JP3846778B2 - Method for electrolytic fluorination of organic ether compounds - Google Patents

Description

【化２】

【０００５】
以下本発明を詳細に説明する。
本発明は、実質的に溶媒を使用することなく、有機エーテル化合物の電解フッ素反応を行うことを特徴とする。
有機エーテル化合物は電解合成用、リチウム２次電池などの電解溶媒として広く使用されており、又フッ素化された有機エーテル化合物は、電解溶媒、２次電池電解液、代替フロン、洗浄剤等として使用され、或いは今後の使用が期待されている。
【０００６】
有機電解合成の１種であるフッ素化プロセスでは、通常反応原料の目的生成物への電解反応を進行させるために、電解条件下で安定な溶媒（例えばアセトニトリル）を選択し使用する必要がある。この溶媒には通常イオン伝導性がないため、電解に対して安定でかつ目的反応を阻害しない電解質（例えば過塩素酸化合物）を溶解混合しておく必要がある。しかしこのような溶媒を使用する有機電解反応では副反応が起こり易く、収率低下と生成物単離の必要性が生じている。
最近になって、テトラアルキルアンモニウムフロリドポリフッ化水素化合物[Ｒ₄ＮＦ・ｎＨＦ（ｎ＝１〜10）]或いはトリアルキルアミンポリフッ化水素塩化合物［Ｒ₃Ｎ・ｎＨＦ（ｎ＝１〜10）］などの電解質が合成され、これらはフッ素化原料でもあるため、電解質とフッ素化原料を単一化合物で兼用できる。従って従来と比較して生成物の分離精製が容易になり、電解質に掛かるコストを低減でき、しかも危険なフッ素原料を別途準備する必要がなくなる。
【０００７】
そしてポリフッ化水素化合物は、通常イオン性液体（ionic liquid）と呼ばれる常温溶融塩（常温でも溶液状態でイオン伝導性を有する塩）であり、有機エーテル化合物の多くは液体で、基質が前記溶融塩に溶けるため、溶媒の使用も省略できる理想的な電解系となる可能性がある。
本発明者らは、ポリフッ化水素化合物と有機エーテル化合物から成る電解系で反応を行わせたところ、反応収率が高く、実用性に富むことを見出し、本発明に到達したものである。
【０００８】
【発明の実施の形態】
本発明の有機エーテル化合物は、（化１）又は（化２）で表されるジメトキシエタン（化１）、テトラヒドロフラン（化２でＸが炭素でｎ＝０）、１，４−ジオキサン（化２でＸが酸素でｎ＝１）及び１，３−ジオキソラン（化２でＸが酸素でｎ＝０）である。
【０００９】
本発明では、前述の通りフッ素原料である含フッ素溶融塩に反応原料である有機エーテル化合物を溶解して電解液とし、専用の溶媒は使用しない。
前記含フッ素溶融塩として、テトラアルキルアンモニウムフロリドポリフッ化水素化合物及びトリアルキルアミンポリフッ化水素塩化合物がある。これらの化合物は常温で溶融しているため、反応原料の有機エーテル化合物を溶解して均一相の電解液を調製できる。
この電解液に通電すると、有機エーテル化合物の水素原子がフッ素原子で置換されてフッ素化エーテルが生成する。フッ素化は通常エーテル酸素に隣接する炭素原子に結合している水素原子で最も起こり易く、モノ置換体が多く得られる。原料の有機エーテル化合物にも依るが、通電時間を延ばすことによりジ置換体やトリ置換体も得られることがある。
【００１０】
反応時間が経過し、原料の有機エーテル化合物が全て消費された後は目的とするフッ素化物と溶融塩の分離のみを行えば良く、特にモノ置換体のみが得られる場合には分離が簡単で、経済的かつ実用的である。
フッ素源である溶融塩が消費された場合には、溶融塩全体でなく、消費対象であるフッ化水素（ＨＦ）のみを補充すれば良く、原料コストが安価になり、かつ原料添加が容易である。従って電解槽に原料の有機エーテル化合物と消費するＨＦのみを添加すれば、連続的な電解合成が可能になる。
生成するフッ素化有機エーテル化合物の沸点が高い場合には、一旦溶媒抽出して電解質である溶融塩と分離し、抽出液から目的のフッ素化有機エーテル化合物を単離することが望ましい。
【００１１】
前記電解液に通電するために、酸化鉛、酸化錫、白金、白金族酸化物被覆陽極（ＤＳＡ）、黒鉛、アモルファスカーボン（grassy carbon、ＧＣ）及び導電性ダイヤモンド等から選択される陽極、及び鉛、鉄、白金、チタン及びカーボン系材料から選択される陰極が使用される。
これらの電極の基体は、長寿命（耐久性）の観点と、処理表面への汚染が生じさせない耐食性の観点から、その材料を選択する必要がある。陽極基体としては、チタンなどの弁金属又はその合金が望ましく、陽極触媒としては白金やイリジウム等の貴金属又はそれらの酸化物が望ましい。集電体は導電性材料であれば問題はないが、チタン、ニオブ、タンタル、シリコン、カーボン、ニッケル、タングステンカーバイドなどの板、打ち抜き板、金網、粉末焼結体、金属繊維焼結体が好ましい。ダイヤモンドを金属などの集電体上に被覆形成しても良い。表面を研磨すると密着性と反応面積が増大する。
【００１２】
電解槽材料としては、有機化合物に対する耐久性、安定性の観点から、ガラスライニング材料、カーボン、耐食性の優れたチタン、ステンレス及びＰＴＦＥ樹脂などが好ましく使用できる。
電解条件は、温度が０〜60℃、電流密度が0.1〜100Ａ／ｄｍ²であることが好ましい。反応効率を向上させるために、超音波を照射し、物質移動を促進しても良い。
【００１３】
次に本発明に係る有機エーテル化合物の電解フッ素化反応の実施例及び比較例を記載するが、これらは本発明を限定するものではない。
【００１４】
実施例１
陽極及び陰極としてそれぞれ白金板（縦20mm×横20mm）を無隔膜電解槽内に装着した。
フッ素化原料であるＥｔ₃Ｎ・４ＨＦを２Ｍ、有機エーテル化合物であるジメトキシエタンを60ミリモル使用して、10mlの電解液を作製した。この電解液を、窒素雰囲気とした前記無隔膜電解槽内に入れ、室温下で定電流電解（電流密度：0.1Ａ、２Ｆ／モル）を行った。
反応終了後、電解液を常圧蒸留し、ＮＭＲ及びＭＳを使用して単離された生成エーテルの構造決定を行ったところ、反応生成物としてメチル基炭素或いはメチレン炭素上の水素がフッ素と置換したフッ化エーテル化合物（ＣＨ₃−Ｏ−ＣＨ₂ＣＨ₂−Ｏ−ＣＨ₂Ｆ及びＣＨ₃−Ｏ−ＣＨ₂ＣＨＦ−Ｏ−ＣＨ₃）が、合わせて収率89％で得られたことが分かった。
【００１５】
実施例２
ジメトキシエタンの替わりにテトラヒドロフラン60ミリモルを原料として使用したこと以外は実施例１と同様な条件で電解を行い、反応終了後、電解液を常圧蒸留し、ＮＭＲ及びＭＳを使用して単離された生成エーテルの構造決定を行ったところ、反応生成物として２位の水素がフッ素で置換したフッ化エーテル化合物（２-フルオロテトラヒドロフラン）が、収率56％で得られたことが分かった。
【００１６】
実施例３
ジメトキシエタンの替わりに１，４−ジオキサン60ミリモルを原料として使用したこと以外は実施例１と同様な条件で電解を行い、反応終了後、電解液をヘキサン／クロロホルム＝１／５と混合して生成物を抽出した。得られた有機エーテル化合物の構造決定を、ＮＭＲ及びＭＳを使用して行ったところ、反応生成物としてα位の水素がフッ素で置換したフッ化エーテル化合物（２−フルオロ−１，４−ジオキサン）が、収率77％で得られたことが分かった。
【００１７】
比較例１
実施例３の系にアセトニトリルを溶媒として添加し、実施例３と同様の条件で電解を行った。反応終了後、電解液をヘキサン／クロロホルム＝１／５と混合して生成物を抽出した。ＮＭＲ及びＭＳを使用して生成物の構造決定を試みたが、原料の１，４−ジオキサンの炭素−炭素結合の開裂による副生成物が多量に検出され、２−フルオロ−１，４−ジオキサンの収率は50％に達しなかった。
【００１８】
【発明の効果】
本発明は、電解槽内に、（化１）又は（化２）で表されるジメトキシエタン、又はテトラヒドロフラン、１，４−ジオキサン及び１，３−ジオキソランから選択される１又は２以上の有機エーテル化合物（（化２）中、Ｘは酸素又は炭素、ｎは０又は１）と、溶媒として機能する、常温溶融可能なテトラアルキルアンモニウムフロリドポリフッ化水素化合物及び／又はトリアルキルアミンポリフッ化水素塩化合物である含フッ素溶融塩を含む電解液を収容し、該電解液に通電することにより前記有機エーテル化合物をフッ素することを特徴とする方法である。
本発明方法によると、含フッ素溶融塩が溶媒として機能し専用の溶媒を必要としないため、専用の溶媒を使用する有機電解反応と比較して副生成物量が大きく減少し、条件に依っては実質的にゼロになる。従って反応の収率及び選択性が大幅に向上する。
【００１９】
又このように副生成物がないか又は非常に少ないため、副生成物を単離する工程が実質的に不要になり、簡単な操作で目的とするフッ素化有機エーテル化合物が得られる。
フッ素源である前記含フッ素溶融塩は、反応が進行しても消費されるのはフッ化水素のみで、高価な含フッ素溶融塩自体は消耗せず、有機エーテル化合物とフッ化水素の添加のみで反応を継続できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrolytic fluorine method for an organic ether compound, and more particularly, to an electrolytic fluorine method that is substantially free of side reactions and that can provide a desired fluorinated compound without complicated isolation.
[0002]
[Prior art]
Electrolysis is a chemical synthesis method that uses clean electrical energy to perform chemistry without the use of reaction reagents. The reaction rate can be controlled by the current density, and the product can be controlled by regulating the potential. It has a feature that can be selected. In the field of electrolytic synthesis of organic compounds, many organic compound oxidation-reduction processes have been put to practical use by utilizing a non-aqueous solvent that is stable and promotes the reaction. The electrolysis method is not suitable for mass production because it is a heterogeneous phase reaction on the electrode surface, but since selective synthesis is possible, it is considered to produce a high added-value substance in a new electrosynthesis system. Has been.
Fluorine-containing organic compounds are chemical synthetic products that are important as pharmaceuticals and agricultural chemicals, and compounds having a wide variety of molecular structures have been developed in order to enhance the intended effects. It is known that electrolysis is useful as a method for selective molecular conversion of fluorine-containing organic compounds and selective fluorination of organic compounds.
[0003]
[Problems to be solved by the invention]
Among the various conventional electrolysis reactions, the electrosynthesis reaction of partially fluorinated compounds usually uses an organic solvent, so side reactions such as oxidative decomposition of the organic solvent occur, current efficiency decreases, and the produced target substance is reduced. It had to be separated from the electrolyte and purified. Therefore, this conventional method is insufficient in terms of yield and selectivity, and has not been put into practical use particularly from the point of isolation operation.
The present invention provides a method for electrolytic fluorination of an organic ether compound that improves the yield and selectivity in the partial fluorination reaction by electrolysis of such a conventional organic compound and can substantially eliminate the need for isolation. For the purpose.
[0004]
[Means for Solving the Problems]
In the electrolytic cell, the present invention provides one or more organic ethers selected from dimethoxyethane represented by (Chemical Formula 1) or (Chemical Formula 2), or tetrahydrofuran, 1,4-dioxane and 1,3-dioxolane. Compound ((Chemical Formula 2), X is oxygen or carbon, n is 0 or 1), and tetraalkylammonium fluoride polyhydrofluoride compound and / or trialkylamine polyhydrofluoride salt that functions as a solvent and can be melted at room temperature an electrolytic solution containing a fluorine-containing molten salt is a compound containing a method characterized by fluorine the organic ether compound by energizing the electrolytic solution.
[Chemical 1]

[Chemical 2]

[0005]
The present invention will be described in detail below.
The present invention is characterized in that an electrolytic fluorine reaction of an organic ether compound is carried out substantially without using a solvent.
Organic ether compounds are widely used as electrolytic solvents for electrolytic synthesis, lithium secondary batteries, etc. Also, fluorinated organic ether compounds are used as electrolytic solvents, secondary battery electrolytes, CFC substitutes, cleaning agents, etc. Or expected to be used in the future.
[0006]
In the fluorination process, which is a kind of organic electrosynthesis, it is usually necessary to select and use a solvent (for example, acetonitrile) that is stable under electrolytic conditions in order to advance the electrolytic reaction of the reaction raw material to the target product. Since this solvent usually has no ionic conductivity, it is necessary to dissolve and mix an electrolyte (for example, a perchloric acid compound) that is stable to electrolysis and does not inhibit the target reaction. However, in the organic electrolysis reaction using such a solvent, side reactions are likely to occur, resulting in a need for yield reduction and product isolation.
Recently, tetraalkylammonium fluoride polyhydrofluoride compound [R ₄ NF · nHF (n = 1 to 10)] or trialkylamine polyhydrofluoride compound [R ₃ N · nHF (n = 1 to 10) ], And these are also fluorinated raw materials, so that the electrolyte and the fluorinated raw material can be used as a single compound. Accordingly, the product can be easily separated and purified as compared with the conventional case, the cost for the electrolyte can be reduced, and there is no need to separately prepare a dangerous fluorine raw material.
[0007]
The polyhydrofluoric compound is a room temperature molten salt (salt having ionic conductivity in a solution state even at room temperature) usually called an ionic liquid, and most of the organic ether compounds are liquid and the substrate is the molten salt. Therefore, there is a possibility that an ideal electrolytic system can be used in which the use of a solvent can be omitted.
The present inventors have reached the present invention by finding that the reaction is carried out in an electrolytic system composed of a polyhydrofluoride compound and an organic ether compound, and the reaction yield is high and practical.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The organic ether compound of the present invention includes dimethoxyethane represented by (Chemical Formula 1) or (Chemical Formula 2), tetrahydrofuran (Chemical Formula 2 where X is carbon and n = 0), 1,4-dioxane (Chemical Formula 2). in X is n = 1 in oxygen) and 1,3-dioxolane (of n = 0 X is oxygen in 2).
[0009]
In the present invention, as described above, an organic ether compound as a reaction raw material is dissolved in a fluorine-containing molten salt as a fluorine raw material to form an electrolytic solution, and no dedicated solvent is used.
Examples of the fluorine-containing molten salt include a tetraalkylammonium fluoride polyhydrofluoride compound and a trialkylamine polyhydrofluoride compound. Since these compounds are melted at room temperature, it is possible to prepare a homogeneous electrolyte by dissolving the organic ether compound as a reaction raw material.
When this electrolytic solution is energized, hydrogen atoms of the organic ether compound are replaced with fluorine atoms to produce fluorinated ether. Fluorination is most likely to occur with hydrogen atoms bonded to carbon atoms adjacent to ether oxygen, and many mono-substituted products are obtained. Although depending on the organic ether compound as a raw material, di-substituted products and tri-substituted products may be obtained by extending the current application time.
[0010]
After the reaction time has elapsed and all the organic ether compound as a raw material has been consumed, it is only necessary to separate the target fluorinated product and molten salt, especially when only a mono-substituted product is obtained. Economical and practical.
When the molten salt, which is a fluorine source, is consumed, it is only necessary to replenish not only the entire molten salt but also hydrogen fluoride (HF), which is the object of consumption, and the raw material cost is reduced and the addition of the raw material is easy. is there. Therefore, if only the organic ether compound as a raw material and HF to be consumed are added to the electrolytic cell, continuous electrolytic synthesis becomes possible.
When the boiling point of the fluorinated organic ether compound to be produced is high, it is desirable that the target fluorinated organic ether compound is isolated from the extract by once solvent extraction and separation from the molten salt as an electrolyte.
[0011]
A lead selected from lead oxide, tin oxide, platinum, platinum group oxide-coated anode (DSA), graphite, amorphous carbon (GC), conductive diamond, etc., and lead for energizing the electrolyte A cathode selected from iron, platinum, titanium and carbon-based materials is used.
These electrode substrates need to be selected from the viewpoints of long life (durability) and corrosion resistance that does not cause contamination of the treated surface. The anode substrate is preferably a valve metal such as titanium or an alloy thereof, and the anode catalyst is preferably a noble metal such as platinum or iridium or an oxide thereof. There is no problem as long as the current collector is a conductive material, but a plate of titanium, niobium, tantalum, silicon, carbon, nickel, tungsten carbide, etc., a punched plate, a wire mesh, a powder sintered body, and a metal fiber sintered body are preferable. . Diamond may be coated on a current collector such as a metal. Polishing the surface increases adhesion and reaction area.
[0012]
As the electrolytic cell material, glass lining material, carbon, titanium, stainless steel and PTFE resin having excellent corrosion resistance can be preferably used from the viewpoints of durability and stability against organic compounds.
The electrolysis conditions are preferably a temperature of 0 to 60 ° C. and a current density of 0.1 to 100 A / dm ² . In order to improve reaction efficiency, ultrasonic waves may be irradiated to promote mass transfer.
[0013]
Next, examples and comparative examples of the electrolytic fluorination reaction of the organic ether compound according to the present invention will be described, but these do not limit the present invention.
[0014]
Example 1
Platinum plates (vertical 20 mm × horizontal 20 mm) were respectively mounted in the non-diaphragm electrolytic cell as an anode and a cathode.
Using 2M Et ₃ N · 4HF as a fluorination raw material and 60 mmol of dimethoxyethane as an organic ether compound, 10 ml of an electrolytic solution was prepared. This electrolytic solution was placed in the non-diaphragm electrolytic bath in a nitrogen atmosphere, and constant current electrolysis (current density: 0.1 A, 2 F / mol) was performed at room temperature.
After completion of the reaction, the electrolytic solution was distilled at atmospheric pressure, and the structure of the isolated ether was determined using NMR and MS. As a reaction product, hydrogen on the methyl group carbon or methylene carbon was replaced with fluorine. The obtained fluorinated ether compounds (CH ₃ —O—CH ₂ CH ₂ —O—CH ₂ F and CH ₃ —O—CH ₂ CHF—O—CH ₃ ) were obtained in a combined yield of 89%. I understood.
[0015]
Example 2
Electrolysis was carried out under the same conditions as in Example 1 except that 60 mmol of tetrahydrofuran was used as a raw material instead of dimethoxyethane. After completion of the reaction, the electrolyte was distilled at atmospheric pressure and isolated using NMR and MS. The structure of the produced ether was determined, and it was found that a fluorinated ether compound (2-fluorotetrahydrofuran) in which hydrogen at the 2-position was substituted with fluorine as a reaction product was obtained in a yield of 56%.
[0016]
Example 3
Electrolysis was carried out under the same conditions as in Example 1 except that 60 mmol of 1,4-dioxane was used as a raw material instead of dimethoxyethane. After the reaction was completed, the electrolyte was mixed with hexane / chloroform = 1/5. The product was extracted. When the structure of the obtained organic ether compound was determined using NMR and MS, a fluorine-containing ether compound (2-fluoro-1,4-dioxane) in which hydrogen at the α-position was substituted with fluorine as a reaction product. Was found to be obtained with a yield of 77%.
[0017]
Comparative Example 1
Acetonitrile was added as a solvent to the system of Example 3, and electrolysis was performed under the same conditions as in Example 3. After completion of the reaction, the electrolytic solution was mixed with hexane / chloroform = 1/5 to extract the product. An attempt was made to determine the structure of the product using NMR and MS, but a large amount of by-products due to the cleavage of the carbon-carbon bond of the starting 1,4-dioxane was detected, and 2-fluoro-1,4-dioxane was detected. The yield of did not reach 50%.
[0018]
【The invention's effect】
In the electrolytic cell, the present invention provides dimethoxyethane represented by (Chemical Formula 1) or (Chemical Formula 2), or one or more organic ethers selected from tetrahydrofuran, 1,4-dioxane and 1,3-dioxolane. Compound ((Chemical Formula 2), X is oxygen or carbon, n is 0 or 1), and tetraalkylammonium fluoride polyhydrofluoride compound and / or trialkylamine polyhydrofluoride salt that functions as a solvent and can be melted at room temperature an electrolytic solution containing a fluorine-containing molten salt is a compound containing a method characterized by fluorine the organic ether compound by energizing the electrolytic solution.
According to the method of the present invention, since the fluorine-containing molten salt functions as a solvent and does not require a dedicated solvent, the amount of by-products is greatly reduced compared to the organic electrolysis reaction using a dedicated solvent. It becomes virtually zero. Accordingly, the yield and selectivity of the reaction are greatly improved.
[0019]
Further, since in this way or very little or no by-products, by-products isolating becomes substantially unnecessary, Ru fluorinated organic ether compound of interest can be obtained by a simple operation.
The fluorine-containing molten salt that is a fluorine source is consumed only by hydrogen fluoride even if the reaction proceeds, the expensive fluorine-containing molten salt itself is not consumed, and only the addition of an organic ether compound and hydrogen fluoride. The reaction can be continued.

Claims (2)

In the electrolytic cell, (Formula 1) or (Formula 2) dimethoxyethane represented by, or tetrahydrofuran, one or more organic ether compound selected from 1,4-dioxane and 1,3-dioxolane ((of In 2), X is oxygen or carbon, n is 0 or 1), and includes a tetraalkylammonium fluoride polyhydrofluoride compound and / or a trialkylamine polyhydrofluoride compound that functions as a solvent and can be melted at room temperature. wherein the electrolytic solution containing a containing fluorine molten salt, to fluorine the organic ether compound by energizing the electrolytic solution.

The process according to claim 1 , wherein the reaction is continued while adding the consumed organic ether compound and hydrogen fluoride.