阅读说明：本技术 一种七氟异丁腈的合成方法 (Synthetic method of heptafluoroisobutyronitrile ) 是由 周济苍 喻强 廖敏 周遇吉 喻鼎辉 于 2020-08-14 设计创作，主要内容包括：本发明提供了一种七氟异丁腈的合成方法,包括：A)六氟丙烯二聚体在氟碳溶剂和醇的存在下经臭氧裂解制备得到七氟异丁酸酯；B)将所得七氟异丁酸酯与氨反应、脱水,得到七氟异丁腈。本发明DHFP二聚体臭氧裂解反应条件温和,原料转化率和产物收率高,本发明整体生产过程工艺操作安全、简便、可靠,易于工业化生产。(The invention provides a method for synthesizing heptafluoroisobutyronitrile, which comprises the following steps: A) carrying out ozone cracking on hexafluoropropylene dimer in the presence of a fluorocarbon solvent and alcohol to prepare heptafluoroisobutyrate; B) the obtained heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain heptafluoroisobutyronitrile. The DHFP dimer ozone cracking reaction of the invention has mild reaction conditions, high raw material conversion rate and product yield, and the overall production process of the invention has safe, simple and reliable process operation and is easy for industrial production.)

1. A method for synthesizing heptafluoroisobutyronitrile is characterized by comprising the following steps:

A) carrying out ozone cracking on hexafluoropropylene dimer in the presence of a fluorocarbon solvent and alcohol to prepare heptafluoroisobutyrate;

B) the obtained heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain heptafluoroisobutyronitrile.

2. The synthesis method according to claim 1, wherein the fluorocarbon solvent of step a) is chlorofluorocarbon, hydrofluorocarbon, hydrofluoroether or perfluoropolyether; the mass ratio of the hexafluoropropylene dimer to the fluorocarbon solvent is 1 (1-5); the alcohol is one of methanol, ethanol or propanol.

3. The synthesis process according to claim 1, characterized in that the ozonolysis in step A) is carried out using O₃And O₂Mixed gas of O in₃The mass concentration of the components is 0.05-15%; the reaction temperature is-40-80 ℃; the reaction time is 1-20 h; the pressure of the reaction is 0.1-0.5 Mpa.

4. The method for synthesizing heptafluoroisobutyronitrile according to claim 1, wherein in the step B), the obtained heptafluoroisobutyrate is reacted with ammonia and dehydrated, specifically: heating and gasifying heptafluoroisobutyrate, mixing the heptafluoroisobutyrate with ammonia gas to form mixed gas, introducing the mixed gas into a catalyst tower to perform catalytic dehydration reaction with a dehydration catalyst, and obtaining the heptafluoroisobutyronitrile.

5. The synthesis method according to claim 4, wherein the temperature of mixing heptafluoroisobutyrate with ammonia gas is 0-100 ℃; the temperature of the dehydration reaction is 200-800 ℃; the catalyst is selected from one or more of silicon dioxide, aluminum oxide, manganese oxide, boron oxide, vanadium oxide, barium oxide, zirconium oxide, cerium oxide or thorium oxide; the mass ratio of the heptafluoroisobutyrate to the ammonia gas is 1: 1-1: 10.

6. The method for synthesizing heptafluoroisobutyronitrile according to claim 1, wherein in the step B), the obtained heptafluoroisobutyrate is reacted with ammonia and dehydrated, specifically: firstly, reacting heptafluoroisobutyrate with ammonia to obtain heptafluoroisobutyramide; and dehydrating the heptafluoroisobutyramide by using a dehydrating agent to obtain the heptafluoroisobutyronitrile.

7. The method for synthesizing heptafluoroisobutyronitrile according to claim 6, wherein in the step of reacting heptafluoroisobutyrate with ammonia, the molar ratio of ammonia to heptafluoroisobutyrate is (1.0 to 3.0): 1; the reaction temperature is controlled between 0 ℃ and 80 ℃; the reaction pressure is controlled between 0.1MPa and 1 MPa; the reaction time is controlled to be 1-20 h; the ammonia is selected from ammonia water, alcohol solution of ammonia or ammonia gas; the reaction solvent is selected from one or more of alcohol solvents, ether solvents, nitrile solvents, amide solvents and sulfone solvents; the molar ratio of the reaction solvent to the heptafluoroisobutyrate is (1-10): 1.

8. the method for synthesizing heptafluoroisobutyronitrile according to claim 6, wherein in the step of dehydrating heptafluoroisobutyramide with a dehydrating agent, the dehydrating agent is one or more selected from the group consisting of acid chloride, acid anhydride, phosphorus pentoxide and phosphorus oxychloride; the molar ratio of the heptafluoroisobutyramide to the dehydrating agent is (0.5-1): 1; the reaction temperature is-40 ℃ to 200 ℃; the reaction time is 1-20 h.

9. The synthesis method according to claim 1, wherein the preparation method of the hexafluoropropylene dimer specifically comprises: hexafluoropropylene is polymerized under the action of solvent, catalyst and cocatalyst to obtain hexafluoropropylene dimer.

10. The method of synthesizing hexafluoropropylene dimer according to claim 9, wherein said catalyst is a fluoride salt; the fluoride salt is selected from lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride and zinc fluoride; the solvent is an ether solvent, a nitrile solvent, an amide solvent or a sulfone solvent; the cocatalyst is tertiary amine; the tertiary amine is triethylamine, diethylamine or tetramethylethylenediamine;

the mass ratio of the solvent to the catalyst is (25): 1; the mass ratio of the solvent to the cocatalyst is (1-25) to 1; the reaction temperature is-50-80 ℃; the reaction time is 1-20 h; the reaction pressure is 0.1-1 MPa.

Technical Field

The invention relates to the technical field of organic synthesis, in particular to a method for synthesizing heptafluoroisobutyronitrile.

Background

Heptafluoroisobutyronitrile, 2, 3, 3, 3-tetrafluoro-2-trifluoromethylpropionitrile, is a perfluoronitrile compound with a boiling point of-4.7 ℃. Colorless gas at normal temperature and normal pressure. The dielectric composition has the characteristics of low boiling point, high volatility, excellent electrical insulation property, good environmental protection performance and the like, and can be used as a gas dielectric material and used as a dielectric composition of an insulator in an electrical device. The greenhouse effect index (GWP) of heptafluoroisobutyronitrile is only 2210 and is far lower than that of sulfur hexafluoride (GWP is 23500), so that the heptafluoroisobutyronitrile can be used for replacing the traditional sulfur hexafluoride insulating gas, and the problem of the atmospheric greenhouse effect is greatly reduced. Heptafluoroisobutyronitrile has received much attention from the global electrical industry and is beginning to find application.

The synthesis method of heptafluoroisobutyronitrile has been reported at home and abroad, and has three technical routes in summary: firstly, the cyanide is directly reacted with hexafluoropropylene and the like to obtain the product; secondly, the compound is obtained by pyrolysis of heptafluoroisopropyl substituted heterocyclic compound, such as heptafluoroisopropyl triazine; and thirdly, the compound is obtained by dehydrating heptafluoroisobutyramide.

The initially reported synthetic route to heptafluoroisobutyronitrile was cyanide based. For example, U.S. patent 3752840 discloses a synthetic route for the reaction of hydrogen cyanide and hexafluoropropylene in the presence of a catalyst of potassium fluoride in acetonitrile solvent at 100 ℃ to obtain heptafluoroisobutyronitrile. For another example, U.S. Pat. No. 3234267 discloses a synthetic route for perfluoropropyl iodide to form perfluorobutyronitrile by reaction with hydrogen cyanide, potassium ferricyanide, cyanogen iodide, and the like. For another example, chinese patent application CN108863847A discloses a technical route for preparing heptafluoroisobutyronitrile by reacting cyanogen chloride with hexafluoropropylene, and perfluoroolefin compounds, metal fluorides and cyanogen chloride are reacted to obtain perfluoronitrile compounds. Because cyanide is extremely toxic, the technical route has great potential safety hazard and great actual implementation risk.

Chambers and coworkers (J Chem Soc Chem Commun 1987, 1699; J Chem Soc Perkin Trans I1980, 2254; J Chem Soc Perkin Trans I1990, 975) found that reaction of hexafluoropropylene with a fluoroheterocyclic compound, such as trifluorotriazine and tetrafluoropyrimidine, gives heptafluoroisopropyl triazine and heptafluoroisopropyl pyrimidine, etc., which are cleaved at high temperatures to give heptafluoroisobutyronitrile. This finding provides a possible method for synthesizing heptafluoroisobutyronitrile, but this method involves a pyrolysis reaction, requires special equipment and consumes much energy, resulting in high production costs; and a large amount of byproducts are generated in the cracking process, the product is difficult to separate and purify, and the yield is low, so that the method is not suitable for industrial production of the heptafluoroisobutyronitrile.

There are many patent technical documents relating to the preparation of heptafluoroisobutyronitrile by dehydration of heptafluoroisobutyramide, and the details thereof are not repeated herein. The technical route has mild reaction conditions and high conversion rate and yield; the product is easy to separate and purify and has high purity; the raw material (heptafluoroisobutyramide) has low toxicity and safe process, thereby being more suitable for industrial production. However, the technical scheme of preparing heptafluoroisobutyronitrile by dehydrating heptafluoroisobutyramide adopts a chemical reagent dehydration technology. Although the technical route is mature and reliable, the route is long, chemicals such as dehydrating agents are involved, which causes increase of production cost and brings about problems of environmental pollution related to emission, and the like. It is therefore still of practical interest to explore alternatives to this technical route. It is also noted that heptafluoroisobutyramide and starting materials therefor are not readily available, including but not limited to heptafluoroisobutyryl fluoride (chlorine), heptafluoroisobutyric acid, and heptafluoroisobutyrate, among others. The disclosed processes for synthesizing heptafluoroisobutyramide and starting materials therefor, such as heptafluoroisobutyryl fluoride (chlorine), heptafluoroisobutyric acid, and heptafluoroisobutyrate, each have their drawbacks. Therefore, the development of a new low-cost, safe and environment-friendly heptafluoroisobutyramide and a raw material preparation technology thereof is still a great challenge for professional technicians in the industry.

Disclosure of Invention

In view of the above, the technical problem to be solved by the present invention is to provide a method for synthesizing heptafluoroisobutyronitrile, which is simple, mild in conditions, and high in conversion rate and yield of the product.

The invention provides a method for synthesizing heptafluoroisobutyronitrile, which comprises the following steps:

A) carrying out ozone cracking on hexafluoropropylene dimer in the presence of a fluorocarbon solvent and alcohol to prepare heptafluoroisobutyrate;

B) the obtained heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain heptafluoroisobutyronitrile.

Preferably, the fluorocarbon solvent in the step A) is chlorofluorocarbon, hydrofluorocarbon, hydrofluoroether or perfluoropolyether; the mass ratio of the hexafluoropropylene dimer to the fluorocarbon solvent is 1 (1-5); the alcohol is one of methanol, ethanol or propanol;

preferably, the ozone cracking in the step A) adopts O₃And O₂Mixed gas of O in₃The mass concentration of the components is 0.05-15%;

the reaction temperature is-40-80 ℃; the reaction time is 1-20 h; the pressure of the reaction is 0.1-0.5 Mpa.

Preferably, the step B) is specifically: and (3) carrying out dehydration reaction on the heptafluoroisobutyrate and ammonia gas under the action of a catalyst to prepare the heptafluoroisobutyronitrile.

Preferably, the mixing temperature of the heptafluoroisobutyrate and ammonia gas is 0-100 ℃; the temperature of the dehydration reaction is 200-800 ℃; the catalyst is selected from one or more of silicon dioxide, aluminum oxide, manganese oxide, boron oxide, vanadium oxide, barium oxide, zirconium oxide, cerium oxide or thorium oxide; the mass ratio of the heptafluoroisobutyrate to the ammonia gas is 1: 1-1: 10.

Preferably, the step B) is specifically: reacting the heptafluoroisobutyrate with ammonia to obtain heptafluoroisobutyramide; and (3) dehydrating, rectifying and purifying the heptafluoroisobutyramide to obtain the heptafluoroisobutyronitrile.

Preferably, the reaction of heptafluoroisobutyrate with ammonia is carried out in a solvent; the reaction solvent is one or more of an alcohol solvent, an ether solvent, a nitrile solvent, an amide solvent or a sulfone solvent; the ammonia is ammonia gas or an alcohol solution of ammonia; the mass ratio of the solvent to the heptafluoroisobutyrate is (1-10) to 1; the mass ratio of the heptafluoroisobutyrate to the ammonia is 1 (1-3); the reaction temperature is 0-80 ℃; the reaction time is 1-20 h; the pressure of the reaction is 0.1-1 Mpa.

Preferably, the dehydration of heptafluoroisobutyramide specifically comprises: mixing heptafluoroisobutyramide and a dehydrating agent for reaction; the dehydrating agent is selected from one or more of acyl chloride, acid anhydride, phosphorus pentoxide or phosphorus oxychloride.

Preferably, the preparation method of the hexafluoropropylene dimer specifically comprises the following steps: hexafluoropropylene is polymerized under the action of solvent, catalyst and cocatalyst to obtain hexafluoropropylene dimer.

Preferably, the catalyst is a fluoride salt; the fluoride salt is selected from lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride and zinc fluoride; the solvent is an ether solvent, a nitrile solvent, an amide solvent or a sulfone solvent; the cocatalyst is tertiary amine; the tertiary amine is triethylamine, diethylamine or tetramethylethylenediamine;

the mass ratio of the solvent to the catalyst is (1-25) to 1; the mass ratio of the solvent to the cocatalyst is (1-25: 1); the reaction temperature is-50-80 ℃; the reaction time is 1-20 h; the reaction pressure is 0.1-1 MPa.

Compared with the prior art, the invention provides a method for synthesizing heptafluoroisobutyronitrile, which comprises the following steps: A) carrying out ozone cracking on hexafluoropropylene dimer in the presence of a fluorocarbon solvent and alcohol to prepare heptafluoroisobutyrate; B) the obtained heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain heptafluoroisobutyronitrile. The technical scheme for preparing the heptafluoroisobutyronitrile provided by the invention has the following advantages: firstly, the hexafluoropropylene dimer is polymerized by hexafluoropropylene Dimer (DHFP) and Hexafluoropropylene (HFP), so that the price is low; secondly, the DHFP dimer ozone cracking reaction condition is mild, and the raw material conversion rate and the product yield are high. And finally, a heptafluoroisobutyrate and ammonia catalytic dehydration process is adopted, so that the synthetic route is shortened, a dehydrating agent is not used, and the raw material cost and the byproduct emission are reduced. The production process of the invention has simple, convenient and safe process and is easy for industrial production.

Drawings

FIG. 1 is a schematic diagram of the apparatus for preparing heptafluoroisobutyronitrile by catalytic dehydration according to the present invention.

Detailed Description

The invention provides a method for synthesizing heptafluoroisobutyronitrile, and a person skilled in the art can appropriately improve process parameters by referring to the content. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope of the invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and modifications in the methods and applications described herein, as well as other suitable variations and combinations, may be made to implement and use the techniques of this invention without departing from the spirit and scope of the invention.

The invention provides a method for synthesizing heptafluoroisobutyronitrile, which comprises the following steps:

A) carrying out ozone cracking on hexafluoropropylene dimer in the presence of a fluorocarbon solvent and alcohol to prepare heptafluoroisobutyrate;

B) the obtained heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain heptafluoroisobutyronitrile.

Further, the synthesis method of heptafluoroisobutyrate according to step a) of the present invention first prepares hexafluoropropylene dimer. Preferably, the hexafluoropropylene dimer is synthesized as follows: in an autoclave, firstly, a solvent and a catalyst are mixed according to a proportion, and then hexafluoropropylene is introduced for polymerization to obtain hexafluoropropylene dimer. Wherein:

the solvent is an ether solvent, a nitrile solvent, an amide solvent or a sulfone solvent. The method specifically comprises the following steps: the ether solvent preferably comprises one or more of tetrahydrofuran, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the nitrile solvent comprises one or more of acrylonitrile, adiponitrile and acetonitrile; the amide solvent comprises one or more of dimethylformamide and dimethylacetamide. The sulfone solvent is dimethyl sulfoxide. Acetonitrile is most preferred as a solvent in the present invention. The present invention is not limited in its source, and may be commercially available.

The catalyst is a fluoride salt; the fluoride salt is selected from lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride and zinc fluoride.

The cocatalyst is tertiary amine; the tertiary amine is triethylamine, diethylamine or tetramethylethylenediamine.

In the invention, the mass ratio of the solvent to the catalyst is preferably (1-25): 1; more preferably (1-15): 1;

the mass ratio of the solvent to the cocatalyst is preferably (1-25): 1; more preferably (1-15): 1.

The reaction temperature is preferably-50-80 ℃; more preferably-30 to 60 ℃; most preferably-10 to 40 ℃; particularly preferably 0 to 20 ℃;

the reaction time is preferably 1-20 h; more preferably 2-15 h; most preferably 5 to 13 hours. The pressure of the reaction is preferably 0.1-1 MPa; more preferably 0.1 to 0.5 MPa.

The reaction formula in the preferred embodiment of the present invention is as follows:

further, in the method for synthesizing heptafluoroisobutyrate according to step a), preferably, hexafluoropropylene dimer is subjected to ozone cracking in the presence of a fluorocarbon solvent and an alcohol to prepare heptafluoroisobutyrate. Typically, the heptafluoroisobutyrate is synthesized as follows: under the protection of nitrogen or inert gas, hexafluoropropylene Dimer (DHFP), fluorocarbon solvent and alcohol are added into an oxidation kettle, and then ozone/oxygen mixed gas is metered in to carry out ozone cracking on the hexafluoropropylene dimer to produce heptafluoroisobutyrate. And distilling the reaction liquid after the reaction is finished, and collecting fractions to obtain the product. Wherein the fraction of methyl heptafluoroisobutyrate is 35-37 ℃, and the fraction of ethyl heptafluoroisobutyrate is 53-56 ℃; the fraction of the by-product methyl trifluoroacetate is 43-43.5 ℃, and the fraction of the ethyl trifluoroacetate is 60-62 ℃.

Wherein the ozone cracking adopts O₃And O₂Mixed gas of O in₃The mass concentration of the components is preferably 0.05-5%; more preferably 1% to 2%.

The ozone cracking is carried out in a solvent which is a fluorocarbon solvent, preferably chlorofluorocarbon (CFC), Hydrofluorocarbon (HFC), Hydrofluoroether (HFE), perfluoropolyether (PFPE). Preferably, the fluorocarbon solvent is F-113.

The molar ratio of the fluorocarbon solvent to the hexafluoropropylene dimer in the process is preferably (1-5.0): 1 is more preferably (1-3): 1. namely: the molar ratio of the F-113 to the hexafluoropropylene dimer is (1-3): 1.

the alcohol is one of methanol, ethanol and propanol.

The reaction temperature is preferably-40-80 ℃; more preferably, the reaction temperature is-20 to 40 ℃.

The reaction pressure is preferably 0.1-1 MPa; more preferably, the reaction pressure is 0.1 to 0.5 MPa.

The reaction time is preferably 1-20 h; more preferably 2-15 h; most preferably 3-10 h.

In some of the preferred embodiments of the present invention, the reaction formula is as follows:

compared with the prior art, the method for preparing heptafluoroisobutyrate by adopting the ozone oxidation cracking process has the following advantages: 1) the reaction selectivity is good, and the by-product is less. 2) The reaction temperature is low, and the energy consumption is low; meanwhile, the reaction is carried out under normal pressure, and the requirement on equipment is not high. 3) The product is obtained by one-step method, and the efficiency is high.

Further, the preparation of heptafluoroisobutyronitrile from heptafluoroisobutyrate according to step B) of the present invention includes the following two schemes:

the first scheme is as follows: the mixture of heptafluoroisobutyrate and ammonia is catalyzed and dehydrated under the action of a dehydration catalyst to prepare the heptafluoroisobutyronitrile.

FIG. 1 is a schematic diagram of a device for preparing heptafluoroisobutyronitrile by catalytic dehydration, which comprises a gasification kettle R101, an ammonia gas guide tube, a catalyst tower T-101, a water vapor condenser E101, an ammonia water storage tank V101, a heptafluoroisobutyronitrile crude product condenser E102 and a heptafluoroisobutyronitrile crude product storage tank V102.

The catalytic dehydration process comprises the following steps: the catalyst tower is filled with dehydration catalyst, and is dried and activated under the condition of introducing ammonia gas. In the vaporizer, methyl heptafluoroisobutyrate was added. And heating the gasification kettle to a target temperature, and heating the catalyst tower to the target temperature. Ammonia gas is introduced into the gasification kettle from the gas guide tube at a constant speed. The mixed gas of ammonia gas and methyl heptafluoroisobutyrate vapor enters a catalyst tower to undergo catalytic dehydration

In the process, the heptafluoroisobutyrate entering the catalyst tower can be completely reacted by controlling the ammonia gas introduction speed, the temperature in the gasification kettle and the temperature of the catalyst tower.

And the product gas comprises heptafluoroisobutyronitrile, excessive ammonia gas, generated water vapor and the like, and enters a water vapor condenser in a gas form, the water vapor is condensed to be combined with part of excessive ammonia gas to form ammonia water and is collected in an ammonia water storage tank, the residual tail gas enters the heptafluoroisobutyronitrile condenser, the heptafluoroisobutyronitrile is condensed and is collected in a heptafluoroisobutyronitrile crude product storage tank, and the excessive ammonia gas is recycled. And further rectifying the heptafluoro isobutyronitrile crude product to obtain a product.

The temperature in the gasification kettle, namely the mixing temperature of the heptafluoroisobutyrate and the ammonia gas, is preferably 0-100 ℃; preferably 20 to 80 ℃.

In the catalytic dehydration reaction, the proportion range of methyl heptafluoroisobutyrate and ammonia gas in the mixed gas entering the catalyst tower is 1:1 to 1: 10. preferably, the ratio of methyl heptafluoroisobutyrate to ammonia is in the range of 1: 5 to 1: 10. the proportion of the mixed gas can be changed by adjusting the introduction speed of the ammonia gas.

In the catalytic dehydration reaction, the temperature range of a catalyst tower is 200-800 ℃, namely the dehydration reaction temperature. Preferably, the temperature range is 300-700 ℃; more preferably, the temperature range is 400 to 600 ℃.

The dehydration catalyst in the catalytic column relates to oxides, salts and the like of aluminum, manganese, boron, vanadium, barium, zirconium, cerium, thorium and the like. Preferably a dehydration catalyst which is stable at the operating temperature, such as one or more of silica, alumina, manganese oxide, boron oxide, vanadium oxide, barium oxide, zirconium oxide, cerium oxide or thorium oxide. Preferably, an alumina catalyst is used; preferably, SiO is used₂A catalyst. The catalysts can be obtained commercially or can be prepared by methods known to the skilled worker.

Compared with a chemical reagent dehydration process, the catalytic dehydration process for heptafluoroisobutyrate and ammonia gas provided by the invention shortens the production process flow, improves the production efficiency and reduces the production cost. Meanwhile, no chemical reagent is used in the process to realize dehydration, and no related by-product is generated; the catalyst can be used by reaction; the excessive ammonia gas can be recycled, so that the emission is reduced, and the influence on the environment is reduced.

In some of the preferred embodiments of the present invention, the reaction formula is as follows:

the second scheme is as follows: the method comprises the steps of firstly reacting heptafluoroisobutyrate with ammonia to obtain heptafluoroisobutyramide, and then dehydrating the heptafluoroisobutyramide by using a chemical dehydrating agent to obtain the heptafluoroisobutyronitrile.

Specifically, adding heptafluoroisobutyrate and a solvent into a reaction kettle under the protection of nitrogen or inert gas, then metering and introducing ammonia gas, and heating and preserving heat for reaction to obtain heptafluoroisobutyramide; then adding a solvent into a dehydration reaction kettle, metering heptafluoroisobutyramide under the protection of nitrogen or inert gas, slowly dropwise adding a chemical dehydrating agent into the reactant solution for dehydration, and controlling the dehydration reaction temperature in the dehydration process; the crude reaction product is collected after condensation and finally purified by the rectification process. The preparation scheme has the advantages of mature and reliable process and the like.

Preferably, the heptafluoroisobutyramide of the present invention is obtained by reacting heptafluoroisobutyrate with ammonia.

The reaction is carried out in a solvent, and the solvent can be one or a combination of more of an alcohol solvent, an ether solvent, a nitrile solvent, an amide solvent and a sulfone solvent. Wherein the alcohol solvent comprises one or more of methanol, ethanol and isobutanol; the ether solvent comprises one or more of tetrahydrofuran, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the nitrile solvent comprises one or more of acrylonitrile, adiponitrile and acetonitrile; the amide solvent comprises one or more of dimethylformamide and dimethylacetamide. The sulfone solvent is dimethyl sulfoxide. Alcohol solvents are preferred. The ratio of the solvent to the heptafluoroisobutyric acid ester in the reaction is preferably (1-10): 1. preferably, the ratio of the solvent to the heptafluoroisobutyric acid ester in the reaction is (1-5): 1.

the ammonia in the reaction can be ammonia, an alcohol solution of ammonia, and the like, and ammonia gas is preferred. Wherein the ratio of ammonia to heptafluoroisobutyrate is preferably (1.0-3.0): 1. preferably, the ratio of ammonia to heptafluoroisobutyrate is (1.5-2.5): 1.

the reaction temperature is preferably 0-80 ℃. Preferably, the reaction temperature is 10-40 ℃.

The reaction pressure is preferably 0.1-1 MPa. Preferably, the reaction pressure is 0.1-0.5 MPa.

The reaction time is preferably 1-20 h; more preferably 2-15 h; most preferably 2-10 h.

In some of the preferred embodiments of the present invention, the reaction formula is as follows:

preferably, the heptafluoroisobutyronitrile is obtained by dehydrating, rectifying and purifying heptafluoroisobutyramide under the action of a dehydrating agent.

Preferably, in the step of dehydrating heptafluoroisobutyramide with a dehydrating agent, the dehydrating agent includes, but is not limited to, one or more of phosphorus pentoxide, phosphorus pentachloride, phosphorus oxychloride, thionyl chloride, phosgene, (substituted) benzoyl chloride, aliphatic acid anhydride, fluoroaliphatic acid anhydride, (substituted) benzenesulfonic acid and benzenesulfonyl chloride, anhydrous aluminum chloride, boron trifluoride complex, Grignard reagent.

Preferably, in the step of dehydrating heptafluoroisobutyramide with a dehydrating agent, the reaction solvent used is different depending on the type of the dehydrating agent. For example, when the dehydrating agent is an acid chloride, the reaction solvent is a mixed solvent of trifluoroacetic acid and an organic base (e.g., pyridine), and the molar ratio of trifluoroacetic acid to organic base (pyridine) in the reaction solvent is preferably 1 (0.5-2), more preferably 1 (0.67-1.5). When the dehydrating agent is anhydride, the reaction solvent is a mixed solvent consisting of an amide solvent (such as dimethylformamide) and an organic base (such as pyridine); the amide solvent is one or a mixture of more of formamide, hexamethylphosphoramide, dimethylformamide and dimethylacetamide. When the dehydrating agent is phosphorus pentoxide and phosphorus oxychloride, the reaction solvent can be an ether solvent, a nitrile solvent, an amide solvent and a sulfone solvent; the ether solvent comprises diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; nitrile solvents include acrylonitrile, adiponitrile, and acetonitrile; the amide solvent comprises N, N-dimethylformamide, N-dimethylacetamide, N-diethylformamide and N, N-diethylacetamide; the sulfone solvent includes dimethyl sulfoxide.

Preferably, the molar ratio of the heptafluoroisobutyramide to the dehydrating agent is (0.5-1): 1.

preferably, in the step of dehydrating heptafluoroisobutyramide by using a dehydrating agent, the reaction temperature is-40 ℃ to 200 ℃.

More preferably, the reaction temperature is from-20 ℃ to 150 ℃.

Preferably, in the step of dehydrating heptafluoroisobutyramide by using a dehydrating agent, the reaction time is 1 to 20 hours.

In some of the preferred embodiments of the present invention, the reaction formula is as follows:

the present invention is not limited to the specific operation of the rectification purification, and the operation is well known to those skilled in the art.

The technical scheme for preparing the heptafluoroisobutyronitrile provided by the invention has the following advantages: firstly, the hexafluoropropylene dimer is polymerized by hexafluoropropylene Dimer (DHFP) and Hexafluoropropylene (HFP), so that the price is low; secondly, the DHFP dimer ozone cracking reaction condition is mild, and the raw material conversion rate and the product yield are high. And finally, a heptafluoroisobutyrate and ammonia catalytic dehydration process is adopted, so that the synthetic route is shortened, a dehydrating agent is not used, and the raw material cost and the byproduct emission are reduced. The production process of the invention has simple, convenient and safe process and is easy for industrial production.

In order to further illustrate the present invention, the following examples are provided to describe the synthesis method of heptafluoroisobutyronitrile.