A method for synthesizing 2,3-dichloropyridine by electrochemical dechlorination

Abstract

The invention discloses a method for synthesizing 2,3-dichloropyridine by electrochemical dechlorination. The method comprises adopting a diaphragm electrolytic cell, using a noble metal element modified material as a cathode, a chemically inert material as an anode, a solution containing 2,3,6-trichloropyridine as a cathode liquid, an aqueous solution of sulfuric acid or hydrochloric acid as an anolyte, passing an electric current from anode to cathode through a solution containing 2,3,6-trichloropyridine, and electrolytically reducing and dechlorinating the 2,3,6-trichloropyridine in the solution to 2,3-dichloropyridine. After the electrolysis is completed, 2,3-dichloropyridine is recovered. The reaction temperature of the inventive method drops from 140 DEG C to room temperature or the reaction pressure drops from 3MPa to normal pressure; hydrogen is avoided; and the target product yield increases by 5-10%.

Description

(1) Technical field

[0001] The invention belongs to the field of electrolytic synthesis, and particularly relates to a method for synthesizing 2,3-dichloropyridine by electrochemical selective reduction and dechlorination using 2,3,6-trichloropyridine as a raw material. (2) Background technology

[0002] 2,3-Dichloropyridine is a key intermediate in the synthesis of chlorantraniliprole. With the increasing popularity of chlorantraniliprole, demand for 2,3-dichloropyridine is expected to increase significantly, leading to significant interest in its synthesis. The reductive dechlorination method for 2,3,6-trichloropyridine offers the advantages of a short process flow and minimal waste pollution, making it a promising method for synthesizing 2,3-dichloropyridine.

[0003] Currently, the reduction dechlorination of 2,3,6-trichloropyridine is mainly achieved by catalytic hydrogenation with palladium as the catalyst. This method has the following main problems [Rare Metal Materials and Engineering, 2018, 47(5):1637-1642; Guangzhou Chemistry, 2019, 44(4):65-68]:

[0004] (1) The reaction requires high temperature and high pressure conditions.

[0005] (2) The reaction requires the use of extremely dangerous hydrogen.

[0006] (3) The yield of the target product is low. (3) Summary of the invention

[0007] The present invention aims to provide a method for synthesizing 2,3-dichloropyridine by electrochemical dechlorination. 2,3,6-trichloropyridine is used as a raw material to synthesize 2,3-dichloropyridine by electrochemical selective reduction dechlorination. The method can not only avoid high temperature and high pressure conditions and the use of hazardous hydrogen, but also improve the yield of 2,3-dichloropyridine.

[0008] The technical solution adopted in the present invention is:

[0009] The invention provides a method for synthesizing 2,3-dichloropyridine through electrochemical dechlorination. The method comprises the following steps: using a diaphragm electrolytic cell, using a noble metal element modified material as a cathode, using a chemically inert material as an anode, using a solution containing 2,3,6-trichloropyridine as a cathode liquid, and using an aqueous solution of sulfuric acid or hydrochloric acid as an anode liquid; passing an electric current from the anode to the cathode through the solution containing 2,3,6-trichloropyridine; electrolytically reducing and dechlorinating 2,3,6-trichloropyridine (A) in the solution to form 2,3-dichloropyridine (B); the chloride ion concentration of the solution in a reference electrode is 3 mol / L; and recovering the product after the electrolysis is completed.

[0010]

[0011] Furthermore, the noble metal of the cathode is a platinum group metal element including palladium, platinum, ruthenium, rhodium or iridium, and the noble metal loading is 0.1 to 3 mg / cm 2 The carrier of the noble metal-modified material can be any conductive material, including, for example, carbon-based materials and metal materials. The conductive material can be in the form of a plate, mesh, or foam. Preferred carriers for the noble metal-modified material include nickel foam, stainless steel mesh, copper foam, titanium mesh, and carbon felt.

[0012] Further, the anode material includes, for example, platinum mesh, platinum-coated titanium mesh, an electrode coated with ruthenium, iridium, lead or tin oxide, or a graphite electrode.

[0013] Furthermore, the diaphragm can be a mechanical diaphragm or an ion exchange diaphragm, preferably a cationic membrane, such as a perfluorosulfonic acid membrane or a PDFV hydrophilic porous membrane or a ceramic porous membrane.

[0014] Furthermore, the solution containing 2,3,6-trichloropyridine is an aqueous solution containing 2,3,6-trichloropyridine, an organic solvent, an electrolyte, and an acid-binding agent. The organic solvent includes methanol, ethanol, isopropanol, acetonitrile, and N,N-dimethylformamide (DMF); the electrolyte includes ammonium chloride and ammonium acetate; and the acid-binding agent includes ammonia water, trimethylamine, and triethylamine.

[0015] Furthermore, the solution containing 2,3,6-trichloropyridine has a 2,3,6-trichloropyridine concentration of 0.1-1 mol / L, preferably 0.2-0.5 mol / L; an organic solvent volume concentration of 30-80%; an electrolyte concentration of 0.1-1 mol / L; and an acid-binding agent volume concentration of 1-5%.

[0016] Furthermore, the anolyte is a sulfuric acid aqueous solution with a mass concentration of 0.5-20% or a hydrochloric acid aqueous solution with a mass concentration of 1-10%.

[0017] Temperature is not a critical factor of the present invention. The electrochemical selective reduction dechlorination reaction can be carried out at 10-75°C. Considering the volatilization of the solvent, the solubility of the raw materials and products in the electrolyte and the conductivity of the electrolyte, the electrolysis reaction temperature is preferably 30-65°C.

[0018] Furthermore, the conditions for electrolytic reduction are: 10-75° C., -0.1 to -2.0 V vs. Ag / AgCl potential (relative to an Ag / AgCl reference electrode, wherein the concentration of chloride ions in the AgCl solution is 3 mol / L).

[0019] Furthermore, the end of electrolysis means that the electrolysis is stopped when the current drops to 5% or less of the initial current.

[0020] The present invention can also be carried out in a constant current or step-by-step constant current mode. Professionals in this field can determine the preferred electrolysis current density by measuring the preferred electrode potential data provided by the present invention to determine the preferred electrolysis current.

[0021] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: (1) the reaction temperature is reduced from 140°C to room temperature or the reaction pressure is reduced from 3 MPa to atmospheric pressure; (2) the use of hydrogen is avoided; and (3) the yield of the target product is increased by 5 to 10%. (IV) Description of the accompanying drawings

[0022] Figure 1 , Gas chromatogram of the cathode liquid before electrolysis in Example 1, the peak with a retention time of 8.141 min is the gas chromatographic peak of 2,3,6-trichloropyridine.

[0023] Figure 2 , In the gas chromatogram of the cathode liquid after electrolysis in Example 1, the peak with a retention time of 6.521 min is the gas chromatographic peak of 2,3-dichloropyridine. (V) Specific implementation methods

[0024] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0025] In the following examples, H-type electrolytic cell, perfluorosulfonic acid membrane (including Nafion 324, 117 and 211), PDFV hydrophilic porous membrane, ceramic diaphragm, noble metal modified material (noble metal loading 0.1 ~ 3mg / cm 2 ), platinum mesh, titanium-coated ruthenium oxide sheet, titanium-coated iridium oxide sheet and Ag / AgCl reference electrode were all provided by Hangzhou Sai'ao Electrochemical Instrument Co., Ltd.

[0026] The yield of 2,3-dichloropyridine is defined as Y=X / Z, where X is the amount (moles) of 2,3-dichloropyridine in the catholyte at the end of electrolysis and Z is the amount (moles) of 2,3,6-trichloropyridine in the catholyte at the start of electrolysis.

[0027] Example 1: Electrolytic reduction of 2,3,6-trichloropyridine to synthesize 2,3-dichloropyridine

[0028] H-type electrolytic cell was used as the reactor, Nafion 324 was used as the diaphragm, and palladium-modified nickel foam (noble metal loading 1 mg / cm 2) is the cathode, the platinum mesh is the anode, and Ag / AgCl is the reference electrode (the internal solution of the reference electrode is a 3 mol / L potassium chloride aqueous solution). The cathode liquid is 30 mL of an aqueous solution containing 0.2 mol / L 2,3,6-trichloropyridine + 0.1 mol / L ammonium chloride + 60% methanol by volume + 3% ammonia water by volume; the anode liquid is 30 mL of a 5% sulfuric acid aqueous solution by mass. The cathode liquid temperature is controlled at 30-35°C and the pressure is 0.1 MPa, and constant potential electrolysis is performed (potential is -1.0 V vs Ag / AgCl). The electrolysis is stopped when the current drops to 5% of the initial current. The 2,3,6-trichloropyridine and 2,3-dichloropyridine in the cathode liquid before and after electrolysis are analyzed by gas chromatography, see Figure 1 、 2 As shown, the results showed that the yield of 2,3-dichloropyridine was 85.6%.

[0029] Gas chromatography analysis conditions: A Fuli GC9720 gas chromatograph with an FID detector and an AT OV-1701 column (30 m × 0.32 mm ID × 0.5 μm) were used. Instrument parameters were: vaporizer temperature 250°C, detector temperature 250°C, and a programmed column temperature ramp: initially at 100°C, maintained for 5 minutes, then increased at 15°C / min to 250°C, maintained for 5 minutes. Direct injection was used.

[0030] Example 2-6: Effect of cathode potential

[0031] According to Table 1, the potential in Example 1 was changed, while other conditions remained unchanged. The yield of 2,3-dichloropyridine is shown in Table 1. The results show that in the potential range of -0.1 to -2.0 V, 2,3,6-trichloropyridine can be electrolytically reduced to 2,3-dichloropyridine, and in the potential range of -0.5 to -1.5 V, the yield of 2,3-dichloropyridine is higher.

[0032] Table 1 Effect of cathode potential on electrolytic reduction of 2,3,6-trichloropyridine to 2,3-dichloropyridine

[0033]

[0034]

[0035] Examples 7-12: Effect of cathode materials

[0036] According to Table 2, the cathode material in Example 1 was changed, and other conditions remained unchanged. The yield of 2,3-dichloropyridine is shown in Table 2. The results show that when there are platinum group elements on the cathode, a higher yield of 2,3-dichloropyridine can be obtained; when there are no platinum group elements on the cathode, the yield of 2,3-dichloropyridine is extremely low; the platinum group element loading is 0.1~3mg / cm 2 It will be all right.

[0037] Table 2 Effect of cathode materials on electrolytic reduction of 2,3,6-trichloropyridine to 2,3-dichloropyridine

[0038] Example No. cathode materials 2,3-Dichloropyridine yield 7 Platinum modified stainless steel mesh 82.8％ 8 Ruthenium-modified copper foam 75.4％ 9 <![CDATA[Rhodium-modified titanium mesh (rhodium loading: 0.1 mg / cm 2 )]]> 71.9％ 10 <![CDATA[Iridium-modified carbon felt (iridium loading: 3 mg / cm 2 )]]> 73.3％ 11 Nickel foam 3.8％ 12 carbon felt 2.1％

[0039] Note: The other reaction conditions are the same as those in Example 1.

[0040] Examples 13-22: Effects of Catholyte, Anolyte, Anode, and Diaphragm

[0041] According to Table 3, the compositions of the cathode liquid, anolyte, anode and diaphragm in Example 1 were changed, and other conditions remained unchanged unless otherwise specified. The yield of 2,3-dichloropyridine is shown in Table 3. The results show that when methanol, ethanol, acetonitrile or DMF is used as the organic solvent, ammonium chloride or ammonium acetate is used as the electrolyte, and ammonia water, trimethylamine or triethylammonium is used as the acid binding agent, the yield of 2,3-dichloropyridine is relatively high; when no acid binding agent is added, the yield of 2,3-dichloropyridine is significantly reduced; the suitable range of reactant concentration is 0.1 to 1 mol / L, preferably 0.2 to 0.5 mol / L; the anolyte can be an aqueous sulfuric acid solution or an aqueous hydrochloric acid solution; the diaphragm can be an ion exchange membrane or a mechanical diaphragm; the anode can be an iridium oxide, ruthenium oxide, lead oxide coated electrode, or a graphite electrode.

[0042] Table 3 Effect of catholyte on electrolytic reduction of 2,3,6-trichloropyridine to 2,3-dichloropyridine

[0043]

[0044]

[0045] Remark:

[0046] a 30 mL of 0.5% sulfuric acid aqueous solution was used as the anolyte, a titanium-plated iridium oxide sheet was used as the anode, and a Nafion 117 membrane was used as the diaphragm.

[0047] b 30 mL of 20% sulfuric acid aqueous solution was used as the anolyte, a titanium-plated lead oxide sheet was used as the anode, and a Nafion 211 membrane was used as the diaphragm.

[0048] c 30 mL of 1% hydrochloric acid aqueous solution was used as the anolyte, the titanium-plated ruthenium oxide sheet was used as the anode, and the PDFV hydrophilic porous membrane was used as the separator.

[0049] c 30 mL of 10% hydrochloric acid aqueous solution is used as the anolyte, the graphite sheet is used as the anode, and the ceramic porous membrane is used as the diaphragm.

[0050] Examples 23-25: Effect of Catholyte Temperature

[0051] According to Table 4, the catholyte in Example 1 was changed to an aqueous solution containing 0.2 mol / L 2,3,6-trichloropyridine + 0.1 mol / L ammonium chloride + 60 vol% ethanol + 3 vol% ammonia water, and the temperature was changed to that shown in Table 4. Other conditions remained unchanged. The yield of 2,3-dichloropyridine is shown in Table 4. The results show that the yield of 2,3-dichloropyridine is relatively high in the range of 10 to 75°C, and the yield decreases with increasing temperature.

[0052] Table 4 Effect of temperature on electrolytic reduction of 2,3,6-trichloropyridine to 2,3-dichloropyridine

[0053] Example No. Catholyte temperature 2,3-Dichloropyridine yield 23 10～15℃ 90.8％ 24 50～65℃ 81.5％ 25 70～75℃ 73.1％

Claims

1. A method for synthesizing 2,3-dichloropyridine by electrochemical dechlorination, characterized in that: The method comprises the following steps: using a diaphragm electrolytic cell, using a noble metal element modified material as a cathode, using a chemically inert material as an anode, using a solution containing 2,3,6-trichloropyridine as a cathode liquid, and using an aqueous solution of sulfuric acid or hydrochloric acid as an anode liquid; passing an electric current from the anode to the cathode through the solution containing 2,3,6-trichloropyridine; electrolyzing and reducing the 2,3,6-trichloropyridine in the solution to dechlorinate it into 2,3-dichloropyridine; and recovering the 2,3-dichloropyridine after the electrolysis is completed; and the noble metal of the cathode is selected from palladium, platinum, ruthenium, rhodium or iridium.

2. The method according to claim 1, wherein The noble metal loading of the cathode is 0.1-3 mg / cm 2 .

3. The method according to claim 1, wherein Anode materials include platinum mesh, platinum-coated titanium mesh, electrodes coated with ruthenium, iridium, lead or tin oxides, or graphite electrodes.

4. The method according to claim 1, wherein The diaphragm is an ion exchange membrane or a mechanical diaphragm.

5. The method according to claim 4, wherein The diaphragm includes a perfluorosulfonic acid membrane, a PDFV hydrophilic porous membrane, or a ceramic porous membrane.

6. The method according to claim 1, wherein The solution containing 2,3,6-trichloropyridine is an aqueous solution containing 2,3,6-trichloropyridine, an organic solvent, an electrolyte and an acid-binding agent; the organic solvent includes methanol, ethanol, isopropanol, acetonitrile and N,N-dimethylformamide; the electrolyte includes ammonium chloride and ammonium acetate; and the acid-binding agent includes ammonia water, trimethylamine and triethylamine.

7. The method according to claim 6, wherein The solution containing 2,3,6-trichloropyridine has a 2,3,6-trichloropyridine concentration of 0.1-1 mol / L, an organic solvent volume concentration of 30-80%, an electrolyte concentration of 0.1-1 mol / L, and an acid-binding agent volume concentration of 1-5%.

8. The method according to claim 1, wherein The anolyte is a sulfuric acid aqueous solution with a mass concentration of 0.5-20% or a hydrochloric acid aqueous solution with a mass concentration of 1-10%.

9. The method according to claim 1, wherein The conditions for electrolytic reduction are 10-75°C and -0.1~-2.0V vsAg / AgCl potential.

10. The method according to claim 1, wherein The end of electrolysis means that electrolysis is stopped when the current drops to 5% or less of the initial current.

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