Process for the electrocatalytic synthesis of ester compounds with high selectivity for dechlorination

Abstract

The application discloses a method for electrocatalytic synthesis of ester compounds with high selectivity, and the method is characterized in that: by using an electrochemical method, an ORR (oxygen reduction reaction) is coupled with a dechlorination cascade chemical reaction to synthesize ester compounds from trichloromethyl compounds with high selectivity. The method has the advantages of mild preparation conditions, normal temperature and pressure, high selectivity, high yield and the like.

Description

Technical Field

[0001] The present invention relates to the synthesis of ester compounds, and in particular to a method for synthesizing ester compounds by high-selective dechlorination electrocatalysis. Background Art

[0002] Ester compounds are among the most effective organic compounds in industry and are widely used in lubricants, emulsifiers, dispersants, industrial solvents, cosmetic additives, pharmaceutical intermediates, food flavorings, pesticides, plastics, etc. The industrial process of ester production relies on chemical catalysis strategies.

[0003] For example, in the prior art, Chinese patent document (201710993290.8) discloses a method for preparing the corresponding pyridine carboxylate using 4-fluoro-6-trifluoromethyl-3-pyridinecarboxylic acid as a substrate, first undergoing an acylation reaction, followed by an esterification reaction with an alcohol. However, the chemical reaction steps involved in this reaction are too lengthy, making the reaction difficult to control, and the use of highly toxic thionyl chloride poses a significant threat to both the environment and human health. Chinese patent document (200680041607.8) authorized by BASF SE discloses a method using a trichloromethylpyridine derivative as a raw material, first undergoing an acylation reaction in a concentrated sulfuric acid solution at 110-160°C to produce an acyl chloride intermediate, and then undergoing alcoholysis in an alcohol solution to obtain the corresponding pyridine carboxylate. However, this reaction also involves the use of the highly toxic thionyl chloride, which easily produces a large amount of acid waste liquid, and the preparation conditions are unsafe.

[0004] Electrocatalytic technology has the advantages of mild reaction conditions, simple process and low pollution. However, it is challenging to synthesize acyl chloride from trichloromethyl compounds by electrochemical method. This is because trichloromethyl compounds are usually prone to dechlorination and hydrogenation reaction at the cathode, that is, using H in the solution to synthesize acyl chloride. + The adsorbed active hydrogen is then generated and combines with the reactive intermediate trichloromethyl compound produced after dechlorination. Conversely, to synthesize acyl chlorides, the hydrogenation step must be suppressed while promoting the rapid generation of reactive oxygen species, which then combine with the reactive intermediate produced after dechlorination before the active hydrogen. To date, research on electrochemical synthesis of acyl chlorides remains limited, and even fewer studies have utilized this method to further produce esters. Summary of the Invention

[0005] To address these issues, the present invention provides a highly selective dechlorination electrocatalytic synthesis of ester compounds. This method utilizes an electrochemical method to selectively dechlorinate trichloromethyl compounds to synthesize ester compounds through an ORR (oxygen reduction reaction) coupled to a dechlorination cascade chemical reaction. This method, which can be performed under mild conditions at room temperature and pressure, offers advantages such as high selectivity and high yield.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for highly selective dechlorination electrocatalytic synthesis of ester compounds, the method is as follows:

[0008] An H-type electrolytic cell or a flow cell is used as an electrolytic reactor, a cationic membrane is used to separate the cathode and anode reaction cells, an activated silver mesh is used as the cathode, a platinum electrode is used as the anode, and a silver / silver chloride electrode is used as the reference electrode. An electrolyte is added to the cathode reaction cell, and oxygen or air is introduced into the cathode reaction cell. The electrocatalytic reaction is carried out at room temperature and under stirring conditions at a constant voltage of -0.2 to -2 V.

[0009] The cationic membrane can be N117 DuPont proton exchange membrane, which is used to separate the electrolyte and only allow cations to pass through the membrane;

[0010] The electrolyte in the cathode reaction tank is composed of a substrate, a supporting electrolyte, and an organic solvent; the substrate concentration is preferably 10 to 100 mmol / L, and the supporting electrolyte concentration is preferably 0.01 to 3 mol / L (different types or concentrations of supporting electrolytes have different pH values);

[0011] The substrate is selected from: 2-chloro-5-trichloromethylpyridine, 2-chloro-6-trichloromethylpyridine, 2-chloro-3-trichloromethylpyridine, p-chlorobenzotrichloride, benzotrichloride or 1,4-bis(trichloromethyl)benzene, and an electrolytic reduction dechlorination hydrolysis reaction is carried out at the cathode to obtain an ester compound;

[0012] After the electrolysis reaction is completed, the corresponding ester products obtained are: methyl 6-chloronicotinate, methyl 6-chloro-2-pyridinecarboxylate, methyl 2-chloronicotinate, methyl p-chlorobenzoate, methyl benzoate or dimethyl terephthalate;

[0013] The supporting electrolyte is selected from the group consisting of: tetrabutylammonium tetrafluoroborate (C 16 H 36 BF4N, TBAT, ≥98.0%), tetrabutylammonium bromide (C 16 H 36 BrN, TBAB, 99.0%), lithium perchlorate (LiClO4, 99.99%), lithium acetate dihydrate (LiOAc·2H2O, 99%), anhydrous lithium acetate (LiOAc, 99.99%), tetramethylammonium hydroxide ((CH3)4NOH, TMAH, 25%);

[0014] The organic solvent is selected from: anhydrous methanol, anhydrous ethanol, etc.;

[0015] When electrolytic reduction dechlorination hydrolysis is carried out at the cathode, oxygen or air is preferably introduced at a flow rate in the range of 1 to 5 L / min;

[0016] The electrolyte in the anode reaction tank is a sulfuric acid aqueous solution, preferably a 1 mol / L sulfuric acid aqueous solution;

[0017] An activated silver electrode (Ag(a)) was prepared by electrochemical cyclic voltammetry (CV) activation treatment. The specific activation method is as follows:

[0018] First, 1×2cm 2 Silver mesh (100 mesh) was ultrasonically treated in ethanol and deionized water for 10 min in sequence to remove surface impurities. Then, electrochemical activation was performed by scanning CV in a circular tank containing 1 M HCl solution. Platinum sheet, silver mesh, and saturated calomel electrode (SCE) were used as counter electrode, working electrode, and reference electrode, respectively. The scanning range was -1 V to 1.3 V vs. SCE, with a speed of 50 mV s -1 The washed silver mesh was activated for 10 cycles at a scan rate of , rinsed with deionized water, and dried to obtain the Ag(a) electrode.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] In the method for synthesizing ester compounds from trichloromethyl compounds with high selectivity by dechlorination of the present invention, ORR (electroreduction hydrogen evolution reaction) occurs before HER (electroreduction hydrogen evolution reaction) in the cathode reaction, so that the active oxygen formed combines with the generated trichloromethyl compound intermediate before the active hydrogen, effectively inhibiting the hydrogenation reaction after dechlorination, rapidly generating acyl chloride, and further generating ester compounds with high selectivity.

[0021] The reaction is easy to carry out, avoiding the use of highly toxic organic compounds and being environmentally and human-friendly. Furthermore, the electrode materials are inexpensive, readily available, and stable, and electrolysis is performed at room temperature. The pH of the catholyte can be controlled, avoiding problems such as excessive dechlorination, low selectivity, and excessive byproducts caused by unstable pH during electrolysis.

[0022] The ester compounds produced by the present invention have a wide range of applications. For example, methyl 6-chloronicotinate has the effects of protecting the nervous system of animals, alleviating inflammatory reactions, and maintaining fat metabolic balance, with a yield and selectivity as high as 95%. Methyl p-chlorobenzoate is mainly used as a solvent and intermediate in organic synthesis, with a selectivity as high as 100%. DETAILED DESCRIPTION

[0023] The present invention is further described below by means of specific examples, but the protection scope of the present invention is not limited thereto.

[0024] Example 1

[0025] Synthesis of 6-chloronicotinate methyl ester by electrolysis of 2-chloro-5-trichloromethylpyridine

[0026] The electrolysis reactor was an H-type electrode reaction cell, with an N117 cationic membrane as the diaphragm, an activated silver mesh as the cathode, and a platinum electrode as the anode. The catholyte was 40 mL of a 10 mmol / L solution of 2-chloro-5-trichloromethylpyridine and 0.03 mol / L tetrabutylammonium tetrafluoroborate (TBAT) in anhydrous methanol; the anolyte was 1 mol / L aqueous sulfuric acid. Oxygen was introduced into the catholyte during the electrolysis process, and the temperature was controlled at 25-30°C. The electrolysis potential was -0.6 V. Electrolysis was terminated after 6 hours. High-performance liquid chromatography analysis revealed a 100% conversion of 2-chloro-5-trichloromethylpyridine and a 95% yield of methyl 6-chloronicotinate, with a selectivity of 95%.

[0027] Example 2

[0028] Synthesis of Methyl p-Chlorobenzoate by Electrolysis of p-Chlorobenzotrichloride

[0029] The electrolysis reactor was an H-type electrode reaction cell, with an N117 cationic membrane as the diaphragm, an activated silver mesh as the cathode, and a platinum electrode as the anode. The catholyte was 40 mL of a 10 mmol / L solution of para-chlorobenzotrichloride and 0.03 mol / L tetrabutylammonium tetrafluoroborate (TBAT) in anhydrous methanol; the anolyte was 1 mol / L aqueous sulfuric acid. Oxygen was introduced into the catholyte during the electrolysis process, and the temperature was controlled at 25-30°C. The electrolysis potential was -0.7 V. Electrolysis was terminated after 8 hours. High-performance liquid chromatography analysis revealed a conversion of 72.05% for para-chlorobenzotrichloride and a yield of 72.05% for methyl para-chlorobenzoate, with a selectivity of 100%.

[0030] Example 3

[0031] Synthesis of 6-chloro-2-pyridinecarboxylic acid methyl ester by electrolysis of 2-chloro-6-trichloromethylpyridine

[0032] The electrolysis reactor was an H-type electrode reaction cell, with an N117 cationic membrane as the diaphragm, an activated silver mesh as the cathode, and a platinum electrode as the anode. The catholyte was 40 mL of a 10 mmol / L solution of 2-chloro-6-trichloromethylpyridine and 0.03 mol / L tetrabutylammonium tetrafluoroborate (TBAT) in anhydrous methanol; the anolyte was 1 mol / L aqueous sulfuric acid. Oxygen was introduced into the catholyte during the electrolysis process, and the temperature was controlled at 25-30°C. The electrolysis potential was -1 V. Electrolysis was terminated after 12 hours. High-performance liquid chromatography analysis revealed an 84.91% conversion of 2-chloro-6-trichloromethylpyridine, a 69.40% yield of methyl 6-chloro-2-pyridinecarboxylate, and an 81.73% selectivity.

[0033] Example 4

[0034] Synthesis of Methyl Benzoate by Electrolysis of Trichlorotoluene

[0035] The electrolysis reactor was an H-type electrode reaction cell, with an N117 cationic membrane as the diaphragm, an activated silver mesh as the cathode, and a platinum electrode as the anode. The catholyte was 40 mL of a 10 mmol / L solution of benzotrichloride and 0.03 mol / L tetrabutylammonium tetrafluoroborate (TBAT) in anhydrous methanol; the anolyte was 1 mol / L aqueous sulfuric acid. Oxygen was introduced into the catholyte during the electrolysis process, and the temperature was controlled at 25-30°C. The electrolysis potential was -0.7 V. Electrolysis was terminated after 8 hours. High-performance liquid chromatography (HPLC) analysis revealed a benzotrichloride conversion of 80.88%, a methyl benzoate yield of 58.82%, and a selectivity of 72.73%.

[0036] Example 5

[0037] Synthesis of dimethyl terephthalate by electrolysis of 1,4-bis(trichloromethyl)benzene

[0038] The electrolysis reactor was an H-type electrode reaction cell, with an N117 cationic membrane as the diaphragm, an activated silver mesh as the cathode, and a platinum electrode as the anode. The catholyte was 40 mL of a 10 mmol / L 1,4-bis(trichloromethyl)benzene solution in anhydrous methanol containing 0.03 mol / L tetrabutylammonium tetrafluoroborate (TBAT); the anolyte was a 1 mol / L aqueous sulfuric acid solution. Oxygen was introduced into the catholyte during the electrolysis process, and the temperature was controlled at 25-30°C. The electrolysis potential was -0.7 V. Electrolysis was terminated after 7 hours. High-performance liquid chromatography analysis revealed a 1,4-bis(trichloromethyl)benzene conversion of 99.95%, a dimethyl terephthalate yield of 72.14%, and a selectivity of 72.18%.

[0039] Example 6

[0040] Synthesis of 2-chloronicotinate methyl ester by electrolysis of 2-chloro-3-trichloromethylpyridine

[0041] The electrolysis reactor was an H-type electrode reaction cell, with an N117 cationic membrane as the diaphragm, an activated silver mesh as the cathode, and a platinum electrode as the anode. The catholyte was 40 mL of a 10 mmol / L solution of 2-chloro-3-trichloromethylpyridine and 0.03 mol / L tetrabutylammonium tetrafluoroborate (TBAT) in anhydrous methanol; the anolyte was 1 mol / L aqueous sulfuric acid. Oxygen was introduced into the catholyte during the electrolysis process, and the temperature was controlled at 25-30°C. The electrolysis potential was -1 V. Electrolysis was terminated after 10 hours. High-performance liquid chromatography analysis revealed a 96.21% conversion of 2-chloro-3-trichloromethylpyridine, a 66.62% yield of methyl 2-chloronicotinate, and a selectivity of 69.24%.

[0042] The remaining implementation cases refer to Example 1. The different experimental conditions and results are detailed in Tables 1 and 2; TCMP: 2-chloro-5-trichloromethylpyridine, MCN: methyl 6-chloronicotinate.

[0043] Table 1

[0044]

[0045]

[0046] Table 2

[0047] Serial number atmosphere Voltage MCN yield Dechlorination products TCMP conversion rate 1 <![CDATA[N2]]> 0 0 0 0 2 <![CDATA[N2]]> -0.2V 0 2.95％ 2.95％ 3 <![CDATA[N2]]> -0.4V 0 10.89％ 10.89％ 4 <![CDATA[N2]]> -0.6V 0 34.45％ 34.45％ 5 <![CDATA[N2]]> -0.8V 0 58.78％ 58.78％ 6 <![CDATA[N2]]> -1V 0 81.62％ 81.62％ 7 <![CDATA[N2]]> -1.2V 0 94.48％ 94.48％ 8 <![CDATA[N2]]> -1.4V 0 75.06％ 75.06％

Claims

1. A method for highly selective dechlorination electrocatalytic synthesis of ester compounds, characterized in that: The method is as follows: An H-type electrolytic cell or a flow cell is used as an electrolytic reactor, a cationic membrane is used to separate the cathode and anode reaction cells, an activated silver mesh is used as the cathode, a platinum electrode is used as the anode, and a silver / silver chloride electrode is used as the reference electrode. An electrolyte is added to the cathode reaction cell, and oxygen or air is introduced into the cathode reaction cell. The electrocatalytic reaction is carried out at room temperature and under stirring conditions at a constant voltage of -0.2 to -2 V. The silver mesh was activated as follows: first, the silver mesh was ultrasonically treated in ethanol and deionized water for 10 min in sequence to remove surface impurities. Then, electrochemical activation was performed by scanning CV in a circular tank containing 1 M HCl solution. A platinum sheet, silver mesh, and saturated calomel electrode were used as the counter electrode, working electrode, and reference electrode, respectively. The scanning range was -1 V to 1.3 V vs. SCE, and the rate was 50 mV s -1 The washed silver mesh was activated for 10 cycles at a scanning rate of , rinsed with deionized water, and dried to obtain an activated silver mesh; The electrolyte in the cathode reaction tank is composed of substrate, supporting electrolyte and organic solvent; The substrate is selected from: 2-chloro-5-trichloromethylpyridine, 2-chloro-6-trichloromethylpyridine, 2-chloro-3-trichloromethylpyridine, p-chlorobenzotrichloride, benzotrichloride or 1,4-bis(trichloromethyl)benzene; The organic solvent was anhydrous methanol; The corresponding ester products obtained are: methyl 6-chloronicotinate, methyl 6-chloro-2-pyridinecarboxylate, methyl 2-chloronicotinate, methyl p-chlorobenzoate, methyl benzoate or dimethyl terephthalate; The electrolyte in the anode reaction tank is a sulfuric acid aqueous solution.

2. The method for highly selective dechlorination electrocatalytic synthesis of ester compounds according to claim 1, characterized in that: The substrate concentration in the cathode reaction tank electrolyte is 10 to 100 mmol / L.

3. The method for highly selective dechlorination electrocatalytic synthesis of ester compounds according to claim 1, characterized in that: The supporting electrolyte concentration in the cathode reaction tank electrolyte is 0.01 to 3 mol / L.

4. The method for highly selective dechlorination electrocatalytic synthesis of ester compounds according to claim 1, characterized in that: In the cathode reaction tank electrolyte, the supporting electrolyte is selected from the group consisting of tetrabutylammonium tetrafluoroborate, tetrabutylammonium bromide, lithium perchlorate, lithium acetate dihydrate, anhydrous lithium acetate, and tetramethylammonium hydroxide.

5. The method for highly selective dechlorination electrocatalytic synthesis of ester compounds according to claim 1, characterized in that: The electrolyte in the anode reaction tank is a 1 mol / L sulfuric acid aqueous solution.

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