Synthetic method of 3-methyl-2-pyrrolidone
By employing a three-step reaction involving ring-opening, chlorination, and cyclization, the problem of poor regioselectivity and high cost in the synthesis of 3-methyl-2-pyrrolidone in existing technologies has been solved, achieving a highly efficient and green synthesis of 3-methyl-2-pyrrolidone that is suitable for industrial applications.
Patent Information
- Application Number
- CN202511107301.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-08
- Publication Date
- 2025-11-18
AI Technical Summary
Existing technologies are difficult to synthesize 3-methyl-2-pyrrolidone efficiently and economically, especially because the methyl group is located at the 3-position within the ring, resulting in poor regioselectivity, numerous byproducts, and high raw material costs, which makes it difficult to meet the needs of industrial production.
The reaction employs a three-step process of ring-opening, chlorination, and cyclization. 3-methyl-γ-butyrolactone is reacted with an ammonia source to generate 3-methyl-4-hydroxybutyramide, which is then reacted with a combination of chlorinating agents to generate 3-methyl-4-chlorobutyramide. Finally, it is refluxed with an organic base to generate 3-methyl-2-pyrrolidone. This method uses conventional chemical raw materials and mild conditions, thus avoiding existing patent barriers.
The synthesis of 3-methyl-2-pyrrolidone with high selectivity and high yield was achieved, with a total yield of 40.8% and a purity of over 99%. This reduced separation costs, is environmentally friendly, suitable for industrial production, and reduced COD emissions, making it competitive in the market.
Abstract
Description
Technical Field
[0001] This invention relates to the field of chemical synthesis technology, and more particularly to a method for synthesizing 3-methyl-2-pyrrolidone. Background Technology
[0002] Pyrrolidones, as an important class of nitrogen-containing heterocyclic compounds, exhibit irreplaceable application value in pharmaceutical synthesis, fine chemicals, and functional materials due to their unique lactam ring structure. Among them, 3-methyl-2-pyrrolidone, due to the steric hindrance and electronic effects of the methyl group at the 3-position, is a key intermediate in the synthesis of certain drug molecules (such as central nervous system depressants and antiviral drugs), and can also be used as a high-performance solvent in lithium battery electrolytes and polymer polymerization reactions.
[0003] In existing technologies, the synthesis of pyrrolidone compounds has largely focused on products with 5-position substitution (such as 5-methyl-2-pyrrolidone), with the established route involving the reductive amination of levulinic acid with amine compounds to construct a five-membered ring. However, for 2-pyrrolidones with 3-position methyl substitution, the spatial configuration of the methyl group within the ring requires high regioselectivity for the synthetic route, presenting a significant technical bottleneck for existing methods.
[0004] Among the currently disclosed synthetic strategies, the reaction of γ-butyrolactone derivatives with amines tends to generate N-substituted pyrrolidones, and the reaction pathway involves direct cyclization, making it impossible to accurately introduce the methyl group at the 3-position. Other routes attempt to construct structures through olefin cyclization or amide cyclization reactions, but these suffer from problems such as numerous byproducts, poor regioselectivity (easily generating 5-methyl isomers), and high raw material costs (e.g., using rare metal catalysts), making it difficult to meet the needs of industrial production. Summary of the Invention
[0005] To address the problems mentioned in the background section, the present invention provides a method for synthesizing 3-methyl-2-pyrrolidone.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for synthesizing 3-methyl-2-pyrrolidone includes the following steps: Ring-opening step: 3-methyl-γ-butyrolactone is reacted with an ammonia source in a high-pressure reactor to obtain 3-methyl-4-hydroxybutyramide. The molar ratio of 3-methyl-γ-butyrolactone to liquid ammonia in the reaction is 1:1.5 to 2.0, the reaction temperature is 120-150℃, the pressure is 5-10 bar, and the reaction time is 6-12 hours. Chlorination step: 3-methyl-4-hydroxybutyramide obtained from the ring-opening step is reacted with a combination chlorinating agent in anhydrous toluene. The reaction is first carried out at 0-5℃ for 2-4 hours, and then the temperature is raised to 20-30℃ for 1-2 hours to obtain 3-methyl-4-chlorobutyramide. Cyclization step: 3-methyl-4-chlorobutyramide obtained from the chlorination step is refluxed with an organic base in anhydrous ethanol for 4-8 hours to obtain 3-methyl-2-pyrrolidone.
[0007] Preferably, the reaction solvent for the ring-opening step is anhydrous toluene. If methanol is used as the solvent, the mass ratio of methanol to 3-methyl-γ-butyrolactone is 1 to 2:1.
[0008] Preferably, the molar ratio of 3-methyl-4-hydroxybutyramide to the combined chlorinating agent is 1:1.2 to 1.5, and the mass ratio of anhydrous to 3-methyl-4-hydroxybutyramide is 2 to 3:1.
[0009] Preferably, the molar ratio of 3-methyl-4-chlorobutyramide to organic base is 1:1.5 to 2.0, the mass ratio of anhydrous ethanol to 3-methyl-4-chlorobutyramide is 2-3:1, the reflux temperature is 56-58°C, and the organic base is selected from at least one of potassium tert-butoxide, DBN (1,5-diazabicyclo[4.3.0]non-5-ene), and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene).
[0010] Preferably, the preparation step of the 3-methyl-γ-butyrolactone specifically includes: Step 1: Isoprene and peracetic acid are reacted at 20-30℃ for 3-5 hours without a catalyst to obtain 3-methyl-1,2-epoxy-4-butene, wherein the molar ratio of isoprene to peracetic acid is 1:1.2-1.5; Step 2: 3-Methyl-1,2-epoxy-4-butene is mixed with water under acidic conditions (pH=1-3) and reacted at 70-90℃ for 5-7 hours to obtain 3-methyl-1,4-butanediol. The acidic conditions are provided by concentrated hydrochloric acid, and the mass ratio of concentrated hydrochloric acid to 3-methyl-1,2-epoxy-4-butene is 0.04-0.06:1. Step 3: 3-Methyl-1,4-butanediol reacts with the CrO3 / pyridine system. The reactants are first added dropwise at 0°C. After the addition is complete, the reaction is carried out at 20-30°C for 2-4 hours to obtain 3-methyl-γ-butyrolactone, wherein the molar ratio of 3-methyl-1,4-butanediol to CrO3 is 1:0.8-0.9.
[0011] Preferably, the combined chlorinating agent is selected from at least one of oxalate chloride + catalytic amount of DMF (0.05-0.2% eq), triphosgene + catalytic amount of DMAP (0.05-0.1% eq), polystyrene-supported thionyl chloride (PS-SOCl2), and polyethylene glycol-supported thionyl chloride (PEG-SOCl2).
[0012] Preferably, after the cyclization step is completed, the solid residue generated by the reaction is first filtered to remove the unreacted organic base and the generated potassium chloride, and then the filtrate is distilled (distillation temperature is 120-140℃, vacuum degree is 0.08-0.1MPa, to obtain 3-methyl-2-pyrrolidone).
[0013] Preferably, the ammonia source is selected from liquid ammonia, liquid ammonia-alcohol mixed solvent, or ammonia gas generated by in-situ pyrolysis of ammonium salts.
[0014] Preferably, the chlorination step is carried out under microwave or ultrasonic radiation, with a microwave power of 100–500W or an ultrasonic frequency of 15–40kHz, and the amount of combined chlorinating agent is reduced to 1.0–1.2 equivalents.
[0015] Compared with the prior art, the beneficial effects of the present invention are: The method for synthesizing 3-methyl-2-pyrrolidone of this invention employs a three-step reaction of "ring-chlorination-cyclization" and a novel intermediate, 3-methyl-4-hydroxybutyramide, thus avoiding existing patent barriers. It utilizes economical raw materials, starting with isoprene, a readily available and inexpensive chemical raw material. The process is simple, requiring only four steps (including the preparation of the starting material), with mild conditions and low equipment investment, making it suitable for continuous industrial production. It exhibits high selectivity and yield, with each step showing a selectivity exceeding 95% and an overall yield of 40.8%, achieving a 3-methyl isomer purity exceeding 99%, significantly reducing separation costs. Furthermore, it is environmentally friendly. The solvent is recyclable, and the combined chlorinating agent can be replaced with triphosgene to reduce pollution, reducing COD emissions from wastewater by more than 60%. It has strong industrial feasibility, and the reaction can be carried out in conventional equipment. The yield fluctuation is less than 3% when scaled up to 100kg per batch. The product purity is ≥98%, and the application performance is excellent. Moreover, the synthesis strategy can be extended to the preparation of other 3-substituted-2-pyrrolidone derivatives, providing diversified intermediates for the pharmaceutical and materials fields. It solves the problems of poor regional selectivity, cumbersome steps, and high cost in existing technologies, and has efficient, green, and competitive industrial value. Detailed Implementation
[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0017] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.
[0018] Preparation Example 1 The specific steps for preparing the 3-methyl-γ-butyrolactone include: Step 1: At 25℃ and normal pressure, 68g of isoprene (1.0mol) and 114g of 30% peracetic acid (1.3mol) were added to a 500mL glass reactor in one batch, and stirred for 4 hours without a catalyst. GC was stopped when the isoprene concentration was <2%. After separation, washing with saturated NaHCO3, and drying, 75.5g of 3-methyl-1,2-epoxy-4-butene was obtained, with a yield of 88% and a GC purity of 97%.
[0019] Step 2: Add 150 mL of water and 3.1 g of concentrated hydrochloric acid (w / w 37%, 0.05:1 mass ratio) to the crude product from the previous step to adjust the pH to approximately 2. Heat to 80 °C and maintain this temperature for 6 hours. Dehydrate under reduced pressure, and distill the residue under reduced pressure (110–115 °C / 15 mmHg) to obtain 71.2 g of 3-methyl-1,4-butanediol, with a yield of 95%.
[0020] Step 3: Dissolve 59.2 g of 3-methyl-1,4-butanediol (0.56 mol) in 150 mL of anhydrous pyridine. Add 55.1 g of CrO3 (0.55 mol, 0.85 eq) in 150 mL of pyridine composite solution dropwise over an ice bath at 0 °C, completing the addition over 1 h. Continue the reaction at 20 °C for 3 h. Pour the solution into 500 mL of ice water, extract with ethyl acetate, wash with 5% NaHCO3, dry, and distill under reduced pressure (85–90 °C / 20 mmHg) to obtain 55.3 g of 3-methyl-γ-butyrolactone. The overall yield of the three steps is 64%, and the GC purity is 99.2%.
[0021] Preparation Example 2 The process is the same as in Preparation Example 1, except that: Step 1: The molar ratio of isoprene to peracetic acid is 1:1.2, the reaction temperature is 30℃, and the reaction time is 5h.
[0022] Step 2: React with concentrated hydrochloric acid at a mass ratio of 0.04:1 at 90℃ for 5 hours.
[0023] Step 3: CrO3 / diol molar ratio 0.8:1, react at 20℃ for 4h.
[0024] The overall yield of the three steps was 60%, and the GC purity was 98.9%.
[0025] Preparation Example 3 The process is the same as in Preparation Example 1, except that: Step 1: The molar ratio of isoprene to peracetic acid is 1:1.5, and the reaction is carried out at 20°C for 3 hours.
[0026] Step 2: Concentrated hydrochloric acid mass ratio 0.06:1, react at 70℃ for 7h.
[0027] Step 3: CrO3 / diol molar ratio 0.9:1, react at 30℃ for 2h.
[0028] The overall yield of the three steps was 66%, and the GC purity was 99.0%.
[0029] Preparation Example 4 Chlorination agent combination 1: Oxaloyl chloride (COCl)₂ + catalytic amount of DMF (in-situ generation of Vilsmeier reagent). Specific usage steps for chlorination agent combination 1: 1. Dissolve 3-methyl-4-hydroxybutyramide in anhydrous tetrahydrofuran (THF) or acetonitrile, under nitrogen protection, and cool to -40°C to -20°C.
[0030] 2. Add DMF (0.05-0.2 equiv) dropwise.
[0031] 3. Slowly add oxalyl chloride (1.0-1.2 equiv) while maintaining the temperature below -20°C.
[0032] 4. Stir at low temperature for 1-2 hours (monitored by TLC / HPLC).
[0033] 5. Raise the temperature to 0°C and stir for 0.5 hours to ensure complete reaction.
[0034] 6. Quench with low-temperature methanol or saturated NaHCO3 solution, restore to room temperature, and then proceed with conventional extraction, drying, and concentration.
[0035] Chemical reaction formula R-CH2-OH+(COCl)2+HCON(CH3)2→[R-CH2-OC + =N + (CH3)2]Cl - →R-CH2-Cl+CO+CO2+HN(CH3)2 Chlorinating agent combination 2: Triphosgene (C3Cl6O3) + a catalytic amount of Lewis base (such as DMAP or DBU). Specific usage steps for chlorinating agent combination 2: 1. Dissolve 3-methyl-4-hydroxybutyramide in anhydrous toluene and add a catalytic amount of DMAP (0.05-0.1 equiv).
[0036] 2. Add triphosgene (0.35-0.4 equiv, equivalent to 1.05-1.2 equiv Cl) in batches and stir at room temperature.
[0037] 3. Control the exothermic reaction temperature to <40℃, and stir for 3-5 hours until the reaction is complete.
[0038] 4. The reaction solution was directly filtered, the filtrate was concentrated under reduced pressure, and the crude product was rapidly purified by short silica gel column (petroleum ether / ethyl acetate).
[0039] Chlorinating agent combination 3: polymer-supported triphenylphosphine + tetrachloromethane or polymer-supported thionyl chloride analog. Specific usage steps for chlorinating agent combination 3: 1. Dissolve 3-methyl-4-hydroxybutyramide in anhydrous dichloromethane and add polymer-PPh3 (1.2 equiv).
[0040] 2. Add CCl4 (1.5 equiv) dropwise and stir at 0°C to room temperature for 4-6 hours.
[0041] 3. Filter and recover the polymer reagent (key: reusable), and concentrate the filtrate to obtain the crude chlorinated product.
[0042] 4. The polymer can be washed with a simple solvent and then directly reused in the next batch.
[0043] Example 1
[0044] S1. 3-Methyl-γ-butyrolactone (20 g, 0.18 mol) and liquid ammonia (10.2 g, 0.30 mol) were added to a high-pressure reactor and reacted at 130 °C and 8 bar for 8 hours to obtain 3-methyl-4-hydroxybutyramide; S2. Dissolve the above-mentioned 3-methyl-4-hydroxybutyramide (25g, 0.19mol) in anhydrous toluene (50g), add oxaloyl chloride (24.5g, 0.19mol) and catalytic amount DMF (0.5g), react at 0℃ for 3 hours, then raise the temperature to 25℃ and react for 1.5 hours to obtain 3-methyl-4-chlorobutyramide; S3. 3-Methyl-4-chlorobutyramide (20 g, 0.14 mol) and potassium tert-butoxide (23.2 g, 0.17 mol) were refluxed in anhydrous ethanol (40 g) for 6 hours. After filtration, the filtrate was distilled (130 °C / 0.09 MPa) to obtain 3-methyl-2-pyrrolidone. Example 2
[0045] S1, 3-methyl-γ-butyrolactone (20 g, 0.18 mol) and liquid ammonia (10.2 g, 0.30 mol) were reacted in methanol (20 g) at 120 °C and 6 bar for 10 hours to give 3-methyl-4-hydroxybutyramide; S2. Under microwave power of 300W, the product (25g, 0.19mol) and oxalyl chloride (26.3g, 0.21mol) were reacted in anhydrous toluene (50g), with the addition of triphosgene (16.5g, 0.11mol) and AlCl3 (0.9g, catalytic amount). After reacting at 0℃ for 2 hours, the temperature was raised to 20℃ and reacted for 1 hour to obtain 3-methyl-4-chlorobutyramide. S3. 3-Methyl-4-chlorobutyramide (20 g, 0.14 mol) and DBN (25.2 g, 0.20 mol) were refluxed in anhydrous ethanol (40 g) for 6 hours. After filtration, the filtrate was distilled (130 °C / 0.09 MPa) to obtain 3-methyl-2-pyrrolidone.
[0046] Example 3
[0047] S1, 3-methyl-γ-butyrolactone (20 g, 0.18 mol) and ammonium carbonate (15.8 g, 0.16 mol) were pyrolyzed in an autoclave at 140 °C and 9 bar for 12 hours to obtain 3-methyl-4-hydroxybutyramide; S2. At an ultrasonic frequency of 25 kHz, the product (25 g, 0.19 mol) and triphosgene (18.2 g, 0.12 mol) were reacted with anhydrous toluene (60 g), and triphosgene (16.0 g, 0.11 mol) and FeCl3 (0.8 g, catalytic amount) were added. The mixture was reacted at 5 °C for 4 hours, and then the temperature was raised to 30 °C for 1 hour to obtain 3-methyl-4-chlorobutyramide. S3. 3-Methyl-4-chlorobutyramide (20 g, 0.14 mol) and organic base (23.2 g, 0.17 mol) were refluxed in anhydrous ethanol (40 g) for 6 hours. After filtration, the filtrate was distilled (130 °C / 0.09 MPa) to obtain 3-methyl-2-pyrrolidone. Example 4
[0048] S1, 3-methyl-γ-butyrolactone (20 g, 0.18 mol) and liquid ammonia (13.6 g, 0.40 mol) were reacted at 150 °C and 10 bar for 6 hours to obtain 3-methyl-4-hydroxybutyramide; S2. Using a supported chlorination reagent (PS-SO2Cl), the product (25g, 0.19mol) and the reagent (30g, 0.23mol) were reacted with anhydrous toluene (50g), oxaloyl chloride (25.0g, 0.20mol) and DMF (0.6g) in 25°C for 3 hours, and then the temperature was raised to 25°C for 1 hour to obtain 3-methyl-4-chlorobutyramide. S3. 3-Methyl-4-chlorobutyramide (20g, 0.14mol) and potassium tert-butoxide (11.7g) + DBU (14.3g) mixed base were refluxed in anhydrous ethanol (40g) for 6 hours. After filtration, the filtrate was distilled (130℃ / 0.09MPa) to obtain 3-methyl-2-pyrrolidone.
[0049] Example 5
[0050] S1. 3-Methyl-γ-butyrolactone (20 g, 0.18 mol) and liquid ammonia (10.2 g, 0.30 mol) were added to a high-pressure reactor and reacted at 130 °C and 8 bar for 8 hours to obtain 3-methyl-4-hydroxybutyramide; S2. Dissolve the above-mentioned 3-methyl-4-hydroxybutyramide (25g, 0.19mol) in anhydrous toluene (50g), add oxaloyl chloride (24.0g, 0.19mol) and DMF (0.5g), react at 0°C for 3 hours, then raise the temperature to 25°C and react for 1.5 hours to obtain 3-methyl-4-chlorobutyramide; S3, 3-methyl-4-chlorobutyramide (20 g, 0.14 mol) and DBN (22.7 g, 0.18 mol) were refluxed in anhydrous ethanol (60 g) at 58 °C for 8 hours, and then distilled to obtain 3-methyl-2-pyrrolidone.
[0051] The data comparison of the examples is as follows: Example Cyclic solvents Combined chlorination agent types Organic base types auxiliary conditions Total Productivity (%) purity(%) 1 Anhydrous ethanol Oxaloyl chloride + DMF Potassium tert-butoxide none 89 99.4 2 Anhydrous ethanol <![CDATA[Triphosgene + AlCl3]]> DBN 300W Microwave 87 99.1 3 Anhydrous ethanol <![CDATA[Triphosgene + FeCl3]]> DBU 25kHz ultrasound 85 98.9 4 Anhydrous ethanol Oxaloyl chloride + DMF Potassium tert-butoxide + DBU (mixed) none 91 99.5 5 Anhydrous ethanol Oxaloyl chloride + DMF DBN none 87 99.2
[0052] The above embodiments all verify the synergistic effect of the technical features in the claims, proving the universality and operability of the synthesis method under different conditions. Using isoprene, a bulk chemical raw material, as the starting material eliminates the need for rare metal catalysts, and the raw materials for each step are all conventional chemical products, reducing raw material costs and making it suitable for large-scale production. Solvents (such as methanol, anhydrous toluene, and anhydrous ethanol) can be recycled, reducing waste. The combined chlorinating agent can be triphosgene and Lewis base synergistically catalyzing the direct chlorination of primary alcohols. Triphosgene has a high effective chlorine content (theoretical utilization rate 100%), reducing waste salt generation by >50% compared to SOCl2, thus reducing harmful gas emissions. Wastewater COD emissions are reduced by more than 60%, conforming to the trend of green chemical development. Different preparation examples and embodiments show small fluctuations in yield and purity by adjusting reaction parameters (such as molar ratio, temperature, and time) (e.g., total yield fluctuation of 6% in the preparation example and 7% in the embodiment), indicating that the reaction conditions have good controllability and repeatability.
[0053] In summary, this scheme, through an efficient "ring-chlorination-cyclization" route, demonstrates significant advantages in terms of yield, purity, cost, environmental friendliness, and industrial feasibility, effectively solving the bottleneck problems of existing technologies.
[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for synthesizing 3-methyl-2-pyrrolidone, characterized in that, Includes the following steps: Ring-opening step: 3-methyl-γ-butyrolactone is reacted with an ammonia source in a high-pressure reactor to obtain 3-methyl-4-hydroxybutyramide. The molar ratio of 3-methyl-γ-butyrolactone to liquid ammonia in the reaction is 1:1.5 to 2.0, the reaction temperature is 120-150℃, the pressure is 5-10 bar, and the reaction time is 6-12 hours. Chlorination step: 3-methyl-4-hydroxybutyramide obtained from the ring-opening step is reacted with a combination chlorinating agent in anhydrous toluene. The reaction is first carried out at 0-5℃ for 2-4 hours, and then the temperature is raised to 20-30℃ for 1-2 hours to obtain 3-methyl-4-chlorobutyramide. Cyclization step: 3-methyl-4-chlorobutyramide obtained from the chlorination step is refluxed with an organic base in anhydrous ethanol for 4-8 hours to obtain 3-methyl-2-pyrrolidone.
2. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 1, characterized in that, The reaction solvent for the ring-opening step is solvent-free or methanol. If methanol is used as the solvent, the mass ratio of methanol to 3-methyl-γ-butyrolactone is 1 to 2:
1.
3. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 1, characterized in that, The molar ratio of 3-methyl-4-hydroxybutyramide to the combined chlorinating agent is 1:1.2 to 1.5, and the mass ratio of anhydrous to 3-methyl-4-hydroxybutyramide is 2 to 3:
1.
4. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 1, characterized in that, The molar ratio of 3-methyl-4-chlorobutyramide to organic base is 1:1.5 to 2.0, the mass ratio of anhydrous ethanol to 3-methyl-4-chlorobutyramide is 2-3:1, the reflux temperature is 56-58°C, and the organic base is selected from at least one of potassium tert-butoxide, DBN, and DBU.
5. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 2, characterized in that, The specific steps for preparing the 3-methyl-γ-butyrolactone include: Step 1: Isoprene and peracetic acid are reacted at 20-30℃ for 3-5 hours without a catalyst to obtain 3-methyl-1,2-epoxy-4-butene, wherein the molar ratio of isoprene to peracetic acid is 1:1.2-1.5; Step 2: 3-Methyl-1,2-epoxy-4-butene is mixed with water under acidic conditions (pH=1-3) and reacted at 70-90℃ for 5-7 hours to obtain 3-methyl-1,4-butanediol. The acidic conditions are provided by concentrated hydrochloric acid, and the mass ratio of concentrated hydrochloric acid to 3-methyl-1,2-epoxy-4-butene is 0.04-0.06:
1. Step 3: 3-Methyl-1,4-butanediol reacts with the CrO3 / pyridine system. The reactants are first added dropwise at 0°C. After the addition is complete, the reaction is carried out at 20-30°C for 2-4 hours to obtain 3-methyl-γ-butyrolactone, wherein the molar ratio of 3-methyl-1,4-butanediol to CrO3 is 1:0.8-0.
9.
6. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 3, characterized in that, The combined chlorinating agent is either chlorine oxalate + a catalytic amount of DMF or triphosgene and a catalytic amount of Lewis base.
7. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 1, characterized in that, After the cyclization step is completed, the solid residue generated by the reaction is first filtered to remove the unreacted organic base and the generated potassium chloride. Then the filtrate is distilled (distillation temperature is 120-140℃, vacuum degree is 0.08-0.1MPa, to obtain 3-methyl-2-pyrrolidone).
8. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 1, characterized in that, The ammonia source is selected from liquid ammonia, liquid ammonia-alcohol mixed solvent, or ammonia gas generated by in-situ pyrolysis of ammonium salts.
9. The method for synthesizing 3-methyl-2-pyrrolidone according to claim 1, characterized in that, The chlorination step is carried out under microwave or ultrasonic radiation, with a microwave power of 100–500W or an ultrasonic frequency of 15–40kHz, and the amount of combined chlorinating agent is reduced to 1.0–1.2 equivalents.