A method for preparing 2,3-dichloropyridine by catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine

Abstract

The present invention provides a method for preparing 2,3-dichloropyridine by catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine. According to the method, 2,3,6-trichloropyridine is subjected to a photocatalytic reaction in a methanol solvent containing a photocatalyst, and then purified to obtain 2,3-dichloropyridine. The photocatalyst adopts a self-made Ni-MOF, which is a metal-organic framework material with a porous structure and a large specific surface area. The high planarity of the large conjugated system of the material gives it special chemical, thermal and optical stability while having a high photocatalytic effect. Under mild conditions, selective catalytic hydrogenation and dehalogenation can be achieved with high conversion rate, selectivity and stability. The method does not require additional hydrogen supply source, and does not require hydrogen to be used as a hydrogen supply source in the reaction, thereby improving safety.

Description

Technical Field

[0001] The present invention relates to the technical field of fine chemical production, and in particular to a method for preparing 2,3-dichloropyridine by catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine. Background Art

[0002] 2,3-Dichloropyridine is mainly used in the synthesis of pesticide intermediates and is an important raw material for the synthesis of chlorantraniliprole, which is a new environmentally friendly pesticide. With the promotion and application of this pesticide, the market demand for 2,3-dichloropyridine has increased significantly. In the existing technology, 2,3-dichloropyridine can be synthesized using 3-aminopyridine as a raw material through chlorination, diazotization, hydrolysis and other steps. However, this method produces a lot of three wastes and can no longer meet the current environmental protection requirements for chemical industry. Therefore, it is of great significance to actively explore new synthesis methods and paths. In recent years, the route of producing 2,3-dichloropyridine using 2,3,6-trichloropyridine as a raw material has been widely used. First, 2,3,6-trichloropyridine is prepared by chlorination, and then 2,3-dichloropyridine is prepared by selective hydrodechlorination. The chlorination process is relatively mature. The selective dechlorination step is an important link that determines the yield and quality of the product. Among them, the catalyst for selective dechlorination is the key to the technology.

[0003] CN107721913B discloses a method for preparing 2,3-dichloropyridine, comprising the following steps: (a) adding methanol, 2,3,6-trichloropyridine, a palladium-carbon catalyst, and magnesium hydroxide into a reaction kettle according to a proportion, stirring, and heating to dissolve to obtain a first solution; (b) heating the first solution to 35-45°C, displacing oxygen, then introducing hydrogen, maintaining the pressure, and reacting for 4-5 hours to obtain a second solution; and (c) filtering, distilling, and separating the second solution to finally obtain 2,3-dichloropyridine.

[0004] CN110003099B discloses a method for preparing 2,3-dichloropyridine and the resulting 2,3-dichloropyridine. In the presence of a solvent and an acid-binding agent, 2,3,6-trichloropyridine is used as a raw material, hydrogen is used as a hydrogen source, a noble metal organic compound is used as a main catalyst, and other organic phosphine compounds are added as co-catalysts. A catalytic hydrogenation reaction is carried out under certain pressure and temperature conditions, followed by post-treatment to obtain 2,3-dichloropyridine.

[0005] CN116102490A discloses a method for preparing 2,3-dichloropyridine, which uses 2,36-trichloropyridine as a raw material, HCOONa and ammonia water as acid-binding agents, and methanol as a solvent. In the presence of a supported catalyst, a hydrogenation reaction is performed to obtain 2,3-dichloropyridine.

[0006] In summary, in the process of preparing 2,3-dichloropyridine using 2,3,6-trichloropyridine as raw material, although the choice of catalyst is different, the catalytic reaction must be carried out under hydrogenation conditions. The main source of hydrogenation is hydrogen, which is flammable and explosive and has certain risks. Summary of the Invention

[0007] To solve the problems existing in the background technology, the present invention provides a method for preparing 2,3-dichloropyridine by catalytic hydrogenation dehalogenation of 2,3,6-trichloropyridine. During the catalytic reaction, no additional hydrogen source is required, and hydrogen gas is not required to participate in the reaction as a hydrogen source, thereby improving safety.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A method for preparing 2,3-dichloropyridine by catalytically hydrogenating and dehalogenating 2,3,6-trichloropyridine, comprising subjecting 2,3,6-trichloropyridine to a photocatalytic reaction in a methanol solvent containing a photocatalyst, and then purifying the resulting 2,3-dichloropyridine.

[0010] The photocatalyst is Ni-MOF, and its preparation method comprises the following steps:

[0011] S1. Prepare 300 ml of a mixed solvent with N, N-dimethylformamide, ethanol, and water in a volume ratio of 14:1:1;

[0012] S2. To 300 ml of the mixed solvent obtained in S1, add 2.2 g of NiCl2·6H2O and 3.22 g of 4,4'-(1,2,4,5-tetrazine-3,6-diyl)dibenzoic acid, stir evenly, pour into a polytetrafluoroethylene-lined autoclave, and stir at 125°C for 24 h to obtain a reaction solution;

[0013] S3. The reaction solution obtained in S2 was cooled to room temperature, the precipitate in the reaction solution was collected by filtration, washed alternately with anhydrous ethanol and deionized water for 3 times, and then vacuum-dried at 60° C. for 12 h to obtain a photocatalyst.

[0014] Preferably, the photocatalytic reaction is carried out under visible light irradiation for 48-96 hours.

[0015] Preferably, the visible light is a 300W xenon lamp light source.

[0016] Preferably, the purification includes distillation, extraction, washing and drying and concentration.

[0017] Preferably, the method specifically includes the following steps:

[0018] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of photocatalyst and disperse evenly.

[0019] After uniform dispersion, irradiate with a 300W xenon lamp light source at 25-55°C for 48-96 hours while stirring to carry out photocatalytic reaction;

[0020] After the photocatalytic reaction is completed, the temperature is lowered, methanol is distilled off, and then extracted with 100 ml of ethyl acetate, washed with 100 ml of deionized water, separated, and the organic phase is dried and concentrated to obtain 2,3-dichloropyridine.

[0021] This application has the following beneficial effects:

[0022] Metal-organic frameworks (MOFs) are a type of coordination polymer that has developed rapidly over the past two decades. They have a three-dimensional pore structure, generally with metal ions as connection points and organic ligands as support to form a spatial 3D extension. They are an important new type of porous material, in addition to zeolites and carbon nanotubes, and are widely used in catalysis, energy storage, and separation. The self-made photocatalyst Ni-MOF of the present invention has a porous structure and a large specific surface area. The high planarity of the large conjugated system of the material gives it exceptional chemical, thermal, and optical stability while also having a high photocatalytic effect. Under mild conditions, it can achieve selective catalytic hydrogenation and dehalogenation with high conversion rate, selectivity, and stability.

[0023] The present invention directly performs a photocatalytic reaction on 2,3,6-trichloropyridine in a methanol solvent containing a photocatalyst Ni-MOF to produce 2,3-dichloropyridine. During the photocatalytic reaction, no additional hydrogen source is required, and hydrogen is directly supplied by the methanol solvent, which reduces the number of operating steps and makes the method simpler overall. At the same time, hydrogen is not required as a hydrogen source to participate in the reaction, which avoids the introduction of flammable and explosive gases and improves safety.

[0024] The photocatalytic reaction conditions of the present invention are 25-55° C., irradiation with a 300W xenon lamp light source for 48-96 hours, and the reaction conditions are mild and easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 , a schematic diagram of the conversion trend of 2,3,6-trichloropyridine in Examples 1-3 and Comparative Examples 1-5 of the present application;

[0026] Figure 2 , schematic diagram of the selectivity trend of 2,3-dichloropyridine in Examples 1-3 of the present application and Comparative Examples 1-5. DETAILED DESCRIPTION

[0027] The present application is further described in detail below with reference to the embodiments.

[0028] Unless otherwise specified, the raw materials used in the Examples and Comparative Examples of this application are all commercially available. For example, TiO2 was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; graphene oxide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; and Ni-MOF-74 was purchased from Xi'an Qiyue Biotechnology Co., Ltd.

[0029] Example 1

[0030] The photocatalyst is Ni-MOF, and its preparation method includes the following steps:

[0031] S1. Prepare 300 ml of a mixed solvent with N, N-dimethylformamide, ethanol, and water in a volume ratio of 14:1:1;

[0032] S2. To 300 ml of the mixed solvent obtained in S1, add 2.2 g of NiCl2·6H2O and 3.22 g of 4,4'-(1,2,4,5-tetrazine-3,6-diyl)dibenzoic acid, stir evenly, pour into a polytetrafluoroethylene-lined autoclave, and stir at 125°C for 24 h to obtain a reaction solution;

[0033] S3. The reaction solution obtained in S2 was cooled to room temperature, the precipitate in the reaction solution was collected by filtration, washed alternately with anhydrous ethanol and deionized water three times, and then vacuum-dried at 60° C. for 12 h to obtain the photocatalyst Ni-MOF.

[0034] The catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine to prepare 2,3-dichloropyridine comprises the following steps:

[0035] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of the photocatalyst Ni-MOF. After uniform dispersion, irradiate with a 300W xenon lamp at 25°C for 96 hours while stirring. After the reaction is complete, cool the mixture and distill off the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to obtain the 2,3-dichloropyridine product.

[0036] The conversion rate of 2,3,6-trichloropyridine was 88.52%, and the selectivity of 2,3-dichloropyridine was 98.24%.

[0037] Example 2

[0038] The photocatalyst is Ni-MOF, and its preparation method is the same as that in Example 1.

[0039] The catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine to prepare 2,3-dichloropyridine comprises the following steps:

[0040] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of the photocatalyst Ni-MOF. After uniform dispersion, irradiate with a 300W xenon lamp at 40°C for 72 hours while stirring. After the reaction is complete, cool the mixture and distill off the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to obtain the 2,3-dichloropyridine product.

[0041] The conversion rate of 2,3,6-trichloropyridine was 92.33%, and the selectivity of 2,3-dichloropyridine was 98.01%.

[0042] Example 3

[0043] The photocatalyst is Ni-MOF, and its preparation method is the same as that in Example 1.

[0044] The catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine to prepare 2,3-dichloropyridine comprises the following steps:

[0045] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of the photocatalyst Ni-MOF. After uniform dispersion, irradiate with a 300W xenon lamp at 55°C for 48 hours while stirring. After the reaction is complete, cool the mixture and distill off the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to obtain the 2,3-dichloropyridine product.

[0046] The conversion rate of 2,3,6-trichloropyridine was 94.53%, and the selectivity of 2,3-dichloropyridine was 97.84%.

[0047] Comparative Example 1

[0048] The catalyst is Co-MOF, and its preparation method is different from that of Example 2, except that NiCl2·6H2O is used in Example 2, while CoCl2·6H2O is used in this comparative example.

[0049] The specific steps include:

[0050] S1. Prepare 300 ml of a mixed solvent with N, N-dimethylformamide, ethanol, and water in a volume ratio of 14:1:1;

[0051] S2. To 300 ml of the mixed solvent obtained in S1, add 2.2 g of CoCl2·6H2O and 3.22 g of 4,4'-(1,2,4,5-tetrazine-3,6-diyl)dibenzoic acid, stir evenly, pour into a polytetrafluoroethylene-lined autoclave, and stir at 125°C for 24 h to obtain a reaction solution;

[0052] S3. The reaction solution obtained in S2 was cooled to room temperature, the precipitate in the reaction solution was collected by filtration, washed alternately with anhydrous ethanol and deionized water three times, and then vacuum dried at 60° C. for 12 h to obtain the catalyst Co-MOF.

[0053] 2,3,6-trichloropyridine was catalytically hydrogenated and dehalogenated to prepare 2,3-dichloropyridine. The method and steps were compared with those in Example 2, except that the photocatalyst Ni-MOF was used in Example 2, while the catalyst Co-MOF was used in this comparative example.

[0054] The specific steps include:

[0055] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of the Co-MOF catalyst. After uniform dispersion, irradiate with a 300W xenon lamp at 40°C for 72 hours while stirring. After the reaction is complete, cool the mixture and distill off the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to yield the 2,3-dichloropyridine product.

[0056] The conversion rate of 2,3,6-trichloropyridine was 72.69%, and the selectivity of 2,3-dichloropyridine was 81.08%.

[0057] Comparative Example 2

[0058] The catalyst is Cu-MOF, and its preparation method is different from that of Example 2, except that NiCl2·6H2O is used in Example 2, while CuCl2·6H2O is used in this comparative example.

[0059] The specific steps include:

[0060] S1. Prepare 300 ml of a mixed solvent with N, N-dimethylformamide, ethanol, and water in a volume ratio of 14:1:1;

[0061] S2. To 300 ml of the mixed solvent obtained in S1, add 2.1 g of CuCl2·6H2O and 3.22 g of 4,4'-(1,2,4,5-tetrazine-3,6-diyl)dibenzoic acid, stir evenly, pour into a polytetrafluoroethylene-lined autoclave, and stir at 125°C for 24 h to obtain a reaction solution;

[0062] S3. The reaction solution obtained in S2 was cooled to room temperature, the precipitate in the reaction solution was collected by filtration, washed alternately with anhydrous ethanol and deionized water three times, and then vacuum-dried at 60° C. for 12 h to obtain the catalyst Cu-MOF.

[0063] 2,3,6-trichloropyridine was catalytically hydrogenated and dehalogenated to prepare 2,3-dichloropyridine. The method and steps were compared with those in Example 2, except that the photocatalyst Ni-MOF was used in Example 2, while the catalyst Cu-MOF was used in this comparative example.

[0064] The specific steps include:

[0065] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of the Cu-MOF catalyst. After uniform dispersion, irradiate with a 300W xenon lamp at 40°C for 72 hours while stirring. After the reaction, cool the mixture and distill off the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to obtain the 2,3-dichloropyridine product.

[0066] The conversion rate of 2,3,6-trichloropyridine was 78.25%, and the selectivity of 2,3-dichloropyridine was 87.31%.

[0067] Comparative Example 3

[0068] 2,3,6-trichloropyridine was catalytically hydrogenated and dehalogenated to prepare 2,3-dichloropyridine. The method and steps were compared with those in Example 2, except that the photocatalyst Ni-MOF was used in Example 2, while the commercially available catalyst TiO2 was used in this comparative example.

[0069] The specific steps include:

[0070] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of TiO2 catalyst. After uniform dispersion, irradiate with a 300W xenon lamp at 40°C for 72 hours while stirring. After the reaction, cool the mixture and distill off the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to obtain the 2,3-dichloropyridine product.

[0071] The conversion rate of 2,3,6-trichloropyridine was 69.89%, and the selectivity of 2,3-dichloropyridine was 90.74%.

[0072] Comparative Example 4

[0073] 2,3,6-trichloropyridine was catalytically hydrogenated and dehalogenated to prepare 2,3-dichloropyridine. The method and steps were compared with those in Example 2, except that a commercially available graphene oxide catalyst was used in this comparative example, while a photocatalyst Ni-MOF was used in Example 2.

[0074] The specific steps include:

[0075] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of graphene oxide catalyst. After uniform dispersion, irradiate with a 300W xenon lamp at 40°C for 72 hours while stirring. After the reaction, cool the mixture and distill to remove the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to obtain the 2,3-dichloropyridine product.

[0076] The conversion rate of 2,3,6-trichloropyridine was 80.42%, and the selectivity of 2,3-dichloropyridine was 91.86%.

[0077] Comparative Example 5

[0078] 2,3,6-trichloropyridine was catalytically hydrogenated and dehalogenated to prepare 2,3-dichloropyridine. The method and steps were compared with those in Example 2, except that the self-made photocatalyst Ni-MOF was used in Example 2, while the commercially available catalyst Ni-MOF-74 was used in this comparative example.

[0079] The specific steps include:

[0080] Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of catalyst. After uniform dispersion, irradiate with a 300W xenon lamp at 40°C for 72 hours while stirring. After the reaction, cool the mixture and distill off the methanol. Extract the mixture with 100ml of ethyl acetate and wash with 100ml of deionized water. After separation, the organic phase is dried and concentrated to obtain the 2,3-dichloropyridine product.

[0081] The conversion rate of 2,3,6-trichloropyridine was 62.48%, and the selectivity of 2,3-dichloropyridine was 83.59%.

[0082] Comparative results analysis

[0083] Analyze Examples 1-3 and combine Figure 1-Figure 2 It can be seen that this application uses a homemade photocatalyst Ni-MOF to carry out a photocatalytic reaction of 2,3,6-trichloropyridine in a methanol solvent containing the homemade photocatalyst Ni-MOF. The reaction conditions are 25-55°C and irradiation with a 300W xenon lamp light source for 48-96 hours, and finally the 2,3-dichloropyridine product is purified; the conversion rate of 2,3,6-trichloropyridine is above 88.52%, and the selectivity of 2,3-dichloropyridine is above 97.84%.

[0084] Analyze Example 2 and Comparative Examples 1-2 and combine Figure 1-Figure 2It can be seen that compared with Example 2 using the homemade photocatalyst Ni-MOF, Comparative Examples 1-2 use the same preparation method as Example 2 to obtain catalysts Co-MOF and Cu-MOF, respectively, and the homemade catalysts Co-MOF and Cu-MOF are respectively applied to the same method as Example 2 for preparing 2,3-dichloropyridine by catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine, and finally purified to obtain 2,3-dichloropyridine product; the results are as follows: the conversion rate of 2,3,6-trichloropyridine in Comparative Example 1 is 72.69%, and the selectivity of 2,3-dichloropyridine is 81.08%. The conversion rate of 2,3,6-trichloropyridine in Comparative Example 2 is 78.25%, and the selectivity of 2,3-dichloropyridine is 87.31%, which are significantly lower than those in Example 2. This shows that the photocatalyst Ni-MOF obtained by the catalyst preparation method of the present invention can significantly improve the photocatalytic reaction effect, making the photocatalytic reaction effect significantly better than other metal-organic framework materials (Co-MOF, Cu-MOF).

[0085] Analyze Example 2, Comparative Examples 3-4 and combine Figure 1-Figure 2 It can be seen that compared with Example 2 using the homemade photocatalyst Ni-MOF, Comparative Examples 3-4 respectively use existing commercially available TiO2 catalysts and graphene oxide catalysts, and are applied to the same method as Example 2 for preparing 2,3-dichloropyridine by catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine, and finally purified to obtain 2,3-dichloropyridine product; the results show that the conversion rate of 2,3,6-trichloropyridine in Comparative Example 3 is 69.89%, and the selectivity of 2,3-dichloropyridine is 90.74%, and the conversion rate of 2,3,6-trichloropyridine in Comparative Example 4 is 80.42%, and the selectivity of 2,3-dichloropyridine is 91.86%, which are significantly lower than those in Example 2, indicating that the photocatalyst Ni-MOF obtained by the catalyst preparation method of the present invention can significantly improve the photocatalytic reaction effect, making the photocatalytic reaction effect significantly better than the existing commercially available TiO2 catalyst and graphene oxide catalyst.

[0086] Analyze Example 2 and Comparative Example 5 and combine Figure 1-Figure 2 It can be seen that compared with Example 2 using the homemade photocatalyst Ni-MOF, Comparative Example 5 uses the existing commercially available catalyst Ni-MOF-74, and is applied to the same method as Example 2 for preparing 2,3-dichloropyridine by catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine, and finally purified to obtain a 2,3-dichloropyridine product; the results show that the conversion rate of 2,3,6-trichloropyridine in Comparative Example 5 is 62.48%, and the selectivity of 2,3-dichloropyridine is 83.59%, which are significantly lower than those in Example 2, indicating that the photocatalyst Ni-MOF obtained by the catalyst preparation method of the present invention can significantly improve the photocatalytic reaction effect, making the photocatalytic reaction effect significantly better than the existing commercially available catalyst Ni-MOF-74.

Claims

1. A method for preparing 2,3-dichloropyridine by catalytic hydrogenation and dehalogenation of 2,3,6-trichloropyridine, characterized in that: The following steps are involved: Dissolve 15g of 2,3,6-trichloropyridine in 100ml of methanol, then add 15g of triethylamine and 0.75g of photocatalyst and disperse evenly. After uniform dispersion, irradiate with a 300W xenon lamp light source at 25-55°C for 48-96 hours while stirring to carry out photocatalytic reaction; After the photocatalytic reaction is completed, the temperature is lowered, methanol is distilled off, and then extracted with 100 ml of ethyl acetate, washed with 100 ml of deionized water, separated, and the organic phase is dried and concentrated to obtain 2,3-dichloropyridine; The photocatalyst is Ni-MOF, and its preparation method comprises the following steps: S1. Prepare 300 ml of a mixed solvent with N,N-dimethylformamide, ethanol, and water in a volume ratio of 14:1:1; S2. To 300 ml of the mixed solvent obtained in S1, add 2.2 g of NiCl2·6H2O and 3.22 g of 4,4'-(1,2,4,5-tetrazine-3,6-diyl)dibenzoic acid, stir evenly, pour into a polytetrafluoroethylene-lined autoclave, and stir at 125°C for 24 h to obtain a reaction solution. S3. The reaction solution obtained in S2 was cooled to room temperature, the precipitate in the reaction solution was collected by filtration, washed alternately with anhydrous ethanol and deionized water for 3 times, and then vacuum-dried at 60° C. for 12 h to obtain a photocatalyst.

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