JPH0140112B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides p-iodoaniline (hereinafter referred to as
The present invention relates to a method for manufacturing PIA (abbreviated as PIA). PIA has useful applications as a synthetic intermediate for dyes, pigments, pharmaceuticals, aramid fibers, and polyimide resin monomers. (Prior art) Conventionally, as a method for producing PIA by electrolytic oxidation of iodide in the presence of aniline, US Pat.
3975439 is listed. In this method, ammonium iodide or alkali metal iodide and aniline are electrolytically oxidized at 0 to 80°C to obtain PIA. (Problems to be Solved by the Invention) In the conventional technology, when electrolyzing iodide and aniline, the pH of the aqueous layer of the electrolytic solution (hereinafter simply referred to as the aqueous layer) is
is maintained at 5 to 8, and the aqueous layer and organic layer are separated. This PH adjustment is done because sodium hydroxide gets mixed into the anolyte during the process, so it is separated in a decanter. In addition, in the examples of the conventional technology, a diaphragm method and a non-diaphragm method are implemented, but in the case of the diaphragm method, it becomes acidic due to hydrogen iodide generated at the anode, and in the case of the non-diaphragm method, the anode becomes acidic. Since more hydroxide is generated at the cathode than generated hydrogen iodide, it should be alkaline, but there is no description of PH change or PH adjustment. Therefore, there is no description of the relationship between PH and electrolytic results. When the present inventors investigated the relationship between the PH of the water layer and the current efficiency, they found that
As is clear from the comparative examples, it has become clear that high current efficiency can be obtained only within a specific range of pH. In particular, when it becomes alkaline, the current efficiency decreases significantly. For this reason, it is necessary to adjust the pH to a specific range.
This is necessary for completely different reasons than in the prior art. Furthermore, with the electrolyte composition of the prior art, it was difficult to adjust the pH. Particularly in the case of the diaphragmless method, the water layer becomes alkaline, so there is a high risk that the current efficiency will decrease. The present inventors have conducted intensive research to overcome the drawbacks of the conventional methods described above, produce PIA with high current efficiency, and develop an industrial method that allows for easy pH adjustment. By adding salt salts to the electrolyte and maintaining the pH of the water layer within a specific range, high current efficiency can be stably obtained, and in addition to reducing voltage, surprisingly, current efficiency can be further increased. Based on this finding, the present invention was completed. (Means and Effects for Solving the Problems) The present invention provides that ammonium phosphate or Add sodium phosphate or potassium phosphate to the aqueous layer in the electrolyte.
This is a method for producing PIA characterized by carrying out electrolysis while maintaining the pH between 5.5 and 6.9. In the present invention, ammonium phosphate, sodium phosphate, or potassium phosphate is added to the electrolyte to reduce PH changes, facilitate PH adjustment, and further improve current efficiency. In the present invention, ammonium phosphate, sodium phosphate, and potassium phosphate are used as the phosphate, but sodium phosphate is preferred industrially.
The phosphate concentration in the aqueous layer is preferably 1 to 20% by weight, and if it exceeds 20% by weight, the viscosity of the aqueous layer increases. The pH of the aqueous layer is preferably 5.5 to 6.9. When the pH is higher than 6.9, the current efficiency of PIA decreases, and side reaction products such as 4-aminodiphenylamine are produced. Additionally, if the pH is lower than 5.5, what appears to be aniline phosphate will precipitate and adhere to the vessel wall, making it impossible to perform electrolysis normally. In the present invention, ammonium iodide, sodium iodide, or potassium iodide is used as the iodide, and industrially, sodium iodide is particularly preferred. Preferably, the cation is the same as the cation of the phosphate described above. When ammonium iodide, sodium iodide, or potassium iodide is electrolyzed in the presence of aniline, it can be carried out without any problem by either a diaphragm method or a diaphragmless method. In the case of the diaphragm method, hydrogen iodide is produced at the anode and the corresponding hydroxide is produced at the cathode. If hydroxide is required, the diaphragm method is selected. On the other hand, in the case of the non-diaphragm method, there is a high risk that the water layer becomes alkaline due to the hydroxide generated at the cathode and the current efficiency decreases. , 4, there is little PH change and high current efficiency can be stably obtained. This method does not require a diaphragm, simplifies the structure of the container, and allows the electrode spacing to be narrowed, thereby improving the power consumption rate. Anode materials include platinum, ruthenium, rhodium, and iridium alone or plated with titanium or tantalum, alloys and alloy platings, and oxidation of platinum, ruthenium, rhodium, and iridium with valve metals (titanium, tantalum, etc.). Examples include metal alloys, carbon, etc. The cathode material is preferably one with a low hydrogen overvoltage, but is not particularly limited, and examples include iron, nickel, stainless steel, and the like. When using a diaphragm, a cation exchange membrane, an aniline exchange membrane, etc. are used as necessary. The diaphragm method will be described below. The description is generally applicable to the non-diaphragm method, so only examples are shown. The electrolytic layer may be one commonly used in organic electrolytic reactions, as long as it allows the electrolytic solution to pass between the two electrodes. For example, in an electrolytic cell, a cathode plate and an anode plate are opposed in parallel, and a polyethylene plate that defines the membrane-to-electrode distance, a diaphragm, and a polyethylene plate are placed in this order to form a cathode chamber and an anode chamber between the two electrodes. . An opening is provided in the center of each of these polyethylene plates to allow the electrolyte to pass therethrough. The current-carrying area of the electrode is determined by the size of the opening, and the distance between the electrode and the diaphragm is determined by the thickness of the polyethylene plate. The anolyte and catholyte enter the anode and cathode chambers from each tank through the supply ports provided in the electrolytic cell, and while passing through the chambers, a portion reacts and exits from the outlet, and is transferred to the anolyte tank. , return to the catholyte tank,
circulate between the tank and the chamber. The current density is preferably 1 to 30A/ ^dm2 , and 30A/dm2.
Current densities higher than dm ² result in significantly higher voltages, and current densities lower than 1 A/dm ² result in poor productivity. The electrolysis temperature is preferably 20 to 60°C. There is a correlation between the electrolysis temperature and the amount of by-product o-iodoaniline (hereinafter abbreviated as OIA), and the lower the temperature, the more
It is preferable because the p/o isomer ratio becomes large. However, the voltage increases and the power consumption rate worsens. The flow rate of the electrolytic solution in the electrolytic cell is preferably 0.1 to 4 m/sec. At a flow rate lower than 0.1 m/sec, the current efficiency decreases, and at a flow rate higher than 4 m/sec, the pressure loss within the electrolytic cell becomes very large. The distance between the electrode and the diaphragm is usually preferably 0.5 to 3 mm. The pH of the aqueous phase can be adjusted by adding a corresponding hydroxide or hydrogen iodide, if necessary. The anolyte consists of an aqueous layer and an organic layer. The water layer is
The main components are water, phosphate, and iodide, and the main components of the organic layer are aniline, PIA, and OIA. The concentration of PIA in the organic layer is preferably 1 to 60% by weight. The ratio of the organic layer in the anolyte is defined as the org capacity ratio, and the org capacity ratio is preferably 0.01 to 1. As the catholyte, any of an aqueous solution of phosphate, an aqueous iodide, and an aqueous hydroxide can be used, but it is more preferable to use the corresponding hydroxide as a product. (Effects of the Invention) As described above, according to the present invention, by adding phosphate, it is possible to suppress the PH change in the water layer and prevent the current efficiency of PIA from decreasing. Furthermore, current efficiency can be increased. Furthermore, the highest current efficiency can be obtained by maintaining the pH between 5.5 and 6.9. add phosphate
The reason why PH changes can be suppressed and PH adjustment has become easier is that
This is advantageous for industrial implementation. Moreover, by adding phosphate, the voltage can be lowered and the power consumption rate can be improved. In the above points, the method of the present invention has the following features:
This is an extremely superior industrial manufacturing method for PIA. (Example) Next, the present invention will be explained in more detail with reference to Examples. Note that the measured values in the Examples and Comparative Examples were based on the following method. Current efficiency (%) = Number of moles of PIA produced x 2/Amount of current flow (Faraday unit) x 100 p/o (molar ratio) = PIA produced/OIA produced Example 1 As the anolyte, 75 g of sodium dihydrogen phosphate,
75g disodium hydrogen phosphate, sodium iodide
A mixture of 150 g of aniline, 300 g of aniline, and 1200 g of water was used and placed in the anolyte tank. The catholyte tank has 2
% aqueous sodium hydroxide solution was added. The electrolyte in both tanks was circulated to the next electrolytic cell. The electrolytic cell consists of an anolyte and a cathode chamber separated by a diaphragm.The anode is a platinum-plated titanium plate, the cathode is an iron plate, and both electrodes have a current-carrying area of 1 cm x 100 cm, with a current-carrying area between the two electrodes. is 1cm×
Two 2 mm thick polyethylene plates with 100 cm openings and a perfluorocarbon cation exchange membrane placed in the center to form a cathode chamber and an anode chamber were used. The electrolytic cell has an electrolyte supply inlet and an outlet, and the electrolyte has a flow rate of 2.
Flow at m/sec, current density 10A/dm ² , electrolysis temperature 50
Electrolysis was carried out at ℃ for 2 hours. The pH of the anolyte aqueous layer was adjusted to 6.5 in advance, and NaOH was added during electrolysis to increase the pH.
was kept at 6.5. The average voltage was 3.5V. After electrolysis, PIA in the electrolyte was analyzed by gas chromatography. As a result, the current efficiency was 94%. There were few PH changes during operation, and PH adjustment was easy. The p/o ratio of the iodoaniline produced was 24. Comparative Example 1 Electrolysis was carried out under the same conditions as in Example 1, except that sodium phosphate was removed from the anolyte composition. The average voltage was 4.3V. Current effect is 86
It was %. It was difficult to adjust the pH while driving, and the pH fluctuated slightly. The p/o ratio of the iodoaniline produced was 23.5. Example 2 Using the same electrolytic solution and electrolytic cell as in Example 1, the flow rate of the electrolytic solution was 2 m/sec, the electrolysis temperature was 50°C, and the current density was 10 A/sec.
Electrolysis was carried out at dm ² for 2 hours while changing the pH of the aqueous layer. The results are shown in Table 1.

[Table] Comparative Example 2 Electrolysis was carried out for 2 hours using the same electrolytic solution and electrolytic cell as in Comparative Example 1, and the same electrolytic conditions, but only the pH was changed. The results are shown in Table 2.

[Table] Note that even if the pH is 5.0 or 4.6, the organic layer is liquid.
No precipitation occurred. However, at PH=4.6,
The organic layer became very small. This is probably due to the aniline salt being dissolved in the aqueous layer. At pH 7.8, 4-aminodiphenylamine and azobenzene were detected as a result of gas chromatography. Example 3 As an electrolyte, 70 g of sodium dihydrogen phosphate,
70g disodium hydrogen phosphate, potassium iodide
A mixed solution of 150g of aniline, 250g of aniline, and 1210g of water was used, and an electrolyte tank was put in it. The pH of the aqueous layer was 6.0. The electrolytic cell consists of a titanium plate with platinum and titanium mixed, coated, and fired to form an oxide alloy as the anode, and an iron plate as the cathode, with a current-carrying area of 1 cm x 1 cm between the two electrodes.
An electrolytic chamber was formed by placing one 2 mm thick polyethylene plate with 100 cm openings. The electrolytic cell had an electrolytic solution inlet and an outlet, and the electrolytic solution was flowed at a flow rate of 2 m/sec, and electrolysis was performed for 2 hours at a current density of 10 A/dm ² and an electrolysis temperature of 50°C. No PH adjustment was performed during electrolysis. The pH of the aqueous layer after electrolysis was 6.5. The average voltage was 3.2V.
The current efficiency of PIA was 92%. The p/o ratio of the iodoaniline produced was 25. Comparative Example 3 Of the electrolyte composition of Example 3, excluding phosphate,
Electrolysis was carried out for 2 hours in the same manner as in Example 3, except that an electrolytic solution containing 140 g of more water was used. No PH adjustment was performed during electrolysis. PH rose from 6.0 to 11.3. Average voltage is 4.4V and current efficiency is 32%
It was hot. Example 4 Ammonium dihydrogen phosphate 50 as electrolyte
A mixture of 50 g of ammonium hydrogen phosphate, 200 g of ammonium iodide, 300 g of aniline, and 1200 g of water was used and placed in an electrolyte tank. The pH of the water layer is 5.5
It was hot. The same electrolytic cell as in Example 3 was used, the electrolytic solution was flowed at a flow rate of 1.5 m/sec, and electrolysis was carried out for 2 hours at a current density of 10 A/dm ² and an electrolysis temperature of 45°C. No PH adjustment was performed during electrolysis. The pH of the aqueous layer after electrolysis was 6.3. The average voltage was 3.2V. The current efficiency of PIA was 91%. p/o of generated iodoaniline
The ratio was 25.3. Comparative Example 4 The electrolyte composition of Example 4 except for phosphate,
Electrolysis was carried out for 2 hours in the same manner as in Example 4, except that an electrolytic solution containing 100 g of water was used. No PH adjustment was performed during electrolysis. PH rose from 5.5 to 9.1. The average voltage was 4.2V. The current efficiency of PIA is
It was 60%.

Claims (1)

[Claims] 1. When producing p-iodoaniline by electrolytically oxidizing ammonium iodide, sodium iodide, or potassium iodide in the presence of aniline,
A method for producing p-iodoaniline, which comprises adding ammonium phosphate, sodium phosphate, or potassium phosphate to an electrolytic solution and carrying out electrolysis while maintaining the pH of an aqueous layer in the electrolytic solution at 5.5 to 6.9. 2. The method according to claim 1, wherein the cations of ammonium phosphate, sodium phosphate, or potassium phosphate and ammonium iodide, sodium iodide, or potassium iodide are the same. 3. The method according to claim 1, wherein the phosphate concentration in the aqueous layer is 1 to 20% by weight. 4. The method according to claim 1, wherein the current density is 1 to 30 A/ ^dm2 . 5. The method according to claim 1, wherein the electrolysis temperature is 20 to 60°C.