetoxy-2-methyl-2-butenal uses 4-acetoxy-2-methylene-1-butenal as a reactant and carries out an isomerization reaction in an oxygen-containing gas atmosphere. The product 4-acetoxy-2-methyl-2-butenal has a high yield, and because the product does not contain the hydrogenation product of 4-acetoxy-2-methylene-1-butenal, it is easy to separate, which can significantly reduce the energy consumption of separation. Furthermore, no solvent needs to be added during the reaction process, making it safe and environmentally friendly. It is a method for preparing pentacarbon aldehydes that is easy to industrialize.

[0091] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing 4-acetoxy-2-methyl-2-butenal, characterized in that, include: 4-Acetoxy-2-methylene-1-butenal, stabilizer, catalyst and oxygen-containing gas are mixed and isomerized to obtain 4-acetoxy-2-methyl-2-butenal. The stabilizer includes any one or more of pyridine, 3-methylpyridine and 4-dimethylaminopyridine; The catalyst includes a support and a noble metal component; The carrier is aluminum oxide; The precious metal component includes any one or more of palladium, platinum and rhodium; The loading of the precious metal component is 0.1% to 0.8% of the catalyst mass; The oxygen content of the oxygen-containing gas is 10% to 21%; The stabilizer is added at a weight of 0.01% to 0.05% of the weight of 4-acetoxy-2-methylene-1-butenal; The isomerization reaction is carried out at a temperature of 50–90°C. The oxygen-containing gas pressure for the isomerization reaction is 0.1–0.5 MPa.

2. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that, The oxygen-containing gas is air.

3. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that, The isomerization reaction takes 20 to 60 minutes.

4. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that, The liquid hourly space velocity (LHSV) of the 4-acetoxy-2-methylene-1-butenal is 0.5–2.0 h⁻¹. -1 .

5. The method for preparing 4-acetoxy-2-methyl-2-butenal according to any one of claims 1 to 4, characterized in that, The method for preparing 4-acetoxy-2-methyl-2-butenal includes: continuously feeding the 4-acetoxy-2-methylene-1-butenal, a stabilizer, and an oxygen-containing gas into a continuous reactor packed with the catalyst to carry out an isomerization reaction.

6. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 5, characterized in that, The continuous reactor is a trickle bed reactor.

7. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 5, characterized in that, The 4-acetoxy-2-methylene-1-butenal and the stabilizer are preheated to the reaction temperature and then introduced into the continuous reactor for isomerization reaction.

8. The method for preparing 4-acetoxy-2-methyl-2-butenal according to any one of claims 1 to 4, characterized in that, The product of the isomerization reaction was separated by distillation to obtain 4-acetoxy-2-methyl-2-butenal with a purity greater than 99.3%.

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