Method for preparing 4-acetoxy-2-methyl-2-butenal

Abstract

The invention provides a method for preparing 4-acetoxyl-2-methyl-2-butenal, which comprises the following steps of: preparing 4-acetoxyl-2-methyl-2-butenal; the method comprises the following steps: mixing 4-acetoxy-2-methylene-1-butenal, a stabilizer, a catalyst and oxygen-containing gas, and carrying out an isomerization reaction, so as to obtain 4-acetoxy-2-methyl-2-butenal, wherein the stabilizing agent is prepared from any one or more of pyridine, 3-methylpyridine and 4-dimethylaminopyridine. The 4-acetoxyl-2-methylene-1-butenal is used as a reaction raw material, the isomerization reaction is carried out in the oxygen-containing gas atmosphere, the yield of the product 4-acetoxyl-2-methyl-2-butenal is high, the product does not contain a hydrogenation product of the 4-acetoxyl-2-methylene-1-butenal and is easy to separate, and the yield of the product is high. And the energy consumption of separation can be obviously reduced. Furthermore, no solvent needs to be added in the reaction process, so that the method is safe and environment-friendly, and is a pentacarbonaldehyde preparation method which is easy to realize industrial production.

Description

Technical Field

[0001] The present invention relates to the field of chemical intermediate synthesis, and in particular to a method for preparing 4-acetoxy-2-methyl-2-butenal. Background Art

[0002] 4-Acetoxy-2-methyl-2-butenal (abbreviated as pentaldehyde) is an important intermediate in the synthesis of vitamin A. The yield of its preparation directly affects the quality and cost of vitamin A. Therefore, research and optimization of the pentaldehyde process are ongoing. Among the numerous routes, there are four synthetic routes that are more suitable for industrial production. These routes are divided into the following categories based on their starting materials: isoprene route, dimethoxyacetone route, ethylene oxide route, and butenediol route.

[0003] US Patent No. 5,424,478 discloses a method for synthesizing a five-carbon aldehyde using isoprene as the starting material. In this route, the isoprene raw material first undergoes an addition reaction with sodium hypochlorite, then is esterified with acetic acid, and finally oxidized with dimethyl sulfoxide as an oxidant to obtain the five-carbon aldehyde. This method produces a large amount of wastewater and salt, resulting in serious pollution and not meeting current environmental protection requirements.

[0004] Patents US4147886 and US3478060 both disclose a method for synthesizing a five-carbon aldehyde using dimethoxyacetone as the starting material. This route requires five steps to produce the five-carbon aldehyde, resulting in a long process and low overall yield. Furthermore, the reaction involves the use of a nitrating compound, posing significant safety risks.

[0005] US Patent No. 4,873,362 discloses a route for preparing pentaldehyde using ethylene oxide as a raw material. This route uses ethylene oxide as the starting material, and sequentially reacts with acetic acid, undergoes a silver-catalyzed oxidation reaction, and then undergoes a condensation reaction with acrolein to produce the pentaldehyde product. The major issue with this route is the significant safety risk, as the raw material ethylene oxide is highly reactive and the intermediate 2-acetoxyacetaldehyde is also extremely unstable.

[0006] Compared to the above three routes, the butenediol route offers significant advantages due to its shorter synthesis route, reduced safety risks, reduced waste, and good yield. The synthesis of five-carbon aldehydes using butenediol as a raw material is divided into the BASF route and the Roche route.

[0007] Patent US3732287 discloses a method for synthesizing a five-carbon aldehyde using butenediol as a raw material. This method involves first esterifying the butenediol with acetic anhydride, then rearranging it in the presence of a copper catalyst, followed by hydroformylation using a rhodium catalyst, and finally decarboxylating it to produce the five-carbon aldehyde product. However, due to the positional selectivity of the carbon-carbon double bond, the hydroformylation step produces a large amount of byproducts, resulting in a low yield. Furthermore, the rearrangement step has a low single-pass conversion rate of approximately 30%, requiring continuous separation and reuse of the raw materials, resulting in high energy consumption.

[0008] Compared with the BASF route, the reaction steps of the Roche route are esterification, hydroformylation, decarboxylation and isomerization. Its synthesis route is as follows:

[0009]

[0010] This route's hydroformylation step produces virtually no byproducts due to the symmetry of the carbon-carbon double bond, resulting in a higher yield than the hydroformylation reaction of the BASF route. However, the isomerization step requires the reaction to proceed under a hydrogen atmosphere, resulting in the production of a large amount of hydrogenation byproducts. Patents US4124619, CN110734374, and CN103467287 all optimize the hydroisomerization step, minimizing the amount of hydrogenation byproducts. Because the hydrogenation products are very close to the boiling point of the raw materials, the presence of these products results in a high energy consumption for subsequent separation. Summary of the Invention

[0011] The main purpose of the present invention is to provide a method for preparing 4-acetoxy-2-methyl-2-butenal, so as to solve the problem in the prior art that the isomerization reaction product contains hydrogenation products with a boiling point close to that of the raw material, resulting in high separation energy consumption.

[0012] To achieve the above-mentioned object, 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 conducting 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] Further, the catalyst includes a support and a noble metal component;

[0014] The carrier is alumina;

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

[0016] Preferably, the loading amount 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] The oxygen-containing gas is air.

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

[0020] Furthermore, the isomerization reaction temperature is 50-90° C., and the reaction time is 20-60 min.

[0021] Furthermore, the pressure of the oxygen-containing gas in the isomerization reaction is 0.1 to 0.5 MPa.

[0022] Furthermore, the liquid volume space velocity of 4-acetoxy-2-methylene-1-butenal is 0.5 to 2.0 h -1 .

[0023] Furthermore, the method for preparing 4-acetoxy-2-methyl-2-butenal comprises: continuously introducing 4-acetoxy-2-methylene-1-butenal, a stabilizer, and an oxygen-containing gas into a continuous reactor filled 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 a stabilizer are preheated to a reaction temperature and then introduced into a continuous reactor for isomerization reaction.

[0026] Furthermore, the product of the isomerization reaction is subjected to rectification and separation to obtain a 4-acetoxy-2-methyl-2-butenal product with a purity greater than 99.3%.

[0027] The technical solution of the present invention is applied, with 4-acetoxy-2-methylene-1-butenal as a reaction raw material, an isomerization reaction is carried out in an oxygen-containing gas atmosphere, the product 4-acetoxy-2-methyl-2-butenal has a high yield, and since the product does not contain a hydrogenation product of 4-acetoxy-2-methylene-1-butenal, it is easy to separate, and the energy consumption of separation can be significantly reduced. Furthermore, no solvent needs to be added during the reaction, and the reaction is safe and environmentally friendly, and it is a method for preparing a five-carbon aldehyde that is easy to achieve industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 1The HNMR diagram of the raw material 4-acetoxy-2-methylene-1-butenal according to an embodiment of the present invention is shown;

[0030] Figure 2 Shown is a CNMR diagram of the raw material 4-acetoxy-2-methylene-1-butenal according to an embodiment of the present invention;

[0031] Figure 3 The HNMR diagram of the product 4-acetoxy-2-methyl-2-butenal according to Example 1 of the present invention is shown;

[0032] Figure 4 The CNMR diagram of 4-acetoxy-2-methyl-2-butenal, a product of Example 1 according to the present invention, is shown. DETAILED DESCRIPTION

[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 technology of the present application, there is a problem in the prior art that the isomerization reaction product contains a hydrogenation product close to the boiling point of the raw material, resulting in high separation energy consumption. In order to solve this technical problem, the present application 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, performing an isomerization reaction, and obtaining 4-acetoxy-2-methyl-2-butenal; wherein the stabilizer includes any one or more of pyridine, 3-picoline and 4-dimethylaminopyridine (DMAP).

[0035] The above-mentioned method for preparing 4-acetoxy-2-methyl-2-butenal uses 4-acetoxy-2-methylene-1-butenal as a reaction raw material and performs an isomerization reaction in an oxygen-containing gas atmosphere. The product 4-acetoxy-2-methyl-2-butenal has a high yield, and since the product does not contain a hydrogenation product of 4-acetoxy-2-methylene-1-butenal, it is easy to separate and can significantly reduce the energy consumption of separation. Furthermore, no solvent needs to be added during the reaction process, and the reaction is safe and environmentally friendly. It is a method for preparing a five-carbon aldehyde that is easy to achieve industrial production.

[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 butenediol, researchers of this application found that this isomerization reaction can also be carried out efficiently in the presence of an oxygen-containing gas (e.g., air), thereby avoiding the use of hydrogen, thereby solving the problem of hydrogenation by-products produced during the isomerization process, and both selectivity and overall yield have been greatly improved. It is speculated that the possible reaction process of the isomerization reaction is as follows: oxygen molecules dissociate into oxygen atoms on the catalyst surface, then attack the carbon-carbon double bond in the raw material 4-acetoxy-2-methylene-1-butenal molecule to form an epoxy intermediate, followed by deoxygenation to form a carbon-carbon double bond in a new position, completing the isomerization process of the entire carbon-carbon double bond. It is expressed as follows using a chemical reaction formula:

[0039]

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

[0041] In some preferred embodiments of the present application, the added weight of the stabilizer 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. The addition amount of the stabilizer within the above range can effectively prevent the oxidation of the raw materials and products due to the presence of oxygen, effectively inhibit side reactions, and at the same time will not excessively affect the progress of the main reaction, thereby ensuring the purity and yield of the product and facilitating the improvement of the yield of the product.

[0042] In some embodiments of the present application, the above-mentioned catalyst includes a carrier and a precious metal component; wherein the carrier is alumina; the precious metal component includes any one or more of palladium, platinum and rhodium. The above-mentioned alumina-supported precious metal catalyst catalyzes the isomerization reaction more efficiently in the presence of oxygen, and has good stability, can maintain catalytic efficiency for a long time, is suitable for continuous production, reduces the frequency of catalyst replacement, and saves costs. Preferably, the loading amount of the precious metal component is 0.1% to 0.8% of the mass of the catalyst, specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% of the mass of the catalyst, etc., or other values ​​within the above range.

[0043] The above-mentioned catalyst can be prepared by the method in the prior art or purchase a commercially available catalyst with the above-mentioned composition, and the present application is not limited thereto. In some embodiments of the present application, the catalyst is prepared according to the following method: first, the carrier is calcined for pretreatment, and then the active metal is loaded to obtain a catalyst precursor, the catalyst precursor is dried and calcined, and finally the catalyst is reduced with hydrogen. The method of loading the active metal can be selected in the prior art, such as the equal volume impregnation method. The specific process conditions for drying or calcining the carrier or precursor can also be referred to the prior art, and the present application is not limited thereto.

[0044] In some typical embodiments of the present application, the temperature of the isomerization reaction is 50-90°C and the time is 20-60 minutes, which is conducive to further improving the selectivity and yield of the product 4-acetoxy-2-methyl-2-butenal. Specifically, the temperature of the isomerization reaction is 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc., and can also be other values ​​within the above range. The mild reaction conditions reduce energy consumption, reduce equipment maintenance costs, and also reduce the impact on the environment, making it suitable for environmentally friendly industrial production.

[0045] In some embodiments of the present application, the oxygen content of 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, is highly safe, 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. At such a pressure, the reaction rate is moderate, which not only ensures the sufficient progress of the reaction but also avoids the safety hazards caused by high-pressure operation, and is suitable for 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, etc., and can also be other values ​​within the above range.

[0047] In some preferred embodiments of the present application, the liquid volume space velocity of 4-acetoxy-2-methylene-1-butenal is 0.5 to 2.0 h -1 The optimized liquid volume space velocity can improve the processing capacity of the reactor, reduce the volume of the reactor, and thus reduce equipment investment, which is suitable for the needs of industrial large-scale production.

[0048] In some typical embodiments of the present application, the method for preparing 4-acetoxy-2-methyl-2-butenal comprises: continuously introducing 4-acetoxy-2-methylene-1-butenal, a stabilizer, and an oxygen-containing gas into a continuous reactor filled with a catalyst to carry out an isomerization reaction, thereby achieving continuous production of 4-acetoxy-2-methyl-2-butenal, which can achieve automated control, improve production efficiency, reduce 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 the present application, 4-acetoxy-2-methylene-1-butenal and a stabilizer are preheated to the reaction temperature and then introduced into a continuous reactor for isomerization reaction, which is beneficial to further improve the efficiency of the reaction, reduce the formation of by-products, and reduce the thermal shock of the reactor, extend the service life of the reactor, and is suitable for stable and efficient industrial production.

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

[0051] The researchers of this application found in the experimental process that the method of this application has good selectivity for preparing 4-acetoxy-2-methyl-2-butenal. Generally speaking, the by-products include 4-acetoxy-2-methylene-1-butenoic acid, 4-acetoxy-2-methyl-2-butenoic acid and high-boiling polymers, and their boiling points are quite different from those of the product 4-acetoxy-2-methyl-2-butenal, which is convenient for separation by distillation.

[0052] In some typical embodiments of the present 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 transporting the raw material to a preheater at a certain liquid volume space velocity to heat it to a reaction temperature; (2) under a pressure of 0.1 to 0.5 MPa, the preheated material and air are subjected to a gas-liquid-solid three-phase isomerization reaction in a fixed bed reactor filled with a formed catalyst, and the reaction retention time is 20 to 60 minutes to generate the product 4-acetoxy-2-methyl-2-butenal; (3) the mixture after the reaction is distilled and separated to obtain a fine product of 4-acetoxy-2-methyl-2-butenal.

[0053] The main raw material 4-acetoxy-2-methyl-2-butenal used to prepare 4-acetoxy-2-methylene-1-butenal can be homemade or purchased, and this application has no restrictions.

[0054] The following examples and comparative examples will further illustrate the beneficial effects that can be achieved by the present application.

[0055] The raw material 4-acetoxy-2-methylene-1-butenal in the examples and comparative examples of the present application is a self-made intermediate, and its preparation method is as follows: take 200g of trans-1,4-diacetoxy-2-butene, 1.0g of sodium acetate, and 20mg of triphenylphosphine acetylacetonate carbonyl rhodium and put them into a 500ml autoclave respectively, and then replace it with N2 gas 3 times (each time pressurizing 0.5MPa), and finally pressurize it with synthesis gas (H2:CO=1:1) to 5.0MPa, heat it to 80℃, keep it warm for 8h, and end the insulation. GC analysis shows that the crude product content of 4-acetoxy-2-methylene-1-butenal is 92%; the refined product content obtained by distillation separation is more than 99.0%. Nuclear magnetic 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 are 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 Sinoco 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 a solid catalyst of alumina-supported platinum (i.e., Pt / Al2O3), wherein the platinum loading was 0.3 wt %. The catalyst bed temperature was first heated to 60° C., and the raw material 4-acetoxy-2-methylene-1-butenal was mixed with the auxiliary agent DMAP at a weight ratio of 0.01 wt % based on the raw material 4-acetoxy-2-methylene-1-butenal. Then, a metering pump was used to pump the catalyst at a rate of 1.0 h. -1The material was fed continuously at a liquid volume space velocity of 1.5 wt %. The 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 raw material 4-acetoxy-2-methylene-1-butenal underwent a gas-liquid-solid three-phase isomerization reaction in the presence of an air atmosphere and a catalyst, with a retention time of 35 minutes. The crude product after the reaction was collected from the bottom of the reactor, and the composition of the reaction liquid was analyzed by gas chromatography, and the conversion rate of the raw material 4-acetoxy-2-methylene-1-butenal and the product selectivity were calculated. The crude product was then distilled and separated to obtain a fine five-carbon aldehyde. The theoretical number of plates of the distillation tower during distillation was 18, and the reflux ratio during operation was 1.0. The fine five-carbon aldehyde was detected by gas chromatography, and the five-carbon aldehyde content was calculated using the area normalization method. The specific results are shown in Table 2.

[0061] For structural analysis of five-carbon aldehydes, see Figure 3 and Figure 4 The 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 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, and the raw material 4-acetoxy-2-methylene-1-butenal was mixed with the auxiliary agent DMAP at a weight ratio of 0.02 wt% based on the raw material 4-acetoxy-2-methylene-1-butenal. Then, a metering pump was used to pump the catalyst at a rate of 1.0 h. -1The liquid volume space velocity is continuously fed, and the material enters from the top of the reactor after being preheated to 60 DEG C by a preheater;Air is then introduced from the top of the reactor to maintain the reactor pressure at 0.2MPa, and the raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of an air atmosphere and a catalyst, with a retention time of 35min. The crude product after the reaction is extracted from the bottom of the reactor, and the reaction liquid is composed and the raw material 4-acetoxy-2-methylene-1-butenal conversion rate and product selectivity are calculated using gas chromatography;Then the reaction crude product is subjected to rectification and separation to obtain a five-carbon aldehyde fine product. The theoretical number of plates of the distillation tower during rectification is 18, and the reflux ratio during operation is 1.0;And the five-carbon aldehyde fine product is detected by gas chromatography, and the five-carbon aldehyde content is calculated using the area normalization method. The specific results are shown in Table 2. The nuclear magnetic results of the product five-carbon aldehyde are consistent with those in 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 a solid catalyst of alumina-supported platinum (i.e., Pt / Al2O3), wherein the platinum loading was 0.8 wt %. The catalyst bed temperature was first heated to 60° C., and the raw material 4-acetoxy-2-methylene-1-butenal was mixed with the auxiliary agent DMAP at a weight ratio of 0.02 wt % based on the raw material 4-acetoxy-2-methylene-1-butenal. Then, a metering pump was used to pump the catalyst at a rate of 1.0 h. -1 The liquid volume space velocity is continuously fed, and the material enters from the top of the reactor after being preheated to 60 DEG C by a preheater;Air is then introduced from the top of the reactor to maintain the reactor pressure at 0.2MPa, and the raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of an air atmosphere and a catalyst, with a retention time of 35min. The crude product after the reaction is extracted from the bottom of the reactor, and the reaction liquid is composed and the raw material 4-acetoxy-2-methylene-1-butenal conversion rate and product selectivity are calculated using gas chromatography;Then the reaction crude product is subjected to rectification and separation to obtain a five-carbon aldehyde fine product. The theoretical number of plates of the distillation tower during rectification is 18, and the reflux ratio during operation is 1.0;And the five-carbon aldehyde fine product is detected by gas chromatography, and the five-carbon aldehyde content is calculated using the area normalization method. The specific results are shown in Table 2. The nuclear magnetic results of the product five-carbon aldehyde are consistent with those in Example 1.

[0068] Example 4

[0069] 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, and the raw material 4-acetoxy-2-methylene-1-butenal was mixed with the auxiliary agent DMAP at a weight ratio of 0.02 wt% based on the raw material 4-acetoxy-2-methylene-1-butenal. Then, a metering pump was used to pump the catalyst at a rate of 1.0 h. -1 The liquid volume space velocity is continuously fed, and the material enters from the top of the reactor after being preheated to 60 DEG C by a preheater;Air is then introduced from the top of the reactor to maintain the reactor pressure at 0.2MPa, and the raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of an air atmosphere and a catalyst, with a retention time of 35min. The crude product after the reaction is extracted from the bottom of the reactor, and the reaction liquid is composed and the raw material 4-acetoxy-2-methylene-1-butenal conversion rate and product selectivity are calculated using gas chromatography;Then the reaction crude product is subjected to rectification and separation to obtain a five-carbon aldehyde fine product. The theoretical number of plates of the distillation tower during rectification is 18, and the reflux ratio during operation is 1.0;And the five-carbon aldehyde fine product is detected by gas chromatography, and the five-carbon aldehyde content is calculated using the area normalization method. The specific results are shown in Table 2. The nuclear magnetic results of the product five-carbon aldehyde are consistent with those in 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%. The catalyst bed temperature was first heated to 60°C, and the raw material 4-acetoxy-2-methylene-1-butenal was mixed with the auxiliary agent DMAP at a weight ratio of 0.05 wt% based on the raw material 4-acetoxy-2-methylene-1-butenal. Then, a metering pump was used to pump the catalyst at a rate of 1.0 h. -1 The liquid volume space velocity is continuously fed, and the material enters from the top of the reactor after being preheated to 60 DEG C by a preheater;Air is then introduced from the top of the reactor to maintain the reactor pressure at 0.2MPa, and the raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of an air atmosphere and a catalyst, with a retention time of 35min. The crude product after the reaction is extracted from the bottom of the reactor, and the reaction liquid is composed and the raw material 4-acetoxy-2-methylene-1-butenal conversion rate and product selectivity are calculated using gas chromatography;Then the reaction crude product is subjected to rectification and separation to obtain a five-carbon aldehyde fine product. The theoretical number of plates of the distillation tower during rectification is 18, and the reflux ratio during operation is 1.0;And the five-carbon aldehyde fine product is detected by gas chromatography, and the five-carbon aldehyde content is calculated using the area normalization method. The specific results are shown in Table 2. The nuclear magnetic results of the product five-carbon aldehyde are consistent with those in Example 1.

[0072] Examples 6 to 14

[0073] Examples 6 to 14 are performance comparisons of isomerization reactions 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: The 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 pump the catalyst at a rate of 1.0 h. -1 The material is fed continuously at a liquid volume space velocity of 1.5 wt %. The material is preheated to 60°C in a preheater and then enters the top of the reactor. A mixed gas of hydrogen and nitrogen is then introduced from the top of the reactor, wherein the volume fraction of hydrogen is 3%. The reactor pressure is maintained at atmospheric pressure. The raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of a hydrogen atmosphere and a catalyst, with a retention time of 35 minutes. The crude product after the reaction is extracted from the bottom of the reactor and analyzed by gas chromatography. The calculated conversion rate of the raw material is 95.0%, the selectivity of the five-carbon aldehyde is 92.1%, and the selectivity of the hydrogenation product is 6.9%. The crude product is then distilled and separated to obtain a fine five-carbon aldehyde with a five-carbon aldehyde content of 99.2%. The number of theoretical plates of the distillation tower during distillation is 42, and the reflux ratio during operation is 5.0. The fine five-carbon aldehyde is detected by gas chromatography, and the five-carbon aldehyde content is calculated using the area normalization method. Compared with the examples, the number of theoretical plates of the distillation tower used in this comparative example is significantly higher, and the reflux ratio during operation is also significantly higher, 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 pump the catalyst at a rate of 1.0 h. -1The material is fed continuously at a liquid volume space velocity of 1.5 wt %. The material is preheated to 60°C in a preheater and then enters the top of the reactor. A mixed gas of hydrogen and nitrogen is then introduced from the top of the reactor, wherein the volume fraction of hydrogen is 3%. The reactor pressure is maintained at atmospheric pressure. The raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of a hydrogen atmosphere and a catalyst, with a retention time of 35 minutes. The crude product after the reaction is extracted from the bottom of the reactor and analyzed by gas chromatography. The calculated conversion rate of the raw material is 93.8%, the selectivity of the five-carbon aldehyde is 93.1%, and the selectivity of the hydrogenation product is 5.8%. The crude product is then distilled and separated to obtain a fine five-carbon aldehyde with a content of 99.4%. The number of theoretical plates of the distillation tower during distillation is 42, and the reflux ratio during operation is 5.0. The fine five-carbon aldehyde is detected by gas chromatography, and the content of the five-carbon aldehyde is 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 pump the catalyst at a rate of 1.0 h. -1 The material is fed continuously at a liquid volume space velocity of 1000 ℃. The material is preheated to 60℃ in a preheater and then enters the top of the reactor. Then, a mixed gas of hydrogen and nitrogen is introduced from the top of the reactor, wherein the volume fraction of hydrogen is 3%. The reactor pressure is maintained at atmospheric pressure. The raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of a hydrogen atmosphere and a catalyst, with a retention time of 35 minutes. The crude product after the reaction is extracted from the bottom of the reactor and analyzed by gas chromatography. The calculated conversion rate of the raw material is 90.8%, the selectivity of the five-carbon aldehyde is 90.8%, and the selectivity of the hydrogenation product is 7.7%. The crude product is then distilled and separated to obtain a fine five-carbon aldehyde with a content of 99.3%. The number of theoretical plates of the distillation tower during distillation is 42, and the reflux ratio during operation is 5.0. The fine five-carbon aldehyde is detected by gas chromatography, and the content of the five-carbon aldehyde is 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 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 raw material 4-acetoxy-2-methylene-1-butenal was added using a metering pump at a rate of 1.0 h. -1The material was fed continuously at a liquid volume space velocity of 1.5 wt %. The 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 raw material 4-acetoxy-2-methylene-1-butenal underwent a gas-liquid-solid three-phase isomerization reaction in the presence of an air atmosphere and a catalyst, with a retention time of 35 minutes. The crude product after the reaction was collected from the bottom of the reactor, and the composition was analyzed by gas chromatography and the reaction yield was calculated. The crude product was then distilled and separated to obtain a fine five-carbon aldehyde. The theoretical number of plates of the distillation tower during distillation was 18, and the reflux ratio during operation was 1.0. The fine five-carbon aldehyde was detected by gas chromatography, and the five-carbon aldehyde 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 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, and the raw material 4-acetoxy-2-methylene-1-butenal was mixed with the auxiliary agent triethylamine at a weight ratio of 0.02 wt% based on the raw material 4-acetoxy-2-methylene-1-butenal. Then, a metering pump was used to pump the catalyst at a rate of 1.0 h. -1 The liquid volume space velocity is continuously fed, and the material is preheated to 60°C in a preheater and then enters from the top of the reactor; air is then introduced from the top of the reactor to maintain the reactor pressure at 0.2MPa. The raw material 4-acetoxy-2-methylene-1-butenal undergoes a gas-liquid-solid three-phase isomerization reaction in the presence of an air atmosphere and a catalyst, with a retention time of 35min. The crude product after the reaction is extracted from the bottom of the reactor, and the composition is analyzed by gas chromatography and the reaction yield is calculated; the crude product is then distilled and separated to obtain a fine five-carbon aldehyde. The theoretical number of plates of the distillation tower during distillation is 18, and the reflux ratio during operation is 1.0; and the fine five-carbon aldehyde is detected by gas chromatography, and the content of the five-carbon aldehyde is calculated using the area normalization method. The specific results are shown in Table 3. The nuclear magnetic resonance results of the product five-carbon aldehyde are consistent with those in Example 1.

[0088] Table 3

[0089]

[0090] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: the above-mentioned method for preparing 4-acetoxy-2-methyl-2-butenal, with 4-acetoxy-2-methylene-1-butenal as reaction raw materials, isomerization reaction is carried out in an oxygen-containing gas atmosphere, the product 4-acetoxy-2-methyl-2-butenal yield is high, and because the product does not contain the hydrogenation product of 4-acetoxy-2-methylene-1-butenal, it is easy to separate, and the energy consumption of separation can be significantly reduced. Further, there is no need to add a solvent during the reaction, safety and environmental protection, and it is a five-carbon aldehyde preparation method that is easy to realize industrial production.

[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 shall be included 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: Mixing 4-acetoxy-2-methylene-1-butenal, a stabilizer, a catalyst and an oxygen-containing gas, and performing an isomerization reaction to obtain 4-acetoxy-2-methyl-2-butenal; The stabilizer includes any one or more of pyridine, 3-methylpyridine and 4-dimethylaminopyridine.

2. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that: The catalyst comprises a carrier and a noble metal component; The carrier is alumina; The precious metal component includes any one or more of palladium, platinum and rhodium; Preferably, the loading amount of the noble metal component is 0.1% to 0.8% of the mass of the catalyst.

3. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that: The oxygen content of the oxygen-containing gas is 10% to 21%; The oxygen-containing gas is air.

4. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that: The added weight of the stabilizer is 0.01% to 0.05% of the weight of 4-acetoxy-2-methylene-1-butenal.

5. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that: The temperature of the isomerization reaction is 50-90° C. and the time is 20-60 min.

6. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that: The oxygen-containing gas pressure of the isomerization reaction is 0.1-0.5 MPa.

7. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 1, characterized in that: The liquid volume space velocity of the 4-acetoxy-2-methylene-1-butenal is 0.5 to 2.0 h -1 .

8. The method for preparing 4-acetoxy-2-methyl-2-butenal according to any one of claims 1 to 7, characterized in that The method for preparing 4-acetoxy-2-methyl-2-butenal comprises: continuously introducing the 4-acetoxy-2-methylene-1-butenal, a stabilizer and an oxygen-containing gas into a continuous reactor filled with the catalyst to carry out an isomerization reaction; Preferably, the continuous reactor is a trickle bed reactor.

9. The method for preparing 4-acetoxy-2-methyl-2-butenal according to claim 8, 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.

10. The method for preparing 4-acetoxy-2-methyl-2-butenal according to any one of claims 1 to 7, characterized in that: The product of the isomerization reaction is distilled and separated to obtain a 4-acetoxy-2-methyl-2-butenal product with a purity greater than 99.3%.

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