A catalyst for synthesizing 2,3-dichloropyridine, a preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and relates to a catalyst and a preparation method and application thereof. Specifically, the catalyst is a phosphorus-doped cobalt-rhodium composite oxide catalyst, and the preparation method is that different atomic ratios of Rh and P are doped in Co3O4 by using a coprecipitation method and a hydrothermal method. The method for preparing 2,3-dichloropyridine by using the catalyst has simple process and mild reaction conditions, can effectively control excessive dechlorination of polychloropyridine, reduce generation of by-products, the conversion rate of raw materials can reach 98%, the selectivity of the target product 2,3-dichloropyridine reaches 95%, and the mild reaction conditions have low requirements on equipment and small demand on energy, and are suitable for industrialized production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalyst technology, and particularly relates to a catalyst and a preparation method and application thereof, wherein the catalyst is a phosphorus-doped cobalt-rhodium composite oxide catalyst. BACKGROUND

[0002] 2,3-dichloropyridine (molecular formula: C5H3Cl2N, CAS: 2402-77-9) is a white to light yellow solid, slightly soluble in water, with a melting point of 65-69℃ and a boiling point of 192.5℃ (at normal pressure). As an important fine chemical intermediate, it is widely used in the fields of medicine and pesticide. In the field of pesticide, 2,3-dichloropyridine is a key intermediate of novel insecticides such as chlorantraniliprole, cyantraniliprole, cyclaniliprole and tetraniliprole. In particular, chlorantraniliprole has a unique mechanism of action, with characteristics of broad spectrum, high efficiency, low toxicity, high specificity, environmental friendliness, etc., and no cross-resistance with other insecticides, which makes it have a very wide application and development prospect. With the wide use of chlorantraniliprole at home and abroad, the demand for 2,3-dichloropyridine will increase significantly, and its synthesis method has also attracted much attention.

[0003] At present, the synthesis methods of 2,3-dichloropyridine reported in the literature mainly include 2,3,6-trichloropyridine reduction method, 2-chloropyridine synthesis method, 3-chloropyridine synthesis method, 2-chloro-3-nitro-pyridine synthesis method, and 3-aminopyridine synthesis method.

[0004] 1) 2,3,6-trichloropyridine reduction method

[0005] JP1193246, CN102153507B and CN103145609B disclose that 2,3-dichloropyridine is obtained by using 2,3,6-trichloropyridine as raw material, using palladium, platinum, Raney nickel, Raney copper, etc. as catalyst, using hydrogen gas, formic acid, etc. as hydrogen source, and under the action of acid-binding agent. The problem is that palladium, platinum, etc. are easily poisoned and lose activity in the dechlorination environment, which leads to rapid decline of the conversion rate of 2,3,6-trichloropyridine and the selectivity of 2,3-dichloropyridine, and seriously affects the reaction;

[0006] CN108380208B discloses a preparation method of Pd-Mg / C catalyst for catalytic hydrogenation of 2,3,6-trichloropyridine to 2,3-dichloropyridine. The catalyst preparation process realizes high dispersion of nano metal on the carrier, adjusts the acid-base state of the catalyst surface through the aid Mg, improves the selectivity of 2,3-dichloropyridine to a certain extent, enhances the interaction between noble metal palladium and the carrier, has good stability, improves the reuse performance of the catalyst, and is conducive to reducing production cost. However, the catalyst has high noble metal content and high water content, the active components of the catalyst are seriously lost under stirring state in the catalytic reaction, and the selectivity of the catalyst for 2,3-dichloropyridine is not high (76%), which still has room for further improvement.

[0007] CN110003099B discloses a method for preparing 2,3-dichloropyridine by homogeneous catalysis. In the presence of a solvent and an acid-binding agent, 2,3,6-trichloropyridine is used as raw material, hydrogen is used as hydrogen source, tris(triphenylphosphine)rhodium chloride is used as main catalyst, and an organic phosphine compound is added as cocatalyst. Under certain pressure and temperature conditions, catalytic hydrogenation reaction is carried out, and after treatment, 2,3-dichloropyridine is obtained. The conversion rate of 2,3,6-trichloropyridine is as high as 99%, and the selectivity of 2,3-dichloropyridine is more than 94%. However, the separation, recovery and regeneration process of the catalyst in homogeneous catalysis is complex, the central metal of the homogeneous complex catalyst is mainly noble metal, the cost of the catalyst is very high, and the non-mild reaction conditions can easily cause changes in the structure of the catalyst, resulting in loss of catalytic effect.

[0008] 2) 2-chloropyridine synthesis method

[0009] There are few reports on the synthesis of 2,3-dichloropyridine from 2-chloropyridine. US5380862A and EP591624A1 have reported this method. First, 2-chloropyridine is etherified under alkaline conditions to obtain 2-butoxy pyridine, and then chlorinated to obtain a mixture of 3-chloro 2-butoxy pyridine and 5-chloro 2-butoxy pyridine. Finally, phosphorus oxychloride is used for chlorination to obtain a mixture of 2,3-dichloropyridine and 2,5-dichloropyridine. The separation of the product is difficult, and the total yield is not ideal, which is not suitable for large-scale production.

[0010] 3) 3-chloropyridine synthesis method

[0011] There are many reports on the synthesis of 2,3-dichloropyridine from 3-chloropyridine as starting material, mainly including the following two routes:

[0012] D. Hebel et al. (see Journal of Organic Chemistry (1988), 53(5): 1123-1125) disclosed that 3-chloropyridine was reacted with acetyl hypofluorite to form a pair of resonance forms with N-F bond, then by removing fluorine, dichloromethane chlorination, selectively forming 2,3-dichloropyridine with a yield of 80%. This method is difficult to be industrialized because the electrophilic substitution is not easy to proceed due to the insufficient activity of the 3-position of pyridine, and the starting material 3-chloropyridine is expensive.

[0013] S. Choppin et al. (see European Journal of Organic Chemistry (2001), 3: 603-606) disclosed that 3-chloropyridine was selectively activated at the 2-position carbon atom by using dimethylaminoethanol lithium and butyl lithium as reagents and n-hexane as solvent, then using hexachloroethane as chlorination reagent and tetrahydrofuran as solvent to obtain 2,3-dichloropyridine with a yield of 60%. This method is not suitable for industrialization because the reagents butyl lithium and hexachloroethane are expensive and the yield is not high.

[0014] 4) Synthesis of 2-chloro-3-nitropyridine

[0015] There are few reports on the synthesis of 2,3-dichloropyridine using 2-chloro-3-nitropyridine as starting material.

[0016] US62242631B and E. Bay et al. (Journal of Organic Chemistry (1988), 53(12): 2858-2859) respectively disclosed the synthesis of 2,3-dichloropyridine from 2-chloro-3-nitropyridine using phenyl tetrachlorophosphonium and phenyldichlorophosphonium as chlorination reagents. This method is not suitable for industrialization because the reagents are expensive and difficult to prepare.

[0017] 5) Synthesis of 3-aminopyridine

[0018] CN1910152B, CN1807414A, WO2005070888A2, US20070161797A1, CN100357272C, US20100160641A1 and CN101302190B respectively disclose that 3-aminopyridine is chlorinated with concentrated hydrochloric acid to generate 2-chloro-3-aminopyridine, and then 2-chloro-3-aminopyridine is subjected to diazotization and Sandmeyer chlorination to obtain 2,3-dichloropyridine, and cuprous chloride is used as a catalyst for the chlorination reaction. This synthesis method needs to go through multiple steps of chlorination, diazotization and chlorination, and the production cost of 3-aminopyridine as the starting material is also high. Moreover, the diazotization and chlorination operations will generate a large amount of waste liquid, which seriously pollutes the environment and restricts the industrial production scale of the product.

[0019] In addition, CN107266357B discloses a preparation method of a nano IrO2-ZnO-MnO2 composite catalyst for catalyzing the hydrogenation of polychloropyridine to produce 2,3-dichloropyridine. The catalyst has the advantages of high conversion rate and selectivity, stable product quality, and simple production operation, and overcomes the shortcomings of the existing synthesis method that the quality of 2,3-dichloropyridine obtained is unstable and must be subjected to multiple rectifications to make the quality of 2,3-dichloropyridine reach the standard. However, the preparation process of the catalyst is complex and involves electrolytic manganese plating. In an acidic aqueous environment, hydrogen is easily electrolyzed, which is dangerous. In addition, the uniformity of the electrode plate material will result in poor stability of the prepared catalyst, and compared with the traditional calcination preparation method, the electrolytic equipment is complex and the cost is high.

[0020] In summary, although the existing preparation process is relatively mature, the catalysts used for the catalytic hydrogenation reaction of chlorinated pyridine mostly have the disadvantages of high preparation cost, low catalytic performance, poor stability, and difficult post-reaction treatment. In addition, most of the processes for generating chlorinated pyridine are pyridine chlorination. This process has poor selectivity for 2,3,6-trichloropyridine, and there are a large amount of by-products such as 2,3,5-trichloropyridine, 2,3,4-trichloropyridine, tetrachloropyridine (including 2,3,5,6-tetrachloropyridine, 2,3,4,5-tetrachloropyridine and 2,3,4,6-tetrachloropyridine) and pentachloropyridine. The separation of 2,3,6-trichloropyridine, 2,3,4-trichloropyridine, 2,3,5-trichloropyridine and tetrachloropyridine is difficult, which results in a very low yield of 2,3,6-trichloropyridine and high production cost. Therefore, it is particularly important to develop a catalyst for efficiently catalyzing the hydrogenation of polychloropyridine mixture to prepare 2,3-dichloropyridine. SUMMARY

[0021] Problem to be solved by the invention

[0022] The application provides a novel catalyst and a preparation method and application thereof, and the catalyst is a phosphorus-doped cobalt-rhodium composite oxide catalyst; the catalyst can improve raw material conversion rate and product selectivity in the preparation of 2,3-dichloropyridine through dechlorination hydrogenation of polychloropyridine; the preparation method of the catalyst and the method for preparing 2,3-dichloropyridine by using the catalyst are simple in process, can reduce production cost, can stably improve the yield of 2,3-dichloropyridine to more than 90%, and can keep the content of 2,3-dichloropyridine at more than 99% after reaction and separation treatment, so that the purity of the intermediate meets the qualified requirements.

[0023] Solution to the problem

[0024] To solve the above problems, the application provides a catalyst, which has a chemical formula of Rh x P y CoO a ;

[0025] x represents 1000 times of the atomic ratio of Rh to Co, x is 1-10, preferably 3-8;

[0026] y represents the atomic ratio of P to Co, y is 0.1-1, preferably 0.3-0.5;

[0027]

[0028] Preferably, the atomic ratio of Rh to P to Co in the catalyst is 0.001:0.1:1.0-0.01:1.0:1.0, preferably 0.003:0.3:1.0-0.008:0.5:1.0.

[0029] Preferably, x is 4-7.

[0030] More preferably, x is 4, 5, 6 or 7.

[0031] Preferably, y is 0.4.

[0032] In another aspect, the application provides a preparation method of the above catalyst, and the method dopes Rh and P with different atomic ratios into Co3O4 by using a coprecipitation method and a hydrothermal method, and the method comprises the following steps:

[0033] 1) mixing rhodium salt or a hydrate thereof, a phosphate, a cobalt salt or a hydrate thereof with water, then adding a base or an aqueous solution thereof to obtain a colloidal substance, stirring, then performing a hydrothermal reaction, cooling after the reaction, filtering, washing the filter cake, and obtaining a solid product;

[0034] 2) drying and calcining the solid product to obtain the catalyst.

[0035] The aforementioned hydrothermal reaction refers to a reaction using a hydrothermal method, which is a method of dissolving and recrystallizing a powder using water as a solvent in a sealed pressure vessel. In the present application, the hydrothermal reaction is a process reaction of crystal growth of the aforementioned gel in a sealed container under isothermal and constant volume conditions.

[0036] Preferably, the rhodium salt in step 1) is rhodium dicarbonyl acetylacetone, rhodium chloride, tris(triphenylphosphine)rhodium chloride or tris(triphenylphosphine)carbonyl hydride, more preferably rhodium chloride.

[0037] Preferably, the cobalt salt in step 1) is cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt halide or cobalt perhalogenate, more preferably cobalt nitrate.

[0038] Preferably, the phosphate salt in step 1) is ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, ammonium phosphate, sodium phosphate or potassium phosphate, more preferably diammonium hydrogen phosphate.

[0039] Preferably, the base in step 1) is an inorganic base or an organic base, preferably an inorganic base, more preferably ammonia.

[0040] Preferably, the mixing in step 1) is carried out at room temperature, preferably under stirring at room temperature.

[0041] Preferably, the pH value of the gel in step 1) is 8-12, more preferably 9-10.

[0042] Preferably, the stirring in step 1) is carried out at room temperature, preferably for 12-36 h at room temperature.

[0043] Preferably, the temperature of the hydrothermal reaction in step 1) is 70-120°C, more preferably 80-100°C.

[0044] Preferably, the temperature of the cooling in step 1) is room temperature.

[0045] Preferably, the target pH value of the washing in step 1) is neutral.

[0046] Preferably, the temperature of the drying in step 2) is 50-80°C.

[0047] Preferably, the calcination in step 2) is carried out under temperature rising conditions; preferably, the rate of the temperature rising is 1-5°C / min, preferably 1.5-3°C / min.

[0048] Preferably, the temperature of the calcination in step 2) is 300-600°C, more preferably 400-550°C.

[0049] Preferably, the time for the calcination in step 2) is 2-6h, more preferably 3-5h.

[0050] In another aspect, the present application provides a catalyst prepared by the above preparation method.

[0051] In another aspect, the present application provides an application of the above catalyst in a dechlorination hydrogenation reaction.

[0052] Preferably, the raw material of the dechlorination hydrogenation reaction is a compound with chlorine atoms substituted on an aromatic ring or a heteroaromatic ring.

[0053] More preferably, the dechlorination hydrogenation reaction is a reaction for preparing 2,3-dichloropyridine from polychloropyridine.

[0054] Further preferably, the polychloropyridine is at least one selected from 2,3,6-trichloropyridine, 2,3,5-trichloropyridine, 2,3,4-trichloropyridine, 2,3,4,5-tetrachloropyridine, 2,3,4,6-tetrachloropyridine, 2,3,5,6-tetrachloropyridine and pentachloropyridine.

[0055] In another aspect, the present application provides a preparation method of 2,3-dichloropyridine, which comprises the following steps: using polychloropyridine as a raw material, hydrogen as a hydrogen source, and performing a hydrogenation reaction in the presence of the above catalyst, a solvent and an acid-binding agent to obtain 2,3-dichloropyridine.

[0056] Preferably, the polychloropyridine is at least one selected from 2,3,6-trichloropyridine, 2,3,5-trichloropyridine, 2,3,4-trichloropyridine, 2,3,4,5-tetrachloropyridine, 2,3,4,6-tetrachloropyridine, 2,3,5,6-tetrachloropyridine and pentachloropyridine.

[0057] Preferably, the solvent is water, an organic solvent or a mixture of the two, preferably water, alcohol or an alcohol aqueous solution, more preferably water, methanol or a methanol aqueous solution, further preferably methanol or a methanol aqueous solution.

[0058] Preferably, the acid-binding agent is an inorganic base or an organic base, preferably an organic base, more preferably an amine, further preferably triethylamine.

[0059] Preferably, the amount of the catalyst relative to the polychloropyridine is 0.1wt%-2wt%, more preferably 1wt%.

[0060] Preferably, the molar ratio of the acid-binding agent to the polychloropyridine is 0.2:1-4:1, more preferably 2:1.

[0061] Preferably, the mass ratio of the solvent to the polychloropyridine is 1:1-5:1, more preferably 4:1.

[0062] Preferably, the hydrogen pressure of the hydrogenation reaction is 0.1-2.5 MPa, more preferably 2 MPa.

[0063] Preferably, the temperature of the hydrogenation reaction is 30-120°C, more preferably 90°C.

[0064] Preferably, the time of the hydrogenation reaction is 6-20 h, more preferably 10 h.

[0065] Effects of the invention

[0066] The catalyst of the present application is a phosphorus-doped cobalt-rhodium composite oxide catalyst prepared by a specific preparation method, which has the following technical effects: (1) the catalyst is simple to prepare, convenient to recycle, low in raw material cost, good in catalytic activity, high in selectivity, and wide in application range, and can be used for fixed bed reaction and one-pot batch stirring reaction, and at the same time, solves the problems of poor stability of traditional catalysts, such as strict storage conditions, flammability, low mechanical strength, serious loss of active components, short service life of the catalyst, and difficulty in separation of reactants and catalysts; (2) the catalyst of the present application has excellent stability and good mechanical strength to improve the service life of the catalyst and enhance the stability of the active components, and has the characteristics of magnetism and high recovery rate; (3) the method for preparing 2,3-dichloropyridine by using the catalyst has simple process and mild reaction conditions, can effectively control the excessive dechlorination of polychloropyridine, reduce the generation of by-products, the conversion rate of raw materials can reach 98%, the selectivity of the target product 2,3-dichloropyridine can reach 95%, and the mild reaction conditions are low in requirements for equipment and small in energy demand, which is suitable for industrial production. DETAILED DESCRIPTION

[0067] Various exemplary embodiments, features, and aspects of the present application will be described in detail below. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

[0068] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description. Those skilled in the art will understand that the present application can be practiced without certain specific details. In some instances, well-known methods, means, instruments and steps have not been described in detail in order to highlight the principles of the present application.

[0069] EMBODIMENT

[0070] Embodiments of the present application will be described in detail below with reference to Examples, but those skilled in the art will understand that the following Examples are for illustrative purposes only and should not be construed as limiting the scope of the present application. Where specific conditions are not specified in the Examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. Where the manufacturer of the reagent or instrument used is not specified, it is a conventional product that can be obtained on the market.

[0071] Example 1: Catalyst Rh1P 0.1 CoO a Preparation

[0072] Dissolve 29.1 g of Co(NO3)2·6H2O in 300 mL of distilled water, stir at room temperature for 30 min, add 0.026 g of RhCl3·3H2O and 1.32 g of (NH4)2HPO4, stir until the metal salt is completely dissolved, and add 20 mL of an ammonia solution dropwise for co-precipitation until a gel is obtained. Maintain the pH of the reaction system at 9-10, stir at room temperature for 24 h, transfer the gel to a 500 mL polytetrafluoroethylene-lined stainless steel hydrothermal high-pressure kettle, and place it in an 80°C oven for drying for 5 h. Then take out the hydrothermal kettle, cool to room temperature, collect the solid product by filtration, and wash it with distilled water and methanol several times until the pH of the filtrate reaches neutrality. Dry the obtained solid product in a hot air oven at 70°C overnight, and then calcine it in a muffle furnace at 500°C (with a heating rate of 5°C / min) for 5 h to obtain the metal composite oxide catalyst Rh1P 0.1 CoO a ; wherein the atomic ratio of Rh to Co is 1000 to 1,

[0073] Example 2: Preparation of Co3O4 catalysts with different Rh doping amounts

[0074] Repeat Example 1, except that only different amounts of rhodium chloride trihydrate are added to the cobalt nitrate solution to obtain the catalyst Rh x CoO a ; wherein x represents 1000 times the atomic ratio of Rh to Co,

[0075] Example 3: Preparation of Co3O4 catalysts with different P doping amounts

[0076] Repeat Example 1, except that only different amounts of diammonium hydrogen phosphate are added to the cobalt nitrate solution to obtain the catalyst P y CoO a ; wherein y represents the atomic ratio of P to Co,

[0077] Example 4: Preparation of Co3O4 catalysts with different Rh and P doping amounts

[0078] Example 1 was repeated, except that different amounts of a mixed metal salt solution of rhodium chloride trihydrate and diammonium hydrogen phosphate were added to a cobalt nitrate solution to prepare catalyst Rh. x P y CoO a Where x represents 1000 times the atomic ratio of Rh to Co, and y represents the atomic ratio of P to Co.

[0079] Example 5: Preparation of 2,3-dichloropyridine from 2,3,6-trichloropyridine

[0080] The catalysts prepared in Examples 1-4 above were used to catalyze the hydrogenation reaction of polychlorinated pyridine.

[0081] In a 500 mL high-pressure reactor, 30 g of 2,3,6-trichloropyridine, 90 g of methanol, 30 g of water, 0.3 g of catalyst, and 33.3 g of triethylamine were added. First, nitrogen was introduced to purge the air from the reactor, then hydrogen was introduced to purge the nitrogen. Finally, the hydrogen pressure inside the reactor was maintained at 2 MPa. The reaction temperature was set to 90 °C, and heating was initiated. After 10 h, the reaction was stopped, cooled to room temperature, and the reactor was opened after depressurization. The reaction solution was washed and filtered. The filter residue, which was the catalyst, was washed with water and reused. The filtrate was the hydrogenated liquid after the reaction. A suitable amount of the organic phase was taken for gas chromatography analysis. The relative GC results are shown in Table 1.

[0082] Table 1. Conversion rates and selectivity of 2,3,6-trichloropyridine for different catalysts

[0083] Serial number Catalyst Conversion % Selectivity % Co3O4 1 Rh1CoOa 57.4 31.4 2 Rh2CoOa 73.7 33.7 3 Rh4CoOa 84.4 36.2 4 Rh6CoOa 96.3 39.5 5 Rh8CoOa 99.1 44.7 6 P0.1CoOa 99.5 37.1 7 P0.2CoOa 52.5 58.9 8 P0.3CoOa 52.9 66.8 9 P0.4CoOa 58.2 71.2 10 P0.5CoOa 61.1 77.6 11 Rh1P0.1CoOa 57.9 75.1 12 Rh4P0.4CoOa 79.2 76.3 13 Rh5P0.4CoOa 93.8 92.4 14 Rh6P0.4CoOa 98.8 95.5 15 Rh7P0.4CoOa 99.5 95.2 16 ​ 99.3 94.9

[0084] The results in Table 1 show that, compared with the reaction using a Co3O4 catalyst (catalyst 1), when the reaction system uses a Co3O4 catalyst (Rh) containing only different amounts of Rh doping... x CoO a When x is 1 (i.e., catalysts 2-6), the selectivity of the target product 2,3-dichloropyridine does not improve significantly with increasing x, but the conversion rate of the reaction increases significantly (1.3-1.7 times). When x is 1, the conversion rate of the reaction is low (less than 75%). As x increases to 8, the conversion rate of the reaction gradually increases. Among them, when x is 4-8, the conversion rate of the reaction is high (up to 95% or more). Although the selectivity of the target product 2,3-dichloropyridine shows a trend of first increasing and then decreasing with increasing x, the selectivity of 2,3-dichloropyridine is not high (all below 45%).

[0085] Compared to the reaction using a Co3O4 catalyst (catalyst 1), when the reaction system uses a Co3O4 catalyst containing only different amounts of P doping (P... y CoO a When y is at a certain value (i.e., catalyst 7-11), the conversion rate of the reaction does not change significantly with the increase of y, but the selectivity of the target product 2,3-dichloropyridine is significantly improved (1.8-2.5 times). When y is 0.1-0.2, the selectivity of the target product 2,3-dichloropyridine is low (less than 70%). As y increases to 0.4, the selectivity of the target product 2,3-dichloropyridine gradually increases, but when y is further increased from 0.4 to 0.5, the conversion rate of the reaction and the selectivity of the target product 2,3-dichloropyridine decrease. Although the conversion rate of the reaction shows a trend of first increasing and then decreasing with the increase of y, the conversion rate of the reaction is not high (all below 62%).

[0086] Compared to the reaction using a Co3O4 catalyst (catalyst 1), when the reaction system uses a Co3O4 catalyst (Rh) containing different amounts of Rh and P doping, x P y CoO a When the catalyst is 12-16, the conversion rate and selectivity of the target product 2,3-dichloropyridine are significantly improved. When x is 1 and y is 0.1, the conversion rate and selectivity of the target product 2,3-dichloropyridine are low (less than 80%). As x increases to 4 and y increases to 0.4, the conversion rate and selectivity of the target product 2,3-dichloropyridine increase significantly. However, when x is 5-7, the conversion rate and selectivity of the target product 2,3-dichloropyridine do not change significantly (reaching approximately 95% and above). Therefore, from the perspective of saving materials, catalyst Rh is the preferred choice in the dechlorination and hydrogenation reaction system. x P y CoO a The preferred values ​​for x and y are 5 and 0.4, respectively.

[0087] Example 6: Preparation of 2,3-dichloropyridine from 2,3,5-trichloropyridine

[0088] In a 500 mL high-pressure reactor, add 30 g of 2,3,5-trichloropyridine, 90 g of methanol, 30 g of water, and 0.3 g of catalyst Rh5P. 0.4 CoO a, 33.3 g triethylamine, first replace the air in the reactor with nitrogen, then replace the nitrogen in the reactor with hydrogen, finally keep the hydrogen pressure in the reactor at 2 MPa, set the reaction temperature to 90°C, start heating, after 10 h of reaction, end the reaction, cool to room temperature, release the pressure and open the reactor, wash and filter the reaction liquid, the filter residue is the catalyst which is reused after water washing, and the filtrate is the hydrogenation liquid after reaction, take an appropriate amount of organic phase for gas chromatography analysis, the conversion rate of raw material is 98.5%, and the selectivity of 2,3-dichloropyridine is 98.6%.

[0089] Example 7: Preparation of 2,3-dichloropyridine from 2,3,5,6-tetrachloropyridine

[0090] In a 500 mL high-pressure reactor, add 30 g of 2,3,5,6-tetrachloropyridine, 120 g of methanol, 30 g of water, 0.3 g of catalyst Rh5P 0.4 CoO a , 56 g triethylamine, first replace the air in the reactor with nitrogen, then replace the nitrogen in the reactor with hydrogen, finally keep the hydrogen pressure in the reactor at 2 MPa, set the reaction temperature to 90°C, start heating, after 15 h of reaction, end the reaction, cool to room temperature, release the pressure and open the reactor, wash and filter the reaction liquid, the filter residue is the catalyst which is reused after water washing, and the filtrate is the hydrogenation liquid after reaction, take an appropriate amount of organic phase for gas chromatography analysis, the conversion rate of raw material is 98.2%, and the selectivity of 2,3-dichloropyridine is 97.2%.

[0091] Example 8: Preparation of 2,3-dichloropyridine from pentachloropyridine

[0092] In a 500 mL high-pressure reactor, add 30 g of pentachloropyridine, 120 g of methanol, 30 g of water, 0.3 g of catalyst Rh5P 0.4 CoO a , 70 g triethylamine, first replace the air in the reactor with nitrogen, then replace the nitrogen in the reactor with hydrogen, finally keep the hydrogen pressure in the reactor at 2 MPa, set the reaction temperature to 90°C, start heating, after 20 h of reaction, end the reaction, cool to room temperature, release the pressure and open the reactor, wash and filter the reaction liquid, the filter residue is the catalyst which is reused after water washing, and the filtrate is the hydrogenation liquid after reaction, take an appropriate amount of organic phase for gas chromatography analysis, the conversion rate of raw material is 98.8%, and the selectivity of 2,3-dichloropyridine is 90.1%.

[0093] Example 9: Preparation of 2,3-dichloropyridine from 2,3,6-trichloropyridine

[0094] In a 500 mL high-pressure reactor, add 30 g of 2,3,6-trichloropyridine, 90 g of methanol, 0.3 g of catalyst Rh5P 0.4 CoO a, 33.3 g triethylamine, first nitrogen gas to replace the air in the kettle, then hydrogen gas to replace the nitrogen in the kettle, finally the hydrogen pressure in the kettle is 2 MPa, set the reaction temperature to 90°C, start heating, after 10 h of reaction, end the reaction, cool to room temperature, depressurize and open the kettle, wash and filter the reaction liquid, the filter residue is the catalyst for water washing and reuse, the filtrate is the hydrogenation liquid after reaction, take an appropriate amount of organic phase for gas chromatography analysis, the conversion rate of raw material is 97.8%, and the selectivity of 2,3-dichloropyridine is 90.2%.

[0095] Example 10: Preparation of 2,3-dichloropyridine from 2,3,6-trichloropyridine

[0096] In a 500 mL high-pressure reaction kettle, 30 g of 2,3,6-trichloropyridine, 120 g of methanol, 0.3 g of catalyst Rh5P 0.4 CoO a , 6.6 g of magnesium oxide, first nitrogen gas to replace the air in the kettle, then hydrogen gas to replace the nitrogen in the kettle, finally the hydrogen pressure in the kettle is 2 MPa, set the reaction temperature to 60°C, start heating, after 8 h of reaction, end the reaction, cool to room temperature, depressurize and open the kettle, wash and filter the reaction liquid, the filter residue is the catalyst for water washing and reuse, the filtrate is the hydrogenation liquid after reaction, take an appropriate amount of organic phase for gas chromatography analysis, the conversion rate of raw material is 98.4%, and the selectivity of 2,3-dichloropyridine is 82.9%.

[0097] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical applications, or technical improvements in the art, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A catalyst for the synthesis of 2,3-dichloropyridine, having the chemical formula Rh x P y CoO a ; in, x represents 1000 times the atomic ratio of Rh to Co, and x is 3-8; y represents the atomic ratio of P to Co, and y is 0.3-0.5; ； The catalyst is a phosphorus-doped cobalt-rhodium composite oxide catalyst.

2. The catalyst for synthesizing 2,3-dichloropyridine according to claim 1, characterized in that, x is 4-7; y is 0.

4.

3. The catalyst for synthesizing 2,3-dichloropyridine according to claim 2, characterized in that, x is 4, 5, 6 or 7.

4. A method for preparing a catalyst for the synthesis of 2,3-dichloropyridine according to any one of claims 1-3, comprising the following steps: 1) Mix rhodium salt or its hydrate, phosphate, cobalt salt or its hydrate with water, then add alkali or its aqueous solution to obtain a gel-like substance. Stir and carry out a hydrothermal reaction. After the reaction is completed, cool, filter, wash the filter cake, and obtain a solid product. 2) The solid product is dried and then calcined to obtain the catalyst.

5. The preparation method according to claim 4, characterized in that, In step 1), The rhodium salt is rhodium dicarbonylacetylacetone, rhodium chloride, tris(triphenylphosphine) chloride, or tris(triphenylphosphine)carbonyl hydride; and / or, The cobalt salt is cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt halide, or cobalt perhalate; and / or, The phosphate is ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, ammonium phosphate, sodium phosphate, or potassium phosphate; and / or, The base is an inorganic base or an organic base; and / or, The mixing is carried out at room temperature; and / or, The pH value of the gel is 8-12; and / or, The stirring is carried out at room temperature; and / or, The ambient temperature for the hydrothermal reaction is 70-120 °C; and / or, The cooling temperature is room temperature; and / or, The target pH value for the wash is neutral.

6. The preparation method according to claim 5, characterized in that, The rhodium salt is rhodium chloride.

7. The preparation method according to claim 5, characterized in that, The cobalt salt is cobalt nitrate.

8. The preparation method according to claim 5, characterized in that, The phosphate is diammonium hydrogen phosphate.

9. The preparation method according to claim 5, characterized in that, The base is an inorganic base.

10. The preparation method according to claim 5, characterized in that, The alkali is ammonia.

11. The preparation method according to claim 5, characterized in that, The mixing was carried out under stirring conditions at room temperature.

12. The preparation method according to claim 5, characterized in that, The pH value of the gel is 9-10.

13. The preparation method according to claim 5, characterized in that, The stirring was carried out at room temperature for 12-36 h.

14. The preparation method according to claim 5, characterized in that, The ambient temperature for the hydrothermal reaction is 80-100 °C.

15. The preparation method according to claim 4 or 5, characterized in that, In step 2), The drying temperature is 50-80 °C; and / or, The calcination is carried out under heating conditions; and / or, The calcination temperature is 300-600 °C; and / or, The calcination time is 2-6 hours.

16. The preparation method according to claim 15, characterized in that, The heating rate is 1-5 °C / min.

17. The preparation method according to claim 15, characterized in that, The heating rate is 1.5-3 °C / min.

18. The preparation method according to claim 15, characterized in that, The calcination temperature is 400-550 °C.

19. The preparation method according to claim 15, characterized in that, The calcination time is 3-5 hours.

20. A catalyst for the synthesis of 2,3-dichloropyridine, which is prepared by any one of the methods according to claims 4-19.

21. The use of the catalyst for the synthesis of 2,3-dichloropyridine according to any one of claims 1-3 and 20 in the dechlorination and hydrogenation reaction, characterized in that, The dechlorination and hydrogenation reaction is a reaction that prepares 2,3-dichloropyridine from polychlorinated pyridine.

22. The application according to claim 21, characterized in that, The polychloropyridine is selected from at least one of 2,3,6-trichloropyridine, 2,3,5-trichloropyridine, 2,3,4-trichloropyridine, 2,3,4,5-tetrachloropyridine, 2,3,4,6-tetrachloropyridine, 2,3,5,6-tetrachloropyridine, and pentachloropyridine.

23. A method for preparing 2,3-dichloropyridine, comprising the following steps: Using polychlorinated pyridine as a raw material and hydrogen as a hydrogen source, a hydrogenation reaction is carried out in the presence of a catalyst, solvent and acid-binding agent for the synthesis of 2,3-dichloropyridine according to any one of claims 1-3 and 20 to obtain 2,3-dichloropyridine.

24. The preparation method according to claim 23, characterized in that, The polychloropyridine is selected from at least one of 2,3,6-trichloropyridine, 2,3,5-trichloropyridine, 2,3,4-trichloropyridine, 2,3,4,5-tetrachloropyridine, 2,3,4,6-tetrachloropyridine, 2,3,5,6-tetrachloropyridine, and pentachloropyridine; and / or, The solvent is water, an organic solvent, or a mixture of both; and / or, The acid-binding agent is an inorganic or organic base.

25. The preparation method according to claim 24, characterized in that, The solvent is water, alcohol, or an aqueous solution of alcohol.

26. The preparation method according to claim 24, characterized in that, The solvent is water, methanol, or an aqueous methanol solution.

27. The preparation method according to claim 24, characterized in that, The solvent is methanol or an aqueous methanol solution.

28. The preparation method according to claim 24, characterized in that, The acid-binding agent is an organic base.

29. The preparation method according to claim 24, characterized in that, The acid-binding agent is an amine.

30. The preparation method according to claim 24, characterized in that, The acid-binding agent is triethylamine.

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