CN105152949A - Amino-acid ester derivative cation type chiral ionic liquid and preparation method thereof - Google Patents

Abstract

A novel amino acid ester derivative cationic chiral ionic liquid and a preparation method thereof. The general formula of the amino acid ester derivative cationic chiral ionic liquid is A ⁺ X ^- , wherein A ⁺ is an amino acid ester cationic derivative, and X ^- is BF ₄ ^- , PF ₆ ^- , HSO ₄ ^- . The preparation method is: react amino acid with methanol and thionyl chloride at low temperature to obtain amino acid ester hydrochloride; react amino acid ester hydrochloride with paraformaldehyde and acetone through Mannich reaction to obtain amino acid ester derivative Mannich base Amino acid ester derivative Mannich base reacts with brominated hydrocarbon to obtain bromide salt chiral ionic liquid of amino acid ester derivative; amino acid ester derivative is obtained by exchanging the bromide ion of amino acid ester derivative bromide salt chiral ionic liquid Cationic chiral ionic liquid. The invention has many advantages such as high selectivity of chiral substances, non-volatile, non-toxic, non-polluting ionic liquid, and is suitable for large-scale production in the fine chemical industry.

Description

Amino acid ester derivative cationic chiral ionic liquid and preparation method thereof

technical field

The invention relates to an amino acid derivative cationic ionic liquid and a preparation method thereof, in particular to a cationic amino acid ester derivative cationic chiral ionic liquid and a preparation method thereof, belonging to the technical field of chemical materials and their preparation.

Background technique

Ionic liquids are salts composed of organic cations and organic or inorganic anions that are liquid at or near room temperature. Ionic liquids have excellent physical and chemical properties such as low vapor pressure, good electrical conductivity, strong polarity, wide electrochemical window, high thermal stability, and good solubility and catalytic properties for certain substances. As well as the anion-cation structure that can be modified/tuned, and can be recycled, it is considered to be a new type of green solvent that can replace commonly used volatile organic solvents, and has been widely used in the field of chemical engineering.

With the continuous development of ionic liquid design and synthesis technology, some scholars have begun to study the design and introduction of chiral centers in ionic liquids in recent years, so as to expand the research field and application range of ionic liquids. Chiral ionic liquids combine the advantages and characteristics of ionic liquids and chiral substances, and can be used in chiral recognition, asymmetric synthesis, enantiomer resolution, stereoselective polymerization, gas chromatography, NMR shift reagents, and liquid crystals.

Therefore, the development of chiral ionic liquids and the introduction of green media in the field of chiral synthesis have important practical significance. At present, there have been many reports on the synthesis and application of chiral ionic liquids. For example, a series of chiral ionic liquids have been synthesized using α-pinene, menthol, ephedrine, etc. as chiral sources.

Amino acid is a kind of natural chiral source, and the raw materials for synthesizing chiral ionic liquid with natural amino acid as chiral source are easy to get, which greatly reduces the cost of synthesizing chiral ionic liquid. In recent years, reports on the synthesis of ionic liquids using amino acids as chiral sources have gradually increased. For example, Chinese patents CN1383920A, CN104693056A and CN1383921A respectively describe a kind of L-amino acid sulfate type chiral ionic liquid and its preparation method and L-amino acid sulfate Type chiral ionic liquid and the technical scheme of preparation method thereof, CN1621152A has described amino acid ester cationic ionic liquid and preparation method thereof, these disclosed technical schemes have enriched the kind of amino acid ionic liquid, have provided beneficial exploration for the application of ionic liquid, but above-mentioned The preparation method of the amino acid ionic liquid described in the patent application is rough, and the structure of the amino acid cation is simple (there is either a carboxyl group or an amino group), which limits its scope of use. Therefore, it is necessary to explore and invent amino acid cationic chiral ionic liquids with complex structures to expand their application fields.

Contents of the invention

The purpose of the present invention is to solve the problems in the prior art. One is to provide a chiral amino acid ester bromide salt type chiral ionic liquid having both chiral characteristics and ionic liquid characteristics. The chiral site of the ionic liquid Regarding amino acid cations, the second is to provide a method for preparing an amino acid ester derivative cationic chiral ionic liquid.

Realize above-mentioned invention object and adopt following technical scheme:

A kind of amino acid ester derivative cationic chiral ionic liquid, its structural formula is as follows:

, the amino acid is D-, L-alanine.

Preferably, in the amino acid cation, R ^' is CH ₃ or CH ₃ CH ₂ ; and X ^- is any one of BF ₄ ^- , PF ₆ ^- , HSO ₄ ^- .

Preferably, the general formula of the amino acid ester derivative cationic chiral ionic liquid is A ⁺ X ^- , wherein A ⁺ is an amino acid ester cationic derivative, and X ^- is BF ₄ ^- , PF ₆ ^- , HSO ₄ ^- .

A preparation method of amino acid ester derivative cationic chiral ionic liquid, the reaction substances used in the preparation process include: α-amino acid, thionyl chloride, paraformaldehyde, bromoethane, NaBF ₄ , KPF ₆ , NaHSO ₄ , and an alcoholic solvent; the preparation steps are as follows:

(1) Slowly add thionyl chloride dropwise to methanol at a low temperature environment of -14°C to -10°C, continue to react for 1 hour after the drop is complete, raise the temperature to room temperature, add amino acids in batches, keep stirring at 50°C for 4 After hours, the solvent was removed by rotary evaporation to obtain the hydrochloride of amino acid ester, which was a viscous liquid;

(2) Mannich reaction: add paraformaldehyde to methanol, adjust the pH to 5 with dilute hydrochloric acid, heat until the paraformaldehyde dissolves, then cool down to room temperature and add the product of step (1) amino acid ester hydrochloride and acetone , heated to reflux for 48 hours, and the solvent was removed by rotary evaporation, and the crude product was purified by column chromatography to obtain the amino acid ester derivative Mannich base;

(3) Quaternization reaction: Dissolve the amino acid ester derivative Mannich base in step (2) with an alcohol solvent, then add ethyl bromide, adjust the pH to 8-9 with NaOH solution, and heat to reflux for 2-3 hours , remove part of the solvent, remove NaBr by filtration, and then remove the solvent to obtain the chiral ionic liquid of amino acid ester derivative bromide salt;

(4) Exchange anions: mix the amino acid ester derivative bromide salt ionic liquid obtained in step (3) with any one of NaBF ₄ , KPF ₆ , and NaHSO ₄ in a round-bottomed flask according to the ratio, add a solvent to react, and react After the end, amino acid ester derivative cationic chiral ionic liquid product is obtained.

Preferably, the molar ratio of amino acid, thionyl chloride and methanol is 1:1:20-30.

Preferably, the molar ratio of paraformaldehyde, acetone, and alanine ester derivative hydrochloride is 2-3:2-3:1;

Preferably, the ratio of the amount of bromoethane to the amino acid ester derivative Mannich base is 1-2:1;

Preferably, the substance ratio of the amino acid ester derivative bromide salt ionic liquid to the added amount of any one of NaBF ₄ , KPF ₆ , and NaHSO ₄ is 1:1-1.5.

Preferably, in the Mannich reaction, the crude product is purified by column chromatography using a mixture of methanol and dichloromethane with a volume ratio of 1:20.

As preferably, the solvent of exchanging anion step is water or acetone, when water is used as solvent, after the reaction finishes, separate layers, discard last liquid, the lower floor liquid is vacuum-dried after washing with ether, obtains product; When using acetone as solvent When the reaction is over, the solid NaBr and unreacted raw materials are removed by suction filtration, and then the acetone solvent is distilled off under reduced pressure to obtain the product.

Using the above technical scheme, compared with the prior art, the general formula of the amino acid ester derivative chiral ionic liquid of the present invention is A ⁺ X ^- , wherein A ⁺ is the cation of the amino acid ester derivative, and X ^- is BF ₄ ^- , PF ₆ ^- any one of HSO ₄ ^- ; amino acid ester derivative hydrochloride is obtained by reacting amino acid with methanol and thionyl chloride at low temperature; amino acid ester derivative hydrochloride, paraformaldehyde and acetone are processed Mannich reaction to obtain tertiary amine (Mannich base of amino acid ester derivative); reaction of tertiary amine of amino acid ester with brominated hydrocarbon to obtain chiral ionic liquid of bromide salt of amino acid ester derivative; obtain target amino acid ester derivative by exchanging anions cationic ionic liquids. The source of raw materials is abundant, the price is low, and the operation is simple. The chiral amino acid ester derivative cationic ionic liquid prepared by the above steps is located on the cation of alanine, and the amino group is connected with a bulky group, and the stereoselectivity is stronger; the anion has a larger structural design. Degree of freedom, with structural diversity and designability. At the same time, the chiral amino acid ester derivative ionic liquid provided by the present invention has both the characteristics of ionic liquid and the characteristics of chiral substances, such as: wide liquid range, low vapor pressure, good conductivity, strong polarity, and can be used for chiral catalysis and chiral separation. It has the high selectivity and chiral induction effect of chiral substances, and also has the advantages of non-volatility, non-toxicity and pollution-free of ionic liquids. It is suitable for large-scale production in the fine chemical industry and expands new varieties of ionic liquids.

Detailed ways

The present invention is further illustrated below by means of examples, but the present invention is not limited to the scope of the examples.

Example 1

Amino acid ester derivative cationic chiral ionic liquid, its structural formula is as follows:

, the amino acid is D-, L-alanine

In the amino acid derivative cation, R ^' is CH ₃ or CH ₃ CH ₂ . Said X ^- is any one of BF ₄ ^- , PF ₆ ^- , HSO ₄ ^- .

The general formula of the amino acid ester derivative cationic chiral ionic liquid is A ⁺ X ^- , wherein A ⁺ is an amino acid ester cationic derivative, and X ^- is BF ₄ ^- , PF ₆ ^- , HSO ₄ ^- .

Example 2

Preparation method of amino acid ester derivative cationic chiral ionic liquid

(1) Slowly add thionyl chloride dropwise to methanol at a low temperature environment of -14°C to -10°C, continue to react for 1 hour after the drop is complete, raise the temperature to room temperature, add amino acids in batches, keep stirring at 50°C for 4 After hours, the solvent was removed by rotary evaporation to obtain the hydrochloride of amino acid ester, which was a viscous liquid;

(2) Mannich reaction: add paraformaldehyde to methanol, adjust the pH to 5 with dilute hydrochloric acid, heat until the paraformaldehyde dissolves, then cool down to room temperature and add the product of step (1) amino acid ester hydrochloride and acetone , heated to reflux for 48 hours, and the solvent was removed by rotary evaporation, and the crude product was purified by column chromatography (a mixture of methanol and dichloromethane with a volume ratio of 1:20 was used as the eluent) to obtain the amino acid ester derivative Mannich base;

(3) Quaternization reaction: Dissolve the amino acid ester derivative Mannich base in step (2) with an alcohol solvent, then add ethyl bromide, adjust the pH to 8-9 with NaOH solution, and heat to reflux for 2-3 hours , part of the solvent was removed, NaBr was removed by filtration, and then the solvent was removed to obtain the chiral ionic liquid of the bromide salt of the amino acid ester derivative.

(4) Exchange anions: mix the amino acid ester derivative bromide salt ionic liquid obtained in step (3) with any of NaBF ₄ , KPF ₆ , and NaHSO ₄ in a certain proportion in a round bottom flask, and add deionized water or acetone as a solvent, stirring at room temperature for 3 to 24 hours, when water is used as a solvent, after the reaction, separate layers, discard the last liquid, wash the lower liquid with ether and dry it in a vacuum to obtain the product; when using acetone as a solvent, After the reaction, the solid NaBr and unreacted raw materials were removed by suction filtration, and then the acetone solvent was distilled off under reduced pressure to obtain the product.

The substance ratio of the amino acid, thionyl chloride and methanol is 1:1:20-30.

The substance ratio of paraformaldehyde, acetone, and alanine ester derivative hydrochloride is 2-3:2-3:1;

The ratio of the amount of bromoethane to the amino acid ester derivative Mannich base is 1-2:1;

The substance ratio of the added amount of the amino acid ester derivative bromide salt ionic liquid to any one of NaBF ₄ , KPF ₆ , and NaHSO ₄ is 1:1-1.5.

In the Mannich reaction, the crude product was purified by column chromatography using a mixture of methanol and dichloromethane with a volume ratio of 1:20.

The solvent in the anion exchange step is deionized water or acetone. When deionized water is used as a solvent, after the reaction, the layers are separated and the last liquid is discarded. The lower liquid is washed with ether and dried in vacuum to obtain the product; When used as a solvent, after the reaction is over, remove the solid NaBr and unreacted raw materials by suction filtration, and then distill off the acetone solvent under reduced pressure to obtain the product.

Specific preparation method embodiment

Example 3

Preparation of Cationic Chiral Ionic Liquids of Alanine Methyl Ester Derivatives

(1) Synthesis of alanine methyl ester

Take 125mL of methanol and add it to a 250mL three-neck flask (the environment should be anhydrous during the reaction, with a drying device; the reaction will generate HCl and SO ₂ gas, and an alkali absorption device should be used), and cool it in a low-temperature constant temperature reaction bath. -14°C, slowly add 10mL (0.138mol) SOCl ₂ dropwise under magnetic stirring, control the reaction temperature below -10°C during the dropwise addition, and continue the reaction for 1h after the dropwise addition is completed. The reaction solution was transferred to a 250mL round-bottomed flask, the temperature was naturally raised to room temperature, 12.21g (0.137mol) of alanine was added, and the reaction was stopped after heating to reflux under magnetic stirring for 4 hours. The product was rotary evaporated, and after the solvent was evaporated, alanine methyl ester hydrochloride was obtained as a yellow viscous liquid with a yield of 98%, which could be directly used in the next step of synthesis without purification.

(2) Synthesis of alanine methyl ester derivative Mannich base

Take 10.43g (0.0747mol) of alanine methyl ester hydrochloride in a 250mL three-necked flask, dissolve it in 80mL of methanol, add 12.21g (0.21mol) of acetone, then add 6.25g (0.21mol) of paraformaldehyde, drop Add dilute hydrochloric acid to pH = 5, use nitrogen as a protective gas, and heat to reflux for 48 hours under magnetic stirring. After the reaction is complete, remove the insoluble matter by suction filtration, spin the filtrate to remove the solvent, and obtain a dark brown liquid.

The crude product was purified by column chromatography, and the eluent was a mixture of methanol and dichloromethane with a volume ratio of 1:20, and the yield was 86%.

(3) Synthesis of cationic bromide salts of alanine methyl ester derivatives

Take 4.0g (0.0143mol) of the alanine methyl ester derivative Mannich base of the previous step product in a 100mL round bottom flask, add 40mL of methanol, adjust the pH=9, then add 1.66g (0.0152mol) of bromoethane, heat Reflux for 2 hours. After the reaction is complete, remove the insoluble matter by filtration, and the filtrate is rotary evaporated to obtain a yellow liquid crude product.

The product was purified by column chromatography using a 1:20 mixture of methanol and dichloromethane as the eluent, and the yield was 92%.

(4) Put 4.5g (0.0116mol) of the alanine methyl ester derivative cationic bromide salt ionic liquid obtained in step (3) into a 100mL three-necked flask, add 2.15g (0.0117mol) KPF ₆ , add 30mL deionized water, stirred at room temperature for 10 hours, stopped the reaction, allowed to stand for stratification, discarded the previous liquid, washed the lower liquid twice with 20 mL of ether, and dried in vacuo to obtain the product with a yield of 80%.

Example 4

(1) Synthesis of alanine methyl ester

Take 120mL of methanol and add it to a 250mL three-neck flask (the environment should be anhydrous during the reaction, with a drying device; the reaction will generate HCl and SO ₂ gas, and an alkali absorption device should be used), and cool it in a low-temperature constant temperature reaction bath. -13°C, slowly add 9mL (0.124mol) SOCl ₂ dropwise under magnetic stirring, control the reaction temperature below -10°C during the dropwise addition, and continue the reaction for 1h after the dropwise addition is completed. The reaction solution was transferred to a 250mL round-bottomed flask, the temperature was naturally raised to room temperature, 11.14g (0.125mol) of alanine was added, and the reaction was stopped after heating to reflux under magnetic stirring for 4 hours. The product was rotary evaporated, and after the solvent was evaporated, alanine methyl ester hydrochloride was obtained as a yellow viscous liquid with a yield of 97%, which could be directly used in the next step of synthesis without purification.

(2) Synthesis of alanine methyl ester derivative Mannich base

Take 9.85g (0.0705mol) of alanine methyl ester hydrochloride in a 250mL three-necked flask, dissolve it in 80mL of methanol, add 12.05g (0.207mol) of acetone, then add 6.04g (0.203mol) of paraformaldehyde, drop Add dilute hydrochloric acid to pH = 5, use nitrogen as a protective gas, and heat to reflux for 48 hours under magnetic stirring. After the reaction is complete, remove the insoluble matter by suction filtration, spin the filtrate to remove the solvent, and obtain a dark brown liquid.

The crude product was purified by column chromatography, and the eluent was a mixture of methanol and dichloromethane with a volume ratio of 1:20, and the yield was 85%.

(3) Synthesis of cationic bromide salts of alanine methyl ester derivatives

Take 4.08g (0.0146mol) of the alanine methyl ester derivative Mannich base of the previous step product in a 100mL round bottom flask, add 40mL of methanol, adjust the pH=9, then add 1.85g (0.0169mol) of bromoethane, and heat Reflux for 2 hours. After the reaction is complete, remove the insoluble matter by filtration, and the filtrate is rotary evaporated to obtain a yellow liquid crude product.

The product was purified by column chromatography using a 1:20 mixture of methanol and dichloromethane as the eluent, and the yield was 94%.

(4) Put 4.30g (0.0111mol) of the alanine methyl ester derivative cationic bromide salt ionic liquid obtained in step (3) into a 100mL three-necked flask, add 1.50g (0.0125mol) NaHSO ₄ , and add 30mL of acetone, Stir at room temperature for 24 hours, stop the reaction, remove solid NaBr and excess bisulfate by suction filtration, and then distill off the acetone solvent under reduced pressure to obtain the target product with a yield of 95%.

Example 5

(1) Synthesis of alanine methyl ester

Take 120mL of methanol and add it to a 250mL three-neck flask (the environment should be anhydrous during the reaction, with a drying device; the reaction will generate HCl and SO ₂ gas, and an alkali absorption device should be used), and cool it in a low-temperature constant temperature reaction bath. -12°C, slowly add 9.5mL (0.131mol) SOCl ₂ dropwise under magnetic stirring, control the reaction temperature below -10°C during the dropwise addition, and continue the reaction for 1h after the dropwise addition is completed. The reaction solution was transferred to a 250mL round-bottomed flask, the temperature was naturally raised to room temperature, 11.59g (0.130mol) of alanine was added, and the reaction was stopped after heating to reflux under magnetic stirring for 4 hours. The product was rotary evaporated, and after the solvent was evaporated, alanine methyl ester hydrochloride was obtained as a yellow viscous liquid with a yield of 98%, which could be directly used in the next step of synthesis without purification.

(2) Synthesis of alanine methyl ester derivative Mannich base

Take 10.22g (0.0730mol) of alanine methyl ester hydrochloride in a 250mL three-necked flask, dissolve it in 82mL of methanol, add 12.01g (0.206mol) of acetone, then add 6.01g (0.202mol) of paraformaldehyde, drop Add dilute hydrochloric acid to pH = 5, use nitrogen as a protective gas, and heat to reflux for 48 hours under magnetic stirring. After the reaction is complete, remove the insoluble matter by suction filtration, spin the filtrate to remove the solvent, and obtain a dark brown liquid.

The crude product was purified by column chromatography, and the eluent was a mixture of methanol and dichloromethane with a volume ratio of 1:20, and the yield was 85%.

(3) Synthesis of cationic bromide salts of alanine methyl ester derivatives

Take 3.98g (0.0142mol) of Mannich base, a derivative of alanine methyl ester from the previous step, in a 100mL round bottom flask, add 41mL of methanol, adjust the pH to 9, then add 1.73g (0.0158mol) of bromoethane, and heat Reflux for 2 hours. After the reaction is complete, remove the insoluble matter by filtration, and the filtrate is rotary evaporated to obtain a yellow liquid crude product.

The product was purified by column chromatography using a 1:20 mixture of methanol and dichloromethane as the eluent, and the yield was 95%.

(4) Put 4.25g (0.0111mol) of the alanine methyl ester derivative cationic bromide salt ionic liquid obtained in step (3) into a 100mL three-neck flask, add 1.37g (0.0125mol) NaBF ₄ , add 30mL of acetone, Stir at room temperature for 5 hours, stop the reaction, remove solid NaBr and excess sodium fluoroborate by suction filtration, and then distill off the acetone solvent under reduced pressure to obtain the target product with a yield of 96%.

Claims (10)

1. an amino acid ester derivative cationic chiral ionic liquid is characterized in that its structural formula is as follows: , the amino acid is D-, L-alanine. 2. = The amino acid ester derivative cationic chiral ionic liquid according to claim 1, characterized in that, in the amino acid cation, R ^' is CH ₃ or CH ₃ CH ₂ ; the X ^- is BF ₄ Any of ^- , PF ₆ ^- , HSO ₄ ^- . 3. amino acid ester derivative cationic chiral ionic liquid according to claim 1, is characterized in that, the general formula of described amino acid ester derivative cationic chiral ionic liquid is A ⁺ X ^- , wherein A ⁺ is an amino acid Ester cationic derivatives, X ^- is BF ₄ ^- , PF ₆ ^- , HSO ₄ ^- . 4. A method for preparing an amino acid ester derivative cationic chiral ionic liquid, characterized in that the reaction substances used in the preparation process include: α-amino acid, thionyl chloride, paraformaldehyde, bromoethane, NaBF ₄ , KPF ₆ , NaHSO ₄ , and alcohol solvents; the preparation steps are as follows: (1) Slowly add thionyl chloride dropwise to methanol at a low temperature environment of -14°C to -10°C, continue to react for 1 hour after the drop is complete, raise the temperature to room temperature, add amino acids in batches, keep stirring at 50°C for 4 After hours, the solvent was removed by rotary evaporation to obtain the hydrochloride of amino acid ester, which was a viscous liquid; (2) Mannich reaction: add paraformaldehyde to methanol, adjust the pH to 5 with dilute hydrochloric acid, heat until the paraformaldehyde dissolves, then cool down to room temperature and add the product of step (1) amino acid ester hydrochloride and acetone , heated to reflux for 48 hours, and the solvent was removed by rotary evaporation, and the crude product was purified by column chromatography using a mixture of methanol and dichloromethane with a volume ratio of 1:20 to obtain the amino acid ester derivative Mannich base; (3) Quaternization reaction: Dissolve the amino acid ester derivative Mannich base in step (2) with an alcohol solvent, then add ethyl bromide, adjust the pH to 8-9 with NaOH solution, and heat to reflux for 2-3 hours , remove part of the solvent, remove NaBr by filtration, and then remove the solvent to obtain the chiral ionic liquid of amino acid ester derivative bromide salt; (4) Exchange anions: mix the amino acid ester derivative bromide salt ionic liquid obtained in step (3) with any one of NaBF ₄ , KPF ₆ , and NaHSO ₄ in a certain proportion in a round-bottomed flask, add a solvent to react, After the reaction is finished, a cationic chiral ionic liquid product of the amino acid ester derivative is obtained. 5 . The preparation method of amino acid ester derivative cationic chiral ionic liquid according to claim 4 , characterized in that the molar ratio of amino acid, thionyl chloride and methanol is 1:1:20-30. 6. according to the preparation method of the described amino acid ester derivative cationic chiral ionic liquid of claim 4, it is characterized in that, the substance molar ratio of described paraformaldehyde, acetone, alanine ester derivative hydrochloride is 2 ~3:2~3:1. 7. according to the preparation method of the described amino acid ester derivative cationic chiral ionic liquid of claim 4, it is characterized in that, the ratio of the amount of substance of described bromoethane and amino acid ester derivative Mannich base is 1～2 :1. 8. The preparation method of the amino acid ester derivative cationic chiral ionic liquid according to claim 4, characterized in that, the amino acid ester derivative bromide salt ionic liquid and any one of NaBF ₄ , KPF ₆ , NaHSO ₄ The amount ratio of the added amount of substances is 1:1~1.5. 9. according to the preparation method of the described amino acid ester derivative cationic chiral ionic liquid of claim 4, it is characterized in that, in Mannich reaction, the eluent of crude product column chromatography purification adopts methanol and dichloromethane volume ratio It is a 1:20 mixture. 10. according to the preparation method of the described amino acid ester derivative cationic chiral ionic liquid of claim 4, it is characterized in that, the solvent of exchanging anion step is water or acetone, when water is used as solvent, after reaction finishes, layering, discarding Remove the previous liquid, wash the lower liquid with ether and dry it in vacuum to obtain the product; when acetone is used as the solvent, after the reaction is over, remove the solid NaBr and unreacted raw materials by suction filtration, and then distill off the acetone solvent under reduced pressure to obtain the product .