阅读说明：本技术 一种4-氨基-3,6-二氯吡啶甲酸的电解合成方法 (Electrolytic synthesis method of 4-amino-3, 6-dichloropicolinic acid ) 是由 徐颖华 石凯 储诚普 丁旭芬 张洋亮 于 2019-08-23 设计创作，主要内容包括：本发明公开了一种4-氨基-3,6-二氯吡啶甲酸的电解合成方法,采用隔膜电解槽,以pH 0.5～1.5碱金属氯化盐水溶液为阳极液,以溶解有4-氨基-3,5,6-三氯吡啶甲酸的碱金属氢氧化物水溶液为阴极液,以银为阴极进行电解反应；用浓盐酸将阴极液的pH调至0.5～1.5,析晶,过滤,取滤饼获得含4-氨基-3,6-二氯吡啶甲酸的有机物,收集滤液用有机溶剂萃取,获得萃余液；萃余液用吸附剂吸附后,过滤,取滤液,即为回收阴极液,回收用于下一批电解的阳极液。本发明采用回收阴极液作为阳极液,使得阴极液的pH更加稳定了,产品收率提高5～8％；碱的消耗大幅度下降了；酸性氯化钠水溶液的排放大幅度下降了。(The invention discloses an electrolytic synthesis method of 4-amino-3, 6-dichloropicolinic acid, which adopts a diaphragm electrolytic cell, takes an alkali metal chloride aqueous solution with the pH value of 0.5-1.5 as an anolyte, takes an alkali metal hydroxide aqueous solution dissolved with 4-amino-3, 5, 6-trichloropicolinic acid as a catholyte and takes silver as a cathode for electrolytic reaction; adjusting the pH value of the catholyte to 0.5-1.5 by using concentrated hydrochloric acid, crystallizing, filtering, taking a filter cake to obtain an organic matter containing 4-amino-3, 6-dichloropicolinic acid, collecting filtrate, and extracting by using an organic solvent to obtain raffinate; absorbing the raffinate with an adsorbent, filtering, taking filtrate, namely recycling catholyte, and recycling anolyte for next batch of electrolysis. According to the invention, the recycled catholyte is used as the anolyte, so that the pH of the catholyte is more stable, and the product yield is improved by 5-8%; the consumption of alkali is greatly reduced; the discharge of the acidic sodium chloride aqueous solution is greatly reduced.)

1. An electrolytic synthesis method of 4-amino-3, 6-dichloropicolinic acid is characterized by comprising the following steps: (1) using a diaphragm electrolytic cell, using an aqueous solution of an alkali metal chloride having a pH of 0.5 to 1.5 as an anolyte, an aqueous solution of an alkali metal hydroxide having 4-amino-3, 5, 6-trichloropicolinic acid dissolved therein as a catholyte, and silver as a cathode, at a current density of 1 to 20A/dm²Carrying out electrolytic reaction at the temperature of 0-90 ℃; the anode is a platinum, graphite and titanium-based ruthenium coating electrode; the alkali metal chloride is lithium chloride, sodium chloride or potassium chloride; the alkali metal hydroxide is LiOH, NaOH or KOH; (2) after the electrolysis reaction is completed, adjusting the pH value of the catholyte to 0.5-1.5 by using concentrated hydrochloric acid, crystallizing, filtering, taking a filter cake to obtain an organic matter containing 4-amino-3, 6-dichloropicolinic acid, and collecting a filtrate; (3) extracting the filtrate collected in step (2) with an organic solvent to remove a part of the organic matterObtaining raffinate; (4) and adsorbing the raffinate by using an adsorbent to remove residual organic matters, filtering, taking filtrate, namely the recovered catholyte, and recovering the anolyte used for the next batch of electrolytic reaction.

2. The method according to claim 1, wherein the concentration of alkali metal chloride in the anolyte is 0.5 to 2.5M; the concentration of the 4-amino-3, 5, 6-trichloropicolinic acid in the catholyte is 0.2-0.6M, and the concentration of the alkali metal hydroxide is 0.3-0.7M.

3. The method of claim 1, wherein the catholyte is supplemented with 4-amino-3, 5, 6-trichloropicolinic acid and an alkali metal hydroxide during electrolysis, and the pH of the catholyte is controlled to be 12.5 to 13.5.

4. The method of claim 1, wherein the anode is a titanium-based ruthenium oxide, titanium oxide, and iridium oxide mixed coated electrode.

5. The method of claim 1, wherein the cathode is activated by: in an aqueous solution containing chloride ions or bromide ions, firstly, silver is used as an anode to carry out oxidation until the electrode potential reaches +0.7vs. SHE, and then silver is used as a cathode to carry out reduction until the electrode potential reaches-0.4 vs. SHE, so as to obtain activated silver; the current density of the silver in the oxidation-reduction process is 0.1-5A/dm²The temperature is 0-50 ℃.

6. The method of claim 1, wherein the membrane is a perfluorosulfonic acid cation membrane.

7. The method of claim 1, wherein the current density is 3.75 to 10A/dm²And the electrolytic reaction temperature is 40-50 ℃.

8. The method of claim 1, wherein the organic solvent used for extraction is dichloromethane, n-butanol, butanone, or ethyl acetate.

9. The method of claim 1, wherein the adsorbent is activated carbon or macroporous resin SD 300.

10. The method of claim 1 or 5, wherein the aqueous solutions are formulated with deionized water.

(I) technical field

The invention relates to an electrolytic synthesis method of 4-amino-3, 6-dichloropicolinic acid.

(II) background of the invention

4-amino-3, 6-dichloropicolinic acid, which is commercially available as triclopyr, aminopyralid, and clopyralid, is a picolinic acid herbicide that rapidly enters the plant body, causing the plant growth to be interrupted and rapidly dying, and is mainly used for weed control in pastures, plantations, and non-crop areas. In addition, 4-amino-3, 6-dichloropicolinic acid is also a key intermediate for the synthesis of chlorofluoropyridine ester and chlorofluoropyridine ester. The fluroxypyridine ester and the fluroxypyridine ester are novel aryl picolinate herbicides developed by the Dow Yinong company, are new varieties in hormone herbicides, and have the characteristics of lower dosage and wider weed control spectrum.

U.S. Pat. Nos. 6352635, 7666293, 8685222 and 0090639 disclose methods for the electrochemical selective dechlorination of 4-amino-3, 5, 6-trichloropicolinic acid to prepare 4-amino-3, 6-dichloropicolinic acid. The method takes a diaphragm-free electrolytic cell as a reactor, Hastelloy C as an anode material, an activated silver net as a cathode material and an alkaline aqueous solution containing 4-amino-3, 5, 6-trichloropicolinic acid as an electrolyte, and after the electrolysis is finished, a 4-amino-3, 6-dichloropicolinic acid product is separated out by acidifying the electrolyte. There are two main problems with this approach: (1) the product purity is not high, and the color is red; (2) large consumption of alkali and large amount of waste salt.

In order to solve the first problem, chinese patent 201611135958 discloses a method for preparing 4-amino-3, 6-dichloropicolinic acid by electrochemical selective dechlorination of 4-amino-3, 5, 6-trichloropicolinic acid. The method takes a diaphragm electrolytic cell as a reactor, 316 stainless steel as an anode material and silver as a cathode material; the alkaline aqueous solution is an anolyte, and the alkaline aqueous solution containing 4-amino-3, 5, 6-trichloropicolinic acid is a catholyte. The method can avoid the contact of the raw materials and the products with the anode material, thereby avoiding the reduction of the purity of the product and the reddening of the color, but the problems of unstable pH of the catholyte, low yield of the product, high alkali consumption, high waste salt generation and the like are caused.

Disclosure of the invention

The invention provides a method for electrolytic synthesis of 4-amino-3, 6-dichloropicolinic acid aiming at the problems of large alkali consumption and large waste salt generation in the prior art, which adopts recovered catholyte as anolyte to stabilize the pH value of the catholyte, reduce the alkali consumption, reduce the discharge of acidic sodium chloride and improve the product yield.

The technical scheme adopted by the invention is as follows:

the invention provides an electrolytic synthesis method of 4-amino-3, 6-dichloropicolinic acid, which comprises the following steps: (1) adopting a diaphragm electrolytic cell, taking an aqueous solution of alkali metal chloride with pH of 0.5-1.5 as an anolyte (deionized water preparation), taking an aqueous solution of alkali metal hydroxide dissolved with 4-amino-3, 5, 6-trichloropicolinic acid (II) as a catholyte (deionized water preparation), taking silver as a cathode, and carrying out electrolysis at a current density of 1-20A/dm²Carrying out electrolytic reaction at the temperature of 0-90 ℃, enabling current to pass through anolyte, a diaphragm and catholyte from an anode and finally reach a cathode, and stopping electrolysis after the required electric quantity is reached; the anode is a platinum, graphite and titanium-based ruthenium coating electrode; the alkali metal chloride is lithium chloride, sodium chloride or potassium chloride, preferably sodium chloride; the alkali metal hydroxide is LiOH, NaOH or KOH, preferably NaOH; (2) after the electrolysis reaction is completed, adjusting the pH value of the catholyte to 0.5-1.5 (preferably 1.0) by using concentrated hydrochloric acid (preferably with the mass concentration of 36%), crystallizing, filtering, taking a filter cake to obtain an organic matter containing 4-amino-3, 6-dichloropicolinic acid, and collecting filtrate; (3) extracting the filtrate collected in the step (2) by using an organic solvent, and removing partial organic matters to obtain raffinate; (4) and adsorbing the raffinate by using an adsorbent to remove residual organic matters, filtering, taking filtrate, namely the recovered catholyte, and recovering the anolyte for next batch of electrolysis.

The concentration of the alkali metal chloride in the anolyte is 0.5-2.5M (preferably 1.3-1.9M). The concentration of the 4-amino-3, 5, 6-trichloropicolinic acid in the catholyte is 0.2-0.6M (preferably 0.4M), and the concentration of the alkali metal hydroxide is 0.3-0.7M (preferably 0.5M). In the electrolytic synthesis process, 4-amino-3, 5, 6-trichloropicolinic acid and alkali metal hydroxide can be added into the catholyte, and the pH of the catholyte is controlled to be 12.5-13.5.

The anode is a titanium-based ruthenium coating electrode which can be a titanium-based ruthenium oxide, titanium oxide and iridium oxide mixed coating electrode, or a titanium-based ruthenium oxide and titanium oxide mixed coating electrode, or a titanium-based ruthenium oxide, titanium oxide and cobalt oxide mixed coating electrode, or a titanium-based ruthenium oxide, titanium oxide and tin oxide mixed coating electrode. What occurs at the anode is the oxidation of chloride ions to chlorine gas.

The cathode material is silver, preferably an activated silver mesh. The activated silver is prepared by an oxidation-reduction method, such as: in an aqueous solution containing chloride ions or bromide ions (deionized water preparation), silver is used as an anode to oxidize the electrode to +0.7vs. SHE (relative to the standard hydrogen electrode potential), and then silver is used as a cathode to reduce the electrode to-0.4 vs. SHE. The current density of the silver in the oxidation-reduction process is 0.1-5A/dm²Preferably 0.5 to 2A/dm²(ii) a The temperature is 0-50 ℃, preferably 20-40 ℃. The cathode is used for generating the reaction of dechlorinating 4-amino-3, 5, 6-trichloropicolinic acid to generate 4-amino-3, 6-dichloropicolinic acid.

The diaphragm is a cationic membrane, which can be various types of acid-base-resistant and oxidation-resistant cationic membranes, preferably perfluorosulfonic acid, such as 117 perfluorosulfonic acid membranes from DuPont. During electrolysis, sodium ions or potassium ions or hydrogen ions in the anolyte simultaneously pass through the cation membrane to reach the cathode chamber.

The current of the electrolytic synthesis is direct current, and the current density is preferably 3.75-10A/dm²The electrolysis reaction temperature is preferably 40-50 ℃.

The organic solvent for extraction is dichloromethane, n-butanol, butanone and ethyl acetate. The adsorbent is active carbon or macroporous resin SD 300.

The electrolytic cell adopts a diaphragm electrolytic cell, the structure of the electrolytic cell is not a key factor, and the electrolytic cell can adopt an H-shaped structure or a plate-and-frame structure.

Compared with the prior art, the invention has the following beneficial effects: the method adopts the mother liquor obtained after the catholyte is adsorbed and filtered in the previous 1 batch of experiments as the anolyte, so that the pH of the catholyte is more stable, the yield of the 4-amino-3, 6-dichloropicolinic acid product is improved, and the yield can be improved by 5-8%; the consumption of alkali is greatly reduced, and the dosage of alkali metal hydroxide (NaOH for example) can be reduced by more than 500Kg for each ton of 4-amino-3, 6-dichloropicolinic acid product; the discharge of the acidic sodium chloride aqueous solution is greatly reduced, and the discharge of the alkali metal chloride waste salt (NaCl waste salt for example) is reduced by more than 800 Kg.

The method can not only recycle the acidic waste water containing high-concentration chloride salt generated in the previous reaction, but also reduce the alkali consumption in the anode liquid and stabilize the pH value of the cathode liquid, thereby being beneficial to improving the product yield.

(IV) description of the drawings

FIG. 1 is a schematic diagram of an H-type electrolytic cell with a Nafion 117 cation membrane as a diaphragm, the distance between the cathode and the anode is about 8cm, the ion membrane is placed in the middle, and the area of the ion membrane is 3.14 multiplied by 2 which is 12.56cm²。

(V) detailed description of the preferred embodiments

The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto:

all aqueous solutions in the examples of the invention were prepared with deionized water.