Preparation method of 2-chloro-5-trichloromethylpyridine

Abstract

The invention provides a preparation method of 2-chloro-5-(trichloromethyl) pyridine. The 2-chloro-5-(trichloromethyl) pyridine is used as a raw material. The preparation method comprises the following steps: introducing 2-chloro-5-methylpyridine and chlorine into a first-stage kettle, and carrying out a pre-chlorination reaction; 2-chloro-5-methylpyridine and chlorine are introduced into a first-stage kettle at the same time, a first-stage chlorination reaction is conducted, and a first-stage chlorination product is obtained; the first-stage chlorination product and chlorine are introduced into a second-stage kettle for a second-stage chlorination reaction, and a 2-chloro-5-trichloromethylpyridine crude product is obtained; the method comprises the following steps: sequentially carrying out light component removal and rectification on a 2-chloro-5-trichloromethylpyridine crude product to obtain 2-chloro-5-trichloromethylpyridine; wherein the temperature of the second-stage chlorination reaction is higher than that of the first-stage chlorination reaction. The method has the advantages that no solvent is needed in the reaction process, and no catalyst or initiator is used, so that the post-treatment process is reduced, the production cost is reduced, the generation of by-products can be effectively reduced, and the 2-chloro-5-trichloromethylpyridine product with high yield and good selectivity is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemicals, and in particular to a method for preparing 2-chloro-5-trichloromethylpyridine. Background Art

[0002] 2-Chloro-5-trichloromethylpyridine is widely used in the synthesis of fine chemicals such as fluazifop-p-ethyl, fluazifop-p-ethyl, and flubosaccharide. It is an important intermediate for pyridine pesticides and medicines and has broad market prospects.

[0003] There are usually three methods for synthesizing 2-chloro-5-trichloromethylpyridine. The main difference is the main raw materials. They are synthesized by reacting 2-chloro-5-methylpyridine, 2-chloro-5-chloromethylpyridine and 3-methylpyridine with chlorine.

[0004] Patent document CN105439943B discloses an industrial production method of 2-chloro-5-trichloromethylpyridine. The method uses 2-chloro-5-chloromethylpyridine and chlorine as raw materials, trifluoromethyl dichlorobenzene and other materials as solvents, reacts under the irradiation of ultraviolet light, and then obtains 2-chloro-5-trichloromethylpyridine products through nitrogen degassing and rectification. The method overcomes the shortcomings of poor reaction selectivity, high polymer generation, and low yield in the existing production method, and it is easier to industrialize production without adding a catalyst. However, the process uses trifluoromethyl dichlorobenzene and other materials as solvents, which increases the cumbersomeness of the post-processing process.

[0005] Patent document CN103058918B discloses a method for synthesizing two products, 2-chloro-5-trichloromethylpyridine and 2,3-dichloro-5-trichloromethylpyridine. The method uses 2-chloro-5-methylpyridine as a raw material, adds catalyst A (azobisisobutyronitrile or benzoyl peroxide) and catalyst B (chloride or oxide of molybdenum or tungsten) to catalyze the reaction to generate 2-chloro-5-trichloromethylpyridine and 2,3-dichloro-5-trichloromethylpyridine. This process can obtain two products at the same time, but the disadvantage is that it uses a catalyst-catalyzed reaction, which increases the subsequent separation process.

[0006] Patent document CN104610136B discloses a method for synthesizing 2-chloro-5-trichloromethylpyridine. The method uses 3-methylpyridine as a raw material, nitrobenzene as a solvent, and an acidic buffer solution and an initiator to generate a crude product. The finished product is then obtained by nitrogen degassing and negative pressure distillation. The yield of the process product can reach 90%, but the process requires the use of solvents, acidic buffer solutions and initiators, which is not conducive to the separation of subsequent products and increases production costs.

[0007] Patent document CN109384709B discloses a method for preparing 2-chloro-5-trichloromethylpyridine. In this method, 3-methylpyridine is mixed with a solvent and then vaporized, and then sent to a quartz tube catalyst bed to react with chlorine in a gas phase chlorination reaction. After the reaction, the material is condensed and distilled to obtain 2-chloro-5-trichloromethylpyridine. This preparation process has the advantages of easy raw material availability, easy operation, and simple process. Patent public document CN104496890A discloses a method for preparing 2-chloro-5-trichloromethylpyridine. This method uses 3-methylpyridine as a raw material, reacts in a microchannel reactor in the presence of an organic solvent and an initiator, and then separates and purifies by desolventizing and high vacuum distillation to obtain the product. This process has the advantages of sufficient gas-liquid contact, large heat exchange area, and mild reaction conditions. However, the yields of the above two invention patents are relatively low, only 70% to 80%, and solvents, catalysts or initiators are required, which increases production costs and the complexity of post-processing.

[0008] Therefore, how to provide a method for preparing 2-chloro-5-trichloromethylpyridine without adding a catalyst, an initiator or a solvent, so as to further improve the yield and purity of 2-chloro-5-trichloromethylpyridine and meet the application requirements of the substance. Summary of the invention

[0009] The main purpose of the present invention is to provide a method for preparing 2-chloro-5-trichloromethylpyridine, so as to solve the problem that the yield of 2-chloro-5-trichloromethylpyridine prepared in the prior art is low.

[0010] In order to achieve the above object, according to a first aspect of the present invention, a method for preparing 2-chloro-5-trichloromethylpyridine is provided, the method comprising: introducing 2-chloro-5-methylpyridine and chlorine into a primary kettle to carry out a pre-chlorination reaction; after the pre-chlorination reaction, introducing 2-chloro-5-methylpyridine and chlorine into the primary kettle at the same time to carry out a primary chlorination reaction to obtain a primary chlorination product; introducing the primary chlorination product and chlorine into a secondary kettle to carry out a secondary chlorination reaction to obtain a crude 2-chloro-5-trichloromethylpyridine; introducing the crude 2-chloro-5-trichloromethylpyridine into a light removal tower and a distillation tower in sequence to carry out light removal and distillation to obtain 2-chloro-5-trichloromethylpyridine; wherein the temperature of the secondary chlorination reaction is higher than the temperature of the primary chlorination reaction.

[0011] Furthermore, in the pre-chlorination reaction, the amount of chlorine added is 1.3 to 1.5 times that of 2-chloro-5-methylpyridine, based on the total moles; preferably, the reaction time of the pre-chlorination is 5 to 10 hours; preferably, the reaction temperature of the pre-chlorination is 130 to 140°C.

[0012] Furthermore, in the primary chlorination reaction, the flow ratio of 2-chloro-5-methylpyridine to chlorine is 1:1.3-1.5 based on the total moles; preferably, the reaction time of the primary chlorination reaction is 5-10 hours; preferably, the reaction temperature of the primary chlorination reaction is 130-140°C.

[0013] Furthermore, in the secondary chlorination reaction, the flow ratio of 2-chloro-5-methylpyridine to chlorine is 1:2.6-3.0, based on the total molar number; preferably, the reaction time of the secondary chlorination reaction is 10-20h; preferably, the reaction temperature of the secondary chlorination reaction is 160-180°C.

[0014] Furthermore, after the secondary chlorination reaction, the preparation method further comprises: sequentially degassing and heat-insulating the products of the secondary chlorination reaction to obtain a crude product of 2-chloro-5-trichloromethylpyridine.

[0015] Furthermore, the insulation time is 2 to 4 hours; preferably, the insulation temperature is 160-180°C.

[0016] Furthermore, the absolute pressure of light removal is 5-10 mmHg; preferably, the reflux ratio of light removal is 2-3:1; preferably, the temperature of light removal is 130°C-145°C; preferably, the number of plates of the light removal tower is 40-50.

[0017] Furthermore, the absolute pressure of the distillation is 5-10 mmHg; preferably, the reflux ratio of the distillation is 3-4:1; preferably, the temperature of the distillation is 145° C.-160° C.; preferably, the number of plates of the distillation tower is 50-60.

[0018] Furthermore, the material at the top of the light removal tower is introduced into a secondary kettle to carry out a secondary chlorination reaction; preferably, when carrying out the primary chlorination reaction, the connecting valve connecting the primary kettle and the secondary kettle is opened, and the primary chlorination product overflows into the secondary kettle.

[0019] Furthermore, the volume ratio of the first kettle to the second kettle is 1:2; preferably, the ratio of the first chlorination reaction time to the second chlorination reaction time is 1:2 to 2.5.

[0020] The technical scheme of the present invention is applied, 2-chloro-5-methylpyridine and chlorine are used, and 2-chloro-5-trichloromethylpyridine is synthesized by gradient temperature reaction. No solvent is needed to dissolve the raw materials during the reaction, and no catalyst or initiator is used, which reduces the post-processing process and also reduces the production cost. The preparation method of the present application has a simple process flow, can effectively reduce the generation of by-products, and obtains a 2-chloro-5-trichloromethylpyridine product with high yield and good selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 The schematic diagram of the process for preparing 2-chloro-5-trichloromethylpyridine in the present application is shown. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0024] As mentioned in the background technology, in the existing methods for preparing 2-chloro-5-trichloromethylpyridine, most of them require the use of solvents, catalysts or initiators and other substances to participate in the reaction, which will make the subsequent product purification and separation treatment more complicated, increase production costs, and affect the yield and purity of the final product 2-chloro-5-trichloromethylpyridine. Therefore, the present application intends to provide a preparation method that can improve the yield of 2-chloro-5-trichloromethylpyridine and has a relatively simple process.

[0025] In a first typical embodiment of the present application, a method for preparing 2-chloro-5-trichloromethylpyridine is provided, the method comprising: introducing 2-chloro-5-methylpyridine and chlorine into a primary kettle to carry out a pre-chlorination reaction; after the pre-chlorination reaction, introducing 2-chloro-5-methylpyridine and chlorine into the primary kettle at the same time to carry out a primary chlorination reaction to obtain a primary chlorination product; introducing the primary chlorination product and chlorine into a secondary kettle to carry out a secondary chlorination reaction to obtain a crude 2-chloro-5-trichloromethylpyridine; introducing the crude 2-chloro-5-trichloromethylpyridine into a light removal tower and a distillation tower in sequence to carry out light removal and distillation to obtain 2-chloro-5-trichloromethylpyridine; wherein the temperature of the secondary chlorination reaction is higher than the temperature of the primary chlorination reaction.

[0026] like Figure 1As shown, the 2-chloro-5-trichloromethyl pyridine preparation reaction of the present application is carried out in two series-connected reactors, namely, one-level reactor and two-level reactor. First, reactant 2-chloro-5-methyl pyridine and chlorine are passed into one-level reactor to heat up, pre-chlorination reaction is carried out, a large amount of intermediates (2-chloro-5-chloromethyl pyridine) are generated, and then 2-chloro-5-methyl pyridine and chlorine are passed into one-level reactor simultaneously, and one-level chlorination reaction is completed, and in the two-level reactor further heated up, 2-chloro-5-trichloromethyl pyridine crude product is obtained by the reaction generation of one-level chlorination reaction product and chlorine, and then by de-lightening and rectification, the 2-chloro-5-trichloromethyl pyridine product after purification is further obtained. In the above-mentioned preparation reaction process, by constantly heating up, free radicals can be produced without the need to add a catalyst, and because the fluidity of the material is good at high temperature, there is no need to add a solvent, and then the target product with a higher yield can be obtained under relatively simple operation.

[0027] Among them, the chemical reaction equations of the pre-chlorination reaction and the primary chlorination reaction are shown in Formula 1 below:

[0028]

[0029] The chemical reaction equation of the secondary chlorination reaction is shown in Formula 2 below:

[0030]

[0031] If do not carry out pre-chlorination reaction, directly carry out one-level chlorination reaction, namely in one-level still, when being empty still state, pass into chlorine and 2-chloro-5-picoline simultaneously, because now in still, 2-chloro-5-picoline liquid level is lower, chlorine has shorter contact time with it, can cause chlorine utilization rate to reduce, cause the waste of chlorine.And in order to be easy to control the degree of one-level chlorination reaction, need to carry out pre-chlorination reaction, make in one-level still, before carrying out one-level chlorination reaction, first have a large amount of 2-chloro-5-chloromethylpyridine, now only need to continue leading chlorine for carrying out one-level chlorination reaction more completely.Otherwise when only carrying out one-level chlorination reaction, then need to control the flow of chlorine and 2-chloro-5-picoline simultaneously, difficult to operate, increase industrial production difficulty.

[0032] In order to enable the primary chlorination reaction to be further carried out efficiently and more completely, in a preferred embodiment, in the pre-chlorination reaction, the amount of chlorine added is 1.3 to 1.5 times that of 2-chloro-5-methylpyridine, based on the total molar number; preferably, the reaction time of the pre-chlorination is 5 to 10 hours; preferably, the reaction temperature of the pre-chlorination is 130 to 140°C.

[0033] In order to further efficiently complete the primary chlorination reaction, in a preferred embodiment, in the primary chlorination reaction, the flow ratio of 2-chloro-5-methylpyridine to chlorine is 1:1.3-1.5 based on the total molar number; preferably, the reaction time of the primary chlorination reaction is 5-10 hours; preferably, the reaction temperature of the primary chlorination reaction is 130-140°C. Among them, the primary chlorination reaction is mainly for the synthesis of 2-chloro-5-chloromethylpyridine. Since the boiling point of the reactant 2-chloro-5-methylpyridine is only 188°C, under solvent-free conditions, when reacting at a higher temperature, the material taken out of the system by hydrogen chloride will increase, that is, the loss is large, which is not conducive to improving the yield.

[0034] In order to further efficiently complete the secondary chlorination reaction, in a preferred embodiment, in the secondary chlorination reaction, the flow ratio of 2-chloro-5-methylpyridine to chlorine is 1:2.6-3.0 based on the total molar number; preferably, the reaction time of the secondary chlorination reaction is 10-20 hours; preferably, the reaction temperature of the secondary chlorination reaction is 160-180° C. Among them, the main purpose of the secondary chlorination reaction is to generate 2-chloro-5-trichloromethylpyridine. Since the reactants are all high-boiling point products, low-temperature reaction is not required, and high-temperature reaction is conducive to increasing the reaction rate.

[0035] Since chlorine and generated hydrogen chloride exist in the reactants, in order to further remove the dissolved chlorine and hydrogen chloride in the secondary chlorination reaction product and facilitate the subsequent separation of liquid materials, the reaction product needs to be degassed. In a preferred embodiment, after the secondary chlorination reaction, the preparation method further includes: degassing the product of the secondary chlorination reaction in turn and keeping it warm to obtain a crude 2-chloro-5-trichloromethylpyridine.

[0036] To further improve the gas removal effect, chlorine and hydrogen chloride are removed as much as possible, and the gas removal kettle is kept warm for a certain period of time. In a preferred embodiment, the warming time is 2 to 4 hours; preferably, the warming temperature is 160-180°C.

[0037] In order to further efficiently remove the unreacted intermediate products and a small amount of reactants in the chlorination reaction, so as to increase the content of the 2-chloro-5-trichloromethylpyridine product obtained in the subsequent distillation, in a preferred embodiment, the absolute pressure of the light removal is 5-10 mmHg; preferably, the reflux ratio of the light removal is 2-3:1. Wherein, the reflux ratio is the ratio of the mass of the material returned to the light removal tower by the gas phase condensate at the top of the tower during light removal to the mass of the distillate. Preferably, the temperature of light removal is 130°C-145°C; preferably, the number of plates of the light removal tower is 40-50. Wherein, the top composition of the light removal tower is a mixture of 2-chloro-5-chloromethylpyridine, 2-chloro-5-dichloromethylpyridine, and 2-chloro-5-trichloromethylpyridine, and the mass ratio of the three is about 1:8:1. The lower part of the light removal tower is a large amount of 2-chloro-5-trichloromethylpyridine, which is subjected to subsequent distillation treatment.

[0038] In order to further purify and extract 2-chloro-5-trichloromethylpyridine in the chlorination reaction product, in a preferred embodiment, the absolute pressure of the distillation is 5-10 mmHg; preferably, the reflux ratio of the distillation is 3-4:1. The reflux ratio is the ratio of the mass of the gas phase condensate returned to the distillation tower during distillation to the mass of the distillate. Preferably, the distillation temperature is 145°C to 160°C; preferably, the number of plates of the distillation tower is 50-60. The material at the top of the distillation tower is the finished product 2-chloro-5-trichloromethylpyridine.

[0039] In order to further improve the efficiency of the primary chlorination reaction and the secondary chlorination reaction and improve the degree of complete reaction, in a preferred embodiment, the top material of the light removal tower is passed into the secondary kettle to carry out the secondary chlorination reaction, and the light-removed component is returned to the secondary kettle to react with chlorine, which can further improve the product yield.

[0040] In a preferred embodiment, when performing the primary chlorination reaction, the connecting valve connecting the primary kettle and the secondary kettle is opened, and the primary chlorination product overflows into the secondary kettle. After the pre-chlorination reaction is completed, the material in the primary kettle has contained a large amount of "cooked" 2-chloro-5-chloromethylpyridine. At this time, the primary chlorination reaction is carried out, and two reactant raw materials are continuously introduced at the same time. It is necessary to open the connecting valve and discharge the materials synchronously while the reaction is carried out to avoid the primary kettle from overflowing. And the reactor for the reaction in this application is a full mixed flow reactor. During the continuous reaction, the content of the primary chlorination reaction product is always the same as the pre-chlorination reaction product present in the kettle, and the material composition remains unchanged.

[0041] In a preferred embodiment, the volume ratio of the first kettle to the second kettle is 1:2; preferably, the ratio of the first chlorination reaction time to the second chlorination reaction time is 1:2-2.5.

[0042] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0043] Example 1

[0044] The volumes of the first and second stages of the two-stage series-connected kettles are 1000ml and 2000ml respectively.

[0045] Pre-chlorination reaction: Add 5.5 mol of 2-chloro-5-methylpyridine to the first-stage kettle, raise the temperature to 135°C, pass 7.7 mol of chlorine gas into the kettle, control the temperature to remain unchanged, and end the chlorine gas passing after 7.5 hours.

[0046] Primary chlorination reaction: continuously input 2-chloro-5-methylpyridine and chlorine gas into the primary kettle at a molar flow rate of 0.733 mol / h and 1.03 mol / h respectively, control the molar flow ratio to 1:1.4, open the side valve of the primary kettle to overflow the material in the kettle to the secondary kettle, control the primary chlorination reaction time in the first kettle to 7.5h, and maintain the reaction temperature at 135°C.

[0047] Secondary chlorination reaction: heat the secondary kettle material to 170°C, continuously introduce chlorine gas and primary chlorination reaction product into the secondary kettle at molar flow rates of 2.06 mol / h and 0.733 mol / h, control the secondary chlorination reaction time to 15 h, open the secondary kettle side valve to discharge the material in the kettle into the gas-dripping kettle, maintain the material temperature at 170°C in the gas-dripping kettle for 3 h.

[0048] Light removal and distillation: The crude 2-chloro-5-trichloromethylpyridine is transported to the light removal tower. The absolute pressure in the light removal tower is 7.5 mmHg, the reflux ratio is 2.5:1, the tower bottom temperature is controlled at 137°C, and the theoretical plate number is 45. The top material of the light removal tower is added to the secondary reactor, and the light removal tower material is transported to the distillation tower. The absolute pressure in the distillation tower is 7.5 mmHg, the reflux ratio is 3.5:1, the tower bottom temperature is controlled at 153°C, and the theoretical plate number is 55.

[0049] After the system was stabilized, the mass of the material collected from the top of the distillation tower for 1 hour was 156.95 g, the content (purity) was 99.2%, and the calculated yield was 91.97%.

[0050] Example 2

[0051] The volumes of the first and second stages of the two-stage series-connected kettles are 1000ml and 2000ml respectively.

[0052] Pre-chlorination reaction: Add 5.5 mol of 2-chloro-5-methylpyridine to the first-stage kettle, raise the temperature to 130°C, pass 7.15 mol of chlorine gas into the kettle, control the temperature to remain unchanged, and end the chlorine gas passing for 5 hours.

[0053] Primary chlorination reaction: continuously input 2-chloro-5-methylpyridine and chlorine gas into the first kettle at a molar flow rate of 1.1 mol / h and 1.43 mol / h respectively, and control the molar flow ratio to 1:1.3. Open the side valve of the first kettle to overflow the material in the kettle to the second kettle. Control the primary chlorination reaction time in the first kettle to be 5h, and maintain the reaction temperature at 130°C.

[0054] Secondary chlorination reaction: heat the secondary kettle material to 160°C, continuously introduce chlorine gas and primary chlorination reaction product into the kettle at molar flow rates of 2.86 mol / h and 1.1 mol / h, control the secondary chlorination reaction time to 10 h, open the secondary kettle side valve to discharge the material in the kettle into the gas-dripping kettle, maintain the material temperature at 160°C in the gas-dripping kettle, and keep it warm for 2 h.

[0055] Light removal and distillation: The crude 2-chloro-5-trichloromethylpyridine is transported to the light removal tower. The absolute pressure in the light removal tower is 5 mmHg, the reflux ratio is 2:1, the tower bottom temperature is controlled at 130°C, and the theoretical number of plates is 40. The top material of the light removal tower is added to the secondary reactor, and the light removal tower material is transported to the distillation tower. The absolute pressure in the distillation tower is 5 mmHg, the reflux ratio is 3:1, the tower bottom temperature is controlled at 145°C, and the theoretical number of plates is 50.

[0056] After the system was stabilized, the mass of the material collected from the top of the distillation tower for 1 hour was 228.48 g, the content was 99.05%, and the calculated yield was 89.1%.

[0057] Example 3

[0058] The volumes of the first and second stages of the two-stage series-connected kettles are 1000ml and 2000ml respectively.

[0059] Pre-chlorination reaction: Add 5.5 mol of 2-chloro-5-methylpyridine to the first-stage kettle, raise the temperature to 140°C, and pass a total of 8.25 mol of chlorine gas into the kettle. Control the temperature to remain unchanged and end the chlorine gas passing after 10 hours.

[0060] Primary chlorination reaction: continuously input 2-chloro-5-methylpyridine and chlorine gas into the first kettle at a molar flow rate of 0.55 mol / h and 0.825 mol / h respectively, and control the molar flow ratio to 1:1.5. Open the side valve of the first kettle to overflow the material in the kettle into the second kettle. Control the primary chlorination reaction time in the first kettle to be 10 hours, and maintain the reaction temperature at 140°C.

[0061] Secondary chlorination reaction: heat the secondary kettle material to 180°C, continuously introduce chlorine gas and primary chlorination reaction product into the kettle at molar flow rates of 1.65 mol / h and 0.55 mol / h, control the secondary chlorination reaction time to 20 h, open the side valve of the secondary kettle to discharge the material in the kettle into the gas-dripping kettle, maintain the material temperature in the gas-dripping kettle at 180°C, and keep it warm for 4 h.

[0062] Light removal and distillation: The crude 2-chloro-5-trichloromethylpyridine is transported to the light removal tower. The absolute pressure in the light removal tower is 10 mmHg, the reflux ratio is 3:1, the tower bottom temperature is controlled at 145°C, and the theoretical plate number is 50. The top material of the light removal tower is added to the secondary reactor, and the light removal tower material is transported to the distillation tower. The absolute pressure in the distillation tower is 10 mmHg, the reflux ratio is 4:1, the tower bottom temperature is controlled at 160°C, and the theoretical plate number is 60.

[0063] After the system was stabilized, the mass of the material collected from the top of the distillation tower for 1 hour was 114.2 g, the content was 99.3%, and the calculated yield was 89.3%.

[0064] Comparative Example 1

[0065] The volumes of the first and second stages of the two-stage series-connected kettles are 1000ml and 2000ml respectively.

[0066] Pre-chlorination reaction: Add 5.5 mol of 2-chloro-5-methylpyridine to the first-stage kettle, raise the temperature to 100°C, pass 7.7 mol of chlorine gas into the kettle, control the temperature to remain unchanged, and end the chlorine gas passing after 7.5 hours.

[0067] Primary chlorination reaction: continuously input 2-chloro-5-methylpyridine and chlorine gas into the primary kettle at a molar flow rate of 0.733 mol / h and 1.03 mol / h respectively, control the molar flow ratio to 1:1.4, open the side valve of the primary kettle to overflow the material in the kettle to the secondary kettle, control the primary chlorination reaction time in the first kettle to 7.5h, and maintain the reaction temperature at 100°C.

[0068] Secondary chlorination reaction: heat the secondary kettle material to 170°C, continuously introduce chlorine gas and primary chlorination reaction product into the kettle at molar flow rates of 2.06 mol / h and 0.733 mol / h, control the secondary chlorination reaction time to 15 h, open the secondary kettle side valve to discharge the material in the kettle into the gas-dripping kettle, maintain the material temperature at 170°C in the gas-dripping kettle, and keep it warm for 3 h.

[0069] Light removal and distillation: The crude 2-chloro-5-trichloromethylpyridine is transported to the light removal tower. The absolute pressure in the light removal tower is 7.5 mmHg, the reflux ratio is 2.5:1, the tower bottom temperature is controlled at 137°C, and the theoretical plate number is 45. The top material of the light removal tower is added to the secondary reactor, and the light removal tower material is taken out of the distillation process. The absolute pressure of the distillation process is controlled to be 7.5 mmHg, the reflux ratio is 3.5:1, the tower bottom temperature is controlled to be 153°C, and the theoretical plate number is 55.

[0070] After the system stabilized, the mass of the material collected from the top of the distillation tower for 1h was 142.6g, the content was 95.2%, and the calculated yield was 80.2%. In Comparative Example 1, the first-stage reactor used a lower reaction temperature, and the product yield and content were lower. The main reason was that the reaction temperature of the chlorine gas was too low, resulting in more 2,3-dichloro-5-dichloromethylpyridine impurities.

[0071] Comparative Example 2

[0072] The volumes of the first and second stages of the two-stage series-connected kettles are 1000ml and 2000ml respectively.

[0073] Pre-chlorination reaction: Add 5.5 mol of 2-chloro-5-methylpyridine to the first-stage kettle, raise the temperature to 170°C, pass 7.7 mol of chlorine gas into the kettle, control the temperature to remain unchanged, and end the chlorine gas passing for 7.5 hours.

[0074] Primary chlorination reaction: continuously input 2-chloro-5-methylpyridine and chlorine gas into the first kettle at a molar flow rate of 0.733 mol / h and 1.03 mol / h respectively, control the molar flow ratio to 1:1.4, open the side valve of the first kettle to overflow the material in the kettle to the second kettle, control the primary chlorination reaction time in the first kettle to 7.5h, and maintain the reaction temperature at 170℃.

[0075] Secondary chlorination reaction: control the temperature of the secondary kettle material to 170°C, continuously introduce chlorine gas and the primary chlorination reaction product into the kettle at a molar flow rate of 2.06 mol / h and 0.733 mol / h, and control the secondary chlorination reaction time to 15 h. Open the side valve of the secondary kettle to discharge the material in the kettle into the gas-dripping kettle. Maintain the material temperature at 170°C in the gas-dripping kettle for 3 h.

[0076] Light removal and distillation: The crude 2-chloro-5-trichloromethylpyridine is transported to the light removal tower. The absolute pressure in the light removal tower is 7.5 mmHg, the reflux ratio is 2.5:1, the tower bottom temperature is controlled at 137°C, and the theoretical plate number is 45. The top material of the light removal tower is added to the secondary reactor, and the light removal tower material is taken out of the distillation process. The absolute pressure of the distillation process is controlled to be 7.5 mmHg, the reflux ratio is 3.5:1, the tower bottom temperature is controlled to be 153°C, and the theoretical plate number is 55.

[0077] After the system stabilized, the mass of the material collected from the top of the distillation tower for 1h was 133.6g, the content was 99.3%, and the calculated yield was 78.4%. In Comparative Example 2, the first-stage kettle adopted a higher reaction temperature, the product content was higher, and the yield was lower. The main reason was that the reaction temperature of the first-stage kettle was too high, and part of the raw materials were brought into the tail gas system by the generated hydrogen chloride, resulting in a reduction in the actual reaction materials, resulting in a lower product yield.

[0078] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: 2-chloro-5-methylpyridine and chlorine are used to synthesize 2-chloro-5-trichloromethylpyridine by gradient temperature reaction. No need to use solvent to dissolve raw materials during the reaction, and catalyst or initiator is not used, while post-processing steps are reduced, production costs are also reduced. The preparation method process of the present application is simple, can effectively reduce the generation of by-products, and obtains 2-chloro-5-trichloromethylpyridine products with high yield and good selectivity.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing 2-chloro-5-trichloromethylpyridine, characterized in that: The preparation method comprises: 2-chloro-5-methylpyridine and chlorine gas are introduced into a first-stage kettle to carry out a pre-chlorination reaction; After the pre-chlorination reaction, the 2-chloro-5-methylpyridine and the chlorine gas are simultaneously introduced into the primary kettle to carry out a primary chlorination reaction to obtain a primary chlorinated product; Passing the primary chlorination product and the chlorine gas into a secondary kettle to carry out a secondary chlorination reaction to obtain a crude 2-chloro-5-trichloromethylpyridine; The crude 2-chloro-5-trichloromethylpyridine is sequentially passed into a light removal tower and a distillation tower for light removal and distillation to obtain the 2-chloro-5-trichloromethylpyridine; Wherein, the temperature of the secondary chlorination reaction is higher than the temperature of the primary chlorination reaction.

2. The preparation method according to claim 1, characterized in that: In the pre-chlorination reaction, the amount of chlorine added is 1.3 to 1.5 times that of 2-chloro-5-methylpyridine, based on the total moles; Preferably, the reaction time of the pre-chlorination is 5 to 10 hours; Preferably, the reaction temperature of the pre-chlorination is 130-140°C.

3. The preparation method according to claim 1, characterized in that: In the primary chlorination reaction, the flow ratio of the 2-chloro-5-methylpyridine to the chlorine gas is 1:1.3-1.5 based on the total moles; Preferably, the reaction time of the primary chlorination reaction is 5 to 10 hours; Preferably, the reaction temperature of the primary chlorination reaction is 130-140°C.

4. The preparation method according to claim 1, characterized in that: In the secondary chlorination reaction, the flow ratio of the 2-chloro-5-methylpyridine to the chlorine gas is 1:2.6-3.0 based on the total moles; Preferably, the reaction time of the secondary chlorination reaction is 10 to 20 hours; Preferably, the reaction temperature of the secondary chlorination reaction is 160-180°C.

5. The preparation method according to claim 1, characterized in that: After the secondary chlorination reaction, the preparation method further comprises: sequentially removing gas from the products of the secondary chlorination reaction and keeping them warm to obtain the crude 2-chloro-5-trichloromethylpyridine.

6. The preparation method according to claim 5, characterized in that: The insulation time is 2 to 4 hours; Preferably, the insulation temperature is 160-180°C.

7. The preparation method according to claim 1, characterized in that: The absolute pressure of the light removal is 5 to 10 mmHg; Preferably, the reflux ratio of the light removal is 2 to 3:1; Preferably, the temperature of the delightening is 130°C to 145°C; Preferably, the lightness removal tower has 40 to 50 plates.

8. The preparation method according to claim 1, characterized in that: The absolute pressure of the distillation is 5 to 10 mmHg; Preferably, the reflux ratio of the distillation is 3 to 4:1; Preferably, the distillation temperature is 145°C to 160°C; Preferably, the distillation tower has 50 to 60 plates.

9. The preparation method according to claim 1, characterized in that: The top material of the light removal tower is passed into the secondary kettle to carry out the secondary chlorination reaction; Preferably, when the primary chlorination reaction is carried out, the connecting valve connecting the primary kettle and the secondary kettle is opened, and the primary chlorination product overflows into the secondary kettle.

10. The preparation method according to claim 1, characterized in that: The volume ratio of the first-stage kettle to the second-stage kettle is 1:2; Preferably, the ratio of the primary chlorination reaction time to the secondary chlorination reaction time is 1:2 to 2.5.

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