阅读说明：本技术 一种芳基吡唑腈的制备方法 (Preparation method of aryl pyrazole nitrile ) 是由 江飞 张继钱 顾佳林 王任伟 李红梅 于 2020-12-02 设计创作，主要内容包括：本方案公开了一种芳基吡唑腈的制备方法,将2,6-二氯-4-三氟甲基苯胺在酸性条件下与亚硝酸钠进行重氮化反应,得到的重氮物随即与2,3二氰基丙酸乙酯发生偶联反应,偶联反应结束后,调节到弱酸性条件下环合,再调节到弱碱性条件下脱羧,脱羧结束后,中和到中性,过滤除盐,再经脱溶、精馏、精制等过程,得到芳基吡唑腈、脲烷和碳酸二乙酯。该方法通过改进制备工艺,使得重氮化反应和偶联反应几乎同时进行,这样偶联反应所释放出的一分子酸使整个反应的用酸量减少一半以上,合成后产生的废无机盐也减少一半以上。(The scheme discloses a preparation method of aryl pyrazolecarbonitrile, which comprises the steps of carrying out diazotization reaction on 2, 6-dichloro-4-trifluoromethylaniline and sodium nitrite under an acidic condition, carrying out coupling reaction on the obtained diazo and 2, 3-dicyanopropionic acid ethyl ester, adjusting to be cyclized under a weakly acidic condition after the coupling reaction is finished, adjusting to be decarboxylated under a weakly alkaline condition, neutralizing to be neutral after the decarboxylation is finished, filtering to remove salt, and then carrying out processes of desolventizing, rectifying, refining and the like to obtain the aryl pyrazolecarbonitrile, the urethane and the diethyl carbonate. The method enables diazotization reaction and coupling reaction to be almost simultaneously carried out by improving the preparation process, so that the acid consumption of the whole reaction is reduced by more than half by one molecule of acid released by the coupling reaction, and the waste inorganic salt generated after synthesis is also reduced by more than half.)

1. A process for preparing an arylpyrazolecarbonitrile, the process comprising:

diazotization reaction of 2, 6-dichloro-4-trifluoromethyl aniline and sodium nitrite is carried out in a solution containing 2, 3-dicyanopropionic acid ethyl ester, and a nitrous acid quenching agent is added to a certain extent after the reaction is carried out to obtain a conjugate reaction solution.

2. The method of claim 1, further comprising:

dissolving 2, 6-dichloro-4-trifluoromethylaniline in a mixed solvent of absolute ethanol and hydrogen chloride ethanol to form 2, 6-dichloro-4-trifluoromethylaniline acid ethanol solution, and performing diazotization reaction with sodium nitrite.

3. The preparation method according to claim 2, wherein when the 2, 6-dichloro-4-trifluoromethylaniline is dissolved in a mixed solvent of absolute ethanol and ethanol hydrochloride, the molar ratio of the 2, 6-dichloro-4-trifluoromethylaniline to the absolute ethanol is 1: 10-100; the molar ratio of the 2, 6-dichloro-4-trifluoromethylaniline to the hydrogen chloride in the mixed solvent is 1: 1.0-5; preferably, the molar ratio of the 2, 6-dichloro-4-trifluoromethylaniline to the hydrogen chloride in the mixed solvent is 1: 1.1-1.5.

4. The method according to claim 1, wherein the solution containing ethyl 2, 3-dicyanopropionate is a solution obtained by dissolving ethyl 2, 3-dicyanopropionate in ethanol hydrogen chloride.

5. The method according to claim 1, wherein the temperature of the diazotization reaction is-5 to 35 ℃, and preferably the temperature of the diazotization reaction is 15 to 25 ℃.

6. The method according to claim 1, wherein the nitrous acid quencher is added to such an extent that the content of 2, 6-dichloro-4-trifluoromethylaniline in the reaction solution is 0.5 wt% or less, and then the quencher is added to quench excess sodium nitrite.

7. The method of claim 1, further comprising:

adding the obtained coupling product into absolute ethyl alcohol, and adjusting the pH value of the solution to enable the coupling product to generate cyclization reaction;

continuously adjusting the pH value of the solution to enable the cyclization reaction product to generate decarboxylation reaction, thereby obtaining a mixed solution containing the aryl pyrazole nitrile;

and carrying out subsequent treatment on the mixed solution containing the aryl pyrazole nitrile to obtain the aryl pyrazole nitrile.

8. The production method according to claim 7, wherein the basic substance added to the solution in the cyclization reaction and the decarboxylation reaction by adjusting the pH of the solution to be higher is anhydrous ammonia.

9. The method according to claim 8, wherein the molar ratio of the total anhydrous ammonia added to the 2, 6-dichloro-4-trifluoromethylaniline added during the reaction is 1.5-3.5: 1.

10. The preparation method according to claim 7, wherein the solution of the cyclization reaction has a pH value of 4.5-6.5; and the pH value of the solution subjected to the decarboxylation reaction is 9-12.

Technical Field

The invention relates to the technical field of chemical substance synthesis, in particular to a preparation method of aryl pyrazole nitrile.

Background

The arylpyrazolecarbonitriles are known by the chemical name 5-amino-3-cyano-1- (2, 6-dichloro-4-trifluoromethylphenyl) pyrazole, also known as the pyrazole ring, and have the following structural formula:

the arylpyrazole nitrile is a special intermediate of N-phenylpyrazole pesticides such as fipronil, ethiprole, butene fipronil and the like. The action principle of N-phenylpyrazole pesticides such as fipronil, ethiprole and the like is that chlorine channels regulated by gamma-aminobutyric acid interfere with chloride ion channels to destroy the activity of a normal central nervous system, so that insects die. Due to the unique action mechanism, the pesticide has the remarkable characteristics different from the conventional pesticide: the series of insecticides have extremely high sensitivity to pests such as hemiptera, lepidoptera, thysanoptera and coleopteran and pests with drug resistance to cyclopentadiene, pyrethroid and carbamate insecticides, and have the characteristics of long-acting property (the effective period is generally 2-4 weeks and the longest period is 6 weeks), high activity (the using dosage is low, and only dozens of grams of active ingredients are needed per hectare to control piercing-sucking or chewing mouthpart pests) and the like. The first pesticide to enter the market is fipronil. Fipronil was developed in 1989 by the company rona pluronic, france, 1993 and introduced into the pesticide market, also known as Fipronil, with the generic name Fipronil, with the trade name Regent, and with the chemical name 5-amino-3-cyano-1- (2, 6-dichloro-4-trifluoromethyl-phenyl) -4-trifluoromethylsulfinylpyrazole. Fipronil is popular with the albizzia due to the excellent insecticidal effect since entering the pesticide market, and the annual sale amount of fipronil in the first ten pesticide categories for years is within the middle level of pesticide in the world, so that fipronil becomes one of the most popular pesticide categories. Other insecticides such as ethiprole (ethiprole) and butene-fipronil are also excellent insecticides, and aryl pyrazolecarbonitriles are important intermediates for this class of insecticides.

In the existing synthesis of aryl pyrazole nitrile, 2, 6-dichloro-4-trifluoromethylaniline is adopted for diazotization, the obtained diazonium salt is coupled with 2, 3-dicyanopropionic acid ethyl ester, and the conjugate is cyclized and decarboxylated to obtain aryl pyrazole nitrile, but the existing synthesis process, such as the process in CN201710605773.6, can generate a large amount of acidic and alkaline wastewater, and increases the treatment difficulty of subsequent steps of crystallization, separation, drying and the like.

Disclosure of Invention

An object of the present invention is to provide a process for preparing arylpyrazolecarbonitriles, which comprises improving the preparation process such that the diazotization reaction and the coupling reaction are almost simultaneously carried out, and thus the amount of acid used in the whole reaction is reduced by more than half by one molecule of acid released by the coupling reaction, and the amount of waste inorganic salts generated after the synthesis is reduced by more than half.

In order to achieve the purpose, the scheme is as follows:

a process for preparing an arylpyrazolecarbonitrile, the process comprising:

diazotization reaction of 2, 6-dichloro-4-trifluoromethyl aniline and sodium nitrite is carried out in a solution containing 2, 3-dicyanopropionic acid ethyl ester, and a nitrous acid quenching agent is added to a certain extent after the reaction is carried out to obtain a conjugate reaction solution.

Preferably, the method further comprises:

dissolving 2, 6-dichloro-4-trifluoromethylaniline in a mixed solvent of absolute ethanol and hydrogen chloride ethanol to form 2, 6-dichloro-4-trifluoromethylaniline acid ethanol solution, and performing diazotization reaction with sodium nitrite.

Preferably, when the 2, 6-dichloro-4-trifluoromethylaniline is dissolved in a mixed solvent of absolute ethyl alcohol and hydrogen chloride ethyl alcohol, the molar ratio of the 2, 6-dichloro-4-trifluoromethylaniline to the absolute ethyl alcohol is 1: 10-100; the molar ratio of the 2, 6-dichloro-4-trifluoromethylaniline to the hydrogen chloride in the mixed solvent is 1: 1.0-5; preferably, the molar ratio of the 2, 6-dichloro-4-trifluoromethylaniline to the hydrogen chloride in the mixed solvent is 1: 1.1-1.5.

Preferably, the solution containing ethyl 2, 3-dicyanopropionate is a solution of ethyl 2, 3-dicyanopropionate in ethanol hydrogen chloride.

Preferably, the temperature of the diazotization reaction is-5-35 ℃, and preferably the temperature of the diazotization reaction is 15-25 ℃.

Preferably, the nitrous acid quenching agent is added to a certain extent after the content of the 2, 6-dichloro-4-trifluoromethylaniline in the solution to be reacted is less than or equal to 0.5 wt%, and the quenching agent is added to quench excessive sodium nitrite.

Preferably, the method further comprises:

adding the obtained coupling product into absolute ethyl alcohol, and adjusting the pH value of the solution to enable the coupling product to generate cyclization reaction;

continuously adjusting the pH value of the solution to enable the cyclization reaction product to generate decarboxylation reaction, thereby obtaining a mixed solution containing the aryl pyrazole nitrile;

and carrying out subsequent treatment on the mixed solution containing the aryl pyrazole nitrile to obtain the aryl pyrazole nitrile.

Preferably, the alkaline substance added in the cyclization reaction and the decarboxylation reaction for adjusting the pH value of the solution to be increased is anhydrous ammonia.

Preferably, the molar ratio of all anhydrous ammonia added in the reaction process to the 2, 6-dichloro-4-trifluoromethylaniline is 1.5-3.5: 1.

Preferably, the pH value of the solution of the cyclization reaction is 4.5-6.5; and the pH value of the solution subjected to the decarboxylation reaction is 9-12.

The scheme has the following beneficial effects:

compared with other production processes, the scheme almost simultaneously performs the diazo reaction and the coupling reaction, reduces the danger of the synthetic reaction, simultaneously limits the byproducts to be the urethane and the diethyl carbonate by controlling the reaction conditions under the condition of not influencing the quality and the yield of the aryl pyrazolonitrile, and can respectively obtain the urethane and the diethyl carbonate products by multistage rectification and recrystallization; compared with the existing preparation process, the acid used in the whole reaction is reduced by more than half, the production amount of inorganic salt is also reduced, and the reduction and resource utilization of solid waste and waste liquid in the production of the aryl pyrazole nitrile are realized. Water is not used in the synthesis process of producing the aryl pyrazole nitrile by the process, the inorganic salt generated in the diazotization and cyclization processes can be removed in a filtering (filter pressing) mode, and only a small amount of water is added after the desolventization is finished to remove the residual inorganic salt, so that the production amount of waste water is greatly reduced, and the green production concept is met.

Detailed Description

Embodiments of the present solution are described in further detail below. It is clear that the described embodiments are only a part of the embodiments of the present solution, and not an exhaustive list of all embodiments. It should be noted that, in the present embodiment, features of the embodiment and the embodiment may be combined with each other without conflict.

The scheme provides an improved process for synthesizing the aryl pyrazole nitrile, aiming at the phenomena that in the prior art, a reaction product for synthesizing the aryl pyrazole nitrile contains acidic and alkaline wastewater, and the crystallization separation of a synthesis byproduct is difficult to carry out. The amount of acid used in the reaction is reduced by controlling the reaction conditions, and reaction byproducts which are easy to treat are obtained at the same time.

The conception of the scheme is that 2, 6-dichloro-4-trifluoromethyl aniline and sodium nitrite are subjected to diazotization under an acidic condition, obtained diazo is subjected to coupling reaction with 2,3 dicyanopropionic acid ethyl ester, after the coupling reaction is finished, the diazo is adjusted to be cyclized under a weak acidic condition, then the diazo is adjusted to be decarboxylated under a weak alkaline condition, after the decarboxylation is finished, the neutralization is carried out to be neutral, the salt is removed by filtration, and then the processes of desolventizing, rectifying, refining and the like are carried out to obtain aryl pyrazolonitrile, urethane and diethyl carbonate, wherein the synthesis and the formula of the byproduct generation are as follows:

in the scheme, an acidic substance in the diazotization reaction and the coupling reaction is hydrogen chloride or hydrogen chloride ethanol, and a reaction solvent is absolute ethyl alcohol; the cyclized decarboxylation solvent is ethanol, and the alkaline substance used for adjusting the alkalinity of the solution is anhydrous ammonia. The process scheme is controlled by process conditions, diazo salt generated by diazotization and 2, 3-dicyanopropionic acid ethyl ester are subjected to coupling reaction, side reaction is reduced, main byproducts are diethyl carbonate and urethane, the generated byproducts can be separated and prepared into byproducts by a conventional process method, and the organic waste liquid generated after synthesis by adopting the scheme is reduced by more than 80%; in the synthesis process of the scheme, no water is added, the conjugate is dissolved in an absolute ethyl alcohol solvent, sodium chloride generated by diazotization and ammonium chloride generated by decarboxylation are separated out in the solvent, solid-liquid separation is carried out after synthesis, a small amount of residual inorganic salt is removed after desolventization, organic solvents such as toluene, chlorobenzene and the like are added to dissolve products, and then a small amount of water is added to wash the products to remove the residual inorganic salt. The amount of waste water generated in the whole synthesis process is reduced by more than 90 percent compared with the prior synthesis process. In general diazotization synthesis, 1 mole (equivalent) of primary amine needs to consume 2 moles (equivalent) of acidic substances, excessive acid needs to be added during synthesis, and the molar ratio of acid to primary amine is usually 2.5: 1 or more. In the scheme, because diazotization and coupling are almost simultaneously carried out, one molecule of acid is released during coupling, so that the using amount of the acid can be reduced by more than half, and the waste inorganic salt generated after synthesis is also reduced by more than half.

The method comprises the following steps:

(1) respectively dissolving 2, 6-dichloro-4-trifluoromethylaniline and 2, 3-dicyanopropionic acid ethyl ester in hydrogen chloride ethanol, dropwise adding the 2, 6-dichloro-4-trifluoromethylaniline solution into the 2, 3-dicyanopropionic acid ethyl ester solution, simultaneously adding sodium nitrite, diazotizing with sodium nitrite under an acidic condition, then carrying out coupling reaction on the formed diazo and the 2, 3-dicyanopropionic acid ethyl ester, and adding sulfamic acid or sodium sulfamate to quench excessive sodium nitrite when the content of the 2, 6-dichloro-4-trifluoromethylaniline in the synthetic solution is less than or equal to 0.5% to obtain a coupling reaction solution;

(2) dropwise adding the conjugate generated in the step (1) into absolute ethyl alcohol, simultaneously introducing anhydrous ammonia, controlling a certain pH value, and carrying out cyclization under a weakly acidic condition to obtain a cyclization reaction solution;

(3) after the cyclization is finished, continuously introducing anhydrous ammonia into the cyclization reaction liquid obtained in the step (2), and decarboxylating under an alkaline condition to obtain an arylpyrazolecarbonitrile decarboxylation synthetic liquid;

(4) after decarboxylation is finished, adding acid ethanol into the step (3), neutralizing to be neutral, cooling, filtering or centrifuging, and performing filter pressing to obtain filter cakes which are inorganic salts such as sodium chloride and ammonium chloride, wherein the filter cakes can be dried to recover ethanol and then treated as solid waste;

(5) distilling the filtrate obtained in the step (4) under reduced pressure until the filtrate is basically evaporated to dryness, adding an organic solvent and water, stirring and heating until the filtrate is completely dissolved, standing for phase splitting to discharge a water phase, transferring the organic phase to a crystallizer for cooling crystallization, separating crystals, and drying to obtain the aryl pyrazolonitrile;

(6) performing multi-stage rectification on the material obtained by desolventizing and distilling in the step (5), wherein the extract at the top of the first-stage rectification tower is ethanol with the concentration of over 95 percent, and the absolute ethanol can be obtained by the processes of extractive rectification, azeotropic rectification, molecular sieve adsorption, membrane separation, reduced pressure rectification and the like for recycling; the produced material at the bottom of the first-stage rectifying tower is mainly a mixture containing diethyl carbonate, urethane, a small amount of water and ethanol, and enters a second-stage rectifying tower for rectification. The produced substance at the top of the second-stage rectifying tower is a mixture of water, ethanol, a small amount of diethyl carbonate and urea alkane, and can return to the first-stage rectifying tower for rectification, and the produced substance at the bottom of the tower is a mixture of diethyl carbonate, urea alkane and a small amount of impurities, and enters the third-stage rectifying tower for rectification. Diethyl carbonate is extracted from the top of the third-stage rectifying tower, and the urethane product can be obtained by recrystallization from the bottom of the third-stage rectifying tower.

In one embodiment, when 2, 6-dichloro-4-trifluoromethylaniline is dissolved in a mixed solvent of absolute ethanol and ethanol hydrochloride, the molar ratio of 2, 6-dichloro-4-trifluoromethylaniline to absolute ethanol is 1: 10-100.

In one embodiment, in the diazo coupling reaction, when 2, 6-dichloro-4-trifluoromethylaniline is dissolved in a mixed solvent of absolute ethanol and ethanol hydrogen chloride, the molar ratio of 2, 6-dichloro-4-trifluoromethylaniline to hydrogen chloride in the mixed solvent is 1: 1.0-5, preferably 1:1.1 to 1.5.

In one embodiment, the diazotization reaction is carried out at a temperature of-5 to 35 ℃, preferably 15 to 25 ℃.

In one embodiment, the nitrous acid quencher is sulfamic acid or sodium sulfamate, and no other quencher is used.

In one embodiment, the pH value during cyclization is 4.5-6.5.

In one embodiment, the pH during decarboxylation is between 9 and 12.

In one embodiment, the total amount of anhydrous ammonia added in the reaction process is that the molar ratio of the anhydrous ammonia to the 2, 6-dichloro-4-trifluoromethylaniline is 1.5-3.5: 1.

compared with other production processes, the scheme almost simultaneously performs the diazo reaction and the coupling reaction, reduces the danger of the synthetic reaction, simultaneously limits the byproducts to be the urethane and the diethyl carbonate by controlling the reaction conditions under the condition of not influencing the quality and the yield of the aryl pyrazolonitrile, and can respectively obtain the urethane and the diethyl carbonate products by multistage rectification and recrystallization; compared with the existing preparation process, the acid used in the whole reaction is reduced by more than half, the production amount of inorganic salt is also reduced, and the reduction and resource utilization of solid waste and waste liquid in the production of the aryl pyrazole nitrile are realized. Water is not used in the synthesis process of producing the aryl pyrazole nitrile by the process, the inorganic salt generated in the diazotization and cyclization processes can be removed in a filtering (filter pressing) mode, and only a small amount of water is added after the desolventization is finished to remove the residual inorganic salt, so that the production amount of waste water is greatly reduced, and the green production concept is met.

The present embodiment will be described in detail with reference to the following examples.

Example 1

In this example, the content of each substance is represented by mass%.

(1) The ethanol hydrochloride with the mass percentage concentration of 5.6 percent is prepared by adding 30 percent of commercial acid ethanol (ethanol hydrochloride) and absolute ethanol.

(2) Adding 400kg of 5.6 mass percent hydrogen chloride ethanol (8.21 kmol ethanol and 0.61kmol hydrogen chloride) into a glass lining kettle a with the volume of 1000L, stirring, adding 200kg of 2, 6-dichloro-4-trifluoromethylaniline (99.52 percent and 0.86kmol), stirring until the mixture is completely dissolved, and preparing 2, 6-dichloro-4-trifluoromethylaniline ethanol solution;

400kg of 5.6 mass percent hydrogen chloride ethanol (8.21 kmol ethanol and 0.61kmol hydrogen chloride) is added into a 2000L glass lining kettle b provided with an electric solid feeder, 135kg of 2, 3-dicyanopropionic acid ethyl ester (98.2 percent and 0.87kmol) is added, stirred and cooled to about 10 ℃;

(3) 63.5kg (98.16%, 0.9kmol) of sodium nitrite is loaded into an electric solid feeder, a kettle bottom valve is opened, and a metering pump is started; starting a solid feeder, and simultaneously adding 2, 6-dichloro-4-trifluoromethyl aniline acid ethanol and sodium nitrite into the kettle b; regulating and controlling the flow of 2, 6-dichloro-4-trifluoromethylaniline acid ethanol, controlling the flow to be 6.5-6.8L/min, controlling the flow of sodium nitrite to be 520-540 g/min, keeping the temperature at 15-25 ℃, and finishing the feeding within about 2 hours; preserving the temperature until the content of the 2, 6-dichloro-4-trifluoromethylaniline acid is detected to be less than 0.5 percent, and finishing the reaction; adding sodium sulfamate to quench excessive nitrous acid, and adding 5.1 kg of sodium sulfamate in total, wherein the starch potassium iodide test paper does not change color when being detected;

(3) adding 300kg (6.52kmol) of absolute ethyl alcohol into a 2000L glass lining kettle c, stirring, cooling to about 10 ℃, after the step (2) is finished, dropwise adding the reaction liquid obtained in the step (2) into the kettle c, introducing anhydrous ammonia, adjusting the dropwise adding speed and the ammonia introducing speed, controlling the pH value to be 4.5-6.5, preserving heat at the pH value of 5.5-6.5 after the dropwise adding is finished, and finishing the reaction until the content of the coupling substance is less than 0.5%;

(4) after the step (3) is finished, continuously introducing ammonia gas into the kettle c, keeping the pH value at 10-11, detecting that the content of 4-position ester (cyclized decarboxylated intermediate) is less than 0.2%, and finishing the reaction;

(5) after the reaction in the step (4) is finished, 30% acid ethanol (hydrogen chloride ethanol) is dripped into the kettle c to reach the pH value of about 7; cooling to 0 ℃, keeping the temperature for 1 hour, performing filter pressing, pressing filtrate into a desolventizing kettle, washing a filter cake once by using absolute ethyl alcohol at the temperature of 30 ℃, merging washing liquid into the desolventizing kettle, and performing vacuum drying on the filter cake to obtain 93.6kg of waste salt;

(6) and (4) distilling the filtrate and the washing liquid in the step (5) under reduced pressure to obtain 278.7kg of light yellow loose powder solid and 1140.9kg of distilled condensed liquid under the conditions of-0.099 MPa and 73.5 ℃. Detecting the obtained solid by an HPLC external standard method and an area normalization method respectively, wherein the content of the arylpyrazole nitrile is 92.26 percent and 95.85 percent, and the conversion rate of the arylpyrazole nitrile (calculated by 2, 6-dichloro-4-trifluoromethylaniline) is 92.94 percent; the distillation condensate was checked by GC and the contents of the components were as follows: 91.29% of ethanol, 6.02% of diethyl carbonate, 2.17% of urethane, 0.52% of the rest, and 1.31% of Karl Fischer water content;

(7) adding 750kg of chlorobenzene and 30kg of water into a glass lining kettle with the volume of 1000L, adding the solid material obtained in the step (6), heating to 70 ℃, standing, discharging 40.6kg of water phase (wastewater), cooling the organic phase to 0-5 ℃, performing centrifugal separation, drying a filter cake to obtain 220.6kg of light yellow crystal powder, and detecting by an HPLC (high performance liquid chromatography) external standard method to obtain 98.75% of arylpyrazolecarbonitrile; concentrating the centrifugal mother liquor by reduced pressure distillation, distilling 620kg of chlorobenzene out, cooling the kettle liquor to 0 to-5 ℃, performing centrifugal separation again, drying a filter cake to obtain 32.1kg of light yellow crystal powder, detecting the aryl pyrazolonitrile content by an HPLC (high performance liquid chromatography) external standard method to 97.69%, distilling the centrifugal mother liquor by reduced pressure to recover 13.6kg of brown solid after the chlorobenzene is recovered, detecting the aryl pyrazolonitrile content by 39.2%, and disposing the brown solid as solid waste.

(8) Carrying out three-stage rectification on the vacuum distillation condensate in the step (6), and collecting 1018kg of 98.6 percent ethanol from the top of the first-stage rectification tower; 3.2kg (containing 57.41% ethanol, 42.13% diethyl ester and 0.47% water) is extracted from the top of the second-stage rectification column, 63.7kg (containing 99.93%) diethyl carbonate is extracted from the top of the third-stage rectification column, 28.1kg is extracted from the bottom of the third-stage rectification column, and 24.6kg of 99.2% urethane is obtained by recrystallization with absolute ethyl alcohol.

It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.