Method for synthesizing 2, 3-dichloropyridine through electrochemical dechlorination

Abstract

The invention discloses a method for synthesizing 2, 3-dichloropyridine through electrochemical dechlorination, which comprises the following steps of: adopting a diaphragm electrolytic tank, taking a noble metal element modified material as a cathode, taking a chemical inert material as an anode, taking a solution containing 2, 3, 6-trichloropyridine as a catholyte, taking an aqueous solution of sulfuric acid or hydrochloric acid as an anolyte, and enabling current to pass through the solution containing 2, 3, 6-trichloropyridine from the anode to the cathode, the method comprises the following steps: preparing a solution containing 2, 3, 6-trichloropyridine, performing electrolytic reduction and dechlorination on the 2, 3, 6-trichloropyridine in the solution to obtain 2, 3-dichloropyridine, and recovering the 2, 3-dichloropyridine after electrolysis is finished. According to the method, the reaction temperature is reduced from 140 DEG C to room temperature or the reaction pressure is reduced from 3MPa to normal pressure; the use of hydrogen is avoided; and the yield of the target product is increased by 5-10%.

Description

(I) 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. (II) Background technology

[0002] 2,3-Dichloropyridine is a key intermediate in the synthesis of chlorantraniliprole. With the gradual promotion of chlorantraniliprole, the demand for 2,3-dichloropyridine will increase significantly, so its synthesis method has attracted much attention. The reduction dechlorination method of 2,3,6-trichloropyridine has the advantages of short process flow and less pollution of three wastes, and is a very promising method for the synthesis of 2,3-dichloropyridine.

[0003] At present, the reduction dechlorination method of 2,3,6-trichloropyridine is mainly achieved by catalytic hydrogenation with palladium as 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 gas.

[0006] (3) The yield of the target product is low. (III) 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 dangerous hydrogen, but also improve the yield of 2,3-dichloropyridine.

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

[0009] The invention provides a method for synthesizing 2,3-dichloropyridine by electrochemical dechlorination. The method comprises the following steps: using a diaphragm electrolytic cell, taking a noble metal element modified material as a cathode, taking a chemically inert material as an anode, taking a solution containing 2,3,6-trichloropyridine as a cathode liquid, taking 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 2,3,6-trichloropyridine (A) in the solution to dechlorinate into 2,3-dichloropyridine (B), the chloride ion concentration of the solution in the reference electrode being 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 shape of a plate, a mesh, or a foam. Preferred carriers of the noble metal modified material include nickel foam, stainless steel mesh, copper foam, titanium mesh, carbon felt, and the like.

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

[0013] Furthermore, the diaphragm may 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, 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 to 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 to 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 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 the field can determine the preferred electrolysis current density through 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 3MPa to normal pressure; (2) the use of hydrogen is avoided; (3) the yield of the target product is increased by 5-10%. (IV) Description of the drawings

[0022] Figure 1 , Gas chromatogram of 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 in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0025] In the following embodiments, an H-type electrolytic cell, a perfluorosulfonic acid membrane (including Nafion 324, 117 and 211), a PDFV hydrophilic porous membrane, a ceramic diaphragm, a noble metal modified material (noble metal loading 0.1 to 3 mg / 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 cathode liquid at the end of electrolysis and Z is the amount (moles) of 2,3,6-trichloropyridine in the cathode liquid at the beginning of electrolysis.

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

[0028] H-type electrolytic cell as reactor, Nafion 324 as diaphragm, palladium-modified nickel foam (precious 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 anolyte 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 (the 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 were 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: Fuli GC9720 gas chromatograph, FID detector, AT OV-1701 column (30m×0.32mm id×0.5μm) were used as the detector. The instrument parameters were set as follows: vaporization chamber temperature 250℃, detector temperature 250℃, chromatographic column temperature programmed heating, the heating program was initially 100℃, maintained for 5min, then heated to 250℃ at 15℃ / min, maintained for 5min. The method was direct injection.

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

[0031] According to Table 1, the potential in Example 1 was changed, and 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 synthesize 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 0.1-3 mg / cm 2 It will be all right.

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

[0038] Example No. Cathode material Yield of 2,3-dichloropyridine 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, the anode liquid, the anode and the 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; when the appropriate range of reactant concentration is 0.1-1 mol / L, preferably 0.2-0.5 mol / L; the anode liquid can use sulfuric acid aqueous solution or hydrochloric acid aqueous solution; the diaphragm can use 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 cathode liquid on electrolytic reduction of 2,3,6-trichloropyridine to synthesize 2,3-dichloropyridine

[0043]

[0044]

[0045] Remark:

[0046] a 30 mL of 0.5% sulfuric acid aqueous solution is used as the anolyte, the titanium-plated iridium oxide sheet is used as the anode, and the Nafion117 membrane is used as the diaphragm.

[0047] b 30 mL of 20% sulfuric acid aqueous solution is the anolyte, the titanium-plated lead oxide sheet is the anode, and the Nafion211 membrane is the diaphragm.

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

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

[0050] Examples 23-25: Effect of cathode liquid temperature

[0051] According to Table 4, the cathode liquid 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, the temperature was changed to that shown in Table 4, and other conditions remained unchanged. The yield of 2,3-dichloropyridine is shown in Table 4. The results show that in the range of 10 to 75° C., the yield of 2,3-dichloropyridine is relatively high, and the yield decreases with increasing temperature.

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

[0053] Example No. Catholyte temperature Yield of 2,3-dichloropyridine 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 adopts a diaphragm electrolytic cell, uses a noble metal element modified material as a cathode, uses a chemically inert material as an anode, uses a solution containing 2,3,6-trichloropyridine as a cathode liquid, uses an aqueous solution of sulfuric acid or hydrochloric acid as an anode liquid, passes an electric current from the anode to the cathode through the solution containing 2,3,6-trichloropyridine, electrolyzes, reduces and dechlorinates the 2,3,6-trichloropyridine in the solution to form 2,3-dichloropyridine, and recovers the 2,3-dichloropyridine after the electrolysis is completed.

2. The method according to claim 1, characterized in that The noble metal of the cathode includes palladium, platinum, ruthenium, rhodium or iridium, and the noble metal loading is 0.1-3 mg / cm 2 .

3. The method according to claim 1, characterized in that 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, characterized in that The diaphragm is an ion exchange membrane or a mechanical diaphragm.

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

6. The method according to claim 1, characterized in that 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, characterized in that 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, characterized in that 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, characterized in that The conditions for electrolytic reduction are 10-75°C and -0.1 to -2.0 V vsAg / AgCl potential.

10. The method according to claim 1, characterized in that 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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