Method for high-selectivity dechlorination electrocatalytic synthesis of ester compounds

Abstract

The invention discloses a method for high-selectivity dechlorination electro-catalytic synthesis of ester compounds, according to the method, an electrochemical method is utilized, ORR (oxygen reduction reaction) is coupled with a dechlorination cascade chemical reaction, high-selectivity dechlorination is carried out on trichloromethyl compounds to synthesize the ester compounds, the method is mild in preparation condition and can be carried out at normal temperature and normal pressure, and the method is suitable for industrial production. And the method has the advantages of high selectivity, high yield and the like.

Description

Technical Field

[0001] The 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 one of the most effective organic compounds in industry and are widely used in lubricants, emulsifiers, dispersants, industrial solvents, cosmetic additives, pharmaceutical intermediates, food flavors, pesticides, plastics, etc. The industrial process of ester production relies on chemical catalysis strategies.

[0003] For example, in the prior art, the Chinese patent document (201710993290.8) discloses a method for preparing the corresponding pyridine carboxylic acid ester by first performing an acylation reaction with 4-fluoro-6-trifluoromethyl-3-pyridine carboxylic acid as a substrate and then reacting with alcohol for esterification. However, the chemical reaction steps involved in the above reaction are too lengthy, the reaction is difficult to control, and the use of thionyl chloride, which is highly toxic, is involved, posing a great threat to the environment and human health. The Chinese patent document (200680041607.8) authorized by BASF Europe discloses a method for preparing an acyl chloride intermediate by first performing an acylation reaction in a concentrated sulfuric acid solution at 110-160°C, and then performing alcoholysis in an alcohol solution to obtain the corresponding pyridine carboxylic acid ester. However, the above reaction also uses thionyl chloride, a toxic substance with high toxicity, which is easy to produce 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 less 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 produced and combined with the active intermediate of the trichloromethyl compound produced after dechlorination. On the contrary, if the acyl chloride is to be synthesized, the hydrogenation step must be suppressed, while the active oxygen is promoted to be generated quickly and combined with the active intermediate produced after dechlorination before the active hydrogen. So far, there are still few studies on the electrochemical synthesis of acyl chlorides, and even fewer studies on the further production of ester compounds using this method. Summary of the invention

[0005] To solve the above problems, the present invention provides a method for highly selective dechlorination electrocatalytic synthesis of ester compounds. The present invention utilizes an electrochemical method to couple a dechlorination cascade chemical reaction through ORR (oxygen reduction reaction) to highly selectively dechlorinate trichloromethyl compounds to synthesize ester compounds. The method has mild preparation conditions, can be carried out at room temperature and pressure, and has the advantages of high selectivity and high yield.

[0006] The technical solution of the present invention is 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 positive and negative electrode reaction tank is separated by a cationic membrane, an activated silver mesh is used as a cathode, a platinum sheet electrode is used as an anode, and a silver / silver chloride electrode is used as a reference electrode, an electrolyte is added to the positive and negative electrode reaction tanks, oxygen or air is introduced into the cathode reaction tank, and an electrocatalytic reaction is performed at room temperature and under stirring conditions in a constant voltage electrolysis mode of -0.2 to -2V;

[0009] The cation membrane can be N117 DuPont proton exchange membrane, the purpose of which is 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; preferably, the substrate concentration is 10 to 100 mmol / L, and the supporting electrolyte concentration is 0.01 to 3 mol / L (the pH of supporting electrolytes of different types or concentrations is different);

[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: 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 the electrolytic reduction dechlorination hydrolysis is carried out at the cathode, oxygen or air is preferably introduced at a flow rate ranging from 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] The 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 The silver mesh (100 mesh) was ultrasonically treated in ethanol and deionized water for 10 min to remove surface impurities. Then, the electrochemical activation was performed by scanning CV in a circular tank containing 1 M HCl solution. The platinum sheet, silver mesh, and saturated calomel electrode (SCE) were used as the counter electrode, working electrode, and reference electrode, respectively. The scanning range was from -1 V to 1.3 V vs. SCE at 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 beneficial effects of the present invention are:

[0020] In the method for synthesizing ester compounds by highly selective dechlorination of trichloromethyl compounds involved in the present invention, ORR occurs before HER (electro-reduction 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, quickly generating acyl chlorides, and further generating ester compounds with high selectivity.

[0021] The reaction of the present invention is easy to carry out, and the use of highly toxic organic compounds is avoided, which is friendly to the environment and human health. In addition, the electrode material is cheap, readily available and stable, and the electrolysis is carried out at room temperature. The pH of the cathode liquid of the present invention can be regulated, and the problems of excessive dechlorination, low selectivity, and a large number of by-products caused by unstable pH during electrolysis are avoided.

[0022] The ester compounds prepared by the present invention have wide application value. For example, methyl 6-chloronicotinate has the functions of protecting the nervous system of animals, relieving inflammatory reactions and maintaining fat metabolism balance, and its yield and selectivity are as high as 95%; methyl p-chlorobenzoate is mainly used as a solvent and intermediate in organic synthesis, and its selectivity is as high as 100%. DETAILED DESCRIPTION

[0023] The present invention is further described below by means of specific embodiments, 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 H-type electrode reaction tank is the electrolytic reactor, the N117 cationic membrane is the diaphragm, the activated silver mesh is the cathode, and the platinum electrode is the anode. 40mL 10mmol / L 2-chloro-5-trichloromethylpyridine + 0.03mol / L tetrabutylammonium tetrafluoroborate (TBAT) anhydrous methanol solution is the cathode liquid; 1mol / L sulfuric acid aqueous solution is the anode liquid. During the electrolysis process, oxygen is introduced into the cathode liquid, the temperature is controlled at 25-30℃, and the electrolysis potential is -0.6V. The electrolysis is stopped after 6h of electrolysis. High performance liquid chromatography analysis shows that the conversion rate of 2-chloro-5-trichloromethylpyridine is 100%, the yield of 6-chloronicotinate methyl ester is 95%, and the selectivity is as high as 95%.

[0027] Example 2

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

[0029] The H-type electrode reaction tank is the electrolytic reactor, the N117 cationic membrane is the diaphragm, the activated silver mesh is the cathode, and the platinum electrode is the anode. 40mL 10mmol / L p-chlorotrichlorotoluene + 0.03mol / L tetrabutylammonium tetrafluoroborate (TBAT) anhydrous methanol solution is the cathode liquid; 1mol / L sulfuric acid aqueous solution is the anode liquid. During the electrolysis process, oxygen is introduced into the cathode liquid, the temperature is controlled at 25-30℃, and the electrolysis potential is -0.7V. The electrolysis is stopped after 8h of electrolysis. High performance liquid chromatography analysis shows that the conversion rate of p-chlorotrichlorotoluene is 72.05%, the yield of methyl p-chlorobenzoate is 72.05%, and the selectivity is as high as 100%.

[0030] Example 3

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

[0032] The H-type electrode reaction tank is the electrolytic reactor, the N117 cationic membrane is the diaphragm, the activated silver mesh is the cathode, and the platinum electrode is the anode. 40mL 10mmol / L 2-chloro-6-trichloromethylpyridine + 0.03mol / L tetrabutylammonium tetrafluoroborate (TBAT) anhydrous methanol solution is the cathode liquid; 1mol / L sulfuric acid aqueous solution is the anode liquid. During the electrolysis process, oxygen is introduced into the cathode liquid, the temperature is controlled at 25-30℃, and the electrolysis potential is -1V. The electrolysis is stopped after 12h of electrolysis. High performance liquid chromatography analysis shows that the conversion rate of 2-chloro-6-trichloromethylpyridine is 84.91%, the yield of 6-chloro-2-pyridinecarboxylic acid methyl ester is 69.40%, and the selectivity is 81.73%.

[0033] Example 4

[0034] Synthesis of Methyl Benzoate by Electrolysis of Trichlorotoluene

[0035] The H-type electrode reaction tank is the electrolytic reactor, the N117 cationic membrane is the diaphragm, the activated silver mesh is the cathode, and the platinum electrode is the anode. 40mL 10mmol / L trichlorotoluene + 0.03mol / L tetrabutylammonium tetrafluoroborate (TBAT) anhydrous methanol solution is the cathode liquid; 1mol / L sulfuric acid aqueous solution is the anode liquid. During the electrolysis process, oxygen is introduced into the cathode liquid, the temperature is controlled at 25-30℃, and the electrolysis potential is -0.7V. The electrolysis is stopped after 8h of electrolysis. High performance liquid chromatography analysis shows that the conversion rate of trichlorotoluene is 80.88%, the yield of methyl benzoate is 58.82%, and the selectivity is 72.73%.

[0036] Example 5

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

[0038] The H-type electrode reaction tank is the electrolytic reactor, the N117 cationic membrane is the diaphragm, the activated silver mesh is the cathode, and the platinum electrode is the anode. 40mL 10mmol / L 1,4-bis(trichloromethyl)benzene + 0.03mol / L tetrabutylammonium tetrafluoroborate (TBAT) anhydrous methanol solution is the cathode liquid; 1mol / L sulfuric acid aqueous solution is the anode liquid. During the electrolysis process, oxygen is introduced into the cathode liquid, the temperature is controlled at 25-30℃, and the electrolysis potential is -0.7V. The electrolysis is stopped after 7h. High performance liquid chromatography analysis shows that the conversion rate of 1,4-bis(trichloromethyl)benzene is 99.95%, the yield of dimethyl terephthalate is 72.14%, and the selectivity is 72.18%.

[0039] Example 6

[0040] Synthesis of 2-Chloronicotinoic Acid Methyl Ester by Electrolysis of 2-Chloro-3-Trichloromethylpyridine

[0041] The H-type electrode reaction tank is the electrolytic reactor, the N117 cationic membrane is the diaphragm, the activated silver mesh is the cathode, and the platinum electrode is the anode. 40mL 10mmol / L 2-chloro-3-trichloromethylpyridine + 0.03mol / L tetrabutylammonium tetrafluoroborate (TBAT) anhydrous methanol solution is the cathode liquid; 1mol / L sulfuric acid aqueous solution is the anode liquid. During the electrolysis process, oxygen is introduced into the cathode liquid, the temperature is controlled at 25-30℃, and the electrolysis potential is -1V. The electrolysis is stopped after 10h of electrolysis. High performance liquid chromatography analysis shows that the conversion rate of 2-chloro-3-trichloromethylpyridine is 96.21%, the yield of 2-chloronicotinate methyl ester is 66.62%, and the selectivity is 69.24%.

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

[0043] Table 1

[0044]

[0045]

[0046] Table 2

[0047] Serial number atmosphere Voltage MCN yield Dechlorination products TCMP conversion 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 positive and negative electrode reaction tank is separated by a cationic membrane, an activated silver mesh is used as a cathode, a platinum sheet electrode is used as an anode, and a silver / silver chloride electrode is used as a reference electrode, an electrolyte is added to the positive and negative electrode reaction tanks, oxygen or air is introduced into the cathode reaction tank, and an electrocatalytic reaction is performed at room temperature and under stirring conditions in a constant voltage electrolysis mode of -0.2 to -2V; 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 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 as claimed in 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 as claimed in claim 1, characterized in that: In the cathode reaction tank electrolyte, the supporting electrolyte concentration is 0.01 to 3 mol / L.

4. The method for highly selective dechlorination electrocatalytic synthesis of ester compounds as claimed in claim 1, characterized in that: In the cathode reaction tank electrolyte, the supporting electrolyte is selected from: 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 as claimed in claim 1, characterized in that: In the cathode reaction tank electrolyte, the organic solvent is selected from: anhydrous methanol and anhydrous ethanol.

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

7. The method for highly selective dechlorination electrocatalytic synthesis of ester compounds as claimed in claim 1, characterized in that: The activation method of the silver mesh is as follows: First, the silver mesh was ultrasonically treated in ethanol and deionized water for 10 min in sequence to remove surface impurities. Then, it was electrochemically activated by scanning CV in a circular tank containing 1 M HCl solution. The 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 at 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.

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