An electrochemical synthesis of 2,2'-bipyrazine

Abstract

This invention belongs to the field of fine chemical engineering and organic electrochemical synthesis technology, specifically relating to an electrochemical synthesis method for 2,2′-bipyrazine, comprising the following steps: using an H-type electrolytic cell as a reactor, with a cation exchange membrane separating the anode and cathode chambers; adding sulfuric acid or phosphoric acid solution to the anode chamber; adding saturated ammonium persulfate solution, pyrazine, catalyst, and organic solvent to the cathode chamber, wherein the molar ratio of ammonium sulfate, pyrazine, and catalyst in the saturated ammonium persulfate solution is 20-100:20:1-2, and the volume ratio of saturated ammonium persulfate solution to organic solvent is 1-2:1; maintaining constant temperature and stirring while electrolyzing; after electrolysis, adjusting the pH of the reaction solution in the cathode chamber, separating the organic phase, evaporating the solvent, and recrystallizing to obtain 2,2′-bipyrazine. This invention utilizes an electrochemical method to synthesize 2,2′-bipyrazine, with mild conditions, inexpensive reagents, high yield, and the advantages of easy reaction control and environmental friendliness.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical engineering and organic electrochemical synthesis technology, specifically relating to an electrochemical synthesis method for 2,2'-bipyrazine. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Pyrazines are six-membered aromatic heterocyclic compounds containing nitrogen atoms at the 1,4-position, with C-C bond lengths similar to benzene, and are structurally D-type compounds. 2h Pyrazines are symmetrical hexagonal planar molecules. Due to their strong coordination ability, pyrazines are preferred ligands for constructing coordination polymers. Pyrazine metal complexes were reported 50 years ago, and currently, unique functional molecular solid materials are formed by coordinating the nitrogen atom on the pyrazine with a metal as the coordinating atom and hydrogen bond acceptor.

[0004] 2,2'-Bipyrazines possess superior coordination ability compared to pyrazines due to their intercyclic π-π stacking and abundant hydrogen bond donors and acceptors. While 2,2'-bipyrazines themselves exhibit virtually no fluorescence emission at room temperature, their metal complexes demonstrate strong fluorescence emission. Recent breakthroughs in visible light photocatalysis in organic synthesis have led to widespread research interest in bipyrazine complexes such as ruthenium bipyrazine. However, only a limited number of literature reports describe the synthesis of 2,2'-bipyrazine compounds. Current techniques use 2-chloropyrazine as a reactant, employing palladium catalysts to synthesize 2,2'-bipyrazines. However, this method suffers from low yields and is limited by the high cost of palladium catalysts, hindering industrial application. Although some papers have adjusted the specific preparation conditions in the palladium-catalyzed preparation of 2-chloropyrazine, such as palladium catalyst, organic amine, inorganic base, phase transfer catalyst, solvent and reaction temperature, which have improved the yield of 2,2´-bipyrazine to some extent, the reaction mechanism and process are complex, require the use of a variety of reaction raw materials and catalysts, are costly and do not meet the requirements of green chemistry, and are still not suitable for large-scale industrial preparation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an electrochemical synthesis method for 2,2'-bipyrazine. This invention utilizes an electrochemical method to synthesize 2,2'-bipyrazine under mild conditions, with inexpensive reagents, high yield, and features easy reaction control and environmental friendliness.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides an electrochemical synthesis method for 2,2'-bipyrazine, comprising the following steps: An H-type electrolytic cell is used as the reactor, and a cation exchange membrane separates the anode chamber and the cathode chamber. Add sulfuric acid or phosphoric acid solution to the anode chamber; A saturated ammonium persulfate solution, pyrazine, a catalyst, and an organic solvent are added to the cathode chamber. The molar ratio of ammonium sulfate, pyrazine, and catalyst in the saturated ammonium persulfate solution is 20-100:20:1-2, and the volume ratio of the saturated ammonium persulfate solution to the organic solvent is 1-2:1. Maintain constant temperature and stir while electrolyzing. After electrolysis, adjust the pH of the reaction solution in the cathode chamber, separate the organic phase, evaporate the solvent, and recrystallize to obtain 2,2'-bipyrazine.

[0007] The beneficial effects achieved by one or more technical solutions of the present invention are as follows: (1) The electrochemical synthesis method of the present invention uses saturated ammonium persulfate solution, pyrazine, catalyst, sulfuric acid and organic solvent as raw materials and reagents. The reagents are cheap and readily available, avoiding the use of expensive palladium catalysts and phase transfer catalysts in the prior art, which is beneficial to the industrial preparation of 2,2´-bipyrazine.

[0008] (2) The electrochemical synthesis method of the present invention can be carried out at a lower temperature and atmospheric pressure, avoiding solvent reflux in the traditional palladium catalysis process, and the reaction conditions are mild.

[0009] (3) The products in the electrochemical synthesis method of the present invention are easy to separate, and the by-product sulfuric acid can be recovered and the reaction process can be re-parameterized, which meets the requirements of green chemistry.

[0010] (4) The electrochemical synthesis method of the present invention has excellent yield of 2,2´-bipyrazine, with a yield of 83% or more, and up to 93%. Detailed Implementation

[0011] The H-type electrolytic cell used in this invention includes an anode and a corresponding anode chamber, a cathode and a corresponding cathode chamber, and a cation exchange membrane. Both the anode and cathode are connected to a DC power supply or regulating equipment by wires. The anode chamber and the cathode chamber are connected and separated by a cation exchange membrane.

[0012] A first typical embodiment of the present invention provides an electrochemical synthesis method for 2,2'-bipyrazine, comprising the following steps: An H-type electrolytic cell is used as the reactor, and a cation exchange membrane separates the anode chamber and the cathode chamber. Add sulfuric acid or phosphoric acid solution to the anode chamber; A saturated ammonium persulfate solution, pyrazine, a catalyst, and an organic solvent are added to the cathode chamber. The molar ratio of ammonium sulfate, pyrazine, and catalyst in the saturated ammonium persulfate solution is 20-100:20:1-2, and the volume ratio of the saturated ammonium persulfate solution to the organic solvent is 1-2:1. Maintain constant temperature and stir while electrolyzing. After electrolysis, adjust the pH of the reaction solution in the cathode chamber, separate the organic phase, evaporate the solvent, and recrystallize to obtain 2,2'-bipyrazine.

[0013] The use of saturated ammonium persulfate solution in this application can reduce resistance and energy consumption.

[0014] The relevant electrochemical equations for the electrochemical synthesis method of this invention are as follows: Anode reaction ; cathode reaction

[0015] .

[0016] In one or more embodiments of this implementation, the catalyst includes one or more of chromium sulfate, manganese sulfate, chromium chloride, and manganese chloride.

[0017] In one or more embodiments of this implementation, the organic solvent includes one or more of dichloromethane, chloroform, and carbon tetrachloride.

[0018] In one or more embodiments of this implementation, the cation exchange membrane is Nafion-324 or NaFion-424.

[0019] In one or more embodiments of this implementation, the anode in the H-type electrolytic cell is a DSA electrode or a platinum electrode.

[0020] The DSA electrode is made by coating a metal substrate, such as stainless steel, with catalytically active noble metal oxides such as cadmium and palladium on the metal substrate.

[0021] In one or more embodiments of this implementation, the cathode in the H-type electrolytic cell is an aluminum alloy electrode.

[0022] In one or more embodiments of this implementation, the temperature of the constant temperature stirring is 20-50 ℃.

[0023] In one or more embodiments of this implementation, the current density for electrolysis is 100-150 mA / m 2 .

[0024] In one or more embodiments of this implementation, electrolysis ends when the ratio of the charge to the number of moles of pyrazine reaches 1.5-2 F / mol.

[0025] In one or more embodiments of this implementation, sodium hydroxide or potassium hydroxide solution is used to adjust the pH of the cathode chamber reaction solution to 8-9.

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0027] Example 1 An H-type electrolytic cell was used as the reactor, with a DSA mesh electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-324 cation exchange membrane.

[0028] Add 80 mL of 20% sulfuric acid solution to the anode chamber, and add 50 mL of saturated ammonium persulfate solution, 20 mmol of pyrazine, 1 mmol of chromium sulfate, and 40 mL of dichloromethane to the cathode chamber. Maintain a constant temperature of 30 degrees Celsius while stirring.

[0029] Electrolysis was performed while maintaining a current density of 100 mA / m 2 The current was stopped when the applied current reached 1.5 F / mol. The reaction solution was adjusted to pH 8-9 using sodium hydroxide solution, the organic phase was separated, the solvent was evaporated, and the product was recrystallized to obtain 2,2'-bipyrazine in 83% yield.

[0030] Example 2 An H-type electrolytic cell was used as the reactor, with a DSA mesh electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-324 cation exchange membrane.

[0031] Add 80 mL of 20% sulfuric acid solution to the anode chamber, and add 50 mL of saturated ammonium persulfate solution, 20 mmol of pyrazine, 1 mmol of manganese sulfate, and 40 mL of chloroform to the cathode chamber. Maintain a constant temperature of 40 degrees Celsius while stirring.

[0032] Electrolysis was performed while maintaining a current density of 100 mA / m 2 The current was stopped when the applied current reached 1.5 F / mol. The reaction solution was adjusted to pH 8-9 using sodium hydroxide solution, the organic phase was separated, the solvent was evaporated, and the product was recrystallized to obtain 2,2'-bipyrazine in 90% yield.

[0033] Example 3 An H-type electrolytic cell was used as the reactor, with a DSA mesh electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-424 cation exchange membrane.

[0034] Add 80 mL of 20% sulfuric acid solution to the anode chamber, and add 50 mL of saturated ammonium persulfate solution, 20 mmol of pyrazine, 1 mmol of chromium chloride, and 40 mL of dichloroethane to the cathode chamber. Maintain a constant temperature of 45 degrees Celsius while stirring.

[0035] Electrolysis was performed while maintaining a current density of 150 mA / m 2 The current was stopped when the applied current reached 1.5 F / mol. The reaction solution was adjusted to pH 8-9 using sodium hydroxide solution, the organic phase was separated, the solvent was evaporated, and the product was recrystallized to obtain 2,2'-bipyrazine in 87% yield.

[0036] Example 4 An H-type electrolytic cell was used as the reactor, with a platinum electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-424 cation exchange membrane.

[0037] Add 80 mL of 20% sulfuric acid solution to the anode chamber, and add 50 mL of saturated ammonium persulfate solution, 20 mmol of pyrazine, 1 mmol of manganese chloride, and 40 mL of carbon tetrachloride to the cathode chamber. Maintain a constant temperature of 50 degrees Celsius while stirring.

[0038] Electrolysis was performed while maintaining a current density of 100 mA / m 2 The current was stopped when the applied current reached 1.5 F / mol. The reaction solution was adjusted to pH 8-9 using potassium hydroxide solution, the organic phase was separated, the solvent was evaporated, and the product was recrystallized to obtain 2,2'-bipyrazine in 92% yield.

[0039] Example 5 An H-type electrolytic cell was used as the reactor, with a platinum electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-324 cation exchange membrane.

[0040] Add 80 mL of 20% phosphoric acid solution to the anode chamber, and add 50 mL of saturated ammonium persulfate solution, 20 mmol of pyrazine, 1 mmol of chromium sulfate, and 40 mL of dichloromethane to the cathode chamber. Maintain a constant temperature of 20 degrees Celsius and stir.

[0041] Electrolysis was performed while maintaining a current density of 100 mA / m 2 The current was stopped when the applied current reached 2 F / mol. The reaction solution was adjusted to pH 8-9 using potassium hydroxide solution, the organic phase was separated, the solvent was evaporated, and the product was recrystallized to obtain 2,2'-bipyrazine in 93% yield.

[0042] Comparative Example 1 An H-type electrolytic cell was used as the reactor, with a DSA mesh electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-324 cation exchange membrane.

[0043] Add 80 mL of 20% sulfuric acid solution to the anode chamber, and add 50 mL of saturated ammonium persulfate solution, 20 mmol of pyrazine, and 40 mL of dichloromethane to the cathode chamber. Maintain a constant temperature of 30 degrees Celsius while stirring.

[0044] Electrolysis was performed while maintaining a current density of 100 mA / m 2 The current was stopped when the applied current reached 1.5 F / mol. The reaction solution was adjusted to pH 8-9 using sodium hydroxide solution, the organic phase was separated, the solvent was evaporated, and recrystallization failed to yield 2,2'-bipyrazine.

[0045] Comparative Example 2 An H-type electrolytic cell was used as the reactor, with a DSA mesh electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-324 cation exchange membrane.

[0046] Add 80 mL of 20% sulfuric acid solution to the anode chamber, and add 50 mL of deionized water, 20 mmol of pyrazine, 1 mmol of chromium sulfate, and 40 mL of dichloromethane to the cathode chamber. Maintain a constant temperature of 30 degrees Celsius while stirring.

[0047] Electrolysis was performed while maintaining a current density of 100 mA / m 2 The current was stopped when the applied current reached 1.5 F / mol. The reaction solution was adjusted to pH 8-9 using sodium hydroxide solution, the organic phase was separated, the solvent was evaporated, and recrystallization failed to yield 2,2'-bipyrazine.

[0048] Comparative Example 3 An H-type electrolytic cell was used as the reactor, with a DSA mesh electrode as the anode and a lead alloy electrode as the cathode. The anode chamber and the cathode chamber were separated by a NaFion-324 cation exchange membrane.

[0049] Add 80 mL of 20% sulfuric acid solution to the anode chamber, and add 50 mL of saturated ammonium bisulfate solution, 20 mmol of pyrazine, 1 mmol of chromium sulfate, and 40 mL of dichloromethane to the cathode chamber. Maintain a constant temperature of 30 degrees Celsius while stirring.

[0050] Electrolysis was performed while maintaining a current density of 100 mA / m 2 The current was stopped when the applied current reached 1.5 F / mol. The reaction solution was adjusted to pH 8-9 using sodium hydroxide solution, the organic phase was separated, the solvent was evaporated, and recrystallization failed to yield 2,2'-bipyrazine.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrochemical synthesis method for 2,2'-bipyrazine, characterized in that, Includes the following steps: An H-type electrolytic cell is used as the reactor, and a cation exchange membrane separates the anode chamber and the cathode chamber. Add sulfuric acid or phosphoric acid solution to the anode chamber; A saturated ammonium persulfate solution, pyrazine, a catalyst, and an organic solvent are added to the cathode chamber. The molar ratio of ammonium sulfate, pyrazine, and catalyst in the saturated ammonium persulfate solution is 20-100:20:1-2, and the volume ratio of the saturated ammonium persulfate solution to the organic solvent is 1-2:

1. Maintain constant temperature and stir while electrolyzing. After electrolysis, adjust the pH of the reaction solution in the cathode chamber, separate the organic phase, evaporate the solvent, and recrystallize to obtain 2,2'-bipyrazine. The catalyst includes one or more of chromium sulfate, manganese sulfate, chromium chloride, and manganese chloride.

2. The electrochemical synthesis method according to claim 1, characterized in that, The organic solvent includes one or more of dichloromethane, chloroform, and carbon tetrachloride.

3. The electrochemical synthesis method according to claim 1, characterized in that, The cation exchange membrane is either Nafion-324 or NaFion-424.

4. The electrochemical synthesis method according to claim 1, characterized in that, In the H-type electrolytic cell, the anode is a DSA electrode or a platinum electrode.

5. The electrochemical synthesis method according to claim 1, characterized in that, In the H-type electrolytic cell, the cathode is a lead alloy electrode.

6. The electrochemical synthesis method according to claim 1, characterized in that, The temperature for constant temperature stirring is 20-50 ℃.

7. The electrochemical synthesis method according to claim 1, characterized in that, The current density of the galvanic electrolysis is 100-150 mA / m 2 .

8. The electrochemical synthesis method according to claim 1, characterized in that, Electrolysis ends when the ratio of the charge to the number of moles of pyrazine reaches 1.5-2 F / mol.

9. The electrochemical synthesis method according to claim 1, characterized in that, Adjust the pH of the cathode chamber reaction solution to 8-9 using sodium hydroxide or potassium hydroxide solution.

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