A method for electrochemically selectively debrominating to prepare o-chlorobenzoic acid

Abstract

The present application relates to the technical field of preparation of o-chlorobenzoic acid, and particularly relates to a method for preparing o-chlorobenzoic acid by electrochemical selective debromination. The method comprises the following steps: (1) using sulfuric acid aqueous solution as an anolyte and sodium hydroxide aqueous solution as a catholyte; mixing the reaction raw material chlorobenzoic acid into the catholyte and electrolyzing to debrominate; (2) adjusting the pH value of the catholyte after reaction to be acidic, separating to obtain solid and acid liquid, and performing water washing and drying on the solid to obtain white filter cake, which is o-chlorobenzoic acid; and (3) performing electrodialysis dissociation on the obtained acid liquid to obtain sodium hydroxide and recovered acid liquid respectively. The method uses chlorobenzoic acid as a raw material to prepare o-chlorobenzoic acid by electrochemical selective debromination, and through precise control of electrodes, electrolyte and electrolysis conditions, only debromination but not dechlorination of the raw material chlorobenzoic acid is realized.

Description

Technical Field

[0001] This invention relates to the technical field of o-chlorobenzoic acid preparation, specifically a method for preparing o-chlorobenzoic acid by electrochemical selective debromination. Background Technology

[0002] o-Chlorobenzoic acid is an important organic intermediate widely used in the synthesis of pharmaceuticals, pesticides, fragrances, and chemical materials. Traditional synthesis methods suffer from problems such as cumbersome steps, low yield, low purity, or environmental pollution.

[0003] Currently, methods for preparing o-chlorobenzoic acid include the o-methylaniline diazotization method, the o-chlorotoluene oxidation method, the o-chlorotoluene chlorination hydrolysis method, and the o-chlorobenzonitrile hydrolysis method, but all have drawbacks. For example, CN118420455A discloses a method for preparing 2-chloro-5-bromobenzoic acid. Using 4-bromoaniline as a starting material, 2-amino-5-bromobenzaldehyde is obtained with high yield and selectivity via the Vilsmeier-Haack reaction. Then, 2-chloro-5-bromobenzaldehyde is generated via a diazotization-Sandmeyer reaction. 2-chloro-5-bromobenzaldehyde, under the action of an oxidant, can yield the target compound 2-chloro-5-bromobenzoic acid. Although the o-methylaniline diazotization method has relatively mild reaction conditions, the process route is long, costly, and generates a significant amount of waste.

[0004] CN119118829A discloses a method for preparing methyl o-chlorobenzoate from o-chlorotoluene. The method involves adding o-chlorotoluene, acetic acid, and a supported catalyst to a mixing vessel, heating, and stirring to obtain a mixed solution. This solution is then poured into a reaction vessel, pressurized by air, heated, and reacted. The solution is discharged, cooled, filtered, washed, and distilled to obtain o-chlorobenzoic acid. The o-chlorobenzoic acid and methanol are mixed, stirred, a catalyst is added, and the mixture is heated. After cooling, extraction, washing, and allowing the layers to separate, the upper phase is methyl o-chlorobenzoate. Therefore, the o-chlorotoluene oxidation method used in this patent suffers from a long production cycle.

[0005] CN115594563A discloses a method for preparing o-chlorotrichlorotoluene from o-chlorotoluene using continuous photocatalysis in a micro-reaction process. In this method, preheated o-chlorotoluene is fed into a mixing chamber, and chlorine gas is introduced into the mixing chamber to obtain a reaction solution. The reaction solution flows sequentially through the reaction chamber and undergoes a continuous photocatalytic reaction under an ultraviolet lamp. After post-treatment, o-chlorotrichlorotoluene is obtained. The o-chlorotoluene chlorination and hydrolysis method used in this patent uses chlorine gas as a raw material, first chlorinating the methyl group of o-chlorotoluene before hydrolysis, which has the significant drawback of the high toxicity of the chlorine gas used as the raw material.

[0006] CN119038727B discloses a wastewater treatment method in the production process of o-chlorobenzonitrile using an ammonia oxidation process. After treatment with active oxygen, the wastewater oxidizes o-chlorobenzaldehyde to o-chlorobenzoic acid. Simultaneously, due to the acidic aqueous environment within the oxidation reactor, o-chlorobenzonitrile undergoes hydrolysis under acidic conditions, also generating o-chlorobenzoic acid. This converts the effective components in the wastewater into o-chlorobenzoic acid. Since o-chlorobenzoic acid has a high melting point, it can be recovered and reused through simple solid-liquid separation, yielding high-purity o-chlorobenzoic acid. However, the o-chlorobenzonitrile hydrolysis method has disadvantages such as high raw material costs and the generation of nitrogen-containing wastewater.

[0007] Therefore, there is an urgent need to develop an environmentally friendly, low-cost, and efficient method for synthesizing o-chlorobenzoic acid. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of the prior art by providing a method for the electrochemical selective debromination of o-chlorobenzoic acid. This method uses chlorobromobenzoic acid as a raw material for electrochemical selective debromination to obtain o-chlorobenzoic acid. Through precise control of the electrodes, electrolyte, and electrolysis conditions, it achieves debromination of the raw material chlorobromobenzoic acid without dechlorination.

[0009] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution:

[0010] An electrochemical selective debromination method for preparing o-chlorobenzoic acid includes the following steps:

[0011] (1) Use sulfuric acid aqueous solution as anolyte and sodium hydroxide aqueous solution as catholyte; add the reaction raw material chlorobromobenzoic acid into the catholyte and mix well, then electrolyze to debrominate.

[0012] The electrolysis voltage is 2V-20V, the electrolysis temperature is 0℃-50℃, the electrolysis time is 1-3h, and the current density is 5A / dm³. 2 .

[0013] If the electrolysis voltage is below 2V, the reaction time will exceed 48 hours; if it is above 20V, benzoic acid, a dechlorination impurity, will be produced.

[0014] If the electrolysis temperature is below 0℃, the reaction time will exceed 24 hours; if the electrolysis temperature is above 50℃, it will affect the electrode life.

[0015] If the electrolysis time is less than 1 hour, the raw material reaction will be incomplete; if it is more than 3 hours, the reaction conversion rate will be low and the system will produce a lot of impurities.

[0016] (2) Adjust the pH of the catholyte after the reaction in step (1) to acidic. After cooling and filtration, the solid and acid are separated. The solid is washed with water and dried to obtain a white filter cake, which is o-chlorobenzoic acid. Sulfuric acid is used for adjustment.

[0017] (3) The acid solution obtained in step (2) is subjected to electrodialysis to dissociate it, and sodium hydroxide and recovered acid solution are obtained respectively. The sodium hydroxide is returned to step (1) as a cathode liquid raw material.

[0018] The power supply voltage for electrodialysis is 10V-50V; the current density for electrodialysis is 200-600A / m³. 2 Electrodialysis lasts for 1-2 hours.

[0019] If the power supply voltage is below 10V, the reaction time will be prolonged and the raw material conversion will be incomplete; if the power supply voltage is above 50V, it will affect the lifespan of the electrodialysis membrane. If the reaction time is less than 1 hour, the raw material reaction will be incomplete; if it exceeds 2 hours, electricity will be wasted.

[0020] In this invention, in the method for preparing o-chlorobenzoic acid by electrochemical selective debromination, the raw material chlorobromobenzoic acid in step (1) is 2-chloro-3-bromobenzoic acid or / and 2-chloro-5-bromobenzoic acid.

[0021] When chlorobromobenzoic acid is a mixture of 2-chloro-3-bromobenzoic acid and 2-chloro-5-bromobenzoic acid, the mass ratio of 2-chloro-3-bromobenzoic acid to 2-chloro-5-bromobenzoic acid is 1:1.

[0022] In this invention, in the method for preparing o-chlorobenzoic acid by electrochemical selective debromination, step (1) electrolysis is carried out in an H-type electrolytic cell, and the anode chamber and cathode chamber of the electrolytic cell are separated by a cation membrane.

[0023] Preferably, the cation exchange membrane is Nafion-324.

[0024] In this invention, in the method for electrochemical selective debromination to prepare o-chlorobenzoic acid, the cathode used in step (1) of electrolysis is a copper-zinc electrode; the anode used in electrolysis is a bright platinum electrode. Bright platinum is the counterpart to platinum black, which is usually used in electrolysis. The use of bright platinum in this invention can reduce the adhesion of the feed solution on the electrode.

[0025] In the present invention, in the method for preparing o-chlorobenzoic acid by electrochemical selective debromination, the pH value of the anolyte in step (1) is 1-5, and the pH value of the catholyte is 10-14; the concentration of the reaction raw material in the catholyte is 0.1-0.5 mol / L.

[0026] Preferably, the pH value of the anolyte is 2-3, and the pH value of the catholyte is 12-13; the concentration of the reaction raw materials in the catholyte is 0.2-0.3 mol / L.

[0027] In the present invention, in the method for preparing o-chlorobenzoic acid by electrochemical selective debromination, before electrodialysis of the acid solution in step (3), the pH value of the acid solution is adjusted to 10, and the solid precipitate is removed by filtration; after removing organic matter and heavy metal ions by ion adsorption, the pH value of the obtained filtrate is adjusted to neutral, and then electrodialysis is performed.

[0028] Preferably, hydrobromic acid is used to adjust the pH to neutral.

[0029] In this invention, in the method for electrochemical selective debromination to prepare o-chlorobenzoic acid, the power supply voltage for electrodialysis in step (3) is 22V.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The electrochemical selective debromination method for preparing o-chlorobenzoic acid described in this invention has a simple reaction process, does not produce the dechlorination byproduct benzoic acid, and achieves the recycling and reuse of the generated liquid alkali through the combination of electrolysis and electrodialysis, without discharging wastewater, thus achieving a coordinated development of economic and environmental benefits. The preparation method has a high yield and the obtained product has high purity, and has good application value. Attached Figure Description

[0032] Figure 1 The image shows the HPLC chromatogram of the raw material 2-chloro-5-bromobenzoic acid standard.

[0033] Figure 2 The image shows the HPLC chromatogram of the raw material 2-chloro-3-bromobenzoic acid standard.

[0034] Figure 3 The image shows the HPLC chromatogram of the product, 2-chlorobenzoic acid standard.

[0035] Figure 4 The image shows the HPLC spectrum of the catholyte after the reaction in Example 1.

[0036] Figure 5 This is a graph showing the changes in the content of the raw material 2-chloro-5-bromobenzoic acid and the product 2-chlorobenzoic acid as a function of electrolysis time in Example 1.

[0037] Figure 6 This is a graph showing the change in the content of 2-chlorobenzoic acid in the mixed raw materials and product of Example 2 as a function of electrolysis time.

[0038] Figure 7 The image shows the HPLC spectrum of the catholyte after the reaction in Comparative Example 1.

[0039] Figure 8 The image shows the HPLC spectrum of the catholyte after the reaction in Comparative Example 6. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] In the embodiments and comparative examples provided by this invention, all raw materials and experimental equipment are commercially available materials and experimental equipment commonly used in the art, and their specific sources will not be repeated here.

[0042] Example 1

[0043] The specific steps of the electrochemical selective debromination method for preparing o-chlorobenzoic acid are as follows:

[0044] (1) Electrolysis is carried out in an H-type electrolytic cell, with the anode and cathode chambers separated by a cation exchange membrane (Nafion-324). The cathode is a copper-zinc electrode (5×5×0.1cm), the anode is a bright platinum electrode of the same apparent size (5×5×0.1cm), and the reference electrode is a saturated calomel electrode (SCE).

[0045] The anolyte is 1L of 0.5mol / L H2SO4 aqueous solution; the catholyte consists of 1L of 0.5mol / L NaOH solution and 1L of 0.2mol / L 2-chloro-5-bromobenzoic acid solution; the catholyte is circulated by a magnetic pump.

[0046] Electrolysis was performed in the electrolytic cell by applying direct current for 3 hours; the cell voltage (i.e., electrolysis voltage) was 11V, the reaction temperature during electrolysis was 25℃, and the current density was 5A / dm³. 2 .

[0047] The reaction formula for the electrolytic preparation of 2-chlorobenzoic acid from 2-chloro-5-bromobenzoic acid is as follows:

[0048] .

[0049] (2) After the electrolysis is completed, take out the catholy liquid after the reaction in step (1), adjust the pH value to 2 with sulfuric acid, and obtain solid and acid liquid by cooling and filtration. Wash the solid with water and dry it to obtain 30.0g of white filter cake, which is o-chlorobenzoic acid.

[0050] Combination Figure 4 It can be seen that the purity of the obtained product is 99% and the yield is 94.9%.

[0051] Furthermore, the contents of the raw material 2-chloro-5-bromobenzoic acid and the product 2-chlorobenzoic acid change with electrolysis time as follows: Figure 5 As shown. (Through) Figure 5 It can be seen that the concentration of the raw material 2-chloro-5-bromobenzoic acid decreases with the extension of electrolysis time, while the concentration of the product 2-chlorobenzoic acid increases accordingly. Most of the raw material is converted into the product.

[0052] (3) First, the acid solution obtained in step (2) is adjusted to pH=10 using 10% sodium hydroxide solution, and the solid precipitate is removed by vacuum filtration to obtain the filtrate.

[0053] The filtrate is then passed through an ion-adsorption chelating resin to remove residual organic matter and heavy metal ions. A 5% hydrobromic acid solution is slowly added to the filtrate to adjust the pH to 7.

[0054] Assemble the electrodialysis unit, start the magnetic pump, and add 1L of neutral filtrate, 0.3L of pure water, 0.3L of pure water, and 2L of 1% sodium hydroxide solution to the salt chamber, acid chamber, alkali chamber, and electrode chamber of the bipolar membrane electrodialysis system, respectively.

[0055] With a power supply voltage of 22V and a current density of 400A / m 2 Under these conditions, the process will end after running for 100 minutes.

[0056] The sodium hydroxide content in the effluent from the alkali chamber was 5.45% (recovery rate 99.5%); the hydrobromic acid content in the effluent from the acid chamber was 5.37%. The hydrobromic acid was used to recover bromine.

[0057] Example 2

[0058] The specific steps of the electrochemical selective debromination method for preparing o-chlorobenzoic acid are as follows:

[0059] (1) Electrolysis is carried out in an H-type electrolytic cell, with the anode and cathode chambers separated by a cation exchange membrane (Nafion-324). The cathode is a copper-zinc electrode (5×5×0.1cm), the anode is a bright platinum electrode of the same apparent size (5×5×0.1cm), and the reference electrode is a saturated calomel electrode (SCE).

[0060] The anolyte is 1 L of 0.5 mol / L H₂SO₄ aqueous solution; the catholyte consists of 1 L of 0.5 mol / L NaOH solution and 1 L of 0.2 mol / L chlorobromobenzoic acid, wherein the chlorobromobenzoic acid is a mixture of 2-chloro-3-bromobenzoic acid and 2-chloro-5-bromobenzoic acid in a 1:1 mass ratio. The catholyte is circulated using a magnetic pump.

[0061] Electrolysis was performed in an electrolytic cell under direct current for 3 hours; the cell voltage was 2V, the reaction temperature was 25℃, and the current density was 5A / dm³. 2 .

[0062] The reaction formula for the electrolytic preparation of 2-chlorobenzoic acid from 2-chloro-5-bromobenzoic acid is shown in formula (1):

[0063] (1).

[0064] The reaction formula for the electrolytic preparation of 2-chlorobenzoic acid from 2-chloro-3-bromobenzoic acid is shown in formula (2):

[0065] (2).

[0066] (2) After the electrolysis is completed, take out the catholy liquid after the reaction in step (1), adjust the pH value to 2 with sulfuric acid, and obtain the solid and acid liquid by cooling and filtration. Wash the solid with water and dry it to obtain 29.4g of white filter cake, which is o-chlorobenzoic acid.

[0067] The purity of the obtained product was 94.2%, and the yield was 88.3%.

[0068] Furthermore, the 2-chlorobenzoic acid content in the mixed raw materials and product changes with electrolysis time as follows: Figure 6 As shown. (Through) Figure 6 It is known that both 2-chloro-3-bromobenzoic acid and 2-chloro-5-bromobenzoic acid can be converted into 2-chlorobenzoic acid, but the conversion rate of 2-chloro-3-bromobenzoic acid is lower than that of 2-chloro-5-bromobenzoic acid.

[0069] (3) First, the acid solution obtained in step (2) is adjusted to pH=10 using 10% sodium hydroxide solution, and the solid precipitate is removed by vacuum filtration to obtain the filtrate.

[0070] The filtrate is then passed through an ion-adsorption chelating resin to remove residual organic matter and heavy metal ions. A 5% hydrobromic acid solution is slowly added to the filtrate to adjust the pH to 7.

[0071] Assemble the electrodialysis unit, start the magnetic pump, and add 1L of neutral filtrate, 0.3L of pure water, 0.3L of pure water, and 2L of 1% sodium hydroxide solution to the salt chamber, acid chamber, alkali chamber, and electrode chamber of the bipolar membrane electrodialysis system, respectively.

[0072] With a power supply voltage of 10V and a current density of 600A / m 2 Under these conditions, the process will end after 1 hour.

[0073] The sodium hydroxide content in the effluent from the alkali chamber was 5.23% (recovery rate 98.6%); the hydrobromic acid content in the effluent from the acid chamber was 5.14%. The hydrobromic acid was used to recover bromine.

[0074] Example 3

[0075] The difference from Example 1 is that the cell voltage in step (1) is 20V and the electrolysis reaction lasts for 1 hour.

[0076] 30.3 g of white filter cake was obtained, with a purity of 98.7% and a yield of 95.5%.

[0077] In step (3), the power supply voltage is 50V, the membrane pair voltage is 2.4V / pair, and the current density is 200A / m. 2 Under these conditions, the process will end after 2 hours.

[0078] The sodium hydroxide content in the effluent from the alkali chamber was 5.37% (recovery rate 99%); the hydrobromic acid content in the effluent from the acid chamber was 5.26%.

[0079] The others are the same as in Example 1.

[0080] Example 4

[0081] The difference from Example 1 is that in step (1), the cathode liquid is composed of 1L of 0.5mol / L NaOH solution and 1L of 0.2mol / L 2-chloro-3-bromobenzoic acid.

[0082] 29.7 g of white filter cake was obtained, with a purity of 98.8% and a yield of 93.7%.

[0083] The reaction formula for the electrolytic preparation of 2-chlorobenzoic acid from 2-chloro-3-bromobenzoic acid is as follows:

[0084]

[0085] The sodium hydroxide content in the effluent from the alkali chamber was 5.39% (recovery rate 99.2%); the hydrobromic acid content in the effluent from the acid chamber was 5.26%.

[0086] The others are the same as in Example 1.

[0087] Comparative Example 1

[0088] The difference from Example 1 is that the tank voltage in step (1) is 23V.

[0089] Combination Figure 7 The obtained white filter cake weighed 18.4g, with a purity of 43% and a yield of 25.3%. This indicates that when the electrolysis voltage exceeds 20V, a large amount of dechlorination impurity benzoic acid is generated, leading to a decrease in product purity.

[0090] The electrodialysis process in step (3) ends after 1 hour.

[0091] The sodium hydroxide content in the effluent from the alkali chamber was 4.91% (recovery rate 90.5%); the hydrobromic acid content in the effluent from the acid chamber was 4.87%.

[0092] The others are the same as in Example 1.

[0093] Comparative Example 2

[0094] The difference from Example 1 is that the electrolysis time in step (1) is 0.5 h. The resulting white filter cake is 17.2 g, with a purity of 64.1% and a yield of 35.2%. The electrolysis time is less than 60 min, the raw material reaction is incomplete, and a large amount of raw material remains, which does not meet the requirements of electrochemical dehalogenation.

[0095] The electrodialysis process in step (3) ends after 1 hour.

[0096] The sodium hydroxide content in the effluent from the alkali chamber was 4.18% (recovery rate 77.1%); the hydrobromic acid content in the effluent from the acid chamber was 4.01%.

[0097] The others are the same as in Example 1.

[0098] Comparative Example 3

[0099] The difference from Example 1 is that the electrolysis time in step (1) is 5 hours.

[0100] The resulting white filter cake weighed 27.4 g, with a purity of 89% and a yield of 78%.

[0101] In step (3), the current density for electrodialysis is 100 A / m. 2 The electrodialysis process ended after 1 hour.

[0102] The sodium hydroxide content in the effluent from the alkali chamber was 3.47% (recovery rate 63.9%); the hydrobromic acid content in the effluent from the acid chamber was 3.38%.

[0103] The others are the same as in Example 1.

[0104] Extending the electrolysis time introduces various impurities, reducing the reaction conversion rate. Simultaneously, when the electrodialysis current density is below 200 A / m³, [further issues arise]. 2 At that time, the efficiency of electrodialysis is greatly reduced.

[0105] Comparative Example 4

[0106] The method for preparing o-chlorobenzoic acid by electrochemical selective debromination described in this comparative example

[0107] Step (1) Electrolysis is carried out in an H-type electrolytic cell, with the anode and cathode chambers separated by a cation exchange membrane (Nafion-324). The cathode is a copper-zinc electrode (5×5×0.1cm), the anode is a bright platinum electrode of the same apparent size (5×5×0.1cm), and the reference electrode is a saturated calomel electrode (SCE).

[0108] The anolyte is 1L of 0.5mol / L H2SO4 aqueous solution; the catholyte consists of 1L of 0.5mol / L NaOH solution and 1L of 0.2mol / L 2-chloro-5-bromobenzoic acid solution; the catholyte is circulated by a magnetic pump.

[0109] Electrolysis was performed in an electrolytic cell under direct current for 3 hours; the cell voltage was 11V, the reaction temperature was 25℃, and the current density was 5A / dm³. 2 .

[0110] After the electrolysis is completed, the catholy liquid after the reaction in step (1) is taken out, and the pH value is adjusted to 2 with sulfuric acid. After cooling and filtration, the solid and acid are separated. The solid is washed with water and dried to obtain 29.6g of white filter cake, which is o-chlorobenzoic acid.

[0111] The purity of the obtained product was 99.2%, and the yield was 94%.

[0112] The difference from Example 1 is that the power supply voltage for electrodialysis in step (3) is 8V, and the electrodialysis operation ends after 24 hours.

[0113] The sodium hydroxide content in the effluent from the alkali chamber was 4.66% (recovery rate 85.9%); the hydrobromic acid content in the effluent from the acid chamber was 4.59%.

[0114] The others are the same as in Example 1.

[0115] Comparative Example 5

[0116] The difference from Example 1 is that the electrolysis reaction temperature in step (1) is -5°C and the electrolysis time is 24h.

[0117] The resulting white filter cake weighed 20.8g, with a purity of 62% and a yield of 41%.

[0118] In step (3), the current density for electrodialysis is 700 A / m. 2 The electrodialysis process ended after 1 hour.

[0119] The sodium hydroxide content in the effluent from the alkali chamber was 3.33% (recovery rate 61.4%); the hydrobromic acid content in the effluent from the acid chamber was 3.24%.

[0120] The others are the same as in Example 1.

[0121] When the electrolysis temperature is below 0℃, the reaction time needs to be extended to more than 24 hours, resulting in extremely low electrolysis efficiency. Furthermore, when the current density of electrodialysis exceeds the limiting current density, concentration polarization occurs, leading to reduced desalination rate, decreased current efficiency, scaling, and other adverse phenomena.

[0122] Comparative Example 6

[0123] The difference from Example 1 is that in step (1), the anode is a platinum black electrode with the same apparent size (5×5×0.1cm).

[0124] Combination Figure 8It can be seen that the obtained white filter cake weighed 16.9g, had a purity of 38.5%, and a yield of 20.8%.

[0125] The electrodialysis process in step (3) ends after 1 hour.

[0126] The sodium hydroxide content in the effluent from the alkali chamber was 5.29% (recovery rate 97.5%); the hydrobromic acid content in the effluent from the acid chamber was 5.24%.

[0127] The others are the same as in Example 1.

[0128] Platinum black electrodes have a large specific surface area and high activity. During electrolytic debromination, a dechlorination reaction occurs simultaneously, resulting in low purity and yield.

[0129] Comparative Example 7

[0130] The difference from Example 1 is that in step (1), the anolyte is 1L of 0.5mol / L NaOH aqueous solution.

[0131] The resulting white filter cake weighed 14.87 g, with a purity of 88.4% and a yield of 41.98%.

[0132] The electrodialysis process in step (3) ends after 1 hour.

[0133] Assemble the electrodialysis unit, start the magnetic pump, and add 1L of neutral filtrate, 0.3L of pure water, 0.3L of pure water, and 2L of 1% sodium hydroxide solution to the salt chamber, acid chamber, alkali chamber, and electrode chamber of the bipolar membrane electrodialysis system, respectively.

[0134] With a power supply voltage of 22V, a membrane-to-pair voltage of 2.4V, and a current density of 400A / m, the following conditions were met: 2 Under these conditions, the process will end after running for 100 minutes.

[0135] The sodium hydroxide content in the effluent from the alkali chamber was 4.11% (recovery rate 75.8%); the hydrobromic acid content in the effluent from the acid chamber was 3.98%.

[0136] The others are the same as in Example 1.

Claims

1. A method for preparing o-chlorobenzoic acid by electrochemical selective debromination, characterized in that, Includes the following steps: (1) Use sulfuric acid aqueous solution as anolyte and sodium hydroxide aqueous solution as catholyte; add the reactant chlorobromobenzoic acid into the catholyte and mix well, then electrolyze to debrominate; The electrolysis voltage is 2V-20V, the electrolysis temperature is 0℃-50℃, the electrolysis time is 1-3h, and the current density is 5A / dm³. 2 ; (2) Adjust the pH of the catholyte after the reaction in step (1) to acidic, cool and filter to separate the solid and acid, wash the solid with water and dry it to obtain a white filter cake, which is o-chlorobenzoic acid; (3) The acid solution obtained in step (2) is subjected to electrodialysis to dissociate it, and sodium hydroxide and recycled acid solution are obtained respectively. The sodium hydroxide is returned to step (1) as a cathode liquid raw material. The power supply voltage for electrodialysis is 10V-50V; the current density for electrodialysis is 200-600A / m³. 2 Electrodialysis lasts for 1-2 hours. In step (1), the cathode used for electrolysis is a copper-zinc electrode; the anode used for electrolysis is a bright platinum electrode.

2. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that, The raw material chlorobromobenzoic acid in step (1) is 2-chloro-3-bromobenzoic acid or / and 2-chloro-5-bromobenzoic acid.

3. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 2, characterized in that, When chlorobromobenzoic acid is a mixture of 2-chloro-3-bromobenzoic acid and 2-chloro-5-bromobenzoic acid, the mass ratio of 2-chloro-3-bromobenzoic acid to 2-chloro-5-bromobenzoic acid is 1:

1.

4. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that, The electrolysis in step (1) is carried out in an H-type electrolytic cell, with the anode chamber and cathode chamber of the electrolytic cell separated by a cation membrane.

5. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 4, characterized in that, The cation exchange membrane used is Nafion-324.

6. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that, In step (1), the pH value of the anolyte is 1-5, and the pH value of the catholyte is 10-14; the concentration of the reaction raw materials in the catholyte is 0.1-0.5 mol / L.

7. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 6, characterized in that, The pH value of the anolyte is 2-3, and the pH value of the catholyte is 12-13; the concentration of the reaction raw materials in the catholyte is 0.2-0.3 mol / L.

8. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that, Before electrodialysis of the acid solution in step (3), the pH value of the acid solution is adjusted to 10, and the solid precipitate is removed by filtration. After removing organic matter and heavy metal ions by ion adsorption, the pH value of the obtained filtrate is adjusted to neutral, and then electrodialysis is performed.

9. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that, The power supply voltage for electrodialysis in step (3) is 22V.

Images