A method for preparing 2-vinylpyridine

Abstract

This invention relates to a method for preparing 2-vinylpyridine, which uses 3-methoxypropionitrile and acetylene as raw materials. The reaction is carried out in the presence of a cyclization catalyst and a solvent at a temperature of 140-180℃ and a pressure of 0.6-2.0 MPa. After the reaction is complete, the solvent is distilled off, and 2-methoxyethylpyridine is obtained by vacuum distillation. The 2-methoxyethylpyridine is then catalytically cleaved at 80-180℃ in the presence of a cracking catalyst and a polymerization inhibitor, and the result is obtained by vacuum distillation. This method has the advantages of readily available raw materials and high reaction conversion rate.

Description

Technical Field

[0001] This invention belongs to the field of synthesis technology of alkenylpyridine compounds, specifically relating to a method for preparing 2-vinylpyridine (2-VP). Background Technology

[0002] 2-Vinylpyridine is a key raw material in the synthesis of styrene-butadiene-pyridine latex. The synthesis of 2-vinylpyridine, both domestically and internationally, mainly uses 2-methylpyridine as a raw material, which is condensed with formaldehyde or paraformaldehyde to obtain the intermediate 2-hydroxyethylpyridine, followed by dehydration. Patent CN105237468B uses 2-methylpyridine and paraformaldehyde in the presence of dimethylformamide under organic acid catalysis to prepare the intermediate 2-hydroxyethylpyridine, but the reaction time is as long as 30-40 hours. This method has drawbacks such as long reaction time and low production efficiency. Chinese patent CN1250527C uses 2-hydroxyethylpyridine as a raw material, and dehydrates it in the presence of sulfuric acid, phosphoric acid, sodium hydroxide, or potassium hydroxide to obtain 2-vinylpyridine, but the yield is only 70-86%. US Patent 45588815 uses acrylonitrile as a raw material to directly catalyze the preparation of 2-vinylpyridine with acetylene. Although the method is simple, the preparation of the catalyst is difficult. Furthermore, when acrylonitrile and acetylene are directly synthesized into 2-vinylpyridine, the product 2-vinylpyridine needs to be removed in time under gas-liquid reaction conditions to avoid self-polymerization of 2-vinylpyridine under prolonged heating conditions, which greatly increases the difficulty of the process.

[0003] Therefore, it is urgent to research and develop new synthetic processes for 2-vinylpyridine in order to overcome and solve the problems existing in the current technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing 2-vinylpyridine. This method has advantages such as readily available raw materials, low cost, convenient preparation of the catalyst, high raw material conversion rate, stable intermediate properties, and ease of industrial production. This invention uses 3-methoxypropionitrile and acetylene as raw materials to synthesize 2-methoxyethylpyridine with high conversion rate in the presence of a cyclization catalyst and solvent. Then, catalytic cracking and separation yield 2-vinylpyridine in high yield.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing 2-vinylpyridine, comprising the following steps:

[0007] 1) Using 3-methoxypropionitrile and acetylene as raw materials, in the presence of a cyclization catalyst and solvent, acetylene gas is continuously introduced at a temperature of 140-180℃, and the pressure is maintained at 0.6-2.0 MPa for 5-12 h. After the reaction is completed, the solvent is distilled off, and then the mixture is distilled under reduced pressure to obtain 2-methoxyethylpyridine. The preferred reaction temperature is 150-170℃, and the preferred pressure is 1.0-1.5 MPa.

[0008] 2) 2-Methoxyethylpyridine is catalytically cracked at 80-180℃ (preferably 90-130℃) in the presence of a cracking catalyst and a polymerization inhibitor. The cracking product 2-VP and a mixture of methanol are obtained by vacuum distillation. 2-VP is then obtained by further distillation, or 2-VP is obtained by flash distillation to separate methanol.

[0009] Steps 1) and 2) of the above technical solution can be completed using a batch reaction method, or a continuous reaction method. The organic solvent, 3-methoxypropionitrile, and cyclization catalyst solution are mixed and gradually added to a pipeline reactor, with the temperature controlled at 150-170℃. Acetylene is continuously introduced, and the system pressure is controlled at 0.7-1.6 MPa. The reaction liquid is released from the outlet at the other end of the pipeline reactor via flash evaporation and depressurization. The solvent and product in the reaction liquid are then separated by distillation, followed by further fractional distillation to obtain 2-methoxyethylpyridine. The distillation residue is cooled and separated to remove insoluble matter, and the catalyst is reused. The cracking of 2-methoxyethylpyridine uses a continuous reactive distillation method to reduce the residence time of the product under high-temperature conditions.

[0010] In the above technical solution, specifically, in step 1), the cyclization catalyst used for the reaction of 3-methoxypropionitrile and acetylene to generate 2-methoxyethylpyridine is a tetrahydrofuran-toluene solution of diindenylcobalt or bis(cyclopentadienyl)cobalt, or a 2-methyltetrahydrofuran-toluene solution.

[0011] Specifically, in step 1), the molar ratio of 3-methoxypropionitrile to diindolecobalt or bis(cyclopentadienyl)cobalt (calculated as cobalt chloride) is 50-300:1, preferably 100-300:1.

[0012] Furthermore, in step 1), the solvent is selected from aromatic hydrocarbons such as benzene, toluene, xylene or mixtures thereof, and the weight ratio of the solvent to the raw material 3-methoxypropionitrile is 0.5-5:1.

[0013] In the above technical solution, specifically in step 2), the cracking catalyst is one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide, and the weight ratio of the cracking catalyst to 2-methoxyethylpyridine is 0.01-10:1.

[0014] Furthermore, in step 2), the polymerization inhibitor is one or both of hydroquinone and tert-butylhydroquinone, and the amount of polymerization inhibitor used is 0.1-1% of the weight of 2-methoxyethylpyridine.

[0015] In the above-mentioned technical solution, in a further preferred embodiment, in step 2), a polar solvent needs to be added during catalytic cracking. The selected polar solvent is one or more of water, dimethyl sulfoxide, sulfolane, polyoxyethylene ether, and alkoxy polyoxyethylene ether (alkoxy groups include methoxy, ethoxy, and butoxy groups, with a degree of polymerization ranging from 3 to 200). The weight ratio of the polar solvent to 2-methoxyethylpyridine is 0.1-5:1.

[0016] Furthermore, the cyclized catalyst solution is prepared by the following method:

[0017] a) Add THF or 2-methyltetrahydrofuran and sodium amino acid to the reactor, and then add indene or cyclopentadiene under nitrogen protection. Maintain the temperature at 5-30℃ and react for 1-4 h to obtain a THF or 2-methyltetrahydrofuran solution of sodium indene or sodium cyclopentadiene.

[0018] b) In another reactor, toluene and anhydrous cobalt chloride are added as solvents, followed by the THF or 2-methyltetrahydrofuran solution of sodium indene or sodium cyclopentadiene obtained in step a). The mixture is heated under reflux for 2-4 h, cooled, and filtered to remove insoluble matter, thus obtaining the cyclized catalyst solution.

[0019] Specifically, in step a), the weight ratio of tetrahydrofuran or 2-methyltetrahydrofuran to sodium amide is 4-15:1, and the molar ratio of sodium amide to indene or cyclopentadiene is 0.9-1.1:1. In step b), the weight ratio of the solvent toluene to anhydrous cobalt chloride is 5-20:1, and the molar ratio of anhydrous cobalt chloride to sodium amide is 0.45-0.55:1.

[0020] Compared with the prior art, the beneficial effects of the method of the present invention are as follows:

[0021] This invention uses 3-methoxypropionitrile and acetylene as raw materials in a two-step reaction. In the first step, 2-methoxyethylpyridine is obtained through a cycloaddition reaction in the presence of a cyclization catalyst, with a single-pass conversion rate of over 96% for 3-methoxypropionitrile. In the second step, 2-methoxyethylpyridine undergoes catalytic cracking to generate 2-VP in the presence of a cracking catalyst, with a conversion rate exceeding 97%. Furthermore, the starting material 3-methoxypropionitrile in the first step can be obtained from acrylonitrile and methanol in quantitative yield. Acrylonitrile is a bulk chemical product with relatively stable market prices. The cyclization catalyst in the first step of this invention is a THF-toluene solution or a 2-methyltetrahydrofuran-toluene solution of a cobalt complex, prepared by reacting cobalt chloride with indenyl sodium or cyclopentadienyl sodium. It can be used directly without further purification, making catalyst preparation convenient. The second step uses potassium hydroxide or sodium hydroxide as a cracking catalyst for 2-methoxyethylpyridine, resulting in a high catalytic cracking conversion rate. The product 2-VP is obtained after real-time vacuum distillation. This invention, as an indirect method for preparing 2-VP from acrylonitrile, avoids the stringent limitations on catalysts and reaction conditions imposed by direct methods. It has advantages such as readily available raw materials, high reaction conversion rate (product yield of over 90% and product purity of over 98%), and is suitable for industrial production. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0023] In the following embodiments, unless otherwise specified, all raw materials used are commercially available products that can be purchased directly or can be prepared using conventional methods in the art.

[0024] Example 1

[0025] A method for preparing 2-vinylpyridine, specifically comprising the following steps:

[0026] 1) Preparation of catalyst for the reaction of 3-methoxypropionitrile with acetylene:

[0027] 16.0 g THF and 1.6 g sodium amide (0.04 mol) were added to a reaction flask, followed by the dropwise addition of 4.9 g (0.04 mol) of indene under nitrogen protection. The reaction was carried out at 10-15 °C for 2 h to obtain a THF solution of sodium indene. In another reaction flask, 25.0 g toluene and 2.6 g anhydrous cobalt chloride (0.02 mol) were added, followed by the THF solution of sodium indene prepared above. The mixture was heated under reflux for 2 h, cooled, and filtered to obtain a catalyst solution.

[0028] 2) Synthesis of 2-methoxyethylpyridine:

[0029] 200.0 g of toluene, 200.0 g (2.35 mol) of 3-methoxypropionitrile, and a catalyst solution were added to a pressure reactor. The reactor was gradually heated to 140-160 °C, and acetylene gas was continuously introduced while maintaining the pressure at 1.3-1.5 MPa. The gas introduction was stopped after 9-10 h. After cooling, the reaction solution was removed, and the conversion rate of the raw materials was determined by gas chromatography to be 98.0%. The solvents THF and toluene in the reaction solution were distilled off, and finally, the mixture was distilled under reduced pressure at 130-135 °C (vacuum degree 0.090-0.095 kPa) to obtain 310.1 g of 2-methoxyethylpyridine with a purity of 99.1% (GC determination, area normalized), and a yield of 95.4% based on 3-methoxypropionitrile.

[0030] .

[0031] 3) Cleavage of 2-methoxyethylpyridine:

[0032] Take 150.0 g of 2-methoxyethylpyridine, add 5.0 g of sodium hydroxide, 25.0 g of dimethyl sulfoxide, and 0.50 g of hydroquinone, heat to 120-125 °C and maintain for 2.5 h, distill under reduced pressure to obtain the product 2-VP and methanol. The conversion rate of the raw material was determined by gas chromatography to be 97.2%. Then, further distillation was carried out under a vacuum of 0.080-0.090 kPa. The fraction at 60-100 °C was collected to obtain 109.1 g of 2-vinylpyridine with a purity of 99.4% (GC, area normalized) and a yield of 94.3%.

[0033] .

[0034] Example 2

[0035] A method for preparing 2-vinylpyridine, specifically comprising the following steps:

[0036] 1) Preparation of catalyst for the reaction of 3-methoxypropionitrile with acetylene:

[0037] 16.0 g of 2-methyltetrahydrofuran and 1.6 g of sodium amide (0.04 mol) were added to a reaction flask, followed by the addition of 2.7 g of cyclopentadiene (0.04 mol) under nitrogen protection. The reaction was carried out at 15-20 °C for 2 h to obtain a 2-methyltetrahydrofuran solution of sodium cyclopentadiene. In another reaction flask, 25.0 g of toluene and 2.6 g of anhydrous cobalt chloride (0.02 mol) were added, followed by the 2-methyltetrahydrofuran solution of sodium cyclopentadiene prepared above. The mixture was heated under reflux for 2 h, cooled, and filtered to obtain the catalyst solution.

[0038] 2) Synthesis of 2-methoxyethylpyridine:

[0039] 230.0 g of xylene, 230.0 g (2.71 mol) of 3-methoxypropionitrile, and the catalyst solution obtained in step 1) were mixed and added to a pressure reaction vessel. The mixture was heated to 150-165 °C, and acetylene gas was continuously introduced while maintaining the pressure at 0.8-1.0 MPa. The reaction was completed after 7-9 h. The conversion rate of the raw materials was determined to be 98.5% by gas chromatography. 2-methyltetrahydrofuran, toluene, and xylene in the reaction solution were distilled off, and finally, 359.3 g of 2-methoxyethylpyridine was obtained by vacuum distillation (temperature 120-128 °C, vacuum degree 0.095-0.098 kPa), with a purity of 98.6% and a yield of 95.2% based on 3-methoxypropionitrile.

[0040] 3) Cleavage of 2-methoxyethylpyridine:

[0041] In a reaction flask, 50 g of 30% potassium hydroxide aqueous solution and 0.2 g of hydroquinone as a polymerization inhibitor were added. At 140 °C, 150.1 g of 2-methoxyethylpyridine was gradually added dropwise. The mixture of 2-VP and methanol was distilled off under reduced pressure. The conversion rate of the raw material was determined to be 96.4% by gas chromatography. The mixture was then vacuum distilled at a vacuum degree of 0.080-0.090 kPa. The fraction collected at 60-100 °C yielded 105.4 g of 2-vinylpyridine with a purity of 99.1% (GC, area normalized) and a yield of 90.9%.

[0042] Example 3

[0043] A method for preparing 2-vinylpyridine, specifically comprising the following steps:

[0044] 1) Preparation of catalyst for the reaction of 2-methoxypropionitrile with acetylene:

[0045] 15 g of 2-methyltetrahydrofuran and 1.6 g of sodium amide (0.04 mol) were added to a reaction flask, followed by the dropwise addition of 2.7 g of cyclopentadiene (0.04 mol) under nitrogen protection. The reaction was carried out at 25 °C for 2 h to obtain a 2-methyltetrahydrofuran solution of sodium cyclopentadiene. In another reaction flask, 25 g of toluene and 2.6 g of anhydrous cobalt chloride (0.02 mol) were added, followed by the 2-methyltetrahydrofuran solution of sodium cyclopentadiene prepared above. The mixture was heated under reflux for 3 h, cooled, and filtered to obtain the catalyst solution.

[0046] 2) Synthesis of 2-methoxyethylpyridine:

[0047] 230.0 g of xylene, 230.0 g (2.71 mol) of 3-methoxypropionitrile, and the catalyst solution obtained in step 1) were mixed and added to a pressure reaction vessel. The mixture was heated to 160 °C, and acetylene gas was continuously introduced to maintain the pressure at 1.0-1.5 MPa for 8.5 h, after which the reaction was complete. After cooling, the reaction solution was removed, and gas chromatography determined the conversion rate of the raw materials to be 97.9%. 2-methyltetrahydrofuran, toluene, and xylene in the reaction solution were distilled off sequentially, and finally, the mixture was distilled under reduced pressure (0.090-0.096 kPa) at 129-132 °C to obtain 366.5 g of 2-methoxypyridine with a purity of 97.9% and a yield of 96.7% based on 3-methoxypropionitrile.

[0048] 3) Synthesis and cleavage of 2-methoxyethylpyridine:

[0049] 4.0 g of potassium hydroxide, 50.0 g of dimethyl sulfoxide, and 0.5 g of tert-butylhydroquinone were added to a reaction flask. 150.0 g of 2-methoxyethylpyridine was added dropwise at 120 °C. 2-VP and methanol were distilled off under reduced pressure. Gas chromatography showed a conversion rate of 97.0%. Further vacuum distillation was performed at a vacuum of 0.080-0.090 kPa. The fraction distilled at 60-100 °C was collected to yield 105.6 g of 2-vinylpyridine with a purity of 98.1% (GC, area normalized), and a yield of 90.1%.

Claims

1. A method for preparing 2-vinylpyridine, characterized in that, Includes the following steps: 1) Using 3-methoxypropionitrile and acetylene as raw materials, the reaction was carried out in the presence of a cyclization catalyst and solvent at a temperature of 140-180℃ and a pressure of 0.6-2.0MPa for 5-12 hours. After the reaction was completed, the solvent was distilled off and then the mixture was distilled under reduced pressure to obtain 2-methoxyethylpyridine. 2) 2-Methoxyethylpyridine is catalytically cracked at 80-180℃ in the presence of a cracking catalyst and a polymerization inhibitor, and then 2-vinylpyridine is obtained by vacuum distillation and redistillation. In step 1), the cyclization catalyst is a tetrahydrofuran-toluene solution of diindenylcobalt or bis(cyclopentadienyl)cobalt, or a 2-methyltetrahydrofuran-toluene solution; The cyclized catalyst solution was prepared by the following method: a) Add tetrahydrofuran (THF) or 2-methyltetrahydrofuran and sodium amino acid to a reactor, then add indene or cyclopentadiene under nitrogen protection, and maintain the temperature at 5-30℃ for 1-4 h to obtain a THF or 2-methyltetrahydrofuran solution of sodium indene or sodium cyclopentadiene. b) In another reactor, toluene and anhydrous cobalt chloride are added, followed by the THF or 2-methyltetrahydrofuran solution of sodium indene or sodium cyclopentadiene obtained in step a). The mixture is heated under reflux for 2-4 h, cooled, and the insoluble matter is filtered out to obtain the final product. In step 2), the cracking catalyst is one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide, and the weight ratio of the cracking catalyst to 2-methoxyethylpyridine is 0.01-10:

1. In step 2), the polymerization inhibitor is one or both of hydroquinone and tert-butylhydroquinone.

2. The method for preparing 2-vinylpyridine according to claim 1, characterized in that, In step 1), the molar ratio of 3-methoxypropionitrile to diindolecobalt or bis(cyclopentadienyl)cobalt is 50-300:

1.

3. The method for preparing 2-vinylpyridine as described in claim 1, characterized in that, In step 1), the solvent is selected from benzene, toluene, xylene or a mixture thereof, and the weight ratio of the solvent to the raw material 3-methoxypropionitrile is 0.5-5:

1.

4. The method for preparing 2-vinylpyridine according to claim 1, characterized in that, In step 2), one or more of the selected polar solvents are added during catalytic cracking. The selected polar solvents are water, dimethyl sulfoxide, sulfolane, polyoxyethylene ether, or alkoxy polyoxyethylene ether, wherein the alkoxy group includes methoxy, ethoxy, and butoxy. The degree of polymerization of the polyoxyethylene ether ranges from 3 to 200. The weight ratio of the polar solvent to 2-methoxyethylpyridine is 0.1 to 5:

1.

5. The method for preparing 2-vinylpyridine according to claim 1, characterized in that, In step a), the weight ratio of tetrahydrofuran or 2-methyltetrahydrofuran to sodium amino is 4-15:1, and the molar ratio of sodium amino to indene or cyclopentadiene is 1.0-1.1:

1.

6. The method for preparing 2-vinylpyridine according to claim 1, characterized in that, In step b), the weight ratio of toluene to anhydrous cobalt chloride is 5-20:1, and the molar ratio of anhydrous cobalt chloride to sodium amide is 0.45-0.55:1.