KR20030038112A - Electrochemical synthesis of p-aminophenol - Google Patents

Abstract

PURPOSE: A method for electrochemically synthesizing para-aminophenol from nitrobenzene without organic solvent or surfactant by using a single flat or arc type electrode or a plurality of flat or arc type electrodes as working electrodes and using an agitator is provided. CONSTITUTION: In electrolytically synthesizing para-aminophenol from nitrobenzene, the electrochemical synthesis method of para-aminophenol is characterized in that electrolytic synthesis of para-aminophenol is performed from a cathode compartment solution having 1.0 to 4.0 M concentration of sulfuric acid and 0.5 to 2.0 M concentration of nitrobenzene by using a single flat or arc type electrode or a plurality of flat or arc type electrodes as working electrodes and using an agitator, wherein a material of the working electrodes is graphite, lead, lead-silver alloy or copper, and the material is coated with a single metal or alloy thereof selected from the group consisting of copper, bismuth, tin, antimony, lead and zinc, and wherein the cathode compartment solution further comprises a metal compound containing a metal selected from the group consisting of copper, bismuth, tin, antimony, lead and zinc. The electrochemical synthesizing apparatus of para-aminophenol comprises anode compartment comprising counter electrodes (2), cathode compartment comprising working electrodes (3), and cation exchange membranes (4), wherein the working electrodes are consisted of a single flat or arc type electrode or a plurality of flat or arc type electrodes, and the apparatus further comprises an agitator.

Description

Method of electrochemical synthesis of para-aminophenol {ELECTROCHEMICAL SYNTHESIS OF P-AMINOPHENOL}

The present invention relates to a method of electrochemical synthesis of para-aminophenol, and in particular, a separate organic solvent or interface for dissolving or dispersing nitrobenzene in an electrolytic cell in which a working electrode consists of a flat electrode or an arc electrode. A method for preparing para-aminophenol from nitrobenzene using an electrochemical synthesis method without using an active agent.

As a conventional method of preparing para-aminophenol, a chemical preparation method of hydrogenating para-nitrophenol or nitrobenzene in the presence of a catalyst has been used, but such a chemical method has a relatively low reaction yield and a catalyst used. Since it is a precious metal such as platinum, it was disadvantageous in terms of manufacturing cost.

As a new type of para-aminophenol production method for compensating for the shortcomings of the reaction yield and the production cost, which are the problems of the chemical production method, a lot of researches on electrochemical synthesis (hereinafter referred to as "electrolytic synthesis") have been conducted in recent years. As a representative example thereof, US Pat. No. 3,338,806 can be cited. The above patent is a method for producing para-aminophenol by electrochemically reducing nitrobenzene in an electrolyte mixed with ethanol and sulfuric acid, which produces a lot of undesirable side reaction products such as aniline and azoxybenzene. The yield is low enough to represent approximately 62% and has the problem of recovering ethanol used as an organic solvent.

In addition, although an electrolytic synthesis method using 1-propanol instead of the ethanol as an organic solvent is known, this method also requires a low reaction yield of about 67% in a high concentration nitrobenzene solution and recovers 1-propanol like the ethanol solvent. There is a problem.

On the other hand, according to US Patent No. 4,584,070 dispersing a surfactant (trialkylamine-N-oxide: trialkylamine-N-oxide) as a means for excluding the need for recovery of the organic solvent which is a problem in the manufacturing method A third compartment is formed between the anode chamber and the cathode chamber of the reactor to reduce or prevent the diffusion of oxygen generated from the anode chamber into the cathode chamber while removing oxygen dissolved in the cathode chamber, which is an unnecessary reaction product. A method of inhibiting production of azoxybenzene is disclosed.

However, in the above patent, since a surfactant that is used in a relatively large amount is expensive, and a separate third seal must be provided inside the electrolyzer, the installation cost of the electrolyzer is increased and the overall manufacturing cost is increased because the electrolytic voltage is increased. On the other hand, as mercury in the amalgam metal electrode used as the cathode dissolves in the cathode chamber solution, causing contamination of the reaction product and mercury contamination of the solution, problems such as environmental problems caused by mercury and a decrease in reaction yield due to aging of the electrode Is showing.

As described above, the problem of the negative electrode in the preparation of para-aminophenol from nitrobenzene using electrolytic synthesis is a very important problem: copper electrode, graphite electrode, bismuth coating which is used as a negative electrode other than amalgam metal electrode. The copper electrode also exhibits an electrode dissolution phenomenon when the reaction yield is high and, on the contrary, when the electrode is stable, the reaction yield is low (J. Jayaraman, KS Udupa and HVK Udupa, SAEST, 12, 143 (1977)).

On the other hand, as a method for improving the reaction yield, it is known that a method of increasing the reaction yield by catalysis by injecting a mediator of tin ions into the solution as a method using a catalyst, not an electrode material improvement. Yield increases slightly, but it is considered economically unfavorable due to other problems such as media recovery (HC Rance and JMCoulson, Electrochim. Acta, 14, 283 (1969)).

It is an object of the present invention to increase the surface area of an electrode and agitation of a solution to increase the rate of mass transfer of nitrobenzene to an electrode in view of the above-mentioned disadvantages and problems in the conventional method for preparing para-aminophenol. It is an object to provide a method for the electrochemical synthesis of para amino phenols which, on the other hand, promotes the transfer of reaction products into solution, thereby inhibiting the formation of undesirable reaction by-products, resulting in high reaction yields.

In addition, it is to provide an electrochemical synthesis method of para-aminophenol having further improved reaction yield by further suppressing side reactions by changing the electrochemical synthesis conditions.

1 is a process diagram schematically showing a process for preparing para-aminophenol as a preferred example of the present invention.

2 is a plan view illustrating the structure of an electrolytic cell used in a preferred example of the present invention.

3 is a longitudinal cross-sectional view illustrating the structure of an electrolytic cell used in a preferred example of the present invention.

In the present invention, in electrolytic synthesis of para-aminophenol from nitrobenzene, a single electrode or a plurality of electrodes of plate type or arc type are used as one electrode, and a sulfuric acid of 1.0 to 4.0 M and nitrobenzene of 0.5 to 2.0 M are used. It provides a method for the electrochemical synthesis of para-aminophenol, characterized in that the electrolytic synthesis is carried out from a cathode solution having a concentration.

A preferred example of the entire production method of para-aminophenol by the electrochemical synthesis method of the present invention is a series of mixing, electrolytic reaction, activated carbon treatment, neutralization treatment, separation, etc., as shown in the manufacturing process diagram of FIG. It consists of a sequential process, each of these processes will be described in more detail as follows.

First, in the mixing process, the mixture is mixed with nitrobenzene, sulfuric acid and water used as the cathode chamber solution, and the sulfuric acid and water are mixed with the anode chamber solution. Subsequently, nitrobenzene was cathodic reduced in the state of filling the cathode and anode chambers of the electrolytic cell with each of the above mixed solutions to synthesize para-aminophenol, and then activated carbon was added to the synthesized electrolytic reaction mixture through electrolysis. An activated carbon treatment process is carried out to remove organic matter in the reaction mixture by stirring for several minutes at -100 ° C.

In the subsequent neutralization step, the reaction mixture, which has been treated with activated carbon, is cooled and neutralized within a range of pH 7.0-7.5 using ammonia water or caustic soda in a cooled state to precipitate para-aminophenol. Thereafter, the reaction mixture after the neutralization process is sufficiently cooled, and then the solid para-aminophenol is separated using a centrifugal separator to complete the preparation of para-aminophenol.

The most important step in the production method of the present invention can be said to be the step of electrochemically synthesizing para-aminophenol from nitrobenzene. Therefore, the electrolytic reaction will be described in detail below with reference to FIGS. 2 and 3 illustrating the structure of an electrolytic cell used in a preferred example of the present invention.

Counter electrodes 2 are provided on both sides of the electrolytic cell 1, and one electrode 3 formed by combining a plurality of plate-type or arc-type electrodes alone or plurally is formed on both sides of the center and the counter electrode 2 And cation exchange membrane 4 are formed between the electrode and the one electrode 3, and reference numeral 7 denotes a condenser, (8) a thermometer, (9) a reference electrode, and (10) a heating / cooler. to be.

In the electrolytic synthesis of para-aminophenol as in the present invention, since nitrobenzene and reduction products of nitrobenzene in the cathode chamber are oxidized at the anode, it is essential to separate and separate a diaphragm between the anode chamber and the cathode chamber to prevent this. In addition, when examining the reaction mechanism of the electrolytic synthesis reaction of nitrobenzene to para-aminophenol, hydrogen ion participates in the reaction and sulfuric acid electrolyte is used, so a cation exchange diaphragm is installed between the anode chamber and the cathode chamber. It is preferable to separate the cathode chamber.

In particular, the electrolytic synthesis reaction mechanism of para-aminophenol as in the present invention is the reaction of the production of phenylhydroxylamine as an intermediate product by the electrochemical reduction of nitrobenzene as the first step, and the phenyl which is the intermediate product as the second step. Consisting of chemical potential reaction of hydroxylamine to para-aminophenol. In this two-step reaction mechanism, if the second chemical potential reaction is not performed quickly, the phenylhydroxylamine is electrochemically reduced around the electrode to change to side reaction aniline, and also oxygen in the cathode chamber solution. When is present, phenylhydroxylamine is converted to azoxybenzene, resulting in the formation of unnecessary reaction byproducts, resulting in a decrease in reaction yield. Therefore, the present invention is characterized in that the chemical potential reaction is made quickly, and the side reaction caused by the intermediate product is suppressed.

Accordingly, the plate-type or arc-type single or multiple electrodes and stirrers of the present invention increase the mass transfer speed of the nitrobenzene to the electrodes and increase the electrode surface area and the stirring effect of the solution to increase the reaction rate. do. In addition, as the agitation effect is increased, it promotes the diffusion of the intermediate product phenylhydroxylamine into the solution to increase the reaction yield by allowing the phenylhydroxylamine to be chemically displaced directly with para-aminophenol without being reduced to aniline anymore around the electrode. do. In addition, as described above, in the preparation of para-aminophenol through the conventional electrolytic synthesis method, an expensive interface and a problem in the process of recovering the organic solvent by using an organic solvent or a surfactant to dissolve or disperse nitrobenzene Although there is a problem that the consumption of the active agent is inevitable, when using the electrode and the stirrer of the present invention, since the stirring effect of the solution is very good, without using a separate organic solvent or surfactant for dissolving or dispersing nitrobenzene, As the benzene can be dispersed and electrolyzed, the manufacturing cost can be reduced.

On the other hand, as the material of the electrode of the present invention can be produced in the form of a flat plate or arc shape while being suitable for electrolytic synthesis graphite electrode, lead electrode, lead-silver alloy electrode, or copper electrode, etc. can also be used. On these electrodes, electrodes coated with one or an alloy of copper, bismuth, tin, antimony, lead, and zinc, which are metals having a high hydrogen overvoltage, can be used. The coating of these metals can be carried out by various methods such as chemical vapor deposition, physical vapor deposition, electroplating, and electroless plating. Among these methods, electroplating is the most economical and efficient method.

In the electrolytic synthesis of the present invention, the reaction yield and reaction rate are affected by the electrolytic conditions such as electrolysis temperature, sulfuric acid concentration, nitrobenzene concentration, current density, material of negative electrode and positive electrode. As follows.

First, the higher the electrolysis temperature, the faster the chemical potential reaction of the intermediate product, and the higher the electrolytic current, the higher the electrolysis temperature, the higher the reaction yield and reaction rate. The preferred electrolysis temperature is 50-95 ° C.

In addition, the sulfuric acid concentration affects the reaction yield and the reaction rate. The preferred sulfuric acid concentration is 1.0-4.0 M, the concentration of nitrobenzene mainly affects the reaction yield, and the appropriate concentration of nitrobenzene is 0.5-2.0 M.

The reaction yield may be increased by adding a small amount of a metal compound having a high hydrogen overvoltage in the electrolytic solution and plating these metals on the surface of one electrode during the electrolytic process to suppress the hydrogen generation reaction. The metal compound which can be used at this time is a copper compound, a bismuth compound, a tin compound, an antimony compound, a lead compound, a zinc compound, etc., and a preferable density | concentration is 0.001-0.3 M.

The current density indicates the reaction rate, and productivity increases as the current density increases, but on the contrary, there is an adverse effect that the electrolytic voltage increases and the reaction yield decreases slightly. The desirable current density of the one electrode is 20-200 mA. / cm ² , and the optimum current density is changed depending on the electrolytic reaction characteristics and reaction conditions.

On the other hand, it is possible to increase the electrode area by scratching the surface of the electrode, through which there is a side effect that can increase the stirring effect of the solution. The rotation speed of the stirrer can be made smaller the larger the diameter of the impeller, the preferred range of rotation speed is 100-1000 rpm.

The anode material is preferably a lead electrode stable in a sulfuric acid solution, a lead-silver alloy electrode, and a dimensionally stable anode (DSA (Ti / RuO ₂ )).

The electrolytic reaction is initially carried out by a constant current, but a constant current / constant voltage mixing method in which the electrolysis is carried out at a constant voltage is preferable, and the current is also preferably performed by direct current or pulse current.

In addition, the completion of the electrolytic reaction can be determined by installing a reference electrode in the cathode chamber and measuring the potential of the cathode to the reference electrode or observing hydrogen gas generation at the end of the reaction. Is rapidly increased in the negative (-) direction to reach a certain potential. At this time, the reference electrode used is a saturated calomel electrode (SCE) or a platinum electrode stable in sulfuric acid solution.

Examples of electrolytic synthesis of para-aminophenol from nitrobenzene using the production method of the present invention as described above are as follows.

<Example 1>

Using 2M sulfuric acid + 1M nitrobenzene as cathode chamber solution and 2M sulfuric acid as anode chamber solution without organic solvent or surfactant, stirrer 500 rpm with graphite cathode and Pb-Ag anode at 90 ° C, current density 50 mA / cm Electrolytic synthesis was carried out under ² . Electrolysis was completed when the cathode potential rapidly increased. After electrolytic solution analysis, the reaction yield of para-aminophenol was found to be 79%, 19% for aniline, 2% for azoxybenzene, and 4.0V for electrolytic voltage.

<Example 2>

The solution conditions and the positive electrode were the same as in Example 1, and electrolytic synthesis was carried out using a graphite electrode coated with bismuth as a negative electrode at a stirrer 500 rpm and a current density of 50 mA / cm ² . Electrolysis was completed when the cathode potential rapidly increased. After electrolytic solution analysis, the reaction yield of para-aminophenol was found to be 85%. Aniline was 15% and azoxybenzene was almost absent. The electrolytic voltage was 3.7 V.

<Example 3>

Using 2M sulfuric acid + 1M nitrobenzene + 0.01M CuSO ₄ as cathode chamber solution and 2M sulfuric acid as anode chamber solution without organic solvent or surfactant, stirrer 500 rpm, current with graphite cathode and Pb-Ag anode at 90 ° C Electrolytic synthesis was carried out under a density of 50 mA / cm ² . Electrolysis was completed when the cathode potential rapidly increased. After electrolytic solution analysis, the reaction yield of para-aminophenol was found to be 82%, aniline was 16%, azoxybenzene was 2%, and the electrolytic voltage was 4.0V.

<Example 4>

Using 2M sulfuric acid + 1M nitrobenzene + 0.01M CuSO ₄ as cathode chamber solution without organic solvent or deactivator and 2M sulfuric acid as anode chamber solution, agitator 500 rpm, pulse with graphite anode and Pb-Ag anode at 90 ° C Electrolytic synthesis was carried out under current (100 mA / cm ² 10 msec, 0 mA / cm ² 10 msec). Electrolysis was completed when the cathode potential rapidly increased. After electrolytic solution analysis, the reaction yield of para-aminophenol was found to be 85%, aniline was 15%, and the electrolytic voltage was 4.0V.

As described above, according to the present invention, since nitrobenzene can be dispersed and electrolyzed without using a separate organic solvent or surfactant for dissolving or dispersing nitrobenzene, the separation and recovery step of the organic solvent or surfactant may be performed. Not only is it unnecessary, it is possible to shorten the process, and at the same time, it is possible to obtain a cost-saving effect obtained by not using an expensive surfactant, and thus, the industrial applicability thereof is very high.

Claims (12)

In electrolytic synthesis of para-aminophenol from nitrobenzene, single or multiple electrodes of flat or arc type are used as one electrode and have a concentration of 1.0 to 4.0 M sulfuric acid and 0.5 to 2.0 M sulfuric acid using a stirrer. Electrochemical synthesis method of para-aminophenol, characterized in that the electrolytic synthesis is carried out from the cathode chamber solution. The method of claim 1, wherein the material of the one electrode is graphite, lead, lead-silver alloy or copper, or a single metal or alloy thereof selected from the group consisting of copper, bismuth, tin, antimony, lead and zinc on the material. Electrochemical synthesis of para-aminophenol, characterized in that the coating. The electrochemical synthesis of para-aminophenol according to claim 1, further comprising a metal compound containing a metal selected from the group consisting of copper, bismuth, tin, antimony, lead and zinc. Way. 4. The method of electrochemical synthesis of para-aminophenol according to claim 3, wherein the metal compound is added at 0.001 M to 0.3 M. The electrochemical synthesis method of para-aminophenol according to claim 1, wherein the current density of one electrode is 20 to 200 mA / cm ² . The electrochemical synthesis method of para-aminophenol according to claim 1, wherein the electrolysis temperature is 50 to 95 ° C. The method of electrochemical synthesis of para-aminophenol according to claim 1, wherein the rotation speed of the stirrer is 100 to 1000 rpm. The method of electrochemical synthesis of para-aminophenol according to claim 1, wherein the surface of the electrode is enlarged by making a groove in the electrode surface of the one electrode. The electrochemical synthesis method of para-aminophenol according to claim 1, wherein Pb, Pb-Ag or DSA (Ti / RuO ₂ ) electrodes are used as the anode. The electrochemical synthesis method of para-amino phenol according to claim 1, wherein the electrolytic reaction is carried out by a method of mixing a constant current / constant voltage or a method of mixing a direct current or a pulse current. The electrochemical synthesis of para-aminophenol according to claim 1, wherein the completion of the electrolysis is measured by increasing the potential of the cathode with respect to the reference electrodes (SCE, Pt) or observing hydrogen gas generation at the end of the reaction. Way. In the electrolytic synthesizing apparatus of para-aminophenol consisting of an anode chamber including a counter electrode, a cathode chamber including one electrode, and a cation exchange membrane, the one electrode is composed of a plate type or an arc type single or multiple electrodes, An electrolytic synthesis device of para-aminophenol, further comprising a stirrer.