JP3416066B2 - Electrode for electrolytic fluorination reaction and organic electrolytic fluorination method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The invention of this application relates to an electrode for electrolytic fluorination reaction and an organic electrolytic fluorination method. More specifically, the invention of this application provides fluorine by selective electrolytic oxidation, which is useful for electrolytic production of fluorine-containing organic compounds useful as pharmaceuticals, agricultural chemicals, polymers, detergents and other various chemical products and synthetic intermediates thereof. The present invention relates to a new electrode for electrolytic fluorination reaction that can be converted to an organic electrolytic fluorination method using the same.

[0002]

2. Description of the Related Art Conventionally, various proposals and contrivances regarding electrolytic fluorination reaction methods have been reported. These can be roughly classified into the following three types.
The first method is a method (Simmons method) in which an organic compound is dissolved in anhydrous hydrogen fluoride as an electrolytic solution and electrolysis is performed using a nickel electrode as an anode. The second method is an electrolytic solution composition KF which is generally used for producing fluorine gas as an electrolytic solution.
By using 2HF (potassium fluoride: hydrogen fluoride = 1: 2) and using a porous carbon electrode as the anode, and flowing a gaseous organic compound from the bottom side to the top side inside the electrode, This is a method (Philip method) in which fluorine generated by electrolysis and its organic compound are reacted inside the electrode to fluorinate. The third method is a method in which an aprotic solvent in which a fluorine source and an organic compound are dissolved is used as an electrolytic solution, and a platinum electrode is used as an anode for electrolysis to perform fluorination.

The first and second methods are mainly industrially established as a method for producing a surfactant, an inert gas and an inert liquid, since a completely fluorinated product is obtained. Further, the third method is expected as a method for synthesizing a fluorine-containing organic intermediate because it can be partially fluorinated. However, according to the first method of the prior arts as described above, it is difficult to handle since anhydrous hydrogen fluoride is used for the electrolytic fluorination reaction of an organic compound, and the use of nickel electrodes as electrodes is indispensable. However, there was a problem that facilities and conditions were extremely severely limited. In the case of the second method, although a carbon electrode is used and a molten salt is used, there is an advantage that it is easier to handle in terms of operation, but it is inconvenient due to the reaction of the carbon electrode itself in the molten salt bath. There was a problem that the instability could not be resolved. Moreover, in both the first method and the second method,
There is also a problem that it is difficult to control the fluorination reaction of an organic compound partially.

On the other hand, in the case of the third method, it can be said that the partial fluorination is possible, but it is necessary to use specific conditions due to the use of the platinum electrode, and the electrode by the electrolytic reaction is required. There were inconveniences such as film formation on the surface. Furthermore, when nickel or platinum is used for the electrode as in the first and third methods, oxygen absorption
There was a problem that the oxidation / reduction current flows due to desorption, current efficiency decreases, and the electrode is damaged and the life is short.

Therefore, the inventors of this application have earnestly studied to solve the above-mentioned problems with the conventional electrolytic fluorination method. At that time, the inventors of the present invention are able to easily handle equipment and reaction operation, can operate stably even under relatively severe conditions, and can also perform partial fluorination of organic compounds. The challenge has been to provide system electrodes. The main reason for this is that it is expected that more general-purpose applications will be developed for the electrolytic fluorination reaction using carbon-based electrodes.

[0006]

In order to solve the above-mentioned problems, the invention of the present application provides, firstly, an electrode for electrolytic fluorination reaction characterized by comprising semiconductor diamond. Secondly, the semiconductor diamond is provided with the above-mentioned electrode formed on a substrate, and thirdly, the above-mentioned electrode is obtained by vapor-depositing a boron-doped film on a silicon substrate. And, fourthly, this application is characterized in that the electrolytic fluorination of an organic compound is performed by using the electrolytic fluorination electrode of any one of the first to third aspects as an anode. Fifth,
The organic compound also provides an electrolytic fluorination process where the organic compound is an aromatic compound.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the characteristics as described above, and the embodiments thereof will be described below. First, the electrode for electrolytic fluorination reaction of the invention of this application has semiconductor diamond. In this case, the semiconductor diamond is typically considered to consist of semiconductor diamond formed on the substrate.

For example, as the substrate, silicon, germanium, their compound semiconductors, molybdenum,
Examples thereof include tungsten, quartz glass, and alumina. In terms of taking a lead as an electrode, the substrate is usually said to be preferably an electric conductor or a semiconductor, but in the case of the electrode for the electrolytic fluorination reaction of the invention of this application, a thin film of semiconductor diamond is formed on the substrate. The substrate is not particularly limited to electrical conductors or semiconductors, as the leads can be taken directly.

On the other hand, the substrate is required to be stable at a temperature of 800 ° C. or higher at the time of forming the semiconductor diamond thin film, specifically, for example, have a melting point of 800 ° C. or higher. The semiconductor diamond is realized, for example, by doping impurities, but the semiconductor diamond becomes p-type or n-type depending on the kind of the dopant. When the p-type is used, boron is the mainstream. Other than this, aluminum is known. An n-type example has not been confirmed so far, but it has been reported that nitrogen, phosphorus, sulfur, etc. are effective as dopants.

As a method for vapor phase film formation, various conventionally known methods such as a CVD method will be adopted. This is a vapor phase film formation method by microwave irradiation CVD of hydrocarbons such as methane and ethane and hydrogen. Regarding the size of the electrode, the thickness of the substrate and the semiconductor diamond film, etc.
It may be determined according to the type of electrolytic fluorination reaction in which the electrode is used and the conditions thereof.

The electrode of the invention of this application as described above is
It enables a stable electrolytic fluorination reaction even under relatively severe conditions, has no inconvenience of forming a film on the electrode in the electrolytic reaction, and has excellent reaction operation stability and handleability. Is. By using this electrode, for example, electrolytic fluorination of an organic compound is possible. Control of complete fluorination or partial fluorination of organic compounds is also easy.

The electrolytic fluorination of an organic compound will be further described. The semiconductor diamond electrode of the present invention is used as an anode, and an electrolytic solution is, for example, a quaternary alkylammonium fluoride hydrogen fluoride salt or a hydrogen fluoride solution thereof, or a mixture thereof. As the liquid-based one, aprotic solvents such as acetonitrile, sulfolane, and nitromethane, various ones such as triethylamine hydrogen fluoride salt which also serves as a supporting electrolyte salt and a fluorine source are used.

Various organic compounds may be used as raw materials for fluorination, such as aliphatic compounds, alicyclic compounds,
It may be any such as an aromatic compound. Above all, electrolytic fluorination of aromatic compounds produces highly valuable fluorinated compounds that can be applied in various applications. Therefore, the present invention will be described in more detail with reference to the following examples.

[0014]

EXAMPLES Example 1 1) Preparation of Diamond Thin Film A p-type semiconductor diamond thin film was prepared on a Si substrate by the CVD method. The production conditions are shown in Table 1.

The dopant concentration in the film determined from the SIMS measurement results was 10 ¹⁹ atoms / cm ³ .

[0016]

[Table 1]

2) Preparation of electrolytic cell Teflon and PFA were used as the material of the electrolytic cell in consideration of the corrosion resistance to hydrofluoric acid. A Viton O-ring was used to seal the solution, and carbon fiber was used to take a lead from the diamond surface prepared as described above. The electrode was arranged so that the electrolytic solution was brought into contact only with the diamond surface and the lead was taken directly from the thin film surface. FIG. 1 illustrates the details.

In FIG. 1, reference numerals indicate the following. (A) Electrolyte solution (Et ₄ NF · 4HF, 10 ml) (b) Reference electrode (Ag / Ag ⁺ ) (c) Pt working electrode (1.2 × 10 ⁻¹ cm ² , 1.0 m)
m diameter × 3.5 mm) (d) Counter electrode (Pt plate, 2.2 cm ² , 9 mm × 12 m
m) (e) Teflon cap and button (f) PFA plate (g) Carbon fiber (h) Ni plate (i) PFA tube (j) Semiconductor diamond thin film (k) Viton O-ring (l) Diamond working electrode (1) .3 × 10 ^-1 cm ² ,
(4.0 mm diameter) 3) Measurement of cyclic voltammetry First, the electrolytic cell was connected to a potentio / galvanostat (working electrode: platinum), and the CV of only the electrolytic solution for background measurement was measured. Next, the working electrode was changed to diamond and the background was measured in the same manner.

Using a microsyringe, 9.7 μl of solute (1,4-difluorobenzene) was added to the electrolytic solution (solution concentration was 0.01 M), and the mixture was stirred for about 5 minutes and then the background was measured in the same manner as described above. CV was measured with a platinum electrode and a diamond electrode. Furthermore, 19.4 μl of solute was added,
After stirring for about 5 minutes, the CV at a solution concentration of 0.03M was similarly measured with a platinum electrode and a diamond electrode.

4) The cyclic voltammogram obtained as a result is shown in FIG.
It shows in (C) and FIG. 3 (D)-(F). Comparing the respective voltammograms, the platinum electrode is 1 V to 1.5
In contrast to the oxidation of impurities near V, the reduction of the electrode surface near 0.4 V, and the peak of hydrogen generation below 0 V,
Only the oxidation peak of the electrolyte is seen at the diamond electrode. In both CVs of both electrodes, the peak that increases as the solute concentration increases is the solute oxidation peak.

FIG. 4 shows gas chromatograms of the electrolytic solution before and after performing the potentiostatic electrolytic fluorination using a platinum electrode. From the results of gas chromatography and the literature, the reaction process of the product obtained by electrolytic fluorination at a platinum electrode in this system is represented by the following equation.

[0022]

[Chemical 1]

The diamond electrode has the same C as the platinum electrode.
Since V is obtained, it can be said that electrolytic fluorination of the solute occurs in the diamond electrode as well as in the platinum electrode. From the above, it is confirmed that the electrolytic oxidation using diamond does not cause an excessive oxidation reaction and enables more efficient electrolytic oxidation.

The p-type semiconductor diamond exhibits more ideal characteristics as an electrode than Pt in the electrolytic fluorination of the above examples, and is expected to be used for electrolytic fluorination and fluorine production in other systems. (Example 2) A p-type semiconductor diamond thin film was formed on a 10 mm square Si substrate by the CVD method. The production conditions are shown in Table 2. SIMS (Secondary Ion Mass Spectros
The dopant concentration in the film determined from the measurement result of (copy) was 10 ²⁵ / m ³ . The Raman spectrum of this thin film is shown in FIG. A sharp peak of diamond is observed at 1333 cm ⁻¹ , indicating that the electrode used is a highly pure diamond thin film.

[0025]

[Table 2]

The structure of the electrolytic cell used was the same as in Example 1. Electrolyte solution (Et ₄ NF ・ 4HF) is Et ₄ NF
Prepared by adding anhydrous hydrogen fluoride to 2HF. Commercially available as 1,4-difluorobenzene (Aldrich
Chemical) was used as is. Et ₄ N · BF ₄ (Morita Chemical Industry Co., Ltd.) and AgClO ₄ (Wako Pure Chemical Industries) are 37
Vacuum dried overnight at 3K. Potentiyo / Galvanostat and Function Generator are Hokuto Denko HA-301 and HB-104, and Gas Chromatography is Shimadzu Corporation GC-14A (Column: Chemicals Inspection Society G-450, 40m). I was there.

Materials for the electrolytic cell are PTFE (polytetrafluoroethylene) and PFA (copolymers of tetrafluoroethylene and per) in consideration of corrosion resistance to hydrogen fluoride.
fluoroalkyl vlinyl ether) was used. Fluorine rubber (copolymers of vinylidene fluoride and
An O-ring made of hexafluoropropylene) was used, and carbon fiber was used to take a lead from the diamond surface.
An electrode was devised in which the electrolyte was brought into contact only with the diamond surface and the lead was taken directly from the thin film surface. As a reference electrode, Ag / Ag ⁺ [AgClO ₄ (0.01M) + Et
₄ N · BF ₄ (0.1 M) + Me ₃ CN] was used.

Cyclic voltammetry (CV)
First, platinum was used as the working electrode, the CV of only the electrolytic solution was measured for background measurement, then the working electrode was changed to diamond, and the background was measured in the same manner.
Next, a certain amount of solute 1,4-difluorobenzene was added to the electrolytic solution using a microsyringe to adjust the solution concentration to 0.01.
M. After stirring for about 5 minutes, CV was measured with a platinum electrode and a diamond electrode as in the case of measuring the background. Further, a solute was added, the solution temperature was adjusted to 0.03 M, the mixture was stirred for about 5 minutes, and then the CV was similarly measured at the platinum electrode and the diamond electrode.

In the potentiostatic electrolytic fluorination of 1,4-difluorobenzene using a platinum electrode, the polarities of the electrodes for CV measurement using a platinum electrode were exchanged. That is, the platinum electrode with a large area (Fig. 1, d) is used as the anode and the platinum electrode (Fig. 1,
c) was used as the cathode. 1.0M by adding 1.11 × 10 ⁻² mol of 1,4-difluorobenzene to 10 ml of the electrolytic solution
And a voltage of 2.5 V, using a coulomb meter, approximately 2
When the flow of 000 C (about 1 F × 1.11 × 10 ⁻² mol × 2) was completed, the electrolytic reaction was completed. At the start of electrolysis, a current of about 400 mA flows, and the amount of current decreases with time. Before the reaction, when the electric current of 1000C flows, after the reaction (2000C
Three types of electrolyte solutions (when they flowed) were collected to obtain a gas chromatogram. He is used as the carrier gas (flow rate 2 x 1
0 ³ mm ² / min), and the column temperature is from 323 K to 4
The temperature was raised to 23 K at 10 K / min.

Comparing the obtained cyclita voltammograms, as in Example 1, 1 to 1.5 for platinum electrodes.
V (vs. Ag ^/ Ag ⁺ ) near the electrode surface, which is considered to be the formation of PtO _2.
While a peak of hydrogen generation is observed below O ₂ ) reduction and OV, such a peak is not observed in the diamond electrode in the current scanning potential range. The redox peak of PtO ₂ at the platinum electrode is considered to be due to a trace amount of water in the electrolytic solution.

In both CVs of both electrodes, the peaks that increase with the increase of the solute temperature are the peaks corresponding to the fluorination of the solute. In the chromatogram of the electrolytic solution, as in FIG. 4 of Example 1, the peak that appears after the retention time of 4.2 seconds is the carbon tetrachloride used as the solvent, and 1.0 second (5.581 and 5.581). The peak that appears at 553 seconds) is 1,4
-Difluorobenzene, 5.7 seconds (5.702 and 5.6
The peak that appears after 77 seconds is the reaction product 3,
The peak of 3,6,6-tetrafluoro-1,4-cyclohexadiene, which appears at 9.2 seconds, can be identified as the peak of chlorobenzene added as an internal standard.

[0032]

As described in detail above, the invention of this application makes it easy to handle equipment and reaction operation, and enables stable operation even under relatively severe conditions. It is also possible. In addition, the semiconductor diamond electrode of the invention of this application as a carbon-based electrode is expected to develop a more general application of electrolytic fluorination reaction.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an electrolytic cell as an example and a partial perspective-plan bottom view.

2 (A), (B) and (C) are diagrams exemplifying Cyclic voltammograms in the case of a Pt electrode.

3 (D), (E), and (F) are diagrams exemplifying Cyclic voltammograms in the case of a semiconductor diamond electrode.

4 (A), (B), and (C) are spectrum diagrams of gas chromatograms, respectively.

FIG. 5 is a Raman spectrum diagram of a semiconductor diamond film.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields investigated (Int.Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (5)

(57) [Claims] 1. An electrode for electrolytic fluorination reaction of an organic compound, which is made of semiconductor diamond. 2. The electrode according to claim 1, wherein the semiconductor diamond is formed on a substrate. 3. The electrode according to claim 2, wherein a boron-doped vapor phase film is formed on a silicon substrate. 4. An organic electrolytic fluorination method, which comprises electrolytically fluorinating an organic compound using the electrode for electrolytic fluorination reaction according to claim 1 as an anode. 5. The electrolytic fluorination method according to claim 4, wherein the organic compound is an aromatic compound.