Method for preparing o-chlorobenzoic acid through electrochemical selective debromination

Abstract

The invention relates to the technical field of o-chlorobenzoic acid preparation, in particular to a method for preparing o-chlorobenzoic acid through electrochemical selective debromination. The method comprises the following steps: (1) taking a sulfuric acid aqueous solution as anolyte and a sodium hydroxide aqueous solution as catholyte; adding a reaction raw material chlorobromobenzoic acid into the cathode liquor, uniformly mixing, and carrying out electrolytic debromination; (2) adjusting the pH value of the reacted catholyte to be acidic, separating to obtain a solid and an acid solution, and washing and drying the solid to obtain a white filter cake, namely o-chlorobenzoic acid; and (3) carrying out electrodialysis dissociation on the obtained acid liquor to respectively obtain sodium hydroxide and recovered acid liquor. According to the method, chlorobromobenzoic acid is adopted as a raw material to carry out electrochemical selective debromination to prepare o-chlorobenzoic acid, and the raw material chlorobromobenzoic acid is only debrominated but not dechlorinated through accurate control of electrodes, electrolyte and electrolysis conditions.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of o-chlorobenzoic acid, and in particular to a method for preparing o-chlorobenzoic acid by electrochemical selective debromination. Background Art

[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 complex procedures, low yield, low purity, and environmental pollution.

[0003] At present, the preparation method of o-chlorobenzoic acid has synthetic methods such as o-methylaniline diazotization, o-chlorotoluene oxidation, o-chlorotoluene chlorination hydrolysis and o-chlorobenzonitrile hydrolysis, but all have defects.For example, CN118420455A discloses a kind of preparation method of 2-chloro-5-bromobenzoic acid.With 4-bromoaniline as raw material, 2-amino-5-bromobenzaldehyde is obtained with high yield and high selectivity by Vilsmeier-Haack reaction, then 2-chloro-5-bromobenzaldehyde is generated through diazotization-Sandmeyer reaction, and 2-chloro-5-bromobenzaldehyde can obtain target compound 2-chloro-5-bromobenzoic acid under oxidant action.Although reaction conditions are comparatively mild using o-methylaniline diazotization, operational route is longer, cost is high, and three wastes are more.

[0004] CN119118829A discloses a method for preparing methyl o-chlorobenzoate with o-chlorotoluene, comprising adding o-chlorotoluene, acetic acid and a supported catalyst into a mixing kettle, heating, stirring, and obtaining a mixed solution; pouring the mixed solution into a reactor, introducing air for pressurization, reacting by heating, discharging, cooling, filtering, washing, and distilling to obtain o-chlorobenzoic acid; mixing o-chlorobenzoic acid and methanol, stirring, adding a catalyst, reacting by heating, cooling, extracting, washing, and the upper phase after stratification is methyl o-chlorobenzoate. Thus, the o-chlorotoluene oxidation method adopted in this patent has the defect of a long production cycle.

[0005] CN115594563A discloses a method for preparing o-chlorotrichlorotoluene from o-chlorotoluene via micro-reaction continuous photocatalysis. The method involves transferring preheated o-chlorotoluene to a mixing chamber, introducing chlorine gas into the mixing chamber to produce a reaction solution. The reaction solution then flows through the reaction chamber and undergoes a continuous photocatalytic reaction under ultraviolet light, followed by post-treatment to produce the o-chlorotrichlorotoluene. The o-chlorotoluene chlorination-hydrolysis method employed in this patent uses chlorine gas as a raw material, first chlorinating the methyl group of the o-chlorotoluene and then hydrolyzing it. This method suffers from the significant drawback of the high toxicity of the raw chlorine gas.

[0006] CN119038727B discloses a wastewater treatment method for the production of o-chlorobenzonitrile using an ammonia oxidation process. The wastewater is treated with active oxygen to oxidize o-chlorobenzaldehyde to o-chlorobenzoic acid. Simultaneously, due to the acidic aqueous solution environment within the oxidation reactor, o-chlorobenzonitrile undergoes hydrolysis under acidic conditions to also generate o-chlorobenzoic acid. This converts the active ingredient in the wastewater into o-chlorobenzoic acid, which has a high melting point and can subsequently be recycled by simple solid-liquid separation to obtain high-purity o-chlorobenzoic acid. However, the o-chlorobenzonitrile hydrolysis method has the disadvantages of 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 present invention aims to address the deficiencies of the prior art by providing a method for preparing o-chlorobenzoic acid by electrochemical selective debromination. The method uses chlorobromobenzoic acid as a raw material for electrochemical selective debromination to produce o-chlorobenzoic acid. Through precise control of electrodes, electrolyte, and electrolysis conditions, only debromination without dechlorination of the raw chlorobromobenzoic acid is achieved.

[0009] In order to achieve the above technical effects, the present invention adopts the following technical solutions: A method for preparing o-chlorobenzoic acid by electrochemical selective debromination comprises the following steps: (1) Using aqueous sulfuric acid solution as the anolyte and aqueous sodium hydroxide solution as the catholyte, the raw material chlorobromobenzoic acid is added to the catholyte and mixed evenly, and then debrominated by electrolysis.

[0010] Among them, the electrolysis voltage is 2V-20V, the electrolysis temperature is 0℃-50℃, the electrolysis time is 1-3h, and the current density is 5A / dm 2 .

[0011] If the electrolysis voltage is lower than 2V, the reaction time will exceed 48h; if it is higher than 20V, dechlorinated impurity benzoic acid will be produced.

[0012] If the electrolysis temperature is lower than 0℃, the reaction time will exceed 24h; if the electrolysis temperature is higher than 50℃, it will affect the electrode life.

[0013] If the electrolysis time is less than 1 hour, the raw material reaction is incomplete; if it is longer than 3 hours, the reaction conversion rate is low and the system will produce a lot of impurities.

[0014] (2) The pH value of the cathode liquid after the reaction in step (1) is adjusted to acidic, cooled, filtered and separated to obtain a solid and an acid solution, and 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.

[0015] (3) The acid solution obtained in step (2) is subjected to electrodialysis to obtain sodium hydroxide and recovered acid solution, and the sodium hydroxide is returned to step (1) as a cathode liquid raw material.

[0016] Among them, the power supply voltage of electrodialysis is 10V-50V; the current density of electrodialysis is 200-600A / m 2 ; The electrodialysis time is 1-2h.

[0017] If the power supply voltage is less than 10V, the reaction time will be extended and the raw material conversion will not be complete. If the power supply voltage is higher than 50V, the life of the electrodialysis membrane will be affected. If the reaction time is less than 1h, the raw material reaction will not be complete. If it exceeds 2h, the power will be wasted.

[0018] In the present 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.

[0019] When the 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:2-chloro-5-bromobenzoic acid is 1:1.

[0020] In the method for preparing o-chlorobenzoic acid by electrochemical selective debromination of the present invention, the electrolysis in step (1) is carried out in an H-type electrolytic cell, and the anode chamber and cathode chamber of the electrolytic cell are separated by a cationic membrane.

[0021] Preferably, the cationic membrane is Nafion-324.

[0022] In the present invention, in the method for preparing o-chlorobenzoic acid by electrochemical selective debromination, a copper-zinc electrode is selected as the cathode for electrolysis in step (1); and a bright platinum electrode is selected as the anode for electrolysis. Bright platinum corresponds to platinum black, which is commonly used in electrolysis. The use of bright platinum in the present invention can reduce the adhesion of the feed solution on the electrode.

[0023] In the method for preparing o-chlorobenzoic acid by electrochemical selective debromination of the present invention, 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 materials in the catholyte is 0.1-0.5 mol / L.

[0024] Preferably, the pH value of the anolyte is 2-3, and the pH value of the catholyte is 12-13; in the catholyte, the concentration of the reaction raw materials is 0.2-0.3 mol / L.

[0025] In the method for preparing o-chlorobenzoic acid by electrochemical selective debromination of the present invention, in step (3), before the acid solution is subjected to electrodialysis, the pH value of the acid solution is first adjusted to 10, and the solid precipitate is removed by filtration; after the organic matter and heavy metal ions are removed from the obtained filtrate by ion adsorption, the pH value is adjusted to neutral, and then electrodialysis is performed.

[0026] Preferably, hydrobromic acid is used to adjust the pH to neutral.

[0027] In the present invention, in the method for preparing o-chlorobenzoic acid by electrochemical selective debromination, the power supply voltage of the electrodialysis in step (3) is 22V.

[0028] Compared with the prior art, the present invention has the following beneficial effects: The method for preparing o-chlorobenzoic acid by electrochemical selective debromination of the present invention has a simple reaction process and operation, does not produce benzoic acid as a dechlorination by-product, and through the combination of electrolysis and electrodialysis, the generated liquid alkali is recovered and reused without discharging wastewater, thereby achieving the 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the HPLC spectrum of the raw material 2-chloro-5-bromobenzoic acid standard sample.

[0030] Figure 2 This is the HPLC spectrum of the raw material 2-chloro-3-bromobenzoic acid standard sample.

[0031] Figure 3 This is the HPLC spectrum of the product 2-chlorobenzoic acid standard.

[0032] Figure 4 This is the HPLC spectrum of the cathode liquid after the reaction in Example 1.

[0033] Figure 5 This is a curve chart showing the change in the content of 2-chloro-5-bromobenzoic acid, the raw material, and 2-chlorobenzoic acid, the product, as a function of electrolysis time.

[0034] Figure 6 This is a curve chart showing the change in the content of the mixed raw material and the product 2-chlorobenzoic acid with electrolysis time in Example 2.

[0035] Figure 7 This is the HPLC spectrum of the cathode liquid after the reaction in Comparative Example 1.

[0036] Figure 8 This is the HPLC spectrum of the cathode liquid after the reaction in Comparative Example 6. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings and examples.

[0038] In the embodiments and comparative examples provided by the present invention, all raw materials and experimental equipment are commercially available raw materials and experimental equipment commonly used in the art, and their specific sources are not described in detail here.

[0039] Example 1 The method for preparing o-chlorobenzoic acid by electrochemical selective debromination comprises the following specific steps: (1) Electrolysis was carried out in an H-type electrolytic cell, with the anode and cathode compartments separated by a cationic membrane (Nafion-324). The cathode was a copper-zinc electrode (5 × 5 × 0.1 cm), the anode was a bright platinum electrode of the same apparent size (5 × 5 × 0.1 cm), and the reference electrode was a saturated calomel electrode (SCE).

[0040] The anolyte is 1 L of H2SO4 aqueous solution with a concentration of 0.5 mol / L; the catholyte is composed of 1 L of NaOH solution with a concentration of 0.5 mol / L and 1 L of 2-chloro-5-bromobenzoic acid with a concentration of 0.2 mol / L; the catholyte is circulated by a magnetic pump.

[0041] The electrolysis was carried out for 3 hours with a DC current applied to the electrolytic cell. The cell voltage (i.e., electrolysis voltage) was 11 V, the reaction temperature was 25 °C, and the current density was 5 A / dm 2 .

[0042] The reaction formula for the electrolysis of 2-chloro-5-bromobenzoic acid to produce 2-chlorobenzoic acid is as follows: .

[0043] (2) After the electrolysis is completed, the cathode liquid after the reaction in step (1) is taken out, and the pH value is adjusted to 2 with sulfuric acid. The solid and the acid liquid are separated by cooling and filtration. The solid is washed with water and dried to obtain 30.0 g of a white filter cake, which is o-chlorobenzoic acid.

[0044] Combine Figure 4 It can be seen that the purity of the obtained product is 99% and the yield is 94.9%.

[0045] In addition, the content of raw material 2-chloro-5-bromobenzoic acid and product 2-chlorobenzoic acid changes with electrolysis time as shown in Figure 5 As shown. 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.

[0046] (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 suction filtration to obtain a filtrate.

[0047] The filtrate is then passed through an ion adsorption chelating resin to remove residual organic matter and heavy metal ions. 5% hydrobromic acid solution is slowly added to the filtrate to adjust the pH to 7.

[0048] Assemble the electrodialyzer, start the magnetic pump, and add 1 L of neutral filtrate, 0.3 L of pure water, 0.3 L of pure water, and 2 L of 1% sodium hydroxide solution to the salt chamber, acid chamber, alkali chamber, and polar chamber of the bipolar membrane electrodialysis system, respectively.

[0049] At a power supply voltage of 22V and a current density of 400A / m 2 Under the condition of , the operation ends after 100min.

[0050] The effluent from the alkali chamber contains 5.45% sodium hydroxide (99.5% recovery rate), while the effluent from the acid chamber contains 5.37% hydrobromic acid. The hydrobromic acid is used to recover bromine.

[0051] Example 2 The method for preparing o-chlorobenzoic acid by electrochemical selective debromination comprises the following specific steps: (1) Electrolysis was carried out in an H-type electrolytic cell, with the anode and cathode compartments separated by a cationic membrane (Nafion-324). The cathode was a copper-zinc electrode (5 × 5 × 0.1 cm), the anode was a bright platinum electrode of the same apparent size (5 × 5 × 0.1 cm), and the reference electrode was a saturated calomel electrode (SCE).

[0052] The anolyte was 1L of a 0.5mol / L H2SO4 aqueous solution; the catholyte consisted of 1L of a 0.5mol / L NaOH solution and 1L of 0.2mol / L chlorobromobenzoic acid (a mixture of 2-chloro-3-bromobenzoic acid and 2-chloro-5-bromobenzoic acid in a 1:1 mass ratio). The catholyte was circulated using a magnetic pump.

[0053] The electrolytic cell was electrolyzed for 3 hours with a DC voltage of 2 V, a reaction temperature of 25 ° C, and a current density of 5 A / dm 2 .

[0054] The reaction formula for electrolysis of 2-chloro-5-bromobenzoic acid to produce 2-chlorobenzoic acid is as follows: (1).

[0055] The reaction formula for electrolysis of 2-chloro-3-bromobenzoic acid to produce 2-chlorobenzoic acid is as follows: (2).

[0056] (2) After the electrolysis is completed, the cathode liquid after the reaction in step (1) is taken out, and the pH value is adjusted to 2 with sulfuric acid. The solid and the acid liquid are separated by cooling and filtration. The solid is washed with water and dried to obtain 29.4 g of a white filter cake, which is o-chlorobenzoic acid.

[0057] The purity of the obtained product was 94.2% and the yield was 88.3%.

[0058] In addition, the content of mixed raw materials and product 2-chlorobenzoic acid changes with electrolysis time as shown in Figure 6 As shown. Figure 6 It can be seen 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.

[0059] (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 suction filtration to obtain a filtrate.

[0060] The filtrate is then passed through an ion adsorption chelating resin to remove residual organic matter and heavy metal ions. 5% hydrobromic acid solution is slowly added to the filtrate to adjust the pH to 7.

[0061] Assemble the electrodialyzer, start the magnetic pump, and add 1 L of neutral filtrate, 0.3 L of pure water, 0.3 L of pure water, and 2 L of 1% sodium hydroxide solution to the salt chamber, acid chamber, alkali chamber, and polar chamber of the bipolar membrane electrodialysis system, respectively.

[0062] At a power supply voltage of 10V and a current density of 600A / m 2 Under the condition of , the operation ends after 1 hour.

[0063] The effluent from the alkali chamber contained 5.23% sodium hydroxide (98.6% recovery rate), while the effluent from the acid chamber contained 5.14% hydrobromic acid. The hydrobromic acid was used to recover bromine.

[0064] Example 3 The difference from Example 1 is that in step (1), the cell voltage is 20 V and the electrolysis reaction lasts for 1 hour.

[0065] 30.3 g of white filter cake was obtained with a purity of 98.7% and a yield of 95.5%.

[0066] In step (3), the power supply voltage is 50 V, the membrane pair voltage is 2.4 V / pair, and the current density is 200 A / m 2 Under the condition of , the operation ends after 2h.

[0067] The sodium hydroxide content of the effluent from the alkali chamber is 5.37% (recovery rate 99%); the hydrobromic acid content of the effluent from the acid chamber is 5.26%.

[0068] The rest is the same as in Example 1.

[0069] Example 4 The difference from Example 1 is that the cathode liquid in step (1) consists of 1 L of NaOH solution with a concentration of 0.5 mol / L and 1 L of 2-chloro-3-bromobenzoic acid with a concentration of 0.2 mol / L.

[0070] 29.7 g of white filter cake was obtained with a purity of 98.8% and a yield of 93.7%.

[0071] The reaction formula for the electrolysis of 2-chloro-3-bromobenzoic acid to produce 2-chlorobenzoic acid is as follows:

[0072] The sodium hydroxide content of the effluent from the alkali chamber is 5.39% (recovery rate 99.2%); the hydrobromic acid content of the effluent from the acid chamber is 5.26%.

[0073] The rest is the same as in Example 1.

[0074] Comparative Example 1 The difference from Example 1 is that the cell voltage in step (1) is 23V.

[0075] Combine Figure 7 The obtained white filter cake was 18.4 g, with a purity of 43% and a yield of 25.3%. It can be seen that when the electrolysis voltage is higher than 20 V, a large amount of dechlorinated impurity benzoic acid will be produced, resulting in a decrease in product purity.

[0076] The electrodialysis in step (3) is completed after running for 1 hour.

[0077] The sodium hydroxide content of the effluent from the alkali chamber is 4.91% (recovery rate 90.5%); the hydrobromic acid content of the effluent from the acid chamber is 4.87%.

[0078] The rest is the same as in Example 1.

[0079] Comparative Example 2 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, resulting in incomplete reaction of the raw materials and a large amount of residual raw materials, which does not meet the requirements for electrochemical dehalogenation.

[0080] The electrodialysis in step (3) is completed after running for 1 hour.

[0081] The sodium hydroxide content of the effluent from the alkali chamber is 4.18% (recovery rate 77.1%); the hydrobromic acid content of the effluent from the acid chamber is 4.01%.

[0082] The rest is the same as in Example 1.

[0083] Comparative Example 3 The difference from Example 1 is that the electrolysis time in step (1) is 5 hours.

[0084] The obtained white filter cake was 27.4 g, with a purity of 89% and a yield of 78%.

[0085] The current density of the electrodialysis in step (3) is 100 A / m 2 , the electrodialysis operation ended after 1 h.

[0086] The sodium hydroxide content of the effluent from the alkali chamber is 3.47% (recovery rate 63.9%); the hydrobromic acid content of the effluent from the acid chamber is 3.38%.

[0087] The rest is the same as in Example 1.

[0088] Prolonging the electrolysis time will produce a variety of impurities and reduce the conversion rate of the reaction. At the same time, when the electrodialysis current density is lower than 200A / m 2 The electrodialysis efficiency is greatly reduced.

[0089] Comparative Example 4 The method for preparing o-chlorobenzoic acid by electrochemical selective debromination described in this comparative example, Step (1) electrolysis was carried out in an H-type electrolytic cell, the anode and cathode compartments of which were separated by a cationic membrane (Nafion-324). The cathode was a copper-zinc electrode (5 × 5 × 0.1 cm), the anode was a bright platinum electrode of the same apparent size (5 × 5 × 0.1 cm), and the reference electrode was a saturated calomel electrode (SCE).

[0090] The anolyte is 1 L of H2SO4 aqueous solution with a concentration of 0.5 mol / L; the catholyte is composed of 1 L of NaOH solution with a concentration of 0.5 mol / L and 1 L of 2-chloro-5-bromobenzoic acid with a concentration of 0.2 mol / L; the catholyte is circulated by a magnetic pump.

[0091] The electrolysis was carried out for 3 hours with a DC current of 11 V, a reaction temperature of 25 °C, and a current density of 5 A / dm 2 .

[0092] After the electrolysis is completed, the cathode liquid after the reaction in step (1) is taken out, and the pH value is adjusted to 2 with sulfuric acid. The solid and the acid liquid are separated by cooling and filtration. The solid is washed with water and dried to obtain 29.6 g of a white filter cake, which is o-chlorobenzoic acid.

[0093] The purity of the obtained product was 99.2% and the yield was 94%.

[0094] The difference from Example 1 is that the power supply voltage of the electrodialysis in step (3) is 8V, and the electrodialysis is terminated after running for 24 hours.

[0095] The sodium hydroxide content of the effluent from the alkali chamber is 4.66% (recovery rate 85.9%); the hydrobromic acid content of the effluent from the acid chamber is 4.59%.

[0096] The rest is the same as in Example 1.

[0097] Comparative Example 5 The difference from Example 1 is that the reaction temperature of the electrolysis in step (1) is -5°C and the electrolysis time is 24 hours.

[0098] The obtained white filter cake was 20.8 g, with a purity of 62% and a yield of 41%.

[0099] The current density of the electrodialysis in step (3) is 700 A / m 2 , the electrodialysis operation ended after 1 h.

[0100] The sodium hydroxide content of the effluent from the alkali chamber is 3.33% (recovery rate 61.4%); the hydrobromic acid content of the effluent from the acid chamber is 3.24%.

[0101] The rest is the same as in Example 1.

[0102] When the electrolysis temperature is below 0°C, the reaction time needs to be extended to more than 24 hours, and the electrolysis efficiency is extremely low. When the current density of electrodialysis exceeds the limiting current density, concentration polarization will occur, causing adverse phenomena such as reduced desalination rate, decreased current efficiency, and scaling.

[0103] Comparative Example 6 The difference from Example 1 is that the anode in step (1) is a platinum black electrode of the same apparent size (5×5×0.1 cm).

[0104] Combine Figure 8 It can be seen that the obtained white filter cake is 16.9 g, with a purity of 38.5% and a yield of 20.8%.

[0105] The electrodialysis in step (3) is completed after running for 1 hour.

[0106] The sodium hydroxide content of the effluent from the alkali chamber is 5.29% (recovery rate 97.5%); the hydrobromic acid content of the effluent from the acid chamber is 5.24%.

[0107] The rest is the same as in Example 1.

[0108] Due to its large specific surface area and high activity, the platinum black electrode undergoes dechlorination reaction during electrolytic debromination, resulting in lower purity and yield.

[0109] Comparative Example 7 The difference from Example 1 is that the anolyte in step (1) is 1 L of NaOH aqueous solution with a concentration of 0.5 mol / L.

[0110] The obtained white filter cake was 14.87 g, with a purity of 88.4% and a yield of 41.98%.

[0111] The electrodialysis in step (3) is completed after running for 1 hour.

[0112] Assemble the electrodialyzer, start the magnetic pump, and add 1 L of neutral filtrate, 0.3 L of pure water, 0.3 L of pure water, and 2 L of 1% sodium hydroxide solution to the salt chamber, acid chamber, alkali chamber, and polar chamber of the bipolar membrane electrodialysis system, respectively.

[0113] At a power supply voltage of 22 V, a membrane pair voltage of 2.4 V / pair, and a current density of 400 A / m 2 Under the condition of , the operation ends after 100min.

[0114] The sodium hydroxide content of the effluent from the alkali chamber is 4.11% (recovery rate 75.8%); the hydrobromic acid content of the effluent from the acid chamber is 3.98%.

[0115] The rest is the same as in Example 1.

Claims

1. A method for preparing o-chlorobenzoic acid by electrochemical selective debromination, characterized in that: The steps include: (1) Using aqueous sulfuric acid as the anolyte and aqueous sodium hydroxide as the catholyte, the raw material chlorobromobenzoic acid is added to the catholyte and mixed evenly, and then electrolytically debrominated; Among them, the electrolysis voltage is 2V-20V, the electrolysis temperature is 0℃-50℃, the electrolysis time is 1-3h, and the current density is 5A / dm 2 ; (2) adjusting the pH value of the cathode liquid after the reaction in step (1) to acidic, cooling and filtering to obtain a solid and an acid solution, washing the solid with water, and drying it to obtain a white filter cake, which is o-chlorobenzoic acid; (3) subjecting the acid solution obtained in step (2) to electrodialysis to obtain sodium hydroxide and recovered acid solution, respectively, and returning the sodium hydroxide to step (1) as a cathode liquid raw material; Among them, the power supply voltage of electrodialysis is 10V-50V; the current density of electrodialysis is 200-600A / m 2 ; The electrodialysis time is 1-2h.

2. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that: The raw material of the 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 the 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: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, and the anode chamber and cathode chamber of the electrolytic cell are separated by a cationic membrane.

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

6. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that: In the step (1), the cathode used for electrolysis is a copper-zinc electrode; the anode used for electrolysis is a bright platinum electrode.

7. 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; in the catholyte, the concentration of the reaction raw materials is 0.1-0.5 mol / L.

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

9. The method for preparing o-chlorobenzoic acid by electrochemical selective debromination according to claim 1, characterized in that: In step (3), before the acid solution is subjected to electrodialysis, the pH value of the acid solution is first adjusted to 10, and the solid precipitate is removed by filtration; after the organic matter and heavy metal ions are removed from the obtained filtrate by ion adsorption, the pH value is adjusted to neutral, and then electrodialysis is performed.

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

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