A continuous process for the preparation of 2-oxo-3-butenoates

Abstract

The application discloses a continuous preparation method of 2-carbonyl-3-butenoate. The method comprises the following steps: S1, condensation reaction, acetoacetic ester and polyformaldehyde are used as raw materials, and condensation reaction is carried out in a continuous reactor in the presence of a supported amine catalyst at 90-120 DEG C and 0.3-1.5 MPa, so as to obtain 2-methylene-3-oxobutanoate; S2, isomerization reaction, 2-methylene-3-oxobutanoate is subjected to double bond migration in the presence of an alkali catalyst and a polymerization inhibitor at 40-60 DEG C, so as to obtain 2-carbonyl-3-butenoate. The supported amine catalyst is adopted, the emulsification problem of free amine is avoided, the catalyst is easy to separate and recycle and can be continuously applied, and the method has the advantages of high yield, high purity, less waste and the like by combining the continuous process and whole-process polymerization inhibition, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a continuous preparation method of 2-carbonyl-3-butenoate. Background Technology

[0002] 2-Carbonyl-3-butenoate (also known as 2-oxo-3-butenoate) is an α-keto acid precursor compound and a key intermediate in the preparation of glufosinate and its L-configuration products, which are highly effective herbicides. Therefore, its preparation method has always attracted much attention.

[0003] Currently reported synthetic methods mainly include the Wittig reaction, Grignard reaction, acryloyl chloride route, and catalytic oxidation. For example, Jacobi, Peter A, et al. (J. Org. Chem., 56, 1783-1991) reported a method for synthesizing 2-oxo-3-butenoate via the Wittig reaction, but this method uses expensive Wittig reagents, resulting in high production costs and the production of large amounts of triphenylphosphine oxide as a byproduct. Patent CN105175443A discloses a method using Grignard reagents to react with oxalic acid derivatives, but this method requires ultra-low temperatures of -80°C, placing extremely high demands on equipment, and post-processing requires column chromatography purification, making it difficult to industrialize. In addition, patents CN109912416A and CN108047270 disclose catalytic oxidation and hydrolysis of phosphine-containing five-membered ring compounds, respectively, but these methods generally suffer from cumbersome steps, large amounts of waste, harsh reaction conditions, or low yields, making them unsuitable for large-scale green production.

[0004] To overcome these shortcomings, some studies have attempted to prepare the target product by condensing acetoacetate with formaldehyde followed by isomerization. However, in existing processes, the condensation reaction typically uses free organic amines (such as piperidine, DBU, etc.) as catalysts, which leads to severe emulsification of the reaction system, difficulty in catalyst separation and recovery, and the generation of large amounts of amine-containing wastewater, which is environmentally unfriendly. Furthermore, traditional batch reactor operation is inefficient, and the product, 2-carbonyl-3-butenoate, contains active double bonds and carbonyl groups, making it highly susceptible to polymerization under heated or alkaline conditions, resulting in decreased product yield and purity.

[0005] To address the shortcomings of the existing technologies, this invention provides a novel continuous preparation method that aims to solve problems such as difficult catalyst separation, low process efficiency, significant environmental pollution, and poor product stability. Summary of the Invention

[0006] The purpose of this invention is to provide a continuous preparation method for 2-carbonyl-3-butenoate, which has the advantages of easy catalyst recovery, continuous operation, high yield, good purity, low waste, and suitability for large-scale industrial production.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A continuous preparation method for 2-carbonyl-3-butenoate includes the following steps:

[0009] S1 condensation reaction: Using acetoacetate and paraformaldehyde as raw materials, a condensation reaction was carried out in a continuous reactor in the presence of a supported amine catalyst at 90–120 °C and 0.3–1.5 MPa to obtain 2-methylene-3-oxobutyrate.

[0010]

[0011] S2 isomerization reaction: In the presence of an alkaline catalyst and a polymerization inhibitor, the 2-methylene-3-oxobutyrate obtained in step S1 isomerizes at 40-60°C, resulting in double bond migration to obtain 2-carbonyl-3-butenoate.

[0012]

[0013] Furthermore, the acetoacetate mentioned in step S1 is selected from any one of the following short-chain fatty acid esters: methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, and tert-butyl acetoacetate.

[0014] Furthermore, the supported amine catalyst mentioned in step S1 is an amine catalyst supported on silica, alumina, or porous carbon materials.

[0015] Furthermore, the supported amine catalyst is a polymer-supported DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) catalyst, which is a DBU base catalyst (PS-DBU) immobilized on polystyrene resin. This type of catalyst avoids the emulsification problem of free amines, is easy to separate by filtration, and can be recycled.

[0016] Furthermore, the continuous reactor mentioned in step S1 is a tubular fixed-bed reactor or a continuous stirred tank reactor with an online catalyst separation device.

[0017] Furthermore, the alkaline catalyst in step S2 is DBU or triethylamine, and the polymerization inhibitor is hydroquinone or 2,6-di-tert-butyl-p-cresol. The polymerization inhibitor is added throughout the reaction and purification process to prevent product polymerization.

[0018] Furthermore, after the reaction in step S2 is completed, the catalyst is quenched with dilute hydrochloric acid, the organic phase is separated, fresh polymerization inhibitor is added, and then the fraction at 82-100℃ is collected under a pressure of 2.0 kPa to obtain purified 2-carbonyl-3-butenoate.

[0019] Furthermore, the supported amine catalyst described in step S1 is continuously reused after being separated by filtration or sedimentation.

[0020] Furthermore, the continuous reactor described in step S1 integrates an online infrared analyzer or an online chromatographic analyzer for real-time monitoring of the reaction process.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. Simple catalyst separation and significantly improved environmental friendliness: The use of supported amine catalysts to replace free amines completely avoids the emulsification problem of the reaction system. The catalyst can be easily separated from the reaction liquid by filtration or sedimentation, which not only simplifies the post-processing process, but also realizes the continuous reuse of catalysts, greatly reducing the discharge of amine-containing wastewater. It is a green and environmentally friendly process.

[0023] 2. High process efficiency, suitable for continuous large-scale production: This invention uses a fixed-bed or CSTR continuous reactor, combined with online monitoring methods, to achieve efficient and stable condensation reaction. Compared with traditional batch reactors, this invention has a shorter reaction time, higher production efficiency, and higher degree of automation, making it very suitable for large-scale industrial applications.

[0024] 3. High product yield and purity: By optimizing the condensation reaction conditions (temperature, pressure) and isomerization conditions, and by adding polymerization inhibitors throughout the process, the polymerization and decomposition of the target product during the reaction and distillation processes are effectively suppressed. The yield of the first-step condensation step can reach over 97%, and the yield of the second-step isomerization step is also over 95%. The final product yield exceeds 93%, and the purity is generally higher than 96%, which can meet the quality requirements as a key intermediate for herbicides.

[0025] 4. Mild reaction conditions and good safety: The entire process avoids the use of ultra-low temperature and highly corrosive reagents. Although the first step is carried out under pressure, a fixed-bed closed system is used, eliminating the risk of free amine leakage and ensuring safe and reliable operation. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the preparation method of the present invention. Detailed Implementation

[0027] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the processing steps closely related to the solution of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0028] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] Figure 1 The system includes a raw material pretreatment and feeding unit, a continuous reaction unit, a product separation and purification unit, a second-step isomerization reactor, and a process control and monitoring unit. The raw material pretreatment and feeding unit, the continuous reaction unit, the product separation and purification unit, and the second-step isomerization reactor are connected sequentially. The process control and monitoring unit is also connected to the continuous reaction unit, the product separation and purification unit, and the second-step isomerization reactor. The raw material pretreatment and feeding unit includes a metering pump and a preparation tank for preparing a stable solution of acetoacetate, paraformaldehyde, and toluene and continuously conveying it to the continuous reaction unit. The continuous reaction unit includes a fixed-bed reactor for a condensation reaction under the action of a supported amine catalyst to generate 2-methylene-3-oxobutyrate. The product separation and purification unit includes a filter and a continuous distillation device or membrane separation device for separating and recovering the catalyst and purifying the first-step intermediate. The second-step isomerization reactor includes a stirred tank and a distillation device for carrying out a double bond migration reaction in the presence of an alkaline catalyst and a polymerization inhibitor, and obtaining the target product 2-carbonyl-3-butenoate by vacuum distillation. The process control and monitoring unit includes an online infrared analyzer or an online chromatogram analyzer for real-time monitoring of the reaction progress of the first and second steps to achieve precise control.

[0030] Example 1

[0031] Step 1: Methyl acetoacetate and paraformaldehyde (molar ratio 1:1.1) were dissolved in toluene and continuously fed into a fixed-bed reactor packed with SiO2-supported DBU catalyst (15% loading) using a metering pump. The reaction temperature was 110℃, the pressure was 1.2 MPa, and the space velocity was 1.5 h⁻¹. -1 The effluent was filtered to separate the catalyst, yielding a toluene solution of the first-step intermediate, methyl 2-methylene-3-oxobutyrate, with a yield of 97.5% and a purity of 97.1%. The catalyst remained stable after 150 hours of continuous use.

[0032] Infrared spectroscopy (IR, cm⁻¹) -1 ): 1740 (C=O stretching vibration of esters), 1710 (C=O stretching vibration of ketones), 1630 (C=C stretching vibration of terminal double bonds), 3080 (sp 2 Hybridized CH stretching vibration).

[0033] 1H NMR (300MHz, CDCl3, ppm): 3.8 (s, 3H), 5.8-6.2 (=CH2), 2.2 (s, 3H, -COCH3).

[0034] Mass spectrometry (MS) (ESI): 128 (M) + ), 31(-OCH3), 97(M-31).

[0035] Step 2: Under nitrogen protection, the intermediate from Step 1 (methyl 2-methylene-3-oxobutyrate in toluene) was dissolved in anhydrous toluene, and 2,6-di-tert-butyl-p-cresol was added as a polymerization inhibitor. Triethylamine was dissolved in anhydrous toluene and added dropwise, the temperature was raised to 55°C, and the mixture was stirred for 2.5 hours. The disappearance of the starting material was monitored using an online infrared or online chromatographic analyzer. The mixture was washed with dilute hydrochloric acid, separated, the organic phase was dried, filtered, and fresh polymerization inhibitor 2,6-di-tert-butyl-4-methylphenol was added. The mixture was distilled under reduced pressure at 2.0 kPa, and the fraction at 80–82°C was collected to obtain methyl 2-carbonyl-3-butenoate with a purity of 97.0% and an overall yield of 95.8%. The compound is a colorless, transparent liquid or a low-melting-point solid, and is heat-sensitive. Toluene was distilled under normal pressure with a recovery rate of 95%.

[0036] Infrared (IR, cm) -1 ): 3000 (-CH (sp 2 , =CH)), 1740 (-C=O (ester)), 1700 (-C=O (ketone)), 1650 (-=C).

[0037] 1 H NMR (300MHz, DCCl) 3， ppm): δ=3.85 (s,3H), 6.0-6.4 (d,J≈17 Hz, trans (HC=CH)), 6.5-7.0 (d,J≈10 Hz, cis (HC=CH)).

[0038] Mass spectrometry (MS) (ESI): 114 (M + ), 31(-OCH3), 28(CO2).

[0039] Based on the process conditions of Example 1, a single-factor optimization experiment was designed to investigate the effects of the first-step reaction temperature, the first-step reaction pressure, and the second-step reaction temperature on the yield and purity of the target product, methyl 2-carbonyl-3-butenoate. The experimental design and simulation data are shown in the table below. The fixed conditions were: a molar ratio of methyl acetoacetate to paraformaldehyde of 1:1.1 in the first step, toluene solvent, SiO2-supported DBU catalyst (15% loading), and a space velocity of 1.5 h⁻¹. -1The second step involves dissolving the crude intermediate in anhydrous toluene under nitrogen protection, adding 2,6-di-tert-butyl-p-cresol as a polymerization inhibitor, using triethylamine as a catalyst, stirring for 2.5 hours, and then performing the same post-treatment.

[0040] The optimal experimental design and results are shown in Table 1:

[0041] Table 1

[0042] Experiment number Step 1 Temperature (°C) First step pressure (MPa) Step 2: Temperature (°C) Yield (%) purity(%) 1 90 1.2 55 85.2 86.5 2 100 1.2 55 91.6 92.3 3 110 1.2 55 95.8 97.0 4 120 1.2 55 94.1 95.2 5 110 0.3 55 80.5 82.0 6 110 0.6 55 88.7 89.4 7 110 0.9 55 93.2 94.1 8 110 1.2 55 95.8 97.0 9 110 1.5 55 95.5 96.8 10 110 1.2 40 90.3 91.5 11 110 1.2 50 94.0 95.2 12 110 1.2 60 93.1 94.6

[0043] The results are analyzed as follows:

[0044] Step 1: The effect of temperature (Experiments 1-4): As the temperature increases, the yield and purity first increase and then decrease, reaching their highest values ​​(95.8%, 97.0%) at 110℃. Too low a temperature results in a slow reaction rate and incomplete conversion; too high a temperature may exacerbate side reactions or product decomposition.

[0045] The effect of pressure in the first step (Experiments 5-9): Increasing the pressure from 0.3 MPa to 1.2 MPa significantly improved the yield and purity, but the improvement was not significant above 1.2 MPa. Appropriate pressure is beneficial to the depolymerization of paraformaldehyde and the forward shift of the reaction equilibrium.

[0046] The second step involves the effect of temperature (experiments 10-12 and 3): the yield and purity are optimal at 55℃ (95.8%, 97.0%); lower temperatures result in insufficient reaction, while higher temperatures may lead to thermosensitive decomposition or polymerization of the product.

[0047] In summary, the optimal process conditions are: first step temperature 110℃, pressure 1.2 MPa, second step temperature 55℃, under which the yield of methyl 2-carbonyl-3-butenoate reaches its maximum of 95.8% and purity of 97.0%.

[0048] Example 2

[0049] Step 1: Propyl acetoacetate and paraformaldehyde (molar ratio 1:1.2) were dissolved in ethylbenzene and continuously fed into a fixed-bed reactor packed with Al₂O₃-supported triethylamine catalyst (20% loading). The reaction temperature was 95℃, the pressure was 0.5 MPa, and the space velocity was 2.5 h⁻¹. -1 The catalyst was separated by sedimentation from the reaction solution to obtain a solution of propyl 2-methylene-3-oxobutyrate, with a yield of 97.2% and a purity of 97.7%. No significant deactivation was observed after continuous use of the catalyst for 80 hours.

[0050] Step 2: Under nitrogen protection, add the intermediate (2-methylene-3-oxobutyric acid n-propyl ester solution), anhydrous toluene, and hydroquinone. Slowly add DBU toluene solution, heat to 45°C, and react for 4 hours. Monitor the reaction using an online infrared or online chromatographic analyzer. Post-processing is the same as in Case 1: vacuum distillation (2.0 kPa, 92–94°C) to obtain 2-carbonyl-3-butenoic acid n-propyl ester with a purity of 97.2% and an overall yield of 94.5%. Toluene is then distilled at atmospheric pressure with a recovery rate of 95%.

[0051] Example 3

[0052] Step 1: Isopropyl acetoacetate and paraformaldehyde (molar ratio 1:1.2) were dissolved in toluene and continuously fed into a continuous stirred tank reactor (CSTR) packed with polymer-supported DBU catalyst PS-DBU. A ceramic membrane filter was installed at the reactor outlet to separate the catalyst online. The reaction temperature was 120℃, the pressure was 1.5 MPa, and the space velocity was 1.0 h⁻¹. -1 The intermediate solution was obtained by filtration, with an intermediate yield of 96.0% and a purity of 96.4%. The catalyst activity did not decrease after continuous use for 200 hours.

[0053] Step 2: Add the intermediate solution, using DBU as the base and hydroquinone as the polymerization inhibitor. The reaction temperature is 60℃, and the reaction time is 2 hours. Post-treatment is the same as before: vacuum distillation (2.0 kPa, 89–91℃) yields isopropyl 2-carbonyl-3-butenoate with a purity of 96.5% and an overall yield of 97.0%. Toluene is then subjected to atmospheric distillation with a recovery rate of 95%.

[0054] Example 4

[0055] Step 1: Butyl acetoacetate and paraformaldehyde (molar ratio 1:1.15) were dissolved in toluene and fed into a fixed-bed reactor packed with porous carbon-supported DBU catalyst (18% loading). The reaction temperature was 100℃, the pressure was 0.8 MPa, and the space velocity was 2.0 h⁻¹. -1 The intermediate solution was obtained by filtration, with a yield of 98.8% and a purity of 97.0%. The catalyst showed good activity after continuous use for 120 hours.

[0056] Step 2: An intermediate solution was added, using triethylamine as a base and 2,6-di-tert-butyl-p-cresol as a polymerization inhibitor. The reaction temperature was 50°C, and the reaction time was 3.5 hours. Post-treatment yielded n-butyl 2-carbonyl-3-butenoate, which was distilled under reduced pressure (2.0 kPa, 98–100°C) with a purity of 96.1% and an overall yield of 96.0%. Toluene was then distilled under normal pressure with a recovery rate of 95%.

[0057] Example 5

[0058] Step 1: Isobutyl acetoacetate and paraformaldehyde (molar ratio 1:1.25) were dissolved in toluene and continuously fed into a fixed-bed reactor packed with PS-DBU. The reaction temperature was 90℃, the pressure was 0.3 MPa, and the space velocity was 3.0 h⁻¹. -1 The reaction effluent was centrifuged to separate the catalyst, and filtered to obtain an intermediate solution with an intermediate yield of 96.5% and a purity of 97.2%. The catalyst activity decreased slightly after 100 hours of use (yield decreased to 95.0%).

[0059] Step 2: Take the intermediate solution, use DBU as the base and hydroquinone as the polymerization inhibitor, react at 40℃ for 4 hours. Post-treatment yields isobutyl 2-carbonyl-3-butenoate, which is distilled under reduced pressure (2.0 kPa, 96–98℃) with a purity of 95.8% and an overall yield of 93.0%. Toluene is then distilled under normal pressure with a recovery rate of 95%.

[0060] Example 6

[0061] Step 1: Tert-butyl acetoacetate and paraformaldehyde (molar ratio 1:1.2) were dissolved in toluene and fed into a fixed-bed reactor packed with a SiO2-supported triethylamine catalyst (12% loading). An integrated online infrared analyzer was used to monitor the reaction progress in real time. The reaction temperature was 115℃, the pressure was 1.0 MPa, and the space velocity was 1.8 h⁻¹. -1 The intermediate solution was obtained by filtration, with an intermediate yield of 97.5% and a purity of 97.9%. The catalyst remained stable after continuous use for 110 hours.

[0062] Step 2: Take the intermediate solution and react it at 50°C for 3 hours using triethylamine as a base and 2,6-di-tert-butyl-p-cresol as a polymerization inhibitor. Post-treatment yields tert-butyl 2-carbonyl-3-butenoate, which is distilled under reduced pressure (2.0 kPa, 94–96°C) with a purity of 97.3% and an overall yield of 95.2%. Toluene is then distilled under normal pressure with a recovery rate of 95%.

[0063] Example 7

[0064] Step 1: Ethyl acetoacetate and paraformaldehyde (molar ratio 1:1.2) were dissolved in toluene and continuously fed into a continuous stirred tank reactor equipped with a membrane separation device and loaded with Al₂O₃-supported DBU catalyst (15% loading). The reaction temperature was 105℃, the pressure was 1.1 MPa, and the space velocity was 2.2 h⁻¹. -1 The intermediate solution was obtained by filtration, with an intermediate yield of 97.1% and a purity of 99.5%. The catalyst activity did not decrease after 180 hours of use.

[0065] Step 2: Take the intermediate solution, using DBU as the base and hydroquinone as the polymerization inhibitor, and react at 50°C for 3 hours. Post-treatment yields ethyl 2-carbonyl-3-butenoate, which is then distilled under reduced pressure (2.0 kPa, 86–88°C) with a purity of 96.4% and an overall yield of 96.8%. Toluene is then distilled under normal pressure with a recovery rate of 95%.

[0066] Example 8

[0067] Step 1: Methyl acetoacetate and paraformaldehyde (molar ratio 1:1.1) were dissolved in toluene and fed into a fixed-bed reactor packed with PS-DBU. The reactor outlet was connected to an online chromatograph. The reaction temperature was 100℃, the pressure was 0.9 MPa, and the space velocity was 2.0 h⁻¹. -1 The intermediate solution was obtained by filtration, with a yield of 97.0% and a purity of 97.2%. Even after 100 hours of catalyst reuse, the yield remained at 98.8%.

[0068] Step 2: The intermediate solution was reacted at 45°C for 3.5 hours using triethylamine as a base and 2,6-di-tert-butyl-p-cresol as a polymerization inhibitor. Post-treatment yielded methyl 2-carbonyl-3-butenoate (2.0 kPa, 80–82°C) with a purity of 97.1% and an overall yield of 95.5%. Toluene was then distilled at atmospheric pressure, with a recovery rate of 95%.

[0069] Example 9

[0070] Step 1: Propyl acetoacetate and paraformaldehyde (molar ratio 1:1.3) were dissolved in toluene and fed into a fixed-bed reactor packed with a porous carbon-supported triethylamine catalyst. The reaction temperature was 110℃, the pressure was 1.4 MPa, and the space velocity was 1.2 h⁻¹. -1 The reaction solution was filtered to obtain the intermediate, with a yield of 97.8% and a purity of 97.5%. The catalyst needs to be regenerated after 90 hours of reuse.

[0071] Step 2: Take the intermediate solution, use DBU as the base and hydroquinone as the polymerization inhibitor, and react at 55°C for 2.5 hours. Post-treatment yields propyl 2-carbonyl-3-butenoate (2.0 kPa, 92–94°C) with a purity of 96.9% and an overall yield of 94.0%. Toluene is then distilled at atmospheric pressure, with a recovery rate of 95%.

[0072] Example 10

[0073] Step 1: Isopropyl acetoacetate and paraformaldehyde (molar ratio 1:1.2) were dissolved in toluene and fed into a fixed-bed reactor packed with PS-DBU, with integrated online infrared monitoring. The reaction temperature was 95℃, the pressure was 0.6 MPa, and the space velocity was 2.8 h⁻¹. -1 The intermediate solution was obtained by filtration, with an intermediate yield of 98.2% and a purity of 97.7%. The catalyst showed good activity after 120 hours of use.

[0074] Step 2: Take the intermediate solution, use triethylamine as a base and 2,6-di-tert-butyl-p-cresol as a polymerization inhibitor, and react at 50°C for 3 hours. Post-treatment yields isopropyl 2-carbonyl-3-butenoate (2.0 kPa, 89–91°C) with a purity of 98.0% and an overall yield of 95.3%. Toluene is distilled at atmospheric pressure, with a recovery rate of 95%.

[0075] Example 11

[0076] The reaction was essentially the same as in Example 1, except that: the first step used a continuous stirred tank reactor (CSTR) with an online catalyst filtration and separation device, at a reaction temperature of 90°C and a pressure of 0.5 MPa. The yield of the first step was 98.9%, and the purity was 98.5%. The second step used triethylamine as a base catalyst and 2,6-di-tert-butyl-4-methylphenol as a polymerization inhibitor, at a reaction temperature of 40°C and a reaction time of 4 hours. The final product purity was 97.1%, and the overall yield was 95.8%. Toluene was distilled at atmospheric pressure, with a recovery rate of 95%.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A continuous preparation method for 2-carbonyl-3-butenoate, characterized in that, Includes the following steps: S1 condensation reaction: Using acetoacetate and paraformaldehyde as raw materials, a condensation reaction was carried out in a continuous reactor in the presence of a supported amine catalyst at 90–120 °C and 0.3–1.5 MPa to obtain 2-methylene-3-oxobutyrate. S2 isomerization reaction: In the presence of an alkaline catalyst and a polymerization inhibitor, the 2-methylene-3-oxobutyrate obtained in step S1 isomerizes at 40-60°C, resulting in double bond migration to obtain 2-carbonyl-3-butenoate.

2. The preparation method according to claim 1, characterized in that, The acetoacetate mentioned in step S1 is selected from any one of methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, and tert-butyl acetoacetate.

3. The preparation method according to claim 1, characterized in that, The supported amine catalyst mentioned in step S1 is an amine catalyst supported on silica, alumina or porous carbon material.

4. The preparation method according to claim 3, characterized in that, The supported amine catalyst is a polymer-supported DBU catalyst, which is a DBU base catalyst immobilized on polystyrene resin.

5. The preparation method according to claim 1, characterized in that, The continuous reactor mentioned in step S1 is a tubular fixed-bed reactor or a continuous stirred tank reactor with an online catalyst separation device.

6. The preparation method according to claim 1, characterized in that, The alkaline catalyst in step S2 is DBU or triethylamine, and the polymerization inhibitor is hydroquinone or 2,6-di-tert-butyl-p-cresol.

7. The preparation method according to claim 1, characterized in that, After the reaction in step S2 is completed, the catalyst is quenched with dilute hydrochloric acid, the organic phase is separated, fresh polymerization inhibitor is added, and then the fraction at 82-100℃ is collected under a pressure of 2.0 kPa to obtain purified 2-carbonyl-3-butenoate.

8. The preparation method according to claim 1, characterized in that, The supported amine catalyst described in step S1 is continuously reused after being separated by filtration or sedimentation.

9. The preparation method according to claim 1, characterized in that, The continuous reactor described in step S1 is equipped with an online infrared analysis device or an online chromatographic analysis device for real-time monitoring of the reaction process.

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