Synthetic method of alpha-acetyl-gamma-butyrolactone

Abstract

The invention belongs to the technical field of chemical synthesis, and relates to a synthesis method of alpha-acetyl-gamma-butyrolactone. According to the method, sodium ethoxide and 1-ethyl-3-methylimidazole acetate / sodium imidazole are mixed to serve as a catalyst, the acylation reaction between gamma-butyrolactone and acetate is promoted to proceed forwards, and the yield of the product alpha-acetyl-gamma-butyrolactone is increased. The types of catalysts in the process for synthesizing the alpha-acetyl-gamma-butyrolactone are expanded, and the development of the synthesis process of the alpha-acetyl-gamma-butyrolactone is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical synthesis and relates to a method for synthesizing α-acetyl-γ-butyrolactone. Background Art

[0002] α-acetyl-γ-butyrolactone is an important pharmaceutical intermediate and organic chemical raw material, and is an important intermediate for the preparation of vitamins and chlorophyll. It is also a pharmaceutical intermediate for synthesizing antipsychotic drugs such as risperidone, anticonvulsant and sedative-hypnotic drugs such as clomethiazole, perhexiline and chloroquine. At present, there are mainly two routes for preparing α-acetyl-γ-butyrolactone. One is the process route of ring-opening of ethylene oxide with methyl (or ethyl) acetoacetate and then esterification and ring-closing. The other is the acylation process route using γ-butyrolactone and methyl (or ethyl) acetate as raw materials. The boiling point of ethylene oxide used in the methyl (or ethyl) acetoacetate route is 10.8 °C, which belongs to a first-class flammable and explosive chemical. This will cause serious safety hazards in the storage, transportation and production links. Therefore, this process route has been gradually phased out, and the mainstream production of domestic enterprises has turned to the acylation process route using γ-butyrolactone and methyl (or ethyl) acetate as raw materials.

[0003] In the presence of strong base substances (such as sodium metal, potassium metal, sodium alkoxide, sodium amide, etc.), the acylation process route using γ-butyrolactone and acetate as raw materials was initially reported by F. Korte et al. (Angewandte Chemie, 71, 1959, 23, 709-752). Most of the subsequent processes are improvements based on this.

[0004] CN110804031B discloses a method for synthesizing α-acetyl-γ-butyrolactone, which includes the following steps: After the first reaction kettle is replaced with an inert gas, in an inert gas atmosphere, sodium metal is added and heated to the melting point of sodium metal to obtain liquid sodium metal in a molten state; in the second reaction kettle, γ-butyrolactone and acetate are added, and after heating to the reflux of the system, liquid sodium metal in a molten state is dropped into the system for a condensation reaction. After the dropping of the liquid sodium metal is completed, the system is kept refluxing for 1-16 h; after the condensation reaction is completed, it is neutralized with an acid solution, phase-separated, and the organic phase is obtained by distillation and vacuum rectification to obtain α-acetyl-γ-butyrolactone. By controlling the dropping rate of the liquid sodium metal, the process of the condensation reaction is controlled, avoiding the unsafe hidden danger of too violent condensation reaction and easy material flushing in the traditional method, and at the same time reducing the condensation reaction time.

[0005] CN115417838A discloses a method for preparing α-acetyl-γ-butyrolactone, which includes: (1) in the presence of sodium alkoxide, subjecting γ-butyrolactone and acetate to an acylation reaction, and during the acylation reaction, simultaneously performing azeotropic distillation on part of the acetate and the generated alcohol; (2) after the acylation reaction is completed, subjecting the obtained product to vacuum distillation to remove the acetate and the generated alcohol in the product, obtaining a dry material containing sodium salt of α-acetyl-γ-butyrolactone; (3) dispersing the dry material with an organic solvent and water; adding dilute sulfuric acid to the obtained dispersion for a neutralization reaction; allowing the obtained emulsion to stand for liquid separation, concentrating the obtained aqueous phase to obtain by-product sodium sulfate, and recovering the solvent from the obtained organic phase and obtaining a crude product of α-acetyl-γ-butyrolactone, wherein the organic solvent is a non-polar solvent or a benzene homolog; (4) subjecting the crude product of α-acetyl-γ-butyrolactone to vacuum rectification to obtain α-acetyl-γ-butyrolactone.

[0006] The above two patents respectively use liquid sodium and pure sodium as catalysts, improving the safety of the acylation reaction process and making the acylation reaction milder. However, the recovery rate of α-acetyl-γ-butyrolactone is not high, the reaction time is long, and the production efficiency is low. Moreover, in the current synthesis reaction of α-acetyl-γ-butyrolactone, the types of catalysts are too few, and only a few such as metallic sodium and sodium alkoxide can be used for industrial production. Therefore, more high-performance catalysts should be developed to promote the development of the synthesis process of α-acetyl-γ-butyrolactone. Summary of the Invention

[0007] Aiming at the defects existing in the prior art, the present invention provides a synthesis method of α-acetyl-γ-butyrolactone, which has a higher acylation rate and a higher yield of α-acetyl-γ-butyrolactone.

[0008] A synthesis method of α-acetyl-γ-butyrolactone includes the following steps:

[0009] (1) Acylation reaction: In the presence of a catalyst, subjecting γ-butyrolactone and acetate to an acylation reaction to obtain crude sodium salt of α-acetyl-γ-butyrolactone, and during the acylation reaction, distilling and recovering the acetate and the generated alcohol;

[0010] (2) Solvent recovery: Subjecting the crude sodium salt of α-acetyl-γ-butyrolactone obtained in step (1) to vacuum distillation to remove the acetate and the generated alcohol, obtaining sodium salt of α-acetyl-γ-butyrolactone;

[0011] (3) Neutralization reaction: Disperse the sodium salt of α-acetyl-γ-butyrolactone obtained in step (2) with an organic solvent, perform a neutralization reaction with dilute sulfuric acid, stand for liquid separation, recover the organic solvent and obtain a crude product of α-acetyl-γ-butyrolactone;

[0012] (4) Separation: The crude product of α-acetyl-γ-butyrolactone is subjected to vacuum distillation to obtain α-acetyl-γ-butyrolactone.

[0013] The molar ratio of γ-butyrolactone, acetate and sodium alkoxide in step (1) is 1:(2 - 15):(1 - 2), preferably 1:(3 - 12):(1 - 1.5).

[0014] The catalyst is at least two of imidazoline, 1-ethyl-3-methylimidazolium acetate, and sodium ethoxide, preferably a mixture of sodium ethoxide and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:(0.1 - 1).

[0015] The acetate is one of methyl acetate and ethyl acetate, preferably methyl acetate.

[0016] The temperature of the acylation reaction is 80 - 100°C, preferably 85 - 90°C;

[0017] The pressure of the acylation reaction is 0.09 - 0.1 MPa;

[0018] The time of the acylation reaction is 1 - 15 h, preferably 8 - 10 h.

[0019] The organic solvent in step (3) is at least one of toluene, carbon tetrachloride, hexane, cyclohexane, and petroleum ether; preferably toluene.

[0020] The concentration of dilute sulfuric acid in step (3) is 10 - 80 wt%, preferably 30 - 60 wt%; the molar ratio of γ-butyrolactone to sulfuric acid is (0.5 - 1):1.

[0021] The temperature of the neutralization reaction in step (3) is 15 - 40°C, preferably 15 - 30°C; the time of the neutralization reaction is 0.1 - 5 h, preferably 0.5 - 3 h.

[0022] The temperature of the vacuum distillation in step (4) is 90 - 150°C, and the vacuum degree is 1 - 5 KPa.

[0023] The present invention discovers that using a mixture of sodium ethoxide and 1-ethyl-3-methylimidazolium acetate as a catalyst, or using a mixture of sodium ethoxide and imidazoline as a catalyst, has the effect of promoting the forward progress of the acylation reaction between γ-butyrolactone and acetate, and can improve the yield of the product α-acetyl-γ-butyrolactone.

[0024] In the step of synthesizing α-acetyl-γ-butyrolactone, the role of sodium alcoholate is to participate in the acylation reaction as a catalyst. Specifically, sodium alcoholate is an alkaline reagent formed by the reaction of an alcohol and sodium. In the acylation reaction, the role of sodium alcoholate is to promote the acylation reaction between γ-butyrolactone and acetate, so that the acetate group in the acetate reacts with the hydroxyl group in γ-butyrolactone to form the target product α-acetyl-γ-butyrolactone. The alkalinity of sodium alcoholate can neutralize the acidic carboxylic acid group and promote the progress of the esterification reaction. In this process, sodium alcoholate acts as a catalyst, accelerating the esterification reaction and increasing the reaction rate and yield.

[0025] And 1-ethyl-3-methylimidazolium acetate of the nitrogen-containing basic ionic liquid also has the effect of catalyzing the reaction. However, it can be seen from the test examples that when 1-ethyl-3-methylimidazolium acetate is used alone as a catalyst, its catalytic rate for the acylation reaction between γ-butyrolactone and acetate is not high, and the performance of pure 1-ethyl-3-methylimidazolium acetate is much lower than that of sodium ethoxide. However, when sodium ethoxide and 1-ethyl-3-methylimidazolium acetate are mixed as a catalyst in a suitable ratio, it has a more positive promoting effect on the acylation reaction between γ-butyrolactone and acetate. The present invention believes that this is because the imidazole group in it has a positive promoting effect on the catalytic ability of sodium ethoxide.

[0026] In addition, the positive promoting effect of 1-ethyl-3-methylimidazolium acetate on the acylation reaction between γ-butyrolactone and acetate is stronger than that of sodium imidazole. Although in 1-ethyl-3-methylimidazolium acetate, the imidazole group is ligated by the acetate anion of the conjugate acid, so its alkalinity is relatively weak. The alkalinity of the imidazole group in this compound depends on the influence of the acetate anion and is usually relatively weak. In sodium imidazole, when the imidazole group forms a salt with sodium, it loses a proton to form the basic part of imidazole. In sodium imidazole, the imidazole group exists as a free imidazole ion, and its alkalinity may be stronger than that of the imidazole group in 1-ethyl-3-methylimidazolium acetate. However, 1-ethyl-3-methylimidazolium acetate contains an acetate structure, which has a positive promoting effect on the acylation reaction between γ-butyrolactone and acetate. Therefore, the combination of 1-ethyl-3-methylimidazolium acetate and sodium ethoxide is more conducive to the positive progress of the reaction and increases the yield of α-acetyl-γ-butyrolactone.

[0027] Advantages of the present invention

[0028] The present invention uses sodium ethoxide and 1-ethyl-3-methylimidazol acetate / sodium imidazole as a catalyst to promote the positive acylation reaction between gamma-butyrolactone and acetate, thereby increasing the yield of the product alpha-acetyl-gamma-butyrolactone. The invention develops a catalyst type in the process of synthesizing alpha-acetyl-gamma-butyrolactone, and promotes the development of the synthesis process of alpha-acetyl-gamma-butyrolactone. DETAILED DESCRIPTION

[0029] The raw materials, acids, bases, solvents, etc. used in the following examples and comparative examples were all purchased commercially.

[0030] The purity of α-acetyl-γ-butyrolactone was measured by gas chromatography.

[0031] The yield of α-acetyl-γ-butyrolactone (%) is calculated as follows: actual yield / theoretical yield×100%.

[0032] Example 1

[0033] A method for synthesizing α-acetyl-γ-butyrolactone comprises the following steps:

[0034] (1) Acylation reaction: replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the temperature in the reaction tank to 45° C., add 6 kg of γ-butyrolactone and 6.6 kg of sodium ethoxide in batches, then slowly raise the temperature of the reaction system to 90° C. and reflux for 9 h, maintain the pressure in the tank at 0.1 MPa, and stop heating when the raw material α-acetyl-γ-butyrolactone is less than 2% by gas chromatography detection to obtain crude α-acetyl-γ-butyrolactone sodium salt;

[0035] (2) Solvent recovery: The crude α-acetyl-γ-butyrolactone sodium salt obtained in step (1) is subjected to reduced pressure distillation at 50° C. and a constant pressure of 0.1 MPa to remove acetate and generated alcohol to obtain α-acetyl-γ-butyrolactone sodium salt;

[0036] (3) Neutralization reaction: the sodium salt of α-acetyl-γ-butyrolactone obtained in step (2) is dispersed in 10 kg of toluene and 10 kg of water, cooled to 25° C., a 50% sulfuric acid solution is added dropwise, the pH is adjusted to 3, and the mixture is stirred for 1 hour for neutralization reaction. The mixture is allowed to stand for separation, and the organic solvent is recovered to obtain a crude product of α-acetyl-γ-butyrolactone;

[0037] (4) Separation: The crude α-acetyl-γ-butyrolactone obtained in step (3) is subjected to vacuum distillation to obtain α-acetyl-γ-butyrolactone, wherein the vacuum distillation temperature is 130° C. and the vacuum degree is 2 KPa.

[0038] Example 2

[0039] A method for synthesizing α-acetyl-γ-butyrolactone comprises the following steps:

[0040] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 6.1 kg of sodium imidazolate in batches, then slowly raise the temperature of the reaction system to 90 °C and reflux for 9 h, keep the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude sodium α-acetyl-γ-butyrolactone;

[0041] (2) Solvent recovery: Subject the crude sodium α-acetyl-γ-butyrolactone obtained in step (1) to vacuum distillation at 50 °C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, and obtain sodium α-acetyl-γ-butyrolactone;

[0042] (3) Neutralization reaction: Disperse the sodium α-acetyl-γ-butyrolactone obtained in step (2) with 10 kg of toluene and 10 kg of water, cool down to 25 °C, dropwise add 50% sulfuric acid solution, adjust the pH to 3, stir for 1 h for the neutralization reaction, let it stand for liquid separation, recover the organic solvent and obtain crude α-acetyl-γ-butyrolactone;

[0043] (4) Separation: Subject the crude α-acetyl-γ-butyrolactone obtained in step (3) to vacuum rectification to obtain α-acetyl-γ-butyrolactone, and the temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0044] Example 3

[0045] A method for synthesizing α-acetyl-γ-butyrolactone, comprising the following steps:

[0046] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 11.6 kg of 1-ethyl-3-methylimidazolium acetate in batches, then slowly raise the temperature of the reaction system to 90 °C and reflux for 9 h, keep the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude sodium α-acetyl-γ-butyrolactone;

[0047] (2) Solvent recovery: Subject the crude sodium α-acetyl-γ-butyrolactone obtained in step (1) to vacuum distillation at 50 °C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, and obtain sodium α-acetyl-γ-butyrolactone;

[0048] (3) Neutralization reaction: Disperse the sodium α-acetyl-γ-butyrolactone obtained in step (2) with 10 kg of toluene and 10 kg of water, cool down to 25 °C, dropwise add 50% sulfuric acid solution, adjust the pH to 3, stir for 1 h for the neutralization reaction, let it stand for liquid separation, recover the organic solvent and obtain crude α-acetyl-γ-butyrolactone;

[0049] (4) Separation: The crude α-acetyl-γ-butyrolactone obtained in step (3) is subjected to vacuum rectification to obtain α-acetyl-γ-butyrolactone. The temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0050] Example 4

[0051] A method for synthesizing α-acetyl-γ-butyrolactone, comprising the following steps:

[0052] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 7.0 kg of catalyst in batches, then slowly raise the temperature of the reaction system to 90 °C and reflux for 9 h, keep the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude α-acetyl-γ-butyrolactone sodium salt;

[0053] (2) Solvent recovery: The crude α-acetyl-γ-butyrolactone sodium salt obtained in step (1) is subjected to vacuum distillation at 50 °C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, and obtain α-acetyl-γ-butyrolactone sodium salt;

[0054] (3) Neutralization reaction: Disperse the α-acetyl-γ-butyrolactone sodium salt obtained in step (2) with 10 kg of toluene and 10 kg of water, cool down to 25 °C, dropwise add 50% sulfuric acid solution, adjust the pH to 3, stir for 1 h for the neutralization reaction, stand for liquid separation, recover the organic solvent and obtain the crude α-acetyl-γ-butyrolactone;

[0055] (4) Separation: The crude α-acetyl-γ-butyrolactone obtained in step (3) is subjected to vacuum rectification to obtain α-acetyl-γ-butyrolactone. The temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0056] The catalyst is a mixture of sodium ethoxide and sodium imidazole in a molar ratio of 1:0.4.

[0057] Example 5

[0058] A method for synthesizing α-acetyl-γ-butyrolactone, comprising the following steps:

[0059] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 9.5 kg of catalyst in batches, then slowly raise the temperature of the reaction system to 90 °C and reflux for 9 h, keep the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude α-acetyl-γ-butyrolactone sodium salt;

[0060] (2) Solvent recovery: The crude sodium α-acetyl-γ-butyrolactone obtained in step (1) is subjected to vacuum distillation at 50 °C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, obtaining sodium α-acetyl-γ-butyrolactone;

[0061] (3) Neutralization reaction: The sodium α-acetyl-γ-butyrolactone obtained in step (2) is dispersed with 10 kg of toluene and 10 kg of water, cooled to 25 °C, and a 50% sulfuric acid solution is added dropwise to adjust the pH to 3. Stir for 1 h for the neutralization reaction, then let it stand for liquid separation, recover the organic solvent and obtain the crude α-acetyl-γ-butyrolactone;

[0062] (4) Separation: The crude α-acetyl-γ-butyrolactone obtained in step (3) is subjected to vacuum rectification to obtain α-acetyl-γ-butyrolactone. The temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0063] The catalyst is a mixture of sodium ethoxide and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:0.4.

[0064] Example 6

[0065] A method for synthesizing α-acetyl-γ-butyrolactone, comprising the following steps:

[0066] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 11.0 kg of catalyst in batches, and then slowly raise the reaction system temperature to 90 °C for reflux reaction for 9 h, keeping the pressure in the tank at 0.1 MPa. When the raw material butyrolactone detected by gas chromatography is less than 2%, stop heating to obtain the crude sodium α-acetyl-γ-butyrolactone;

[0067] (2) Solvent recovery: The crude sodium α-acetyl-γ-butyrolactone obtained in step (1) is subjected to vacuum distillation at 50 °C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, obtaining sodium α-acetyl-γ-butyrolactone;

[0068] (3) Neutralization reaction: The sodium α-acetyl-γ-butyrolactone obtained in step (2) is dispersed with 10 kg of toluene and 10 kg of water, cooled to 25 °C, and a 50% sulfuric acid solution is added dropwise to adjust the pH to 3. Stir for 1 h for the neutralization reaction, then let it stand for liquid separation, recover the organic solvent and obtain the crude α-acetyl-γ-butyrolactone;

[0069] (4) Separation: The crude α-acetyl-γ-butyrolactone obtained in step (3) is subjected to vacuum rectification to obtain α-acetyl-γ-butyrolactone. The temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0070] The catalyst is a mixture of imidazolium and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:0.4.

[0071] Comparative Example 1

[0072] A method for synthesizing α-acetyl-γ-butyrolactone includes the following steps:

[0073] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45°C, add 6 kg of γ-butyrolactone and 5.3 kg of sodium methoxide in batches, then slowly raise the temperature of the reaction system to 90°C and reflux for 9 h, maintain the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude α-acetyl-γ-butyrolactone sodium salt;

[0074] (2) Solvent recovery: Subject the crude α-acetyl-γ-butyrolactone sodium salt obtained in step (1) to vacuum distillation at 50°C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, and obtain α-acetyl-γ-butyrolactone sodium salt;

[0075] (3) Neutralization reaction: Disperse the α-acetyl-γ-butyrolactone sodium salt obtained in step (2) with 10 kg of toluene and 10 kg of water, cool down to 25°C, dropwise add 50% sulfuric acid solution, adjust the pH to 3, stir for 1 h for the neutralization reaction, let it stand for liquid separation, recover the organic solvent and obtain crude α-acetyl-γ-butyrolactone;

[0076] (4) Separation: Subject the crude α-acetyl-γ-butyrolactone obtained in step (3) to vacuum rectification to obtain α-acetyl-γ-butyrolactone, and the temperature of the vacuum rectification is 130°C and the vacuum degree is 2 KPa.

[0077] Comparative Example 2

[0078] A method for synthesizing α-acetyl-γ-butyrolactone includes the following steps:

[0079] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45°C, add 6 kg of γ-butyrolactone and 8.5 kg of catalyst in batches, then slowly raise the temperature of the reaction system to 90°C and reflux for 9 h, maintain the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude α-acetyl-γ-butyrolactone sodium salt;

[0080] (2) Solvent recovery: Subject the crude α-acetyl-γ-butyrolactone sodium salt obtained in step (1) to vacuum distillation at 50°C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, and obtain α-acetyl-γ-butyrolactone sodium salt;

[0081] (3) Neutralization reaction: Disperse the sodium salt of α-acetyl-γ-butyrolactone obtained in step (2) with 10 kg of toluene and 10 kg of water, cool down to 25 °C, add dropwise 50% sulfuric acid solution, adjust the pH to 3, stir for 1 h for the neutralization reaction, let it stand for liquid separation, recover the organic solvent and obtain the crude product of α-acetyl-γ-butyrolactone;

[0082] (4) Separation: Subject the crude product of α-acetyl-γ-butyrolactone obtained in step (3) to vacuum rectification to obtain α-acetyl-γ-butyrolactone. The temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0083] The catalyst is a mixture of sodium methoxide and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:0.4.

[0084] Comparative Example 3

[0085] A method for synthesizing α-acetyl-γ-butyrolactone, comprising the following steps:

[0086] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 6.8 kg of catalyst in batches, then slowly raise the reaction system temperature to 90 °C for reflux reaction for 9 h, keep the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain the crude sodium salt of α-acetyl-γ-butyrolactone;

[0087] (2) Solvent recovery: Subject the crude sodium salt of α-acetyl-γ-butyrolactone obtained in step (1) to vacuum distillation at 50 °C, keep the pressure constant at 0.1 MPa, remove the acetate and the generated alcohol to obtain the sodium salt of α-acetyl-γ-butyrolactone;

[0088] (3) Neutralization reaction: Disperse the sodium salt of α-acetyl-γ-butyrolactone obtained in step (2) with 10 kg of toluene and 10 kg of water, cool down to 25 °C, add dropwise 50% sulfuric acid solution, adjust the pH to 3, stir for 1 h for the neutralization reaction, let it stand for liquid separation, recover the organic solvent and obtain the crude product of α-acetyl-γ-butyrolactone;

[0089] (4) Separation: Subject the crude product of α-acetyl-γ-butyrolactone obtained in step (3) to vacuum rectification to obtain α-acetyl-γ-butyrolactone. The temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0090] The catalyst is a mixture of sodium ethoxide and imidazole sodium in a molar ratio of 1:0.1.

[0091] Comparative Example 4

[0092] A method for synthesizing α-acetyl-γ-butyrolactone, comprising the following steps:

[0093] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 7.5 kg of catalyst in batches, then slowly raise the temperature of the reaction system to 90 °C and reflux for 9 h, keep the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude sodium α-acetyl-γ-butyrolactonate;

[0094] (2) Solvent recovery: Subject the crude sodium α-acetyl-γ-butyrolactonate obtained in step (1) to vacuum distillation at 50 °C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, and obtain sodium α-acetyl-γ-butyrolactonate;

[0095] (3) Neutralization reaction: Disperse the sodium α-acetyl-γ-butyrolactonate obtained in step (2) with 10 kg of toluene and 10 kg of water, cool down to 25 °C, dropwise add 50% sulfuric acid solution, adjust the pH to 3, stir for 1 h for the neutralization reaction, let it stand for liquid separation, recover the organic solvent and obtain crude α-acetyl-γ-butyrolactone;

[0096] (4) Separation: Subject the crude α-acetyl-γ-butyrolactone obtained in step (3) to vacuum rectification to obtain α-acetyl-γ-butyrolactone, and the temperature of the vacuum rectification is 130 °C and the vacuum degree is 2 KPa.

[0097] The catalyst is a mixture of sodium ethoxide and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:0.1.

[0098] Comparative Example 5

[0099] A method for synthesizing α-acetyl-γ-butyrolactone, comprising the following steps:

[0100] (1) Acylation reaction: Replace the reaction tank with nitrogen, add 41.2 kg of methyl acetate, raise the internal temperature of the reaction tank to 45 °C, add 6 kg of γ-butyrolactone and 6.3 kg of catalyst in batches, then slowly raise the temperature of the reaction system to 90 °C and reflux for 9 h, keep the pressure in the tank at 0.1 MPa, detect by gas chromatography that the raw material butyrolactone is less than 2%, stop heating, and obtain crude sodium α-acetyl-γ-butyrolactonate;

[0101] (2) Solvent recovery: Subject the crude sodium α-acetyl-γ-butyrolactonate obtained in step (1) to vacuum distillation at 50 °C under a constant pressure of 0.1 MPa to remove the acetate and the generated alcohol, and obtain sodium α-acetyl-γ-butyrolactonate;

[0102] (3) Neutralization reaction: Dispersed the sodium salt of α-acetyl-γ-butyrolactone obtained in step (2) with 10 kg of toluene and 10 kg of water, cooled to 25 °C, added dropwise 50% sulfuric acid solution, adjusted the pH to 3, stirred for 1 h for the neutralization reaction, allowed to stand for liquid separation, recovered the organic solvent and obtained the crude product of α-acetyl-γ-butyrolactone;

[0103] (4) Separation: The crude product of α-acetyl-γ-butyrolactone obtained in step (3) was subjected to vacuum rectification to obtain α-acetyl-γ-butyrolactone. The temperature of the vacuum rectification was 130 °C and the vacuum degree was 2 KPa.

[0104] The catalyst is a mixture of sodium methoxide and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:0.1.

[0105] Test Example 1

[0106] The yield and purity results of α-acetyl-γ-butyrolactone prepared in the examples and comparative examples are shown in Table 1.

[0107] Table 1:

[0108]

[0109]

[0110] As can be seen from Table 1, Example 5 has the highest yield. The catalyst used in it is a mixture of sodium ethoxide and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:0.4, and its effect has a higher yield than that of Example 1 using only sodium ethoxide as the catalyst. It can be seen that the mixture of sodium ethoxide and 1-ethyl-3-methylimidazolium acetate in a molar ratio of 1:0.4 can promote the forward progress of the acylation reaction.

[0111] In the step of synthesizing α-acetyl-γ-butyrolactone, the role of sodium alcoholate is to participate in the acylation reaction as a catalyst. Specifically, sodium alcoholate is a basic reagent formed by the reaction of an alcohol and sodium. In the acylation reaction, the role of sodium alcoholate is to promote the acylation reaction between γ-butyrolactone and acetate, so that the acetate group in the acetate reacts with the hydroxyl group in γ-butyrolactone to form the target product α-acetyl-γ-butyrolactone. The alkalinity of sodium alcoholate can neutralize the acidic carboxylic acid group and promote the progress of the esterification reaction. In this process, sodium alcoholate plays the role of a catalyst, accelerating the esterification reaction and improving the reaction rate and yield.

[0112] 1-Ethyl-3-methylimidazolium acetate of nitrogen-containing basic ionic liquid also has the function of catalyzing the reaction. However, it can be seen from Example 3 that when 1-ethyl-3-methylimidazolium acetate is used alone as the catalyst, the catalytic rate for the acylation reaction between γ-butyrolactone and acetate is not high. By comparing Example 1 and Example 3, it can be seen that in this reaction, the performance of 1-ethyl-3-methylimidazolium acetate alone is much lower than that of sodium ethoxide. However, when sodium ethoxide and 1-ethyl-3-methylimidazolium acetate are mixed as the catalyst in a suitable ratio, it plays a more positive promoting role in the acylation reaction between γ-butyrolactone and acetate. The present invention believes that this is because the imidazole group therein has a positive promoting effect on the catalytic ability of sodium ethoxide.

[0113] From Example 2 using sodium imidazole alone as the catalyst and Example 4 using sodium ethoxide and sodium imidazole mixed in a molar ratio of 1:0.4 as the catalyst, it can be seen that the yield of Example 4 is significantly higher than that of Example 2 and slightly higher than that of Example 1 using sodium ethoxide alone as the catalyst. This indicates that the imidazole ions in 1-ethyl-3-methylimidazolium acetate and sodium imidazole play a promoting role.

[0114] From the comparison between Example 2 and Example 3 and the comparison between Example 4 and Example 5, it can be seen that the positive promoting effect of 1-ethyl-3-methylimidazolium acetate on the acylation reaction between γ-butyrolactone and acetate is stronger than that of sodium imidazole. Although in 1-ethyl-3-methylimidazolium acetate, the imidazole group is ligated by the acetate anion of the conjugate acid, so its basicity is relatively weak. The basicity of the imidazole group in this compound depends on the influence of the acetate anion and is usually relatively weak. In sodium imidazole, when the imidazole group forms a salt with sodium, it loses a proton to form the basic part of imidazole. In sodium imidazole, the imidazole group exists as a free imidazole ion, and its basicity may be stronger than that of the imidazole group in 1-ethyl-3-methylimidazolium acetate. However, 1-ethyl-3-methylimidazolium acetate contains an acetate structure, which has a positive promoting effect on the acylation reaction between γ-butyrolactone and acetate. Therefore, the combination of 1-ethyl-3-methylimidazolium acetate and sodium ethoxide is more conducive to the forward progress of the reaction and increases the yield of α-acetyl-γ-butyrolactone.

[0115] In the present invention, further, sodium methoxide was used as the catalyst in Comparative Example 1, and sodium methoxide and 1-ethyl-3-methylimidazolium acetate were mixed at a molar ratio of 1:0.4 in Comparative Example 2 to continue to verify the promoting effect of 1-ethyl-3-methylimidazolium acetate on the acylation reaction between γ-butyrolactone and acetate. As can be seen from Table 1, the catalytic performance of pure sodium ethoxide is lower than that of pure sodium methoxide. After adding 1-ethyl-3-methylimidazolium acetate, the yield is increased compared with pure sodium methoxide and sodium ethoxide. This also proves that 1-ethyl-3-methylimidazolium acetate has a positive promoting effect on the above reaction. However, the yield of adding 1-ethyl-3-methylimidazolium acetate to sodium methoxide is lower than that of adding 1-ethyl-3-methylimidazolium acetate to sodium ethoxide, indicating that the positive promoting effect of 1-ethyl-3-methylimidazolium acetate on sodium ethoxide is more obvious.

[0116] The molar number of the catalyst added in each example and comparative example is the same.

Claims

1. A method for synthesizing α-acetyl-γ-butyrolactone, characterized in that: The following steps are involved: (1) Acylation reaction; (2) Solvent recovery; (3) Neutralization reaction; (4) separating to obtain α-acetyl-γ-butyrolactone; The catalyst used in the acylation reaction step is at least two of sodium imidazolate, 1-ethyl-3-methylimidazolyl acetate and sodium ethoxide.

2. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 1, characterized in that: The following steps are involved: (1) Acylation reaction: in the presence of a catalyst, γ-butyrolactone and acetate are subjected to an acylation reaction to obtain crude α-acetyl-γ-butyrolactone sodium salt, and the acetate and the generated alcohol are distilled and recovered during the acylation reaction; (2) solvent recovery: subjecting the crude α-acetyl-γ-butyrolactone sodium salt obtained in step (1) to reduced pressure distillation to remove acetate and generated alcohol to obtain α-acetyl-γ-butyrolactone sodium salt; (3) Neutralization reaction: dispersing the α-acetyl-γ-butyrolactone sodium salt obtained in step (2) with an organic solvent, neutralizing it with dilute sulfuric acid, allowing the solution to stand for separation, recovering the organic solvent and obtaining a crude α-acetyl-γ-butyrolactone product; (4) Separation: The crude α-acetyl-γ-butyrolactone is subjected to vacuum distillation to obtain α-acetyl-γ-butyrolactone. The catalyst is sodium ethoxide, 1-ethyl-3-methylimidazol acetate or sodium imidazole mixed in a molar ratio of 1: (0.1-1).

3. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 2, characterized in that: The molar ratio of the γ-butyrolactone, acetate and sodium alcoholate in step (1) is 1:(2-15):(1-2).

4. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 2, characterized in that: The acetate is one of methyl acetate and ethyl acetate.

5. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 2, characterized in that: The temperature of the acylation reaction is 80-100°C, preferably 85-90°C; The pressure of the acylation reaction is 0.09-0.1 MPa; The acylation reaction time is 1-15 h, preferably 8-10 h.

6. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 2, characterized in that: The organic solvent in step (3) is at least one of toluene, carbon tetrachloride, hexane, cyclohexane and petroleum ether; preferably toluene.

7. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 2, characterized in that: Step (3) The concentration of dilute sulfuric acid is 10-80wt%; the molar ratio of γ-butyrolactone to sulfuric acid is: (0.5-1):

1.

8. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 2, characterized in that: The temperature of the neutralization reaction in step (3) is 15-40° C.; the time of the neutralization reaction is 0.1-5 h.

9. The method for synthesizing α-acetyl-γ-butyrolactone according to claim 2, characterized in that: The temperature of the vacuum distillation in step (4) is 90-150° C., and the vacuum degree is 1-5 KPa.

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