The invention relates to 4, 4apos; process for the preparation of-dipyridyl

Abstract

The invention belongs to the field of synthesis of organic fine chemicals, and discloses a preparation method of 4, 4 '-dipyridyl, which comprises the following steps: by taking pyridine as a raw material, metal sodium as a catalyst and sulfolane as a reaction solvent, mixing the metal sodium and the sulfolane to completely dissolve the metal sodium in a nitrogen atmosphere; after the metal sodium is completely dissolved, pyridine is added, air and / or oxygen are / is introduced for oxidation, and 4, 4 '-dipyridyl is obtained through reaction. According to the method, no extra cocatalyst or initiator is needed, the catalytic system has good catalytic activity, the reaction condition is mild, no harsh reaction conditions such as water-free, oxygen-free and low-temperature conditions are needed, the excellent yield can be obtained, and the product purity is high. The environment-friendly and safe aprotic polar solvent sulfolane is used, has good solvent property and coordination capability on metal sodium, is beneficial to dissolution and dispersion of the metal sodium and improves the catalytic activity, and the sulfolane has small harm to a human body.

Description

Technical Field

[0001] The invention belongs to the field of organic fine chemical synthesis, and specifically relates to a method for preparing 4,4'-bipyridine. Background Art

[0002] Global energy consumption and environmental pollution are becoming increasingly serious, and it is urgent for humans to develop efficient and stable electrochemical energy storage systems to make full use of renewable clean energy. As an ideal energy storage method, electrochemical energy storage technology has the advantages of low cost, high voltage, good reversibility, and adjustable structure compared with the high cost, high toxicity, and low electrochemical activity of traditional inorganic flow battery materials. In particular, organic flow batteries are a new type of large-capacity electrochemical energy storage device, and the most notable feature is that they can be stored in large quantities. 4,4'-Bipyridine is an important intermediate material in the electrolyte of organic flow batteries, which can significantly improve the charge and discharge performance of organic flow batteries. At the same time, 4,4'-Bipyridine is also widely used in the synthesis of drugs and agricultural chemicals.

[0003] The direct one-step dehydrogenation coupling method using cheap and readily available pyridine to synthesize 4,4'-bipyridine is a short and low-cost synthetic route, and is also one of the main ways to industrially produce 4,4'-bipyridine. At present, there are two main production processes for 4,4'-bipyridine: alkali metal catalyzed pyridine reaction to produce 4,4'-bipyridine (GB956854A, CN1158852A) and low-temperature sodium ammonia catalyzed pyridine salt oxidation to produce 4,4'-bipyridine (CA771157A).

[0004] The above two process methods have the following disadvantages: the alkali metal-catalyzed pyridine reaction to generate 4,4'-bipyridine requires an initiator or a co-catalyst to improve the catalytic activity of the alkali metal, and the complex components are difficult to remove in the product, which increases the cost and affects the performance of the product in use; the product yield is low, there are many bipyridine by-products, and the separation and purification of isomers is complicated; the hexamethylphosphoric triamide used in CN1158852A is a carcinogenic reagent and has potential safety hazards to the human body. Low-temperature sodium ammonia catalyzes the oxidation of pyridine salts to generate 4,4'-bipyridine, which needs to be carried out at a low temperature of -40°C. The conditions are relatively harsh, the reaction steps are complicated, the operating cost is high, the by-products are more, and the product yield is low.

[0005] Therefore, developing a process technology that can prepare high-purity 4,4'-bipyridine under mild and green conditions is the key to solving its industrial application. Summary of the invention

[0006] The purpose of the present invention is to solve the disadvantages of harsh reaction conditions, low product purity, low yield, complicated steps and potential safety hazards in the existing 4,4'-bipyridine synthesis process, and to provide a new preparation method of 4,4'-bipyridine. The method is carried out under green and mild reaction conditions and can obtain high-purity 4,4'-bipyridine with high yield.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for preparing 4,4'-bipyridine comprises: using pyridine as a raw material, sodium metal as a catalyst, and sulfolane as a reaction solvent, mixing sodium metal and sulfolane under a nitrogen atmosphere to completely dissolve the sodium metal; after the sodium metal is completely dissolved, adding pyridine, introducing air and / or oxygen for oxidation, and reacting to obtain 4,4'-bipyridine.

[0009] The reaction formula is:

[0010]

[0011] The molar ratio of metallic sodium to pyridine is 1:1 to 1:5, preferably 1:1 to 1:3, more preferably 1:2 to 1:3, and most preferably 1:2.

[0012] The mass ratio of pyridine to sulfolane is 1:10 to 1:2, preferably 1:5 to 1:2.

[0013] After introducing air and / or oxygen, the reaction temperature is 10-50°C, preferably 20-30°C, and most preferably 30°C; the reaction time is 6-24h, preferably 12-18h.

[0014] As a further preferred technical scheme of the preparation method of 4,4'-bipyridine of the present invention, it also includes: mixing metallic sodium and cyclopentane sulfone under a nitrogen atmosphere to completely dissolve the metallic sodium; after the metallic sodium is completely dissolved, adding pyridine, introducing air and / or oxygen for oxidation, and reacting to obtain 4,4'-bipyridine; after the reaction is completed, adding ethanol to quench the reaction, centrifuging and filtering, adding saturated brine and ethyl acetate to the filtrate for extraction, taking an organic layer, and concentrating the organic layer under reduced pressure to obtain a crude product, and subjecting the crude product to silica gel column chromatography to separation and purification to obtain 4,4'-bipyridine.

[0015] The eluent of the silica gel column chromatography is petroleum ether:ethyl acetate in a volume ratio of 5:1 to 20:1.

[0016] Specifically, a method for preparing 4,4'-bipyridine includes: adding metallic sodium and cyclopentane sulfone into a reaction device, and adding pyridine after the metallic sodium is dissolved, and reacting to obtain 4,4'-bipyridine.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention does not require additional co-catalysts or initiators, the catalytic system has good catalytic activity, the reaction conditions are mild, and harsh reaction conditions such as anhydrous and oxygen-free, low temperature, etc. are not required. Excellent yields can be obtained, and the product purity is high.

[0019] (2) The present invention uses the green and safe non-protonic polar solvent sulfolane, which has good solubility and coordination ability for metallic sodium, is conducive to the dissolution and dispersion of metallic sodium, improves the catalytic activity, and sulfolane has little harm to the human body.

[0020] (3) The reaction equipment of the present invention is simple and has important industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of 4,4'-bipyridine.

[0022] Figure 2 This is the carbon NMR spectrum of 4,4'-bipyridine. DETAILED DESCRIPTION

[0023] In order to further understand the purpose, content and advantages of the present invention, the technical scheme of the present invention is now described in detail through specific implementation methods, but it is not limited to the following examples, and the reaction conditions should be changed according to actual conditions. Unless otherwise specified, the reagents and instruments used in the following examples are commercially available products.

[0024] Example 1

[0025] Weigh 2.5g of sodium metal, 90g of sulfolane and 18g of pyridine. Under a nitrogen atmosphere, mix sodium metal and sulfolane in a three-necked flask to completely dissolve sodium metal; when sodium metal is completely dissolved, add pyridine, introduce air into the reaction system, and react on a heating plate at 30°C for 18h. After the reaction system cools to room temperature, add ethanol to quench the reaction. The reaction system is centrifuged (the centrifuge speed is 1200rpm) and filtered to obtain a filtrate (the filtrate is analyzed by gas chromatography to calculate the conversion rate of pyridine and the selectivity of 4,4'-bipyridine, see Table 1), 100mL of saturated salt water and 50mL of ethyl acetate are added to the filtrate for extraction, and the organic phase is taken. The organic phase is concentrated under reduced pressure to obtain a crude product, and the crude product is subjected to silica gel column chromatography (200-300 mesh silica gel), and the eluent is petroleum ether: ethyl acetate in a volume ratio of 5:1-20:1, and 4,4'-bipyridine is separated and purified to obtain a purity of 99.8%.

[0026] The H NMR spectrum of 4,4'-bipyridine is shown in Figure 1 , see C NMR spectrum Figure 2 . 1H NMR (400 MHz, CDCl 3 )δ:8.77(d,J=6.1Hz,4H),7.57(d,J=6.1Hz,4H). 13 C NMR (101 MHz, CDCl 3 )δ:150.69,145.58,121.46.

[0027] Example 2

[0028] Weigh 2.5g of sodium metal, 90g of hexamethylphosphoric triamide and 18g of pyridine. Under a nitrogen atmosphere, mix sodium metal and hexamethylphosphoric triamide in a three-necked flask. When the sodium metal is completely dissolved, add pyridine, and introduce air into the reaction system. React on a 30°C heating plate for 18h. When the reaction system cools to room temperature, add ethanol to quench the reaction. Centrifuge and filter the reaction system to obtain a filtrate. Perform gas chromatography on the filtrate to calculate the conversion rate of pyridine and the selectivity of 4,4'-bipyridine, as shown in Table 1.

[0029] Table 1: Effect of solvent on feedstock conversion and product selectivity

[0030] Solvents Conversion rate (%) Selectivity (%) Example 1 Sulfolane 91.8 99.4 Example 2 Hexamethylphosphoric acid triamide 36.8 79.7

[0031] As shown in Table 1, although the reaction activity is certain when hexamethylphosphoric triamide is used as a solvent, the product yield is not as good as that when sulfolane is used as a solvent. It is speculated that sulfolane, as an excellent aprotic polar solvent, has excellent solubility and coordination ability for alkali metals, which is beneficial to the dissolution and dispersion of metallic sodium and improves the catalytic activity.

[0032] Example 3

[0033] Weigh 2.5g of sodium metal, 90g of sulfolane and 9g of pyridine. Under a nitrogen atmosphere, mix 2.5g of sodium metal and 90g of sulfolane in a three-necked flask. When the sodium metal is completely dissolved, add 9g of pyridine, introduce air into the reaction system, and react on a 30°C heating plate for 18h. After the reaction system cools to room temperature, add ethanol to quench the reaction. The reaction system is centrifuged (the centrifuge speed is 1200rpm) and filtered to obtain a filtrate. The filtrate is analyzed by gas chromatography to calculate the conversion rate of pyridine and the selectivity of 4,4'-bipyridine, as shown in Table 2.

[0034] Example 4

[0035] Weigh 2.5g of sodium metal, 90g of sulfolane and 27g of pyridine. Under a nitrogen atmosphere, mix 2.5g of sodium metal and 90g of sulfolane in a three-necked flask. When the sodium metal is completely dissolved, add 27g of pyridine, pass air into the reaction system, and react on a 30°C heating plate for 18h. After the reaction system cools to room temperature, add ethanol to quench the reaction. The reaction system is centrifuged (the centrifuge speed is 1200rpm) and filtered to obtain a filtrate. The filtrate is analyzed by gas chromatography to calculate the conversion rate of pyridine and the selectivity of 4,4'-bipyridine, as shown in Table 2.

[0036] Table 2: Effect of the reaction molar ratio of sodium and pyridine on raw material conversion and product selectivity

[0037] Sodium:pyridine (molar ratio) Conversion rate (%) Selectivity (%) Example 3 1:1 65.7 97.7 Example 1 1:2 91.8 99.4 Example 4 1:3 91.2 91.9

[0038] As shown in Table 2, when the reaction molar ratio of sodium to pyridine is 1:2, excellent conversion rate and selectivity are achieved. When the reaction molar ratio of sodium to pyridine is 1:3, other by-products are generated because the amount of pyridine is much larger than the amount of metallic sodium required for reaction.

[0039] Example 5

[0040] Weigh 2.5g of sodium metal, 90g of sulfolane and 18g of pyridine. Under a nitrogen atmosphere, mix sodium metal and sulfolane in a three-necked flask. When the sodium metal is completely dissolved, add pyridine, pass air into the reaction system, and react on a 40°C heating plate for 18 hours. When the reaction system cools to room temperature, add ethanol to quench the reaction. Centrifuge the reaction system (the centrifuge speed is 1200rpm) and filter to obtain a filtrate. Perform gas chromatography on the filtrate to calculate the conversion rate of pyridine and the selectivity of 4,4'-bipyridine, as shown in Table 3.

[0041] Example 6

[0042] Weigh 2.5g of sodium metal, 90g of sulfolane and 18g of pyridine. Under a nitrogen atmosphere, mix sodium metal and sulfolane in a three-necked flask. When the sodium metal is completely dissolved, add 18g of pyridine, introduce air into the reaction system, and react on a 50°C heating plate for 18h. After the reaction system cools to room temperature, add ethanol to quench the reaction. Centrifuge the reaction system (the centrifuge speed is 1200rpm) and filter to obtain a filtrate. Perform gas chromatography on the filtrate to calculate the conversion rate of pyridine and the selectivity of 4,4'-bipyridine, as shown in Table 3.

[0043] Table 3: Effect of reaction temperature on feedstock conversion and product selectivity

[0044]

[0045]

[0046] As shown in Table 3, when the reaction temperature increases from 20°C to 50°C, the conversion rate of pyridine does not increase significantly, and the selectivity of 4,4'-bipyridine decreases significantly, indicating that other by-products are generated. From the perspective of industrial cost and atom economy, 30°C is the optimal reaction temperature.

[0047] The above describes the optional embodiments of the present invention to teach those skilled in the art how to implement and reproduce the present invention. The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art. In order to teach the scheme of the present invention, some conventional technical aspects have been simplified and omitted. Those skilled in the art should understand that variations arising from this aspect are all within the scope of protection of the present invention.

Claims

1. A method for preparing 4,4'-bipyridine, characterized in that: include: Using pyridine as a raw material, sodium metal as a catalyst, and sulfolane as a reaction solvent, sodium metal and sulfolane are mixed under a nitrogen atmosphere to completely dissolve the sodium metal; After the metallic sodium is completely dissolved, pyridine is added, and air and / or oxygen are introduced for oxidation to obtain 4,4'-bipyridine.

2. The method for preparing 4,4'-bipyridine according to claim 1, characterized in that: The molar ratio of the metallic sodium to the pyridine is 1:1 to 1:

5.

3. The method for preparing 4,4'-bipyridine according to claim 1 or 2, characterized in that: The molar ratio of the metallic sodium to the pyridine is 1:1 to 1:

3.

4. The method for preparing 4,4'-bipyridine according to claim 3, characterized in that: The molar ratio of the metallic sodium to the pyridine is 1:2 to 1:

3.

5. The method for preparing 4,4'-bipyridine according to claim 1, characterized in that: The mass ratio of pyridine to sulfolane is 1:10 to 1:

2.

6. The method for preparing 4,4'-bipyridine according to claim 1 or 5, characterized in that: The mass ratio of pyridine to sulfolane is 1:5 to 1:

2.

7. The method for preparing 4,4'-bipyridine according to claim 1, characterized in that: After introducing air and / or oxygen, the reaction temperature is 10-50° C. and the reaction time is 6-24 hours.

8. The method for preparing 4,4'-bipyridine according to claim 1 or 7, characterized in that: After the air and / or oxygen is introduced, the reaction temperature is 20-30° C. and the reaction time is 12-18 hours.

9. The method for preparing 4,4'-bipyridine according to claim 1, characterized in that: After the reaction is completed, ethanol is added to quench the reaction, centrifuge and filter, saturated brine and ethyl acetate are added to the filtrate for extraction, and the organic layer is taken and concentrated under reduced pressure to obtain a crude product. The crude product is subjected to silica gel column chromatography to separate and purify 4,4'-bipyridine.

10. The method for preparing 4,4'-bipyridine according to claim 9, characterized in that: The eluent for silica gel column chromatography is petroleum ether:ethyl acetate in a volume ratio of 5:1 to 20:1.

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