Method for synthesizing 2-chlorobenzoic acid through diaphragm electrolysis debromination

Abstract

The invention discloses a method for synthesizing 2-chlorobenzoic acid through diaphragm electrolysis debromination. According to the method, a diaphragm electrolytic cell is adopted, copper or silver is used as a cathode, a solution containing brominated 2-chlorobenzoic acid is used as a catholyte, and an alkaline aqueous solution is used as an anolyte; and enabling current to pass through the catholyte from an anode to a cathode under a normal pressure condition, performing electrolytic reduction and debromination on brominated 2-chlorobenzoic acid in the catholyte to obtain 2-chlorobenzoic acid, and recovering 2-chlorobenzoic acid after electrolysis is finished. According to the method, the 2-chlorobenzoic acid is synthesized through electrochemical debromination of the brominated 2-chlorobenzoic acid for the first time, the conversion rate of the brominated 2-chlorobenzoic acid is larger than or equal to 98%, and the yield of the 2-chlorobenzoic acid is larger than or equal to 98%. And the use of a palladium noble metal catalyst, high-explosive hydrogen and high-pressure reaction conditions are avoided.

Description

(I) TECHNICAL FIELD

[0002] The application belongs to the field of reductive debromination, and particularly relates to a method for synthesizing 2-chlorobenzoic acid through electrolytic debromination. (II) BACKGROUND

[0004] 5-bromo-2-chlorobenzoic acid is an important organic intermediate and is widely used in the synthesis of medicines, pesticides, spices and chemical materials. A high-efficiency method for synthesizing 5-bromo-2-chlorobenzoic acid is to use 2-chlorobenzoic acid as a raw material to perform a bromination reaction. However, this method has the problem of producing various bromo-2-chlorobenzoic acid byproducts. A reductive debromination reaction can convert various bromo-2-chlorobenzoic acid byproducts into 2-chlorobenzoic acid. At present, the reductive debromination reaction is mainly realized by using hydrogen as a reducing agent in a catalytic hydrogenation method. For example, patent application 202511076064.4 has the problems of needing to use expensive palladium-carbon catalysts, a large amount of explosive hydrogen and high-pressure conditions.

[0005] The electrolytic reduction method can also theoretically realize the reductive debromination reaction of 5-bromo-2-chlorobenzoic acid, but the selectivity of debromination depends not only on the cathode material but also on the electrolyte formula and operating conditions (current density, temperature, etc.). To the best of our knowledge, there has been no report on the high-selectivity electrolytic reduction of 5-bromo-2-chlorobenzoic acid into 2-chlorobenzoic acid. (III) SUMMARY

[0007] The application aims to provide a method for synthesizing 2-chlorobenzoic acid through membrane electrolytic debromination, using copper or silver as a cathode, a chemically inert conductive material as an anode, an alkaline aqueous solution containing bromo-2-chlorobenzoic acid as a catholyte, an alkaline aqueous solution as an anolyte, and performing an electrolytic reaction in a membrane electrolytic cell under normal pressure conditions, thereby realizing the electrolytic debromination synthesis of 2-chlorobenzoic acid, avoiding the use of noble metals and hydrogen, and also not needing high-pressure conditions. The application effectively solves the problems of needing to use palladium noble metals, explosive hydrogen and high-pressure conditions in the existing catalytic hydrogenation method.

[0008] The technical scheme adopted by the application is as follows:

[0009] The application provides a method for synthesizing 2-chlorobenzoic acid through electrolytic debromination, which uses a membrane electrolytic cell, uses copper or silver as a cathode, uses a solution containing bromo-2-chlorobenzoic acid (A) as a catholyte, and uses an alkaline aqueous solution as an anolyte; under normal pressure conditions, an electric current is passed from the anode to the cathode through the catholyte, the bromo-2-chlorobenzoic acid in the catholyte is electrolytically reduced and debrominated into 2-chlorobenzoic acid (B), and after the electrolysis is completed, 2-chlorobenzoic acid is recovered.

[0010]

[0011] Further, the bromo-2-chlorobenzoic acid in the catholyte is 3-bromo-2-chlorobenzoic acid, 5-bromo-2-chlorobenzoic acid, a mixture of 3-bromo-2-chlorobenzoic acid and 5-bromo-2-chlorobenzoic acid, 3,5-dibromo-2-chlorobenzoic acid, or 3,4,5,6-tetrabromo-2-chlorobenzoic acid.

[0012] Further, the catholyte is an alkaline aqueous solution containing bromo-2-chlorobenzoic acid; and the base is sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, or tetramethylammonium hydroxide.

[0013] Further, the concentration of bromo-2-chlorobenzoic acid in the catholyte is 0.1-3 mol / L, and the concentration of the base is 0.05-3 mol / L.

[0014] Further, a chemically inert conductive material is used as the anode, and the anode is stainless steel 316, stainless steel 316L, stainless steel 317, or pure nickel.

[0015] Further, an ion exchange membrane is used as the separator; and the ion exchange membrane is a sulfonic acid membrane, a carboxylic acid membrane, a sulfonic acid-carboxylic acid composite membrane, or a bipolar membrane.

[0016] Further, the alkaline aqueous solution of the anolyte is an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous tetramethylammonium hydroxide solution, and the concentration ranges from 0.2 to 5 mol / L.

[0017] Further, the current density of the electrolytic reduction is 1-15 A / dm 2 , and the temperature is 20-90 ℃.

[0018] Compared with the prior art, the present application has the following beneficial effects: (1) The present application first realizes the electrochemical debromination of bromo-2-chlorobenzoic acid to synthesize 2-chlorobenzoic acid, and the conversion rate of bromo-2-chlorobenzoic acid is ≥98 %, and the yield of 2-chlorobenzoic acid is ≥98 %; (2) The present application avoids the use of palladium noble metal catalyst, highly explosive hydrogen, and high-pressure reaction conditions. (Four) Description of Drawings

[0020] Figure 1 HPLC charts of 3-bromo-2-chlorobenzoic acid and 2-chlorobenzoic acid standard samples and electrolyte after debromination reaction in Example 1. (Five) Specific Embodiments

[0022] The present application is further described below in conjunction with specific embodiments, but the scope of protection of the present application is not limited to the following:

[0023] In the following examples, the raw materials and equipment used are market sales products unless otherwise specified, and the experiments are all carried out under normal pressure, i.e., 1 standard atmosphere.

[0024] The detection instrument used in the embodiment of the present application is waters 2996, the chromatographic column used is a Hypersil GOLD™ aQ C18 column of thermo, the length is 250 mm, the inner diameter is 4.6 mm, the mobile phase is water:methanol:acetonitrile=4:3:2 (volume ratio, 5 mL of phosphoric acid is contained in 1 L of the mobile phase), the ultraviolet absorption wavelength is 230 nm, the temperature is 30 DEG C, and the flow rate is 1 mL / min.

[0025] Comparative Example 1, De-bromination of 3-bromo-2-chlorobenzoic acid to synthesize 2-chlorobenzoic acid - foamed nickel as cathode

[0026] A diaphragm electrolytic cell is used, Nafion 324 membrane (sulfonic acid membrane) is used as a diaphragm, 2*5 cm 2 foamed nickel and stainless steel 316 sheets with the same length and width are used as cathode and anode, 100 mL of an aqueous solution containing 1.0 mol / L 3-bromo-2-chlorobenzoic acid and 1.0 mol / L sodium hydroxide is used as cathode liquid; 500 mL of an aqueous solution of 1 mol / L sodium hydroxide is used as anode liquid. The temperature of the electrolyte is controlled at 40-50 DEG C, and then electricity is passed to carry out electrolysis (the current is 0.5 A, the current density is 5 A / dm 2 ), and the electrolysis is stopped after 18 h. The electrolyte is analyzed by high performance liquid chromatography, the conversion rate of 3-bromo-2-chlorobenzoic acid is 60.8%, and the yield of 2-chlorobenzoic acid is 43.6%.

[0027] Comparative Example 2, De-bromination of 3-bromo-2-chlorobenzoic acid to synthesize 2-chlorobenzoic acid - palladium modified foamed nickel as cathode

[0028] A diaphragm electrolytic cell is used, Nafion 324 membrane (sulfonic acid membrane) is used as a diaphragm, 2*5 cm 2 palladium modified foamed nickel (the content of palladium is 1 mg / cm 2 ) and stainless steel 316 sheets with the same length and width are used as cathode and anode, 100 mL of an aqueous solution containing 1.0 mol / L 3-bromo-2-chlorobenzoic acid and 1.0 mol / L sodium hydroxide is used as cathode liquid; 500 mL of an aqueous solution of 1 mol / L sodium hydroxide is used as anode liquid. The temperature of the electrolyte is controlled at 40-50 DEG C, and then electricity is passed to carry out electrolysis (the current is 0.5 A, the current density is 5 A / dm 2 ), and the electrolysis is stopped after 18 h. The electrolyte is analyzed by high performance liquid chromatography, the conversion rate of 3-bromo-2-chlorobenzoic acid is 100%, and the yield of 2-chlorobenzoic acid is 53.8%.

[0029] Comparative Example 3, De-bromination of 3-bromo-2-chlorobenzoic acid to synthesize 2-chlorobenzoic acid - diaphragm-free electrolytic cell

[0030] A diaphragm-free electrolytic cell is used, 2*5 cm2 A copper sheet and a 316 stainless steel sheet of the same length and width serve as the cathode and anode, respectively. The electrolyte is a 100 mL aqueous solution containing 1.0 mol / L 3-bromo-2-chlorobenzoic acid and 1.0 mol / L sodium hydroxide. The electrolyte temperature is controlled at 40–50 °C, and electrolysis is then performed by applying an electric current (0.5 A, current density 5 A / dm³). 2 Electrolysis was performed for 18 hours, after which the power supply was stopped. High-performance liquid chromatography (HPLC) analysis of the electrolyte showed a conversion rate of 86.9% for 3-bromo-2-chlorobenzoic acid and a yield of 76.5% for 2-chlorobenzoic acid.

[0031] Example 1: Debromination of 3-bromo-2-chlorobenzoic acid to synthesize 2-chlorobenzoic acid

[0032] A diaphragm electrolyzer was used, with a Nafion 324 membrane (sulfonic acid membrane) as the diaphragm, and the membranes were 2×5 cm. 2 Copper sheets and 316 stainless steel sheets of the same length and width serve as the cathode and anode, respectively. A 100 mL aqueous solution containing 1.0 mol / L 3-bromo-2-chlorobenzoic acid and 1.0 mol / L sodium hydroxide is used as the catholyte; a 500 mL aqueous solution containing 1 mol / L sodium hydroxide is used as the anolyte. The electrolyte temperature is controlled at 40–50 °C, and electrolysis is then performed by applying an electric current (0.5 A, current density 5 A / dm³). 2 Electrolysis was performed for 18 hours, after which the power was stopped. The electrolyte was analyzed by high-performance liquid chromatography (HPLC). Figure 1 The conversion rate of 3-bromo-2-chlorobenzoic acid was 99.5%, and the yield of 2-chlorobenzoic acid was 98.3%.

[0033] Examples 2-5: Debromination of 3-bromo-2-chlorobenzoic acid to synthesize 2-chlorobenzoic acid—Different electrode materials and membranes

[0034] Unless otherwise specified, the reaction conditions were the same as in Example 1. The experimental results are shown in Table 1. It can be seen that excellent electrolysis results can be obtained by using copper or silver as the cathode material, stainless steel 316, 316L, 317, or pure nickel as the anode material, and sulfonic acid membrane, sulfonic acid carboxylic acid composite membrane, or bipolar membrane as the diaphragm.

[0035] Table 1. Effects of debromination of 3-bromo-2-chlorobenzoic acid on the synthesis of 2-chlorobenzoic acid—Electrode materials and membranes

[0036]

[0037] Remark: a A 100 mL aqueous solution containing 1.0 mol / L 3-bromo-2-chlorobenzoic acid and 2.0 mol / L sodium hydroxide is used as the catholy solution.

[0038] Example 6-14, De-bromination of bromo-2-chlorobenzoic acid to 2-chlorobenzoic acid - effect of electrolyte formulation, current density and temperature

[0039] The reaction conditions were the same as in Example 1 except as otherwise specified. The results are shown in Table 2. It can be seen that excellent electrolysis results were obtained with catholyte containing 0.05 to 3 mol / L of base (sodium hydroxide, potassium hydroxide or tetramethylammonium hydroxide) and 0.2 to 3 mol / L of bromo-2-chlorobenzoic acid (3-bromo-2-chlorobenzoic acid, 5-bromo-2-chlorobenzoic acid, a mixture of 3-bromo-2-chlorobenzoic acid and 5-bromo-2-chlorobenzoic acid, 3,5-dibromo-2-chlorobenzoic acid or 3,4,5,6-tetrabromo-2-chlorobenzoic acid) and anolyte containing 0.2 to 5 mol / L of base (sodium hydroxide, potassium hydroxide or tetramethylammonium hydroxide) and a current density of 1 to 15 A / dm 2 at a temperature of 20 to 90 °C.

[0040] Table 2 De-bromination of bromo-2-chlorobenzoic acid to 2-chlorobenzoic acid - effect of electrolyte formulation, temperature and current density

[0041]

[0042] Notes: a Current density was 1 A / dm 2 at a temperature of 20 to 30 °C. b Current density was 15 A / dm 2 at a temperature of 80 to 90 °C.

Claims

1. A process for the electrolytic debromination synthesis of 2-chlorobenzoic acid by means of a diaphragm, characterized in that, The method uses a diaphragm electrolytic cell, takes copper or silver as the cathode, takes a solution containing bromo-2-chlorobenzoic acid as the cathode liquid, and takes an alkaline aqueous solution as the anode liquid; under normal pressure, the current is passed from the anode to the cathode through the cathode liquid, the bromo-2-chlorobenzoic acid in the cathode liquid is electrolytically reduced and debrominated into 2-chlorobenzoic acid, and 2-chlorobenzoic acid is recovered after electrolysis.

2. The method of claim 1, wherein, The bromo-2-chlorobenzoic acid in the cathode liquid is 3-bromo-2-chlorobenzoic acid, 5-bromo-2-chlorobenzoic acid, a mixture of 3-bromo-2-chlorobenzoic acid and 5-bromo-2-chlorobenzoic acid, 3,5-dibromo-2-chlorobenzoic acid, or 3,4,5,6-tetrabromo-2-chlorobenzoic acid.

3. The method of claim 1 or 2, wherein, The cathode liquid is an alkaline aqueous solution containing bromo-2-chlorobenzoic acid; the alkali is sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, or tetramethylammonium hydroxide.

4. The method of claim 3, wherein, The concentration of bromo-2-chlorobenzoic acid in the cathode liquid is 0.1-3 mol / L, and the concentration of alkali is 0.05-3 mol / L.

5. The method of claim 1, wherein, The anode is stainless steel 316, stainless steel 316L, stainless steel 317, or pure nickel.

6. The method of claim 1, wherein, An ion membrane is used as the diaphragm; the ion membrane is a sulfonic acid membrane, a carboxylic acid membrane, a sulfonic acid-carboxylic acid composite membrane, or a bipolar membrane.

7. The method of claim 1, wherein, The alkaline aqueous solution of the anode liquid is an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous tetramethylammonium hydroxide solution, and the concentration ranges from 0.2 to 5 mol / L.

8. The method of claim 1, wherein, The current density of the electrolytic reduction is 1-15 A / dm 2 at a temperature of 20-90 °C.

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