CN111848444A

CN111848444A - Synthesis method of perfluoroisobutyronitrile

Info

Publication number: CN111848444A
Application number: CN202010817713.2A
Authority: CN
Inventors: 周济苍; 喻强; 廖敏; 周遇吉; 喻鼎辉
Original assignee: Jiuding Fluorin Chemicals Co ltd Zhangping Fujian
Current assignee: Jiuding Fluorin Chemicals Co ltd Zhangping Fujian
Priority date: 2020-08-14
Filing date: 2020-08-14
Publication date: 2020-10-30

Abstract

The invention discloses a method for synthesizing perfluoroisobutyronitrile, which comprises the following steps: (1) reacting hexafluoropropylene oxide and hexafluoroacetone serving as raw materials to prepare perfluoro epoxy isobutane; (2) carrying out catalytic isomerization on the perfluoro epoxy isobutane to obtain heptafluoro isobutyryl fluoride; (3) carrying out esterification reaction on heptafluoro isobutyryl fluoride and alcohol to obtain heptafluoro isobutyrate; (4) and reacting heptafluoroisobutyrate with ammonia, and dehydrating to obtain perfluoroisobutyronitrile. The synthesis method has the advantages of easily available raw materials, low raw material cost, few byproducts, mild reaction conditions, high reaction conversion rate and yield, short synthesis route, simple and safe process and easy industrial production.

Description

Synthesis method of perfluoroisobutyronitrile

Technical Field

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

Background

Heptafluoroisobutyronitrile (perfluoroisobutyronitrile), i.e., 2,3,3, 3-tetrafluoro-2-trifluoromethylpropionitrile, is a perfluoronitrile compound having 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 (JChemSocChemCommun1987, 1699; JChemSocPerkinTransI1980, 2254; JChemSocPerkinTransI1990, 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 elevated 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, so that the production cost is increased, and environmental pollution problems related to emission are caused.

Therefore, it is still of practical significance 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

The invention mainly aims to provide a method for synthesizing perfluoroisobutyronitrile, which has the advantages of easily obtained raw materials, few byproducts, mild reaction conditions, high reaction conversion rate and yield, short synthetic route, simple, convenient and safe process and easy industrial production.

In order to achieve the above object, the present invention provides a method for synthesizing perfluoroisobutyronitrile, comprising the steps of:

(1) reacting hexafluoropropylene oxide and hexafluoroacetone serving as raw materials to prepare perfluoro epoxy isobutane;

(2) carrying out catalytic isomerization on the perfluoro epoxy isobutane to obtain heptafluoro isobutyryl fluoride;

(3) carrying out esterification reaction on heptafluoro isobutyryl fluoride and alcohol to obtain heptafluoro isobutyrate;

(4) and reacting heptafluoroisobutyrate with ammonia, and dehydrating to obtain perfluoroisobutyronitrile.

The synthesis method of perfluoroisobutyronitrile of the invention firstly generates CF through the decomposition of hexafluoropropylene oxide₂Free radical, CF₂Reacting the free radicals with hexafluoroacetone to generate perfluoro epoxy isobutane; then carrying out catalytic isomerization reaction on the perfluoro epoxy isobutane to obtain heptafluoro isobutyryl fluoride; then, carrying out esterification reaction on heptafluoro isobutyryl fluoride and alcohol to obtain heptafluoro isobutyrate; and finally, reacting heptafluoroisobutyrate with ammonia, and dehydrating to obtain perfluoroisobutyronitrile. The raw materials selected by the synthesis method are all commercially available, and the main raw materials of hexafluoropropylene oxide and hexafluoroacetone can be supplied in large quantities; the reaction condition is mild, and the reaction conversion rate and yield are high; the process is simple, convenient and safe, and is easy for industrial production.

Preferably, in the step (1), the reaction temperature of the hexafluoropropylene oxide and the hexafluoroacetone is 100-250 ℃; further preferably 150 to 250 ℃.

Preferably, in the step (1), the reaction pressure of the hexafluoropropylene oxide and the hexafluoroacetone is 1MPa to 25 MPa; more preferably 1MPa to 15 MPa.

Preferably, in the step (1), the molar ratio of the hexafluoropropylene oxide to the hexafluoroacetone is 1 (0.5-2); further preferred are (1.5: 1) to (1: 1.5).

Preferably, in the step (1), the reaction time of the hexafluoropropylene oxide and the hexafluoroacetone is 1 h-20 h.

Preferably, in the step (2), the catalyst used in the catalytic isomerization reaction is an organic amine compound, and more preferably a tertiary amine compound, such as trimethylamine, triethylamine, tetramethylethylenediamine, and the like; more preferably a triethylamine based catalyst. The dosage of the catalyst is preferably 1-20% of the mass of the perfluoroepoxy isobutane; further preferably, the using amount of the catalyst is 1-10% of the mass of the perfluoroepoxy isobutane; more preferably 1 to 5%.

Preferably, in the step (2), the solvent used for the catalytic isomerization reaction is one or a combination of several of an ether solvent, a nitrile solvent, an amide solvent and a sulfone solvent; wherein the ether solvent comprises tetrahydrofuran, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and the like; nitrile solvents include acrylonitrile, adiponitrile, acetonitrile, and the like; amide solvents including dimethylformamide, dimethylacetamide and the like; the sulfone solvent includes dimethyl sulfoxide and the like. Further preferably, a nitrile solvent is used; more preferably, acetonitrile is used as the isomerization solvent.

Preferably, in the step (2), the molar ratio of the perfluoro epoxy isobutane to the solvent is 3: 1-1: 3; further preferably, the molar ratio of the perfluoroepoxyisobutane to the solvent is 2:1 to 1: 2.

Preferably, in the step (2), the temperature for catalyzing the isomerization reaction is 0-100 ℃; further preferably, the temperature of the catalytic isomerization reaction is 0-80 ℃; more preferably, the temperature at which the isomerization reaction is catalyzed is from 0 ℃ to 60 ℃.

Preferably, in the step (2), the reaction pressure for catalyzing the isomerization reaction is 0.1 MPa-1 MPa; further preferably, the reaction pressure of the catalytic isomerization reaction is 0.1MPa to 0.8 MPa; more preferably, the reaction pressure for the catalytic isomerization reaction is 0.1MPa to 0.5 MPa.

Preferably, in the step (2), the reaction time for catalyzing the isomerization reaction is 1-20 h.

Preferably, in the step (3), the molar ratio of the heptafluoro isobutyryl fluoride to the alcohol in the esterification reaction is 1 (2-10); further preferably, the molar ratio of the heptafluoro isobutyryl fluoride to the alcohol in the esterification reaction is 1 (2-5).

Preferably, in the step (3), the temperature of the esterification reaction is 0-100 ℃; further preferably, the temperature of the esterification reaction is 20 ℃ to 80 ℃; more preferably, the temperature of the esterification reaction is from 40 ℃ to 60 ℃.

Preferably, in the step (3), the pressure of the esterification reaction is 0.1MPa to 1 MPa; further preferably, the pressure of the esterification reaction is 0.1MPa to 0.8 MPa; more preferably, the pressure of the esterification reaction is 0.2MPa to 0.5 MPa.

Preferably, in the step (3), the esterification reaction time is 1-20 h.

Specifically, in the step (4), the heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain the perfluoroisobutyronitrile, and the method comprises the following two schemes:

the first scheme is as follows:

firstly, reacting heptafluoroisobutyrate with ammonia in a solvent to obtain heptafluoroisobutyramide; then dehydrating heptafluoroisobutyramide under the action of a chemical dehydrating agent to obtain the perfluoroisobutyronitrile.

Preferably, the solvent used for the reaction of the heptafluoroisobutyrate and the ammonia is 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 methanol, ethanol, isobutanol and the like; ether solvents include tetrahydrofuran, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and the like; nitrile solvents include acrylonitrile, adiponitrile, acetonitrile, and the like; amide solvents including dimethylformamide, dimethylacetamide and the like; the sulfone solvent includes dimethyl sulfoxide and the like. Further, it is preferable to use an alcohol solvent.

Preferably, the molar ratio of the solvent to the heptafluoroisobutyrate is (1-10): 1; more preferably, the molar ratio of the solvent to heptafluoroisobutyrate is (1-5): 1.

Preferably, the ammonia used is ammonia gas or an alcoholic solution of ammonia; more preferably ammonia gas.

Preferably, the molar ratio of ammonia to heptafluoroisobutyrate used is (1-3): 1; more preferably, the molar ratio of ammonia to heptafluoroisobutyrate is (1.5-2.5): 1.

Preferably, the reaction temperature of the reaction of heptafluoroisobutyrate with ammonia is from 0 ℃ to 80 ℃; further preferably, the reaction temperature of the reaction of heptafluoroisobutyrate with ammonia is from 10 ℃ to 40 ℃.

Preferably, the reaction pressure of the reaction of heptafluoroisobutyrate with ammonia is from 0.1MPa to 1 MPa; further preferably, the reaction pressure of the reaction of heptafluoroisobutyrate with ammonia is from 0.1MPa to 0.5 MPa.

Preferably, the reaction time of the reaction of heptafluoroisobutyrate with ammonia is from 1h to 20 h.

Specifically, chemical dehydrating agents that may be used include, but are not limited to, phosphorus pentoxide, phosphorus oxychloride, phosphorus pentachloride, thionyl chloride, phosgene, benzoyl chloride, substituted benzoyl chloride, aliphatic acid anhydride, fluoroaliphatic acid anhydride, benzenesulfonyl chloride, substituted benzenesulfonyl chloride, anhydrous aluminum chloride, boron trifluoride complex, and Grignard reagents.

Specifically, when heptafluoroisobutyramide is dehydrated using an acid chloride, the dehydration reaction can be carried out as follows: mixing trifluoroacetic acid and pyridine serving as solvents according to a certain molar ratio, adding the mixture into a reaction kettle, metering heptafluoroisobutyramide, and stirring; slowly dripping acyl chloride, such as benzoyl chloride, into the reactant solution, and controlling the reaction temperature in the dripping process; the crude reaction product is collected after condensation and finally purified by the rectification process.

In the dehydration process, the molar ratio of trifluoroacetic acid to pyridine is (2: 1) - (1: 2); more preferably (1.5: 1) to (1: 1.5); the acyl chloride can be 2, 2-dimethyl propionyl chloride, 2-dimethyl butyryl chloride, benzoyl chloride, etc.; the molar ratio of the heptafluoroisobutyramide to the acyl chloride is (0.5-1): 1; the reaction temperature is-40 ℃ to 40 ℃, and more preferably, the reaction temperature is-20 ℃ to 20 ℃; the reaction time is 1-20 h.

Specifically, when heptafluoroisobutyramide is dehydrated using an acid anhydride, the dehydration reaction can be carried out as follows: dissolving heptafluoroisobutyramide in an amide solvent, adding into a reaction kettle, cooling, slowly adding pyridine at about 10 ℃, and stirring; finally, metering and slowly dripping trifluoroacetic anhydride; controlling the reaction temperature to be about 0 ℃ in the dripping process; the crude reaction product is collected after condensation and finally purified by the rectification process.

In the above dehydration, as the solvent, a mixed solvent composed of an amide-based solvent (e.g., dimethylformamide) and an organic base (e.g., pyridine) can be used; wherein the amide solvent is one or a mixture of more of formamide, hexamethylphosphoramide, dimethylformamide and dimethylacetamide. The molar ratio of the solvent to the heptafluoroisobutyramide is preferably (0.5-8): 1; the molar ratio of pyridine to heptafluoroisobutyramide is preferably (0.5-8): 1; the anhydride is mainly trifluoroacetic anhydride, and the molar ratio of the trifluoroacetic anhydride to the heptafluoroisobutyramide is (0.5-7): 1; preferably, the molar ratio of trifluoroacetic anhydride to heptafluoroisobutyramide is (0.5-5): 1; the reaction temperature is-40 ℃ to 40 ℃, preferably, the reaction temperature is-20 ℃ to 20 ℃; the reaction time is 1-20 h.

Specifically, when heptafluoroisobutyramide is dehydrated using phosphorus pentoxide and phosphorus oxychloride, the dehydration reaction can be carried out as follows: mixing a solvent and a dehydrating agent according to a certain molar ratio, adding the mixture into a reaction kettle, dissolving heptafluoroisobutyramide in the solvent to prepare a solution with a certain concentration, then metering and adding the heptafluoroisobutyramide, and stirring; heating and raising the temperature for reaction; the crude reaction product is collected after condensation and finally purified by the rectification process.

In the dehydration process, the solvent can adopt an ether solvent, a nitrile solvent, an amide solvent and a sulfone solvent; wherein the ether solvent comprises diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and the like; nitrile solvents include acrylonitrile, adiponitrile, acetonitrile, and the like; the amide-based solvent includes N, N-dimethylformamide, N-dimethylacetamide, N-diethylformamide, N-diethylacetamide, etc.; sulfone solvents include dimethyl sulfoxide, etc.; the molar ratio of the solvent to the heptafluoroisobutyramide is (2-5): 1; the dehydrating agent comprises phosphorus pentoxide, phosphorus oxychloride and the like; the molar ratio of the heptafluoroisobutyramide to the dehydrating agent is (0.5-1): 1; the reaction temperature is 0-200 ℃, preferably, the reaction temperature is 50-150 ℃; the reaction time is preferably 1-20 h; the reaction device is an autoclave.

The second scheme is as follows:

introducing the mixed gas of the heptafluoroisobutyrate vapor and the ammonia gas into a catalyst tower, and dehydrating the heptafluoroisobutyrate vapor and the ammonia gas under the action of a dehydration catalyst to obtain the perfluoroisobutyronitrile.

Specifically, the dehydration catalyst is an oxide or salt of aluminum, manganese, boron, vanadium, barium, zirconium, cerium and thorium; it is preferable to use a dehydration catalyst having good stability at the operating temperature, such as alumina, ceria, thoria, zirconia, and the like. The temperature of the catalyst tower is controlled between 200 ℃ and 800 ℃ in the catalytic dehydration process; further preferably, the temperature of the catalyst tower is controlled to be 300-700 ℃; more preferably, the temperature of the catalyst column is controlled to be 400 to 600 ℃. Controlling the molar ratio of heptafluoroisobutyrate to ammonia gas in the mixed gas to be 1 (1-10); preferably 1: (5-10); the molar ratio of the mixed gas can be changed by adjusting the introduction speed of the ammonia gas.

The structure diagram of the catalytic dehydration device used in the scheme is shown in fig. 3, and the catalytic dehydration device mainly comprises a gasification kettle, an ammonia gas guide tube, a catalyst tower, a water vapor condenser, an ammonia water methanol storage tank, a heptafluoroisobutyronitrile crude product condenser and a heptafluoroisobutyronitrile crude product storage tank. A typical catalytic dehydration process is as follows: filling a dehydration catalyst in a catalyst tower, and drying and activating the catalyst tower under the condition of introducing ammonia gas; adding methyl heptafluoroisobutyrate into a gasification kettle; 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 pipe at a constant speed; the mixed gas of ammonia gas and methyl heptafluoroisobutyrate steam enters a catalyst tower to be subjected to catalytic dehydration; the product gas comprises heptafluoroisobutyronitrile, excessive ammonia gas, generated methanol steam, water vapor and the like, and enters a water vapor condenser in a gas form, the methanol and the water vapor are condensed and combined with part of the excessive ammonia gas to form ammonia water, and the ammonia water are collected in an ammonia water methanol storage tank for further separation treatment; the residual tail gas enters a heptafluoroisobutyronitrile condenser, the heptafluoroisobutyronitrile is condensed and 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.

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

Compared with the prior art, the invention has the beneficial effects that:

according to the synthesis method of the perfluoroisobutyronitrile, the selected raw materials are commercially available, and the main raw materials of hexafluoropropylene oxide and hexafluoroacetone can be supplied in large quantities; the process for catalytic dehydration of heptafluoroisobutyrate and ammonia gas adopted by the invention does not need to prepare heptafluoroisobutyramide first, thereby effectively shortening the synthetic route, not using chemical dehydrating agent, and effectively reducing the raw material cost and byproduct emission; the synthesis method has the advantages of mild reaction conditions, high reaction conversion rate and yield, simple and safe process and easy industrial production.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a synthesis scheme of perfluoroisobutyronitrile according to the method for synthesizing perfluoroisobutyronitrile according to example 1 of the present invention.

Fig. 2 is a synthesis scheme of the perfluoroisobutyronitrile synthesis method of example 2 of the present invention.

Fig. 3 is a structural diagram of a catalytic dehydration apparatus in the perfluoroisobutyronitrile synthesis method according to the embodiment of the present invention.

In the above figures, the following reference numerals are included:

1. a gasification kettle; 2. an ammonia gas guide pipe; 3. a catalyst tower; 4. a water vapor condenser; 5. an ammonia water methanol storage tank; 6. a heptafluoroisobutyronitrile crude product condenser; 7. a storage tank for a crude product of heptafluoroisobutyronitrile.

Detailed Description

In order to facilitate an understanding of the present invention, the present invention will be described more fully and in detail with reference to the preferred embodiments, but the scope of the present invention is not limited to the specific embodiments described below.

Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

Example 1:

the synthesis scheme of perfluoroisobutyronitrile according to the embodiment of the invention is shown in fig. 1, and the synthesis method comprises the following steps:

(1) synthesis of perfluoroepoxyisobutane

Firstly, heating a reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the system; cooling the reaction kettle to-30 ℃, metering and introducing Hexafluoroacetone (HFA) (166g, 1mol) into the reaction kettle, and controlling the aeration speed to completely liquefy the HFA; then, hexafluoropropylene oxide (HFPO) (166.02g, 1mol) is metered in, and the aeration speed is controlled to completely liquefy the HFPO; closing the air inlet valve, heating the kettle to 190 ℃ and reacting for 8 hours; and (3) introducing a supersaturated sodium fluoride solution into a washing column of a product after the reaction to obtain a mixture containing the perfluoro-epoxy-isobutane and the perfluoro-epoxy-propane, distilling to obtain the perfluoro-epoxy-isobutane (126.4g, 0.585mol, the yield is 58.5%), and detecting the purity of the product by gas chromatography to be 99.5%.

(2) Synthesis of perfluoroisobutyryl fluoride

Heating the reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the reaction system; adding acetonitrile (205g, 5mol) as a solvent and triethylamine (6.07g, 0.06mol) as a catalyst under the protection of nitrogen, and stirring; then, quickly adding the perfluoro epoxy isobutane (126.4g, 0.585mol) obtained in the first step of reaction into a reaction kettle, stirring, and carrying out heat preservation reaction for 6 hours at the temperature of 30 ℃; after the reaction was completed, the product was distilled to give perfluoroisobutyryl fluoride (119.4g, 0.553mol, yield 94.5%).

(3) Synthesis of heptafluoroisobutyrate

Heating the reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the reaction system; under the protection of nitrogen, putting perfluoroisobutyryl fluoride (119.4g, 0.553mol) and methanol (320g, 10mol) into a reaction kettle rapidly under stirring, and keeping the temperature at 40 ℃ for reaction for 10 hours; the solvent in the reaction product was dried by rotary evaporation to give perfluoroisobutyrate product (120.2g, 0.527mol, yield 95.3%).

(4) Synthesis of perfluoroisobutyramide

Heating the reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the reaction system; under the protection of nitrogen, perfluoroisobutyrate (120.2g, 0.527mol) and methanol (256g, 8mol) are quickly put into a reaction kettle under stirring, and ammonia gas (204g, 17mol) is introduced to carry out heat preservation reaction at 40 ℃ for 10 hours; the solvent in the reaction product was dried by rotary evaporator to obtain crude perfluoromethacrylamide (109.9g, 0.516mol, yield 98%).

(5) Synthesis of perfluoroisobutyronitrile

Heating the reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the reaction system; under the protection of nitrogen, perfluoroisobutyramide (109.9g, 0.516mol) and dimethylformamide (146.2g, 2mol) are quickly put into a reaction kettle under stirring, then pyridine (79.1g, 1mol) is slowly added, and stirring is carried out; finally, trifluoroacetic anhydride (105g, 0.5mol) is slowly dripped into the reaction kettle at the temperature of 20 ℃ for reaction for 5 hours; after the reaction, the gaseous perfluoroisobutyronitrile (89.5g, 0.459mol, yield 88.9%) was collected, and the purity of the perfluoroisobutyronitrile was 99.5% by gas chromatography.

Example 2:

the synthesis scheme of perfluoroisobutyronitrile according to the embodiment of the present invention is shown in fig. 2, and the synthesis method includes the following steps:

(1) synthesis of perfluoroepoxyisobutane

Firstly, heating a reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the system; cooling the reaction kettle to-30 ℃, metering and introducing Hexafluoroacetone (HFA) (166g, 1mol) into the reaction kettle, and controlling the aeration speed to completely liquefy the HFA; then, hexafluoropropylene oxide (HFPO) (166.02g, 1mol) is metered in, and the aeration speed is controlled to completely liquefy the HFPO; closing the air inlet valve, heating the kettle to 190 ℃ and reacting for 8 hours; introducing the product after the reaction into a supersaturated aqueous sodium fluoride washing column to obtain a mixture containing perfluoroepoxyisobutane and perfluoroepoxypropane; perfluoro epoxy isobutane was obtained by distillation (126.4g, 0.585mol, yield 58.5%) and the product was 99.5% pure by gas chromatography.

(2) Synthesis of heptafluoro isobutyryl fluoride

Heating the reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the reaction system; adding acetonitrile (205g, 5mol) as a solvent and triethylamine (6.07g, 0.06mol) as a catalyst under the protection of nitrogen, and stirring; then, perfluoroepoxy isobutane (137.5g, 0.585mol) obtained in the first-step reaction is quickly added into a reaction kettle, stirred and subjected to heat preservation reaction at 30 ℃ for 6 hours; after the reaction was completed, the product was distilled to give perfluoroisobutyryl fluoride (119.4g, 0.553mol, yield 94.5%).

(3) Synthesis of heptafluoroisobutyrate

Heating the reaction system, vacuumizing to remove water, and purging the whole system with high-purity nitrogen to remove oxygen in the reaction system; under the protection of nitrogen, putting perfluoroisobutyryl fluoride (119.4g, 0.553mol) and methanol (256g, 8mol) into a reaction kettle rapidly under stirring, and keeping the temperature at 40 ℃ for reaction for 10 hours; the solvent in the reaction product was dried by rotary evaporator to obtain methyl perfluoroisobutyrate product (120.2g, 0.527mol, yield 95.3%).

(4) Synthesis of heptafluoroisobutyronitrile

The structure diagram of the adopted catalytic dehydration device is shown in fig. 3, and the device comprises a gasification kettle 1, an ammonia gas guide tube 2, a catalyst tower 3, a water vapor condenser 4, an ammonia methanol storage tank 5, a heptafluoroisobutyronitrile crude product condenser 6, a heptafluoroisobutyronitrile crude product storage tank 7 and the like.

Al is packed in the catalyst column 3₂O₃Dehydration catalyst, heat activation, activation processIntroducing ammonia gas; adding methyl heptafluoroisobutyrate (120.2g, 0.527mol) into a gasification kettle 1, heating the gasification kettle 1 to 40 ℃, simultaneously heating a catalyst tower 3 to 500 ℃, introducing ammonia (85g, 5mol) into the gasification kettle 1 at a constant speed from an ammonia gas guide tube 2, and introducing mixed gas of the ammonia and the methyl heptafluoroisobutyrate steam into the catalyst tower 3 to perform catalytic dehydration; in the dehydration process, the heptafluoroisobutyrate entering the catalyst tower 3 can be completely reacted by controlling the ammonia gas introduction rate, the temperature in the vaporization reactor 1 and the temperature of the catalyst tower 3.

The product gas comprises heptafluoroisobutyronitrile, excessive ammonia gas, generated methanol steam, water steam and the like, enters a water vapor condenser 4 in a gas form, the methanol and the water vapor are condensed and combined with the excessive ammonia gas into ammonia water which is collected in an ammonia water methanol storage tank 5, the residual tail gas contains the heptafluoroisobutyronitrile and the excessive ammonia gas, the residual tail gas is further condensed by a heptafluoroisobutyronitrile crude product condenser 6 and then collected in a heptafluoroisobutyronitrile crude product storage tank 7, and the ammonia gas is recovered. The crude product of heptafluoroisobutyronitrile was further rectified to obtain a product (82.5g, 0.423mol) with a yield of 80.3%.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The method for synthesizing the perfluoroisobutyronitrile is characterized by comprising the following steps of:

2. The method for synthesizing perfluoroisobutyronitrile according to claim 1, wherein in the step (1), the reaction temperature of hexafluoropropylene oxide and hexafluoroacetone is 100 ℃ to 250 ℃; the reaction pressure is 1 MPa-25 MPa; the molar ratio of the hexafluoropropylene oxide to the hexafluoroacetone is 1 (0.5-2); the reaction time is 1-20 h.

3. The method for synthesizing perfluoroisobutyronitrile according to claim 1, wherein in the step (2), the catalyst used in the catalytic isomerization reaction is an organic amine compound, and the amount of the catalyst is 1-20% of the mass of perfluoroepoxyisobutane; the solvent used for the catalytic isomerization reaction is one or a combination of more of an ether solvent, a nitrile solvent, an amide solvent and a sulfone solvent; the mol ratio of the perfluoro epoxy isobutane to the solvent is 3: 1-1: 3; the temperature of the catalytic isomerization reaction is 0-100 ℃, the reaction pressure is 0.1-1 MPa, and the reaction time is 1-20 h.

4. The method for synthesizing perfluoroisobutyronitrile according to claim 1, wherein in the step (3), the molar ratio of the heptafluoroisobutyryl fluoride to the alcohol in the esterification reaction is 1 (2-10); the temperature of the esterification reaction is 0-100 ℃; the pressure of the esterification reaction is 0.1MPa to 1 MPa; the time of the esterification reaction is 1 to 20 hours.

5. The method for synthesizing perfluoroisobutyronitrile according to any one of claims 1 to 4, wherein in the step (4), heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain perfluoroisobutyronitrile, specifically: firstly, reacting heptafluoroisobutyrate with ammonia in a solvent to obtain heptafluoroisobutyramide; then dehydrating heptafluoroisobutyramide under the action of a chemical dehydrating agent to obtain the perfluoroisobutyronitrile.

6. The method for synthesizing perfluoroisobutyronitrile according to claim 5, wherein the solvent used for the reaction of heptafluoroisobutyrate with ammonia is one or a combination of several of an alcohol solvent, an ether solvent, a nitrile solvent, an amide solvent and a sulfone solvent, and the molar ratio of the solvent to the heptafluoroisobutyrate is (1-10): 1; the ammonia is ammonia gas or ammonia alcohol solution; the molar ratio of ammonia to heptafluoroisobutyrate is (1-3) to 1; the reaction temperature of the reaction between the heptafluoroisobutyrate and ammonia is 0-80 ℃, the reaction pressure is 0.1-1 MPa, and the reaction time is 1-20 h.

7. The method for synthesizing perfluoroisobutyronitrile according to claim 5, wherein the chemical dehydrating agent comprises phosphorus pentoxide, phosphorus oxychloride, phosphorus pentachloride, thionyl chloride, phosgene, benzoyl chloride, substituted benzoyl chloride, aliphatic acid anhydride, fluoroaliphatic acid anhydride, benzenesulfonyl chloride, substituted benzenesulfonyl chloride, anhydrous aluminum chloride, boron trifluoride complex and Grignard reagent.

8. The method for synthesizing perfluoroisobutyronitrile according to any one of claims 1 to 4, wherein in the step (4), heptafluoroisobutyrate reacts with ammonia and is dehydrated to obtain perfluoroisobutyronitrile, specifically: introducing the mixed gas of the heptafluoroisobutyrate vapor and the ammonia gas into a catalyst tower, and dehydrating the heptafluoroisobutyrate vapor and the ammonia gas under the action of a dehydration catalyst to obtain the perfluoroisobutyronitrile.

9. The method for synthesizing perfluoroisobutyronitrile according to claim 8, wherein the dehydration catalyst is an oxide or salt of aluminum, manganese, boron, vanadium, barium, zirconium, cerium, and thorium; the temperature of the catalyst tower in the catalytic dehydration process is 200-800 ℃.

10. The method for synthesizing perfluoroisobutyronitrile according to claim 8, wherein the molar ratio of heptafluoroisobutyrate to ammonia gas in the mixed gas is 1 (1-10).