JP2006219419A - Method for producing perfluorovinyl ether monomer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a perfluorovinyl ether monomer being a raw material for a heat-resistant and oxidation-resistant perfluorosulfonic acid polymer by a reduced number of processes in a high yield. <P>SOLUTION: The method for producing a perfluorovinyl ether monomer comprises a process (a) for isomerizing a compound represented by general formula (1) to give a compound represented by general formula (3) FCO(CF<SB>2</SB>)<SB>n-1</SB>SO<SB>2</SB>F (3) (n is an integer of 3-8), a process (b) for adding a hexafluoropropylene oxide (HFPO) to the compound represented by general formula (3) to give a compound represented by general formula (4) CF<SB>3</SB>CF(COF)O(CF<SB>2</SB>)<SB>n</SB>SO<SB>2</SB>F and a process (c) for decarboxylating the compound represented by general formula (4) to give a perfluorovinyl ether monomer represented by general formula (2) CF<SB>2</SB>=CFO(CF<SB>2</SB>)<SB>n</SB>SO<SB>2</SB>F. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a perfluorovinyl ether monomer which is a raw material for a perfluorosulfonic acid polymer having excellent heat resistance and chemical stability. Specifically, the present invention relates to a method for producing a perfluorovinyl ether monomer, which is a raw material for a highly durable perfluorosulfonic acid polymer suitable for fuel cell applications.

  Currently, in the field of chloroalkali and fuel cells, the following general formula (6)

(Where k / l = 3-10)
Perfluorosulfonic acid polymers having m ′ = 1 and n ′ = 2 are mainly employed.
This polymer has the following general formula (7)

In this method, a copolymer of perfluorovinyl ether monomer having m ′ = 1 and n ′ = 2 and tetrafluoroethylene (TFE) is formed into a film and then subjected to a hydrolysis reaction.
However, in the fuel cell field, there is a demand for high-temperature operation particularly for in-vehicle use, and a polymer having a higher glass transition temperature and m ′ = 0 in general formula (6) is more suitable for high-temperature operation. I know.
Among the polymers having m ′ = 0, the inventors have studied, and in the perfluorosulfonic acid polymer represented by the general formula (6), m ′ = 0 and n ′ is 3 to 8, preferably 4. In the case of ˜6, it has been found that particularly excellent heat resistance and oxidation resistance are expressed. Therefore, the perfluorovinyl ether monomer which is m ′ = 0 and n ′ = 3 to 8 in the general formula (7), that is, the monomer of the general formula (2), which is the raw material, is extremely useful.

As a known technique relating to the perfluorovinyl ether monomer of the present invention, there have been only a few reports so far on the production method of the monomer (general formula (2)), all of which are advantageous in industrial production. Not the way.
For example, Patent Document 1 discloses a method for producing the monomer (general formula (2)) using tetrafluoroethylene, dimethyl carbonate, and sodium ethyl mercaptide as starting materials. In addition to the low yield of 8%, the production method is limited to n = 3.

Patent Document 2 discloses that RfCH ₂ OCO (CH ₂ ) ₃ SO ₂ F (wherein Rf is a perfluoroalkyl group containing an ether group) is directly fluorinated with elemental fluorine to obtain RfCF ₂ OCO (CF ₂ ) _3. Disclosed is a method of producing a monomer represented by the general formula (2) through two steps after preparing SO ₂ F and treating with KF to produce a compound of n = 4 in the general formula (3). ing. However, in this method, the synthesis of RfCH ₂ OCO (CH ₂ ) ₃ SO ₂ F, which is a starting material, is complicated and involves a multi-step process, and the general formula includes a process for obtaining a starting material from a known compound. A total of 7 steps are required until the monomer (2) is obtained. In addition, there is a problem that the total yield is as low as 16%.

On the other hand, there is a method using a sultone compound (general formula (5)), which is an easily available industrial product, as a starting material (Patent Documents 3 and 4).
However, the method using a sultone compound disclosed in Patent Documents 3 and 4 as a starting material is an acid fluoride compound obtained by electrolytic fluorination of a sultone compound (n = 3,4 in the general formula (5)) in anhydrous hydrofluoric acid. (N = 3,4 in the general formula (3) is disclosed. This method is excellent in that the desired perfluorovinyl ether monomer can be produced in only 3 steps. There are many side reactions due to the chemical conversion reaction, resulting in low yields and a need to dispose of a large amount of by-products.

Thus, a practical method for producing a perfluorovinyl ether monomer represented by the general formula (2), which is a raw material of a perfluorosulfonic acid polymer excellent in heat resistance and chemical stability, has been known so far. The development of an efficient manufacturing method was awaited.
JP-A-56-90054 International Publication No. WO04 / 094365 Specification JP 57-164991 A US Pat. No. 6,624,328

  The present invention provides a method for producing a perfluorovinyl ether monomer, which is a raw material for a perfluorosulfonic acid polymer excellent in heat resistance and chemical stability, with a small number of steps and in a high yield. Specifically, it provides a method for producing a well-known compound (a fluorinated sultone compound (general formula (1)) in 3 steps and a sultone compound (general formula (5)) in 4 steps with a high yield. It is.

As a result of intensive studies, the present inventors have passed a specific process using a perfluorovinyl ether monomer (general formula (2)) as a starting material and an easily available fluorinated sultone compound (general formula (1)). Thus, the present invention was accomplished by finding a method of producing the sultone compound (general formula (5)) with a high yield in 4 steps even with only 3 steps.
That is, the present invention is as follows.
1. The following general formula (1)

(In the formula, n is an integer of 3 to 8.)
As a starting material, the following general formula (2) is obtained by the operations of the following steps (a) to (c).
_{CF 2 = CFO (CF 2)} n SO 2 F (2)
(N is the same as in general formula (1).)
A process for producing a perfluorovinyl ether monomer represented by the formula:

Step (a)
The compound of the general formula (1) is isomerized to give the following general formula (3)
FCO (CF ₂ ) _n-1 SO ₂ F (3)
(N is the same as in general formula (1).)
The process made into the compound represented by these.

Step (b)
Hexafluoropropylene oxide (HFPO) is added to the compound of the general formula (3), and the following general formula (4)
CF ₃ CF (COF) O (CF ₂ ) _n SO ₂ F (4)
(N is the same as in general formula (1).)
The process made into the compound represented by these.

Step (c)
A step of decarboxylating the compound of the general formula (4) to obtain a perfluorovinyl ether monomer of the general formula (2).
2, the compound represented by the general formula (1) is represented by the following general formula (5)

(N is the same as in general formula (1).)
The production method according to 1, wherein the compound represented by the formula is produced by directly fluorinating with a fluorinating agent.
3. Direct fluorination of the compound represented by the general formula (5) is performed in the presence of an inert medium capable of dissolving 1% by mass or more of the compound represented by the general formula (5) at 20 ° C. 2. The production method according to 2, characterized by the above.

  By the method of the present invention, a perfluorovinyl ether monomer (general formula (2)), which is a raw material for a perfluorosulfonic acid polymer excellent in heat resistance and chemical stability, can be produced with a small number of steps and in a high yield.

Hereinafter, the present invention will be described in detail.
First, the method for producing the perfluorovinyl ether monomer represented by the general formula (2) through the three steps from the fluorinated sultone compound represented by the general formula (1), which is the first production method of the present invention, is described below. Explained.
The inventors first prepared a compound represented by the general formula (1) in which a compound represented by the general formula (3) (hereinafter referred to as an acid fluoride compound (3)) is a starting material of the present invention ( Hereinafter, it was found that the compound could be synthesized in one step by isomerization of the fluorinated sultone compound (1) (step (a)). That is, it was found that the fluorinated sultone compound (1) was easily isomerized only by treatment under specific conditions, and the acid fluoride compound (3) of the general formula (3) was produced with good yield.

From the acid fluoride compound (3) of the general formula (3), the perfluorovinyl ether monomer represented by the general formula (2) (hereinafter referred to as perfluoro) is passed through the following two steps (step (b) and step (c)). Vinyl ether monomer (2)) can be produced.
Therefore, the perfluorovinyl ether monomer (2) represented by the general formula (2) can be produced from the fluorinated sultone compound (1) represented by the general formula (1) by only 3 steps by the above method. It became.

  In the perfluorovinyl ether monomer (2) obtained by the above production method, the oxidation resistance when the target perfluorosulfonic acid polymer is obtained is excellent, and in the operation of step (c), that is, vinylation by decarboxylation. Since there is almost no side reaction of the cyclization reaction and the yield is high, the effect of the present invention becomes more remarkable when n is 4 or more. On the other hand, if n is too large, the glass transition temperature when the final polymer is obtained will be low, so n is preferably 6 or less, and more preferably 4 or less. Further, n is preferably 3 or 4 from the viewpoint of easy availability of raw materials, and n = 4 is most preferable since both conditions are satisfied.

The characteristics of the first production method of the present invention have been described above, but more specifically will be described below.
First, the isomerization step (a) will be described.
The fluorinated sultone compound (1) represented by the general formula (1) can be isomerized to the acid fluoride compound (3) of the general formula (3) under various conditions within a specific range. Any isomerization conditions may be employed in the method of the invention.

Examples of the isomerization conditions include, for example, treatment in the presence of various isomerization catalysts as described below. Examples of the isomerization catalyst include various Lewis base compounds such as R ₃ N (R is a hydrocarbon group, hereinafter the same) type tertiary amine compound and heterocyclic compounds containing a hetero atom such as a nitrogen atom, Examples include fluoride ion-containing compounds such as KF, CsF, NaF, R ₄ NF, R ₄ PF, and R ₃ SiF, various inorganic oxides, and inorganic salts. Of these, Lewis base compounds and fluoride ion-containing compounds are preferred, and fluoride ion-containing compounds are particularly preferred.

The conditions for the isomerization treatment are usually carried out under anhydrous conditions in a solvent-free or aprotic solvent. The amount of the isomerization catalyst may be an excess amount equal to or more than the equivalent amount, but may be performed in a catalytic amount. When the catalyst is used in a catalytic amount, the amount of the catalyst used is preferably from 0.1 to 100 mol%, more preferably from 1 to 50 mol%, based on the fluorinated sultone compound (1). The reaction temperature is preferably −30 ° C. to 200 ° C., more preferably 20 ° C. to 180 ° C.
When a solvent is used, various aprotic solvents such as sulfolane, acetonitrile, and glymes can be used as the solvent. The obtained acid fluoride compound (3) of the general formula (3) may be purified by distillation and used in the next step, or a reaction solution containing the acid fluoride compound (3) of the general formula (3) may be used. It may be used in the next step.

Next, the step (b) for adding HFPO will be described.
The acid fluoride compound (3) of the general formula (3) produced as described above is reacted with hexafluoropropylene oxide (HFPO) to give an HFPO addition compound (4) of the acid fluoride represented by the general formula (4). ) Can be manufactured.
The step (b) is preferably carried out in the presence of various polar solvents such as ether solvents such as diglyme and tetraglyme, and nitrile solvents such as adiponitrile. These solvents may be used alone or as a mixed solvent.

  In the reaction, various fluoride ion-containing compounds such as alkali metal fluoride and quaternary ammonium fluoride are usually used as a catalyst, and among these, NaF, KF and CsF are preferable. The amount of the catalyst used is preferably from 0.1 to 100 mol%, more preferably from 1 to 50 mol%, based on the acid fluoride compound (3).

The amount of HFPO used is preferably from 0.1 to 3 mol, more preferably from 0.5 to 2 mol, particularly preferably from 0.9 to 1.1 mol, based on 1 mol of the acid fluoride compound (3). The reaction temperature is preferably in the range of -30 ° C to 50 ° C, more preferably in the range of -20 ° C to 30 ° C.
In addition, when using the same catalyst by a process (a) and a process (b), you may carry out continuously by the same reactor.

Next, the step (c) for decarboxylation will be described.
As a method of producing perfluorovinyl ether monomer (2) from HFPO addition compound (4) of acid fluoride, thermal decomposition synthesis is carried out directly from HFPO addition compound (4) of acid fluoride in the presence of a basic compound or inorganic oxide. Or a method of decarboxylation after passing through various derivatives such as alkali metal salts, alkaline earth metal salts, alkyl esters or silyl esters derived from the HFPO addition compound (4) of the acid fluoride. However, any of these methods may be used. Among these, a method via an alkali metal salt is particularly preferable because the perfluorovinyl ether monomer (2) can be obtained simply and with high yield.

  As a method of passing through an alkali metal salt, an acid fluoride HFPO addition compound (4) may be reacted with an alkali metal carbonate in a solvent or without a solvent to form an alkali metal salt, followed by a heat decarboxylation reaction. Alternatively, the HFPO addition compound (4) of acid fluoride may be contacted with an alkali metal carbonate at a high temperature to carry out the neutralization reaction and the decarboxylation reaction simultaneously. As the alkali metal carbonate, sodium carbonate and potassium carbonate are preferable, and potassium carbonate is more preferable.

When the heat decarboxylation reaction is performed after the neutralization reaction, the amount of the alkali metal carbonate used is preferably 0.8 to 1.5 equivalents (0.4 to 0.75 mol times), and 0 .9 to 1.2 equivalents are more preferred. In addition, when a neutralization reaction is performed using a solvent, various aprotic polar solvents can be employed, among them, from the viewpoint of good operability and yield, nitrile solvents such as acetonitrile, Ether solvents such as dimethoxyethane and diglyme are preferred. The neutralization temperature is preferably 0 to 80 ° C., the decarboxylation reaction is preferably performed after removing the solvent as much as possible, and the decarboxylation reaction is preferably performed at 150 to 250 ° C.
When the neutralization reaction and the decarboxylation reaction are performed simultaneously, the amount of the alkali metal carbonate used is preferably 1 to 3 equivalents (0.5 to 1.5 moles), more preferably 1 to 2.5 equivalents. preferable. The reaction temperature is preferably 200 to 300 ° C.

The first production method of the present invention has been described above. Next, the features and details of the second production method of the present invention will be described.
The second production method of the present invention is a method for producing the fluorinated sultone compound (1) represented by the general formula (1), which is a starting material for the perfluorovinyl ether monomer (2), from the sultone compound (5).

  The fluorinated sultone compound (1) represented by the general formula (1) is represented by the general formula (5) (hereinafter referred to as Non-Patent Document 1 (RJ Lagow et al., Inorganic Chemistry, 30 (1991), 789)). A general method of directly fluorinating a compound of a sultone compound (5) with elemental fluorine to obtain a fluorinated sultone compound (1) of the general formula (1) can be used (non-patent document) 1 discloses only the production method of fluorinated sultone compound (5) where n = 4).

Specifically, as the fluorinating agent used in the direct fluorination reaction, various known fluorinating agents such as elemental fluorine, SF ₄ and XeF ₂ or a mixture thereof are used. Fluorine is preferred. In addition, in fluorination, light irradiation may be performed and a catalyst may be used. Direct fluorination with elemental fluorine may be performed by reacting with fluorine gas in a gas phase or a liquid phase. The fluorine gas to be used may be used alone, or a gas diluted with a gas such as nitrogen, helium, or argon may be used. When diluting, the fluorine gas concentration is preferably 1% by volume or more, more preferably 10% by volume or more, and further preferably 20% by volume or more.

  The pressure of fluorine is preferably normal pressure to 2 MPa. The fluorination temperature is preferably in the range of -100 to 120 ° C, more preferably -80 to 80 ° C, and particularly preferably -60 to 50 ° C. In order to remove HF produced by the reaction, an HF supplement such as NaF may be allowed to coexist. For the fluorination, either a batch method or a flow method can be employed. The fluorination conditions are preferably as low as possible at the beginning of the reaction, using a low concentration of fluorine gas, and increasing the temperature and concentration conditions as the reaction proceeds.

  In the above fluorination reaction, since heat generation is generally intense, it is preferable that the fluorination apparatus has a structure that efficiently removes heat. In general, in a reaction with a large reaction heat, in order to effectively remove the heat of reaction and perform the target reaction under stable conditions, it is preferable to perform the reaction by dissolving and diluting the substrate in a solvent. However, in the fluorination reaction of the sultone compound (5), the hydrocarbon solvent that dissolves the sultone compound (5) causes a fluorination reaction of the solvent itself during the reaction. I can not use it. On the other hand, even if an attempt is made to use a compound such as perfluorohydrocarbon which is stable under the fluorination reaction conditions, the solvent such as perfluorohydrocarbon hardly dissolves the sultone compound (5), so that the sultone compound (5) It is not possible to obtain a heat removal effect due to dissolution / dilution of the solution.

Non-Patent Document 1 discloses a method for producing a fluorinated sultone compound (1), in which the raw material is dispersed in sodium fluoride powder, and the method is performed slowly at a low temperature of −78 ° C. over one week or more. It can be presumed that the yield was low because the heat removal effect was insufficient only by dispersing in a solid.
Accordingly, as a result of intensive studies on the conditions for allowing the fluorination reaction to proceed at a high selectivity, the present inventors have dissolved the sultone compound (5) while the following medium is inactive under the fluorination reaction conditions. It has been found that when the fluorination reaction is carried out in such a medium, the selectivity of the reaction is remarkably improved.

That is, the medium may be any medium as long as it is inert under the fluorination reaction conditions and can dissolve 1% by mass or more of the sultone compound (5) at 20 ° C. Is more preferable, and it is more preferable to dissolve 10% by mass or more. Here, the above “inactive under the fluorination reaction conditions” means that a conversion reaction from C—H bonds to C—F bonds in the medium does not occur under the fluorination conditions. .
The medium is preferably a liquid under fluorination conditions, preferably has a melting point of 0 ° C. or lower, more preferably −30 ° C. or lower, and further preferably −50 ° C. or lower.

  Examples of such a medium include perfluorocarboxylic acid anhydrides such as trifluoroacetic anhydride, pentafluoropropionic anhydride, and heptafluorobutyric anhydride, and perfluorocarbons such as trifluoromethanesulfonic anhydride and pentafluoroethanesulfonic anhydride. Sulfonic anhydrides, bisperfluoroalkylsulfonylimide compounds such as bistrifluoromethanesulfonylimide, perfluoroalkylamide compounds such as trifluoromethanesulfonamide, or mixtures of these compounds, and these compounds and perfluoro A mixture of solvents such as hydrocarbons (which may contain heteroatoms such as oxygen and nitrogen) can be exemplified. The number of carbon atoms in these medium compounds is preferably 15 or less, more preferably 12 or less, further preferably 8 or less, and particularly preferably 5 or less. In addition, an ether bond may be included in the perfluoroalkyl part of these medium compounds.

When the medium is used, the amount of the medium is preferably 1 to 300 times by mass, more preferably 5 to 200 times by mass, and particularly preferably 10 to 100 times by mass with respect to the sultone compound (5).
The fluorination reaction from the sultone compound (5) to the fluorinated sultone compound (1) may be carried out in the presence of a partially fluorinated product of the sultone compound (5) from the viewpoint of yield improvement and reaction thermal dilution. From the viewpoint of extracting and separating the product, the reaction may be carried out in the presence of a solvent such as perfluorohydrocarbon (which may contain a hetero atom such as oxygen or nitrogen).
The method for producing the fluorinated sultone compound (1) from the sultone compound (5), which is the second production method of the present invention, has been described above.

Hereinafter, the present invention will be specifically described based on examples.
[Example 1]
According to the method described in Non-Patent Document 1, 1,4-butane sultone (a compound having n = 4 in the general formula (5)) is dispersed in anhydrous sodium fluoride and described in Non-Patent Document 1 and the cited document. The reaction zone in the apparatus was charged and the reaction was carried out by direct fluorination. As a result, perfluoro-1,4-butane sultone (n = 4 in the general formula (1)) was obtained with an isolation yield of 25%.

Next, 5 g of perfluoro-1,4-butane sultone, 1.4 g of KF, and 20 ml of sulfolane were charged in a 50 ml three-necked flask in a nitrogen stream and stirred at 100 ° C. for 12 hours. The low-boiling components were distilled off under reduced pressure to obtain 4.1 g of liquid (yield 82%).
This liquid was confirmed to be FOC (CF ₂ ) ₃ SO ₂ F by ¹⁹ F-NMR.
¹⁹ F-NMR δ (CFCl ₃ standard): 44.3 ppm (1F), 22.5 ppm (1F), −109.8 ppm (2F), −119.5 ppm (2F), −122.4 ppm (2F)

FOC (CF ₂ ) ₃ SO ₂ F22.1 g obtained by repeating the above method was placed in a 100 mL autoclave together with 1 g of tetraglyme, 10 mL of adiponitrile and 0.6 g of potassium fluoride, and stirred at 0 ° C. 13 g of propylene oxide (HFPO) was introduced. Three hours after the start of introduction, when the gauge pressure reached 0 MPa, the reaction mixture was allowed to stand to separate into two layers. After liquid separation of the lower layer, 29 g of CF ₃ CF (COF) O (CF ₂ ) ₄ SO ₂ F was obtained by distillation under reduced pressure (boiling point 91 ° C./23 kPa) (yield 82%).

Next, 5.6 g of potassium carbonate previously dried and 10 mL of anhydrous 1,2-dimethoxyethane were placed in a 100 mL four-necked flask equipped with a dropping funnel, a Liebig condenser, and a collection flask under a nitrogen stream. While heating in an oil bath at 0 ° C., 15 g of CF ₃ CF (COF) O (CF ₂ ) ₄ SO ₂ F was slowly added dropwise. After the foaming stopped, the mixture was further stirred at 50 ° C. for 1.5 hours, and the raw material was completely neutralized by ¹⁹ F-NMR and converted to CF ₃ CF (CO ₂ K) O (CF ₂ ) ₄ SO ₂ F. It was confirmed. 1,2-Dimethoxyethane was distilled off from the reaction mixture under reduced pressure, and the residue was further heated to 140 ° C. and dried under reduced pressure.

When the residue containing dried CF ₃ CF (CO ₂ K) O (CF ₂ ) ₄ SO ₂ F was heated to 170 ° C. under reduced pressure (12 kPa), decarboxylation reaction occurred, and liquid began to distill. Further, the temperature was gradually raised and finally increased to 185 ° C. The obtained liquid was purified by distillation (boiling point 57 ° C./13.3 kPa) to obtain 10 g of CF ₂ ═CFO (CF ₂ ) ₄ SO ₂ F (yield 80%).
¹⁹ F-NMR δ (CFCl ₃ standard): 43.8 ppm (1F), −87.0 ppm (2F), −110.0 ppm (2F), −116.9 ppm (1F), −122.2 ppm (2F), -124.4 ppm (1F), -127.0 ppm (2F), -138.4 ppm (1F)

[Example 2]
In the same manner as in Example 1, 1,4-butane sultone was charged in an anhydrous sodium fluoride state, and then 15 mass times of 1,4-butane sultone trifluoroacetic anhydride was aggregated in the same reaction zone in the apparatus. I let you. In that state, direct fluorination was carried out in the same manner as in Example 1 to obtain perfluoro-1,4-butane sultone with a yield of 50%.
When 1 g of 1,4-butane sultone and 1 g of trifluoroacetic anhydride were mixed at 20 ° C., they were uniformly dissolved.

The perfluorovinyl ether monomer represented by the general formula (2), which is useful as a raw material for heat-resistant and oxidation-resistant perfluorosulfonic acid polymers, can be produced with a small number of steps and with a high yield.

Claims (3)

The following general formula (1)

(In the formula, n is an integer of 3 to 8.)
As a starting material, the following general formula (2) is obtained by the operations of the following steps (a) to (c).
_{CF 2 = CFO (CF 2)} n SO 2 F (2)
(N is the same as in general formula (1).)
A process for producing a perfluorovinyl ether monomer represented by the formula:
Step (a)
The compound of the general formula (1) is isomerized to give the following general formula (3)
FCO (CF ₂ ) _n-1 SO ₂ F (3)
(N is the same as in general formula (1).)
The process made into the compound represented by these.
Step (b)
Hexafluoropropylene oxide (HFPO) is added to the compound of the general formula (3), and the following general formula (4)
CF ₃ CF (COF) O (CF ₂ ) _n SO ₂ F (4)
(N is the same as in general formula (1).)
The process made into the compound represented by these.
Step (c)
A step of decarboxylating the compound of the general formula (4) to obtain a perfluorovinyl ether monomer of the general formula (2). The compound represented by the general formula (1) is represented by the following general formula (5)

(N is the same as in general formula (1).)
The production method according to claim 1, wherein the compound represented by the formula is produced by directly fluorinating with a fluorinating agent.   The direct fluorination of the compound represented by the general formula (5) is performed in the presence of an inert medium capable of dissolving 1% by mass or more of the compound represented by the general formula (5) at 20 ° C. The production method according to claim 2.